MIC22405
4A Integrated Switch High-Efficiency
Synchronous Buck Regulator with
Frequency Programmable upto 4MHz
Ramp Control is a trademark of Micrel, Inc
MLF and MicroLeadFrame are registered trademarks of Amkor Technology, Inc.
Micrel Inc. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel +1 (408) 944-0800 • fax + 1 (408) 474-1000 • http://www.micrel.com
General Description
The Micrel MIC22405 is a high efficiency, 4A integrated
switch synchronous buck (step-down) regulator. The
MIC22405 is optimized for highest efficiency, achieving
more than 95% efficiency while still switching at 1MHz.
The ultra-high speed control loop keeps the output voltage
within regulation even under the extreme transient load
swings commonly found in FPGAs and low-voltage ASICs.
The output voltage is pre-bias safe and can be adjusted
down to 0.7V to address all low-voltage power needs.
The MIC22405 offers a full range of sequencing and
tracking options. The Enable/Delay (EN/DLY) pin,
combined with the Power Good (PG) pin, allows multiple
outputs to be sequenced in any way during turn-on and
turn-off. The Ramp Control™ (RC) pin allows the device to
be connected to another product in the MIC22xxx and/or
MIC68xxx family, to keep the output voltages within a
certain V on start-up.
The MIC22405 is available in a 20-pin 3mm x 4mm MLF®
with a junction operating range from –40°C to +125°C.
Data sheets and support documentation can be found on
Micrel’s web site at: www.micrel.com.
Features
• Input voltage range: 2.9V to 5.5V
• Output voltage adjustable down to 0.7V
• Output load current up to 4A
• Safe start-up into a pre-biased output
• Full sequencing and tracking capability
• Power Good output
• Efficiency > 95% across a broad load range
• Programmable frequency 300kHz to 4MHz
• Ultra-fast transient response
• Easy RC compensation
• 100% maximum duty cycle
• Fully-integrated MOSFET switches
• Thermal shutdown and current-limit protection
• 20-pin 3mm x 4mm MLF®
• –40°C to +125°C junction temperature range
Applications
• High power density point-of-load conversion
• Servers, routers, and base stations
• DVD recorders / Blu-ray players
• Computing peripherals
• FPGAs, DSP and low voltage ASIC power
_________________________________________________________________________________________________________________________
Typical Application
MIC22405 4A 1MHz Synchronous Output Converter
Efficiency (V
IN
= 5.0V)
vs. Out put Current
70
75
80
85
90
95
100
0123
O UT P UT CU RREN T
4
(
A
)
EFFI CIENCY ( % )
V
IN
= 5.0V
1.8V
3.3V
May 2011 M9999-061511-A
Micrel, Inc. MIC22405
June 2011 2 M9999-061511-A
Ordering Information
Part Number Voltage Junction Temperature Range Package Lead Finish
MIC22405YML Adjustable –40° to +125°C 20-Pin 3x4 MLF®* Pb-Free
Note:
1. MLF® is a GREEN ROHS compliant package. Lead finish is NiPdAu. Mold compound is Halogen Free.
Pin Configur ation
20-Pin 3mm x 4mm MLF® (ML)
Pin Description
Pin Number Pin Name Description
1 PG
PG (Output): This is an open drain output that indicates when the output voltage is below 90% of
its nominal voltage. The PG flag is asserted without delay when the enable is set low or when the
output goes below the 90% threshold.
2 CF Adjustable frequency with external capacitor. Refer to table 2.
4 COMP
Compensation Pin (Input): The MIC22405 uses an internal compensation network containing a
fixed-frequency zero (phase lead response) and pole (phase lag response) which allows the
external compensation network to be much simplified for stability. The addition of a single
capacitor and resistor to the COMP pin will add the necessary pole and zero for voltage mode
loop stability using low-value, low-ESR ceramic capacitors.
6 FB
Feedback: Input to the error amplifier. The FB pin is regulated to 0.7V. A resistor divider
connecting the feedback to the output is used to adjust the desired output voltage.
7 SGND Signal Ground: Internal signal ground for all low power circuits.
8 SVIN
Signal Power Supply Voltage (Input): This pin is connected externally to the PVIN pin. A 2.2µF
ceramic capacitor from the SVIN pin to SGND must be placed next to the IC.
10, 17 PVIN
Power Supply Voltage (Input): The PVIN pins are the input supply to the internal P-Channel
Power MOSFET. A 22µF ceramic is recommended for bypassing at each PVIN pin. The SVIN
pin must be connected to a PVIN pin.
11, 16 PGND Power Ground: Internal ground connection to the source of the internal N-Channel MOSFETs.
12, 13, 14, 15 SW
Switch (Output): This is the connection to the drain of the internal P-Channel MOSFET and drain
of the N-Channel MOSFET. This is a high-frequency, high-power connection; therefore traces
should be kept as short and as wide as practical.
Micrel, Inc. MIC22405
June 2011 3 M9999-061511-A
Pin Description (Continued)
Pin Number Pin Name Description
18 EN/DLY
Enable/Delay (Input): This pin is internally fed with a 1µA current source from SVIN. A delayed
turn on is implemented by adding a capacitor to this pin. The delay is proportional to the
capacitor value. The internal circuits are held off until EN/DLY reaches the enable threshold of
1.24V. This pin is pulled low when the input voltage is lower than the UVLO threshold.
19 NC No Connect: Leave this pin open. Do not connect to ground or route other signal through this.
20 RC
Ramp Control: A capacitor from the RC pin-to-ground determines slew rate of output voltage
during start-up. The RC pin is internally fed with a 1µA current source. The output voltage tracks
the RC pin voltage. The slew rate is proportional by the internal 1µA source and RC pin
capacitor. This feature can be used for tracking capability as well as soft start.
EP GND Exposed Pad (Power): Must be connected to the GND plane for full output power to be realized.
