Micrel Semiconductor 1849 FORTUNE DRIVE SAN JOSE, CA 95131 U.S.A. 1
SEPTEMBER 1999 VOLUME 9
Contents
HTTP:// www.micrel.com/analogsolutions.html
Introducing The Worlds’ Simplest Surface
Mount Switcher!
Micrel’ s SuperSwitcher™ MIC4680 buck regulator is the first
of a new family of products offering unparalleled output power in
the smallest, simplest footprints.
The MIC4680 is the industry’s first surface mount switching
regulator, providing more than 1A of output current in an SO-8
package with only four external components.
Devices capable of providing the MIC4680’s high output
current have traditionally only been available in large, high power
packages such as TO-220 and TO-263, which are more than five
times the size of the MIC4680!
One of the secrets of the MIC4680 is the use of a SO-8
package with half the thermal resistance of a regular SO-8. This is
achieved by utilizing a concept which MOSFET manufacturers
have been using for years: having four pins on one side of the
package connected to the lead frame the die sits on, giving a low
thermal resistance from the die to