Micrel, Inc. MIC22405
June 2011 4 M9999-061511-A
Absolute Maximum Ratings(1, 2)
PVIN to PGND.................................................... –0.3V to 6V
SVIN to PGND..................................................–0.3V to PVIN
VSW to PGND...................................................–0.3V to PVIN
VEN/DLY to PGND .............................................. -0.3V to PVIN
VPG to PGND ...................................................–0.3V to PVIN
Junction Temperature ................................................ 150°C
PGND to SGND ............................................. –0.3V to 0.3V
Storage Temperature Range ....................–65°C to +150°C
Lead Temperature (soldering, 10s)............................ 260°C
ESD Rating.................................................................Note 2
Operating Ratings(3)
Supply Voltage (PVIN/SVIN) .............................. 2.9V to 5.5V
Power Good Voltage (VPG)...................................0V to PVIN
Enable Input (VEN/DLY)...........................................0V to PVIN
Junction Temperature (TJ) ..................–40°C TJ +125°C
Package Thermal Resistance
3mm x 4mm MLF®-20 (θJC)................................25°C/W
3mm x 4mm MLF®-20 (θJA)................................55°C/W
Electrical Characteristics(4)
SVIN = PVIN = VEN/DLY = 3.3V, VOUT = 1.8V, TA = 25°C, unless noted. Bold values indicate –40°C< TJ < +125°C.
Parameter Condition Min. Typ. Max. Units
Power Input Supply
Input Voltage Range (PVIN) 2.9 5.5 V
Under-voltage Lockout Trip Level PVIN Rising 2.55 2.78 2.9 V
UVLO Hysteresis 420 mV
Quiescent Supply Current VFB = 0.9V (not switching) 1.3 2 mA
Shutdown Current VEN/DLY = 0V 5 10 µA
Reference
Feedback Reference Voltage 0.686 0.7 0.714 V
Load Regulation IOUT = 100mA to 4A 0.2 %
Line Regulation VIN = 2.9V to 5.5V; IOUT = 100mA 0.2 %
FB Bias Current VFB = 0.5V 1 nA
Enable Control
EN/DLY Threshold Voltage 1.14 1.24 1.34 V
EN Hysteresis 10 mV
EN/DLY Bias Current VEN/DLY = 0.5V; VIN = 2.9V and VIN = 5.5V 0.6 1.0 1.8 µA
RC Ramp Control
RC Pin Source Current VRC = 0.35V 0.5 1.0 1.7 µA
Oscillator
Switching Frequency 0.8 1.0 1.2 MHz
Maximum Duty Cycle VFB 0.5V 100 %
Short Current Protection
Current Limit VFB = 0.5V 4 7.8 14 A
Internal FETs
Top MOSFET RDS(ON) V
FB = 0.5V, ISW = 1A 60 m
Bottom MOSFET RDS(ON) V
FB = 0.9V, ISW = -1A 35 m
Power Good (PG)
PG Threshold Threshold % of VFB from VREF −7.5 −10 −12.5 %
Hysteresis 2.0 %
PG Output Low Voltage IPG = 5mA (sinking), VEN/DLY = 0V 135 mV
PG Leakage Current VPG = 5.5V; VFB = 0.9V 1.0
2.0 A
Micrel, Inc. MIC22405
June 2011 5 M9999-061511-A
Electrical Characteristics(4) (Continued)
VIN = PVIN = VEN/DLY = 3.3V, VOUT = 1.8V, TA = 25°C, unless noted. Bold values indicate –40°C< TJ < +125°C.
Parameter Condition Min. Typ. Max. Units
Thermal Protection
Over-temperature Shutdown TJ Rising 150 °C
Over-temperature Shutdown
Hysteresis 10 °C
Notes:
1. Exceeding the absolute maximum rating may damage the device.
2. Devices are ESD sensitive. Handling precautions recommended.
3. The device is not guaranteed to function outside its operating rating.
4. Specification for packaged product only.
Micrel, Inc. MIC22405
June 2011 6 M9999-061511-A
Typical Characteristics
VIN Operating Supply Current
vs. Input Vo ltage
8
10
12
14
16
18
2.5 3.0 3.5 4.0 4.5 5.0 5.5
I NPUT VOLTA GE ( V)
SUPPLY CURRENT (mA)
V
OUT
= 1.8V
I
OUT
= 0A
SWITCHING
VIN Shut dow n C urrent
vs. Input V olt age
2
4
6
8
10
2.5 3.0 3.5 4.0 4.5 5.0 5.5
I NPUT VOLTA G E (V)
SHUTDOWN CURRENT (µ A)
V
EN/DLY
= 0V
Feedback Vol tage
vs. Input Voltage
0.690
0.694
0.698
0.702
0.706
0.710
2.5 3.0 3.5 4.0 4.5 5.0 5.5
I NPUT VOLTA GE ( V)
FEEDBACK VO L TAGE ( V)
V
OUT
= 1.8V
Load Regulation
vs. Input V oltage
-0.4%
-0.2%
0.0%
0.2%
0.4%
0.6%
2.5 3.0 3.5 4.0 4.5 5.0 5.5
I NPUT VOLTA GE ( V)
TO TAL REG ULATI ON (% )
V
OUT
= 1.8V
I
OUT
= 0A to 4A
Current Li m it
vs. Input Voltage
0
5
10
15
20
2.5 3.0 3.5 4.0 4.5 5.0 5.5
I NPUT VOLTA G E (V)
CURRENT LIM IT ( A)
V
OUT
= 1.8V
Switching Frequency
vs. Input V oltage
800
850
900
950
1000
1050
1100
2.53.03.54.04.55.05.5
INPUT VOLTAGE (V)
SW I T CHING F REQUENCY
(kHz)
V
OUT
= 1.8V
I
OUT
= 0A
Enabl e Threshol d
vs. Input Voltage
1.00
1.10
1.20
1.30
1.40
1.50
2.5 3.0 3.5 4.0 4.5 5.0 5.5
INPUT VOLTAGE (V)
ENABLE THRESHOLD ( V)
Rising
Enabl e Input Current
vs. Input V oltage
0.00
0.25
0.50
0.75
1.00
1.25
1.50
2.5 3.0 3.5 4.0 4.5 5.0 5.5
I NPUT VO LT A GE ( V)
ENABLE INPUT CURRENT
(µA)
V
EN/DLY
= 0V
Power Good Threshold/VREF
Rat io vs. Input V oltage
8.0
9.0
10.0
11.0
12.0
2.5 3.0 3.5 4.0 4.5 5.0 5.5
I NPUT VO LT AG E ( V)
V
PG
THRESHO L D/V
REF
(%)
V
REF
= 0.7V
Micrel, Inc. MIC22405
June 2011 7 M9999-061511-A
Typical Characteristics (Continued)
VIN Operati ng Supply Current
vs. Temperat ure
6.0
8.0
10.0
12.0
14.0
-50 -25 0 25 50 75 100 125
TEMPERATURE ( °C)
SUPPLY CURRENT (mA)
V
IN
=3.3V
V
OUT
= 1.8V
I
OUT
= 0A
SW ITCHING
V
IN
Shut down Current
vs. Temperature
0
3
6
9
12
15
-50 -25 0 25 50 75 100 125
TEM PERATURE (°C)
SHUTDO WN CURRENT ( uA)
V
IN
= 3.3V
I
OUT
= 0A
V
EN/DLY
=
0V
V
IN UVLO Threshold
vs. Temperat ure
2.0
2.2
2.4
2.6
2.8
3.0
-50 -25 0 25 50 75 100 125
TEM PERATURE (° C)
VI N THRESHOLD ( V )
Rising
Falling
Feedback Vol tage
vs. Temperature
0.650
0.670
0.690
0.710
0.730
0.750
-50 -25 0 25 50 75 100 125
TEM PERATURE (°C)
FEEDBACK VO L TAGE ( V)
V
IN
= 3.3V
V
OUT
= 1.8V
I
OUT
= 0A
Load R egulati on
vs. Temperature
-0.4%
-0.2%
0.0%
0.2%
0.4%
0.6%
-50 -25 0 25 50 75 100 125
TEMPERA T URE (° C)
LO AD REGULATIO N (% )
V
IN
= 3.3V
V
OUT
= 1.8V
I
OUT
= 0A to 4A
Line Regulati o n
vs. Temperature
-0.2%
-0.1%
0.0%
0.1%
0.2%
-50 -25 0 25 50 75 100 125
TEM PERATURE (°C)
LI NE REGULATION (% )
V
IN
= 2.9V to 5.5V
V
OUT
= 1.8V
I
OUT
= 0A
Swi tchi ng Frequency
vs. Temperature
800
850
900
950
1000
1050
1100
-50 -25 0 25 50 75 100 125
TEM P ERATURE ( °C)
SW I T CHI NG FREQUENCY
(kHz)
V
IN
= 3.3V
V
OUT
= 1.8V
I
OUT
= 0A
Enable Threshold
vs. Temperature
1.16
1.18
1.20
1.22
1.24
1.26
1.28
-50 -25 0 25 50 75 100 125
TEM PERATURE ( °C)
ENABLE THRESHOLD ( V)
V
IN
= 3.3V
Current Li m it
vs. Temperat ure
0
5
10
15
-50 -25 0 25 50 75 100 125
TEM PERATURE (° C)
CURRENT LIM IT ( A)
V
IN
= 3.3V
V
OUT
= 1.8V
Micrel, Inc. MIC22405
June 2011 8 M9999-061511-A
Typical Characteristics (Continued)
Efficiency
vs. Output Current
50
55
60
65
70
75
80
85
90
95
100
01234
O UTP UT CURRENT (A )
EFFICI ENCY ( %)
V
OUT
= 1.8V
V
IN
=3.3V
V
IN
=5.0V
Feedback Vol tage
vs. Output Current
0.675
0.685
0.695
0.705
0.715
0.725
01234
O UTP UT CURRENT (A )
FEEDBACK VOLTAGE (V)
V
IN
= 3.3V
V
OUT
= 1.8V
Li ne Regul ati on
vs. Output Current
-0.02%
0.00%
0.02%
0.04%
0.06%
01234
O UTP UT CURRENT (A )
LI NE REG ULATION (% )
V
IN
= 2.9V to 5.5V
V
OUT
= 1.8V
Swit ch ing Frequency
vs. Output Current
900
950
1000
1050
1100
01234
O U TPU T CURRE NT ( A)
SWITCHI NG FREQ UENCY
(kHz)
V
IN
= 3.3V
V
OUT
= 1.8V
I
OUT
= 0A
Output V olt age (V
IN
= 3.3V)
vs. Output Current
2.3
2.8
3.3
3.8
4.3
01234
O UTP UT CURRENT (A )
O UTPUT VO LTAG E ( V)
V
IN
= 3.3V
V
FB
< 0.8V
T
A
25ºC
85ºC
125ºC
Output V olt age (V
IN
= 5.0V)
vs. Output Current
4.0
4.5
5.0
5.5
6.0
01234
O UTP UT CURRENT (A )
O UTPUT VO LTAG E ( V)
V
IN
= 5.0V
V
FB
< 0.8V
T
A
25ºC
85ºC
125ºC
Ef fi ciency ( V
IN
= 3.3V)
vs. O utput Current
65
70
75
80
85
90
95
100
012345
O UTP UT CURRENT (A )
EFFICI ENCY ( %)
6
V
IN
= 3.3V
2.5V
1.8V
1.5V
1.2V
1.0V
0.9V
0.8V
0.7V
I C Pow er Di ssipation ( V
IN
= 3.3V)
vs. O utput Current
0.00
0.25
0.50
0.75
1.00
1.25
01234
O UTP UT CURRENT (A )
I C POWER DISSI PAT I ON ( W )
V
IN
= 3.3V
2.5V
1.8V
1.5V
1.2V
1.0V
0.9V
0.8V
0.7V
Case Temperat ure* ( V
IN
= 3.3V)
vs. Output Current
0
20
40
60
80
01234
O UTP UT CURRENT (A )
CASE TEM PERATURE ( °C)
V
IN
= 3.3V
V
OUT
= 1.8V
Micrel, Inc. MIC22405
June 2011 9 M9999-061511-A
Typical Characteristics (Continued)
Ef fi ciency ( V
IN
= 5.0V)
vs. Output Current
70
75
80
85
90
95
100
012345
O UTP UT CURRENT (A )
EFFICI ENCY ( %)
6
V
IN
= 5.0V
3.3V
2.5V
1.8V
1.5V
1.2V
1.0V
0.9V
0.8V
0.7V
IC Power Dissipation (V
IN
= 5.0V)
vs. Output Current
0.00
0.24
0.48
0.72
0.96
1.20
01234
O UTP UT CURRENT (A )
IC POWER DISSIPATION (W)
V
IN
= 5.0V
3.3V
2.5V
1.8V
1.5V
1.2V
1.0V
0.9V
0.8V
0.7V
Case Temperat ure* ( V
IN
= 5.0V)
vs. Output Current
0
20
40
60
80
01234
O UTP UT CURRENT (A )
DI E TEMPERATURE ( °C)
V
IN
= 5V
V
OUT
= 1.8V
Die Temperature* : The temperature measurement was taken at the hottest point on the MIC22405 case and mounted on a five-
square inch PCB (see Thermal Me asurement s section). Actual results will depend upon the size of the PCB, ambient temperature, and
proximity to other heat-emitting components.
Micrel, Inc. MIC22405
June 2011 10 M9999-061511-A
Functional Characteristics
Micrel, Inc. MIC22405
June 2011 11 M9999-061511-A
Functional Characteristics (Continued)
Micrel, Inc. MIC22405
June 2011 12 M9999-061511-A
Functional Characteristics (Continued)
Micrel, Inc. MIC22405
June 2011 13 M9999-061511-A
Functional Diagram
Figure 1. MIC22405 Functional Diagram
Micrel, Inc. MIC22405
June 2011 14 M9999-061511-A
Application Information
The MIC22405 is a 4A synchronous voltage mode PWM
step down regulator IC with a programmable frequency
range from 300kHz to 4MHz. Other features include
tracking and sequencing control for controlling multiple
output power systems and power on reset (POR).
By controlling the ratio of the on-to-off time, or duty
cycle, a regulated DC output voltage is achieved. As
load or supply voltage changes, so does the duty cycle
to maintain a constant output voltage. In cases where
the input supply runs into a dropout condition, the
MIC22405 will run at 100% duty cycle.
The internal MOSFETs include a high-side P-channel
MOSFET from the input supply to the switch pin and an
N-channel MOSFET from the switch pin to ground. Since
the low-side N-channel MOSFET provides the current
during the off cycle, a very low amount of power is
dissipated during the off period.
The PWM control technique also provides fixed-
frequency operation. By maintaining a constant
switching frequency, predictable fundamental and
harmonic frequencies are achieved. Other methods of
regulation, such as burst and skip modes, have
frequency spectrums that change with load that can
interfere with sensitive communication equipment.
Component Selection
Input Capacitor
A 22µF X5R or X7R dielectrics ceramic capacitor is
recommended on each of the PVIN pins for bypassing. A
Y5V dielectric capacitor should not be used. Aside from
losing most of their capacitance over temperature, they
also become resistive at high frequencies. This reduces
their ability to filter out high-frequency noise.
Output Capacitor
The MIC22405 was designed specifically for use with
ceramic output capacitors. The output capacitor can be
increased from 100µF to a higher value to improve
transient performance. Since the MIC22405 is in voltage
mode, the control loop relies on the inductor and output
capacitor for compensation. For this reason, do not use
excessively large output capacitors. The output capacitor
requires either an X7R or X5R dielectric. Y5V and Z5U
dielectric capacitors, aside from the undesirable effect of
their wide variation in capacitance over temperature,
become resistive at high frequencies. Using Y5V or Z5U
capacitors can cause instability in the MIC22405.
Inductor Selection
Inductor selection will be determined by the following
(not necessarily in the order of importance):
• Inductance
• Rated current value
• Size requirements
• DC resistance (DCR)
The MIC22405 is designed for use with a 0.47µH to
4.7µH inductor.
Maximum current ratings of the inductor are generally
given in two methods: permissible DC current and
saturation current. Permissible DC current can be rated
either for a 40°C temperature rise or a 10% loss in
inductance. Ensure the inductor selected can handle the
maximum operating current. When saturation current is
specified, make sure that there is enough margin so that
the peak current will not saturate the inductor. The ripple
current can add as much as 1.2A to the output current
level. The RMS rating should be chosen to be equal or
greater than the current limit of the MIC22405 to prevent
overheating in a fault condition. For best electrical
performance, the inductor should be placed very close to
the SW nodes of the IC. For this reason, the heat of the
inductor is somewhat coupled to the IC, so it offers some
level of protection if the inductor gets too hot (In such
cases IC case temperature is not a true indication of
IC diss ipation ). It is important to test all operating limits
before settling on the final inductor choice.
The size requirements refer to the area and height
requirements that are necessary to fit a particular
design. Please refer to the inductor dimensions on their
datasheet.
DC resistance is also important. While DCR is inversely
proportional to size, DCR increase can represent a
significant efficiency loss. Refer to the “Efficiency
Considerations” sub-section for a more detailed
description.
Efficiency Considerations
Efficiency is defined as the amount of useful output
power, divided by the amount of power consumed.
100
IV
IV
% Efficiency
ININ
OUTOUT ×
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
×
×
=
Maintaining high efficiency serves two purposes. First, it
decreases power dissipation in the power supply,
reducing the need for heat sinks and thermal design
considerations and it decreases consumption of current
for battery powered applications. Reduced current
demand from a battery increases the devices operating
time, critical in hand held devices.
There are mainly two loss terms in switching converters:
static losses and switching losses. Static losses are
simply the power losses due to VI or I2R. For example,
power is dissipated in the high side switch during the on
cycle. Power loss is equal to the high-side MOSFET
Micrel, Inc. MIC22405
June 2011 15 M9999-061511-A
RDS(ON) multiplied by the RMS switch current squared
(ISW
2). During the off-cycle, the low-side N-channel
MOSFET conducts, also dissipating power. Similarly, the
inductor’s DCR and capacitor’s ESR also contribute to
the I2R losses. Device operating current also reduces
efficiency by the product of the quiescent (operating)
current and the supply voltage. The current required to
drive the gates on and off at a constant 1MHz frequency
and the switching transitions make up the switching
losses.
Figure 2 illustrates a typical efficiency curve. From 0A to
0.2A, efficiency losses are dominated by quiescent
current losses, gate drive, transition and core losses. In
this case, lower supply voltages yield greater efficiency
in that they require less current to drive the MOSFETs
and have reduced input power consumption.
Ef fi c iency ( V
IN
= 5.0V)
vs. Output Current
70
75
80
85
90
95
100
0123
O UT PUT CURRENT (A )
EFF ICIENCY (% )
4
V
IN
= 5.0V
1.8V
3.3V
Figure 2. Efficiency Curve
From 0.5A to 4A, efficiency loss is dominated by
MOSFET RDS(ON) and inductor DC losses. Higher input
supply voltages will increase the gate-to-source voltage
on the internal MOSFETs, thereby reducing the internal
RDS(ON). This improves efficiency by decreasing DC
losses in the device. All but the inductor losses are
inherent to the device. In which case, inductor selection
becomes increasingly critical in efficiency calculations.
As the inductors are reduced in size, the DC resistance
(DCR) can become quite significant. The DCR losses
can be calculated as follows:
LPD = IOUT
2 × DCR
From that, the loss in efficiency due to inductor
resistance can be calculated as follows:
()
100
LIV
IV
1Loss Efficiency
PDOUTOUT
OUTOUT ×
⎥
⎥
⎦
⎤
⎢
⎢
⎣
⎡
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
+×
×
−=
Efficiency loss due to DCR is minimal at light loads and
gains significance as the load is increased. Inductor
selection becomes a trade-off between efficiency and
size in this case.
Alternatively, under lighter loads, the ripple current due
to the inductance becomes a significant factor. When
light load efficiencies become more critical, a larger
inductor value maybe desired. Larger inductances
reduce the peak-to-peak inductor ripple current, which
minimize losses.
Compensation
The MIC22405 has a combination of internal and
external stability compensation to simplify the circuit for
small, high efficiency designs. In such designs, voltage
mode conversion is often the optimum solution. Voltage
mode is achieved by creating an internal ramp signal
and using the output of the error amplifier to modulate
the pulse width of the switch node, thereby maintaining
output voltage regulation. With a typical gain bandwidth
of 100kHz − 200kHz, the MIC22405 is capable of
extremely fast transient response.
The MIC22405 is designed to be stable with a typical
application using a 1µH inductor and a 100µF ceramic
(X5R) output capacitor. These values can be varied
dependent upon the tradeoff between size, cost and
efficiency, keeping the LC natural frequency
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
××× CL2
1 ideally less than 26 kHz to ensure
stability can be achieved. The minimum recommended
inductor value is 0.47µH and minimum recommended
output capacitor value is 22µF. The tradeoff between
changing these values is that with a larger inductor,
there is a reduced peak-to-peak current which yields a
greater efficiency at lighter loads. A larger output
capacitor will improve transient response by providing a
larger hold up reservoir of energy to the output.
Micrel, Inc. MIC22405
June 2011 16 M9999-061511-A
The integration of one pole-zero pair within the control
loop greatly simplifies compensation. The optimum
values for CCOMP (in series with a 20k resistor) are shown
below.
CÆ
LÈ 22µF 47µF 47µF 100µF 100µF 470µF
0.47µH 0* 10pF 22pF 33pF
1µH 0† 15pF 15 22pF 33pF
2.2µH 15 33pF 33 47pF 100 220pF
* VOUT > 1.2V, † VOUT > 1V
Table 1. Compensation Capacito r Selection
Note: Compensation values for various output voltages and
inductor values refer to table 3.
Feedback
The MIC22405 provides a feedback pin to adjust the
output voltage to the desired level. This pin connects
internally to an error amplifier. The error amplifier then
compares the voltage at the feedback to the internal
0.7V reference voltage and adjusts the output voltage to
maintain regulation. The resistor divider network for a
desired VOUT is given by:
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛−
=
1
V
V
R1
R2
REF
OUT
where VREF is 0.7V and VOUT is the desired output
voltage. A 10k or lower resistor value from the output
to the feedback (R1) is recommended since large
feedback resistor values increase the impedance at the
feedback pin, making the feedback node more
susceptible to noise pick-up. A small capacitor (50pF –
100pF) across the lower resistor can reduce noise pick-
up by providing a low impedance path to ground.
Enable/Delay (EN/DLY) Pin
Enable/Delay (EN/DLY) sources 1µA out of the IC to
allow a startup delay to be implemented. The delay time
is simply the time it takes 1µA to charge CEN/DLY to
1.25V. Therefore:
6
EN/DLY
EN/DLY 101
C1.24
t−
×
×
=
CF Capacitor
Adding a capacitor to this pin can adjust switching
frequency from 800kHz to 4MHz. CF sources 400µA out
of the IC to charge the CF capacitor to set up the
switching frequency. The switch period is simply the time
it takes 400µA to charge CF to 1.0V. Therefore:
CF Capacitor Frequency
56pF 4.4MHz
68pF 4MHz
82pF 3.4MHz
100pF 2.8MHz
150pF 2.1MHz
180pF 1.7MHz
220pF 1.4MHz
270pF 1.2MHz
330pF 1.1MHz
390pF 1.05MHz
470pF 1MHz
Table 2. CF vs. Frequency
It is necessary to connect the CF capacitor between the
CF pin and signal ground.
300kHz to 800kHz Operation
The frequency range can be lowered by adding an
additional resistor (RCF) in parallel with the CF capacitor.
This reduces the amount of current used to charge the
capacitor, reducing the frequency. The following
equation can be used to for frequencies between
800kHz to 300kHz.:
2.9KR
t
R4000
1.0V
1lnCR
CF
CF
CFCF
>
=
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
×
+××−
RC Pin (Soft-Start)
The RC pin provides a trimmed 1µA current source/sink
for accurate ramp-up (soft-start). This allows the
MIC22405 to be used in systems requiring voltage
tracking or ratio-metric voltage tracking at startup.
There are two ways of using the RC pin:
1. Externally driven from a voltage source
2. Externally attached capacitor sets output ramp-
up/down rate
In the first case, driving RC with a voltage from 0V to
VREF will program the output voltage between 0 and
100% of the nominal set voltage as shown in figure 3.
In the second case, the external capacitor sets the ramp-
up and ramp-down time of the output voltage. The time
is given by
6
RC
RAMP 101
C0.7
t−
×
×
=
Where tRAMP is the time from 0 to 100% nominal output
voltage.
During start-up, a light load condition (IOUT < 1.25A) can
lead to negative inductor current. Under these
Micrel, Inc. MIC22405
June 2011 17 M9999-061511-A
conditions, the maximum ramp-up time should not
exceed the critical ramp-up time period to keep regulator
in continuous mode operation when VFB reaches 90% of
reference voltage.
Beyond the critical ramp-up time, the regulator is in
discontinuous mode which leads to prolonged N-channel
MOSFET conduction, which in turn causes negative
inductor current.
The maximum CRC value is calculated as follows.
V
V
1
10•F•L•C•2.86
<C
IN
OUT
6
SWOUT
RC
Pre-Bias Start-Up
The MIC22405 is designed for safe start-up into a pre-
biased output. This prevents large negative inductor
currents and excessive output voltage oscillations. The
MIC22405 starts with the low-side MOSFET turned off,
preventing reverse inductor current flow. The
synchronous MOSFET stays off until the Power Good
(PG) goes high after the VFB is above 90 percent of VREF.
A pre-bias condition can occur if the input is turned off
then immediately turned back on before the output
capacitor is discharged to ground. It is also possible that
the output of the MIC22405 could be pulled up or pre-
biased through parasitic conduction paths from one
supply rail to another in multiple voltage (VOUT) level
ICs such as a FPGA.
Figure 3 shows a normal start-up waveform. A 1µA
current source charges the soft-start capacitor CRC. The
CRC capacitor forces the VRC voltage to come up slowly
(VRC trace), thereby providing a soft-start ramp. This
ramp is used to control the internal reference (VREF).
The error amplifier forces the output voltage to follow the
VREF ramp from zero to the final value.
Figure 3. EN Turn-On Time − Normal Start-Up
If the output is pre-biased to a voltage above the
expected value, as shown in Figure 4, then neither
MOSFET will turn on until the ramp control voltage (VRC)
is above the reference voltage (VREF). Then, the high-
side MOSFET starts switching, forcing the output to
follow the VRC ramp. Once the feedback voltage is
above 90 percent of the reference voltage, the low-side
MOSFET will begin switching.
Figure 4. EN Turn-On at 1V Pre-Bias
When the MIC22405 is turned off, the low-side MOSFET
will be disabled and the output voltage will decay to zero.
During this time, the ramp control voltage (VRC) will still
control the output voltage fall-time with the high-side
MOSFET if the output voltage falls faster than the VRC
voltage. Figure 5 shows this operating condition. Here a
4A load pulls the output down fast enough to force the
high-side MOSFET on (VSW trace).
Figure 5. EN Turn-OFF − 7A Load
If the output voltage falls slower than the VRC voltage,
then the both MOSFETs will be off and the output will
decay to zero as shown in the VOUT trace in Figure 6 with
both MOSFETs off, any resistive load connected to the
output will help pull down the output voltage. This will
occur at a rate determined by the resistance of the load
and the output capacitance.
Micrel, Inc. MIC22405
June 2011 18 M9999-061511-A
Figure 6. EN Turn-Off − 200mA Load
Current Limit
The MIC22405 uses a two-stage technique to protect
against overload. The first stage is to limit the current in
the P-channel switch; the second is over temperature
shutdown.
Current is limited by measuring the current through the
high-side MOSFET during its power stroke and
immediately switching off the driver when the preset limit
is exceeded.
The circuit in Figure 7 describes the operation of the
current limit circuit. Since the actual RDSON of the P-
channel MOSFET varies from part to part, and with
changes in temperature and with input voltage, simple IR
voltage detection is not employed. Instead, a smaller
copy of the Power MOSFET (Reference FET) is fed with
a constant current which is a directly proportional to the
factory set current limit. This sets the current limit as a
current ratio and thus, is not dependant upon the RDSON
value. Current limit is set to nominal value. Variations in
the scale factor K between the power PFET and the
reference PFET used to generate the limit threshold
account for a relatively small inaccuracy.
Figure 7. Current-Limit Detail
Thermal Considerations
The MIC22405 is packaged in a MLF® 3mm x 4mm – a
package that has excellent thermal-performance
equaling that of the larger TSSOP packages. This
maximizes heat transfer from the junction to the exposed
pad (ePad) which connects to the ground plane. The
size of the ground plane attached to the exposed pad
determines the overall thermal resistance from the
junction to the ambient air surrounding the printed circuit
board. The junction temperature for a given ambient
temperature can be calculated using:
TJ = TAMB + PDISS × RθJA
where:
• P
DISS is the power dissipated within the MLF®
package and is at 4A load. RθJA is a combination of
junction-to-case thermal resistance (RθJC) and
Case-to-Ambient thermal resistance (RθCA), since
thermal resistance of the solder connection from the
ePAD to the PCB is negligible; RθCA is the thermal
resistance of the ground plane-to-ambient, so RθJA =
RθJC + RθCA.
• T
AMB is the operating ambient temperature.
Example:
The Evaluation board has two copper planes
contributing to an RθJA of approximately 55°C/W. The
worst case RθJC of the MLF 3mmx4mm is 25oC/W.
RθJA = RθJC + RθCA
RθJA = 25 + 30 = 55oC/W
To calculate the junction temperature for a 50°C
ambient:
TJ = TAMB+PDISS . RθJA
TJ = 50 + (0.89 x 55)
TJ = 98.95°C
This is below the maximum of 125°C.
Micrel, Inc. MIC22405
June 2011 19 M9999-061511-A
Thermal Measurements
Measuring the IC’s case temperature is recommended to
ensure it is within its operating limits. Although this might
seem like a very elementary task, it is easy to get
erroneous results. The most common mistake is to use
the standard thermal couple that comes with a thermal
meter. This thermal couple wire gauge is large, typically
22 gauge, and behaves like a heat-sink, resulting in a
lower case measurement.
Two better methods of temperature measurement are
using a smaller thermal couple wire or an infrared
thermometer. If a thermal couple wire is used, it must be
constructed of 36 gauge wire or higher then (smaller
wire size) to minimize the wire heat-sinking effect. In
addition, the thermal couple tip must be covered in either
thermal grease or thermal glue to make sure that the
thermal couple junction is making good contact with the
case of the IC. Omega brand thermal couple (5SC-TT-K-
36-36) is adequate for most applications.
Whenever possible, an infrared thermometer is
recommended. The measurement spot size of most
infrared thermometers is too large for an accurate
reading on a small form factor ICs. However, an IR
thermometer from Optris has a 1mm spot size, which
makes it a good choice for measuring the hottest point
on the case. An optional stand makes it easy to hold the
beam on the IC for long periods of time.
Sequencing and Tracking
There are four variations which are easily implemented
using the MIC22405. The two sequencing variations are
Delayed and Windowed. The two tracking variants are
Normal and Ratio Metric. The following diagrams
illustrate methods for connecting two MIC22405’s to
achieve these requirements.
Window Sequencing:
Time (4.0ms/div)
Micrel, Inc. MIC22405
June 2011 20 M9999-061511-A
Delayed Sequencing:
Time (4.0ms/div)
Normal Tracking:
Time (4.0ms/div)
Micrel, Inc. MIC22405
June 2011 21 M9999-061511-A
Ratio Metric Tracking:
Time (4.0ms/div)
Micrel, Inc. MIC22405
June 2011 22 M9999-061511-A
VIN = 5V
VOUT L COUT C
COMP R
COMP C
FF R
FF C
FB R
FB
4.2V 1.5µH 2 x 47µF 100pF 20k 1nF 4.7k 100pF 953
Table 3. Compensation Selection
Figure 8. Schematic Reference
Micrel, Inc. MIC22405
June 2011 23 M9999-061511-A
PCB Layout Guidelines
Warning!!! To minimize EMI and output noise, follow
these layout recommendations.
PCB Layout is critical to achieve reliable, stable and
efficient performance. A ground plane is required to
control EMI and minimize the inductance in power,
signal and return paths.
The following guidelines should be followed to insure
proper operation of the MIC22405 converter:
IC
• The 2.2µF ceramic capacitor, which is connected to
the SVIN pin, must be located right at the IC. The
SVIN pin is very noise sensitive and placement of
the capacitor is very critical. Use wide traces to
connect to the SVIN and SGND pins.
• The signal ground pin (SGND) must be connected
directly to the ground planes. Do not route the
SGND pin to the PGND Pad on the top layer.
• Place the IC close to the point of load (POL).
• Use fat traces to route the input and output power
lines.
• Signal and power grounds should be kept separate
and connected at only one location.
Input Capacitor
• A 22µF X5R or X7R dielectrics ceramic capacitor is
recommended on each of the PVIN pins for
bypassing.
• Place the input capacitors on the same side of the
board and as close to the IC as possible.
• Keep both the PVIN pin and PGND connections
short.
• Place several vias to the ground plane close to the
input capacitor ground terminal.
• Use either X7R or X5R dielectric input capacitors.
Do not use Y5V or Z5U type capacitors.
• Do not replace the ceramic input capacitor with any
other type of capacitor. Any type of capacitor can be
placed in parallel with the input capacitor.
• If a Tantalum input capacitor is placed in parallel
with the input capacitor, it must be recommended for
switching regulator applications and the operating
voltage must be derated by 50%.
• In “Hot-Plug” applications, a Tantalum or Electrolytic
bypass capacitor must be used to limit the over-
voltage spike seen on the input supply with power is
suddenly applied.
Inductor
• Keep the inductor connection to the switch node
(SW) short.
• Do not route any digital lines underneath or close to
the inductor.
• Keep the switch node (SW) away from the feedback
(FB) pin.
• To minimize noise, place a ground plane underneath
the inductor.
• The inductor can be placed on the opposite side of
the PCB with respect to the IC. It does not matter
whether the IC or inductor is on the top or bottom as
long as there is enough air flow to keep the power
components within their temperature limits. The
input and output capacitors must be placed on the
same side of the board as the IC.
Output Capacitor
• Use a wide trace to connect the output capacitor
ground terminal to the input capacitor ground
terminal.
• Phase margin will change as the output capacitor
value and ESR changes. Contact the factory if the
output capacitor is different from what is shown in
the BOM.
• The feedback divider network must be place close to
the IC with the bottom of R2 connected to SGND.
• The feedback trace should be separate from the
power trace and connected as close as possible to
the output capacitor. Sensing a long high-current
load trace can degrade the DC load regulation.
RC Snubber
• Place the RC snubber on either side of the board
and as close to the SW pin as possible.
Micrel, Inc. MIC22405
June 2011 24 M9999-061511-A
Evaluation Board Schematic
Bill of Materials
Item Part Number Manufacturer Description Qty.
08056D226MAT AVX(1)
C2012X5R0J226M TDK(2)
C1, C2
GRM21BR60J226ME39L Murata(3)
Capacitor, 22µF, 6.3V, X5R, Size 0805 2
06036D225MAT2A AVX(2)
GRM188R60J225M Murata(3)
C3
C1608X5R0J225M TDK(1)
2.2µF/6.3V, Ceramic Capacitor, X5R, Size 0603 1
GRM188R71H102KA01D Murata(3) Capacitor, 1nF, 50V, X7R, Size 0603
C1608C0G1H102J TDK(2)
C4, C12
06035C102KAT2A AVX(1) Capacitor, 1nF, 10V, COG, Size 0603 2
GRM188R71H471KA01D Murata(3)
C1608X7RH471K TDK(2)
C6
06035C471KAT2A AVX(1)
Capacitor, 470pF, 50V, X7R, Size 0603 1
GRM188R71H390JA01 Murata(3)
C1608COG1H390J TDK(2)
C7
06035A390JAT2A AVX(1)
Capacitor, 39pF, 50V, Size 0603 1
GRM188R71H391JA01 Murata(3)
1608COG1H391J TDK(2)
C8
06035A391JAT2A AVX(1)
Capacitor, 390pF, 50V, Size 0603 1
Micrel, Inc. MIC22405
June 2011 25 M9999-061511-A
Bill of Materials (Continued)
Item Part Number Manufacturer Description Qty.
GRM188R71H101JA01 Murata(3)
C1608COG1H101J TDK(2)
C9
06035A101JT2A AVX(1)
Capacitor, 100pF, 50V, Size 0603 1
GRM31CR60J476ME19 Murata(3)
C3216X5R0J476M TDK(2)
C10, C11
12066D476MAT2A AVX(1)
Capacitor, 47µF, 6.3V, X5R, Size 1206 2
Cin B41125A3477M Epcos 470µF, 10V, Electrolytic, 8x10-case
L1 FP3-1R0-R( 7.2x6.7x3mm ) Cooper(5) Inductor, 1µH, 6.26A 1
CDRH8D28NP-1R0NC ( 8x6x3mm ) Sumida(6) Inductor, 1µH, 8A 1
SPM6530T-1R0M120 ( 7x6.5x3mm ) TDK(2) Inductor, 1µH, 12A 1
R1 CRCW06031101FKEYE3 Vishay(4) Resistor, 1.1k, 1%, Size 0603 1
R2 CRCW06036980FKEYE3 Vishay(4) Resistor, 698, 1%, Size 0603 1
R3 CRCW06032002FKEYE3 Vishay(4) Resistor, 20k, 1%, Size 0603 1
R4 CRCW06034752FKEYE3 Vishay(4) Resistor, 47.5k, 1%, Size 0603 1
R5 (Open) CRCW06031003FKEYE3 Vishay(4) Resistor, 100k, 1%, Size 0603 1
R6 CRCW06032R20FKEA Vishay(4) Resistor, 2.2, 1%, Size 0603 1
R7 CRCW060349R9FKEA Vishay(4) Resistor, 49.9, 1%, Size 0603 1
Q1 2N7002E Vishay(4) Open 1
U1 MIC22405YML Micrel(7) Integrated 4A Synchronous Buck Regulator 1
Notes:
1. AVX: www.avx.com
2. TDK: www.tdk.com
3. Murata: www.murata.com
4. Vishay: www.vishay.com
5. Cooper Bussmann: www.cooperet.com
6. Sumida: www.sumida.com
7. Micrel, Inc.: www.micrel.com
Micrel, Inc. MIC22405
June 2011 26 M9999-061511-A
PCB Layout Recomme ndations
MIC22405 Evaluation Board Top Layer
MIC22405 Evaluation Board Top Silk
Micrel, Inc. MIC22405
June 2011 27 M9999-061511-A
PCB Layout Recommendations (Continued)
MIC22405 Evaluation Board Mid-Layer 1 (Ground Plane)
MIC22405 Evaluation Board Mid-Layer 2
Micrel, Inc. MIC22405
June 2011 28 M9999-061511-A
PCB Layout Recommendations (Continued)
MIC22405 Evaluation Board Bottom Layer
MIC22405 Evaluation Board Bottom Silk
Micrel, Inc. MIC22405
June 2011 29 M9999-061511-A
Package Information
20-Pin 3mm × 4mm MLF® (ML)
Micrel, Inc. MIC22405
June 2011 30 M9999-061511-A
Recommended Landing Pattern
MICREL, INC. 2180 FORTUNE DRIVE SAN JOSE, CA 95131 USA
TEL +1 (408) 944-0800 FAX +1 (408) 474-1000 WEB http://www.micrel.com
Micrel makes no representations or warranties with respect to the accuracy or completeness of the information furnished in this data sheet. This information
is not intended as a warranty and Micrel does not assume responsibility for its use. Micrel reserves the right to change circuitry, specifications and
descriptions at any time without notice. No license, whether express, implied, arising by estoppel or otherwise, to any intellectual property rights is granted
by this document. Except as provided in Micrel’s terms and conditions of sale for such products, Micrel assumes no liability whatsoever, and Micrel
disclaims any express or implied warranty relating to the sale and/or use of Micrel products including liability or warranties relating to fitness for a particular
purpose, merchantability, or infringement of any patent, copyright or other intellectual property right.
Micrel Products are not designed or authorized for use as components in life support appliances, devices or systems where malfunction of a product can
reasonably be expected to result in personal injury. Life support devices or systems are devices or systems that (a) are intended for surgical implant into the
body or (b) support or sustain life, and whose failure to perform can be reasonably expected to result in a significant injury to the user. A Purchaser’s use or
sale of Micrel Products for use in life support appliances, devices or systems is a Purchaser’s own risk and Purchaser agrees to fully indemnify Micrel for
any damages resulting from such use or sale.
© 2010 Micrel, Incorporated.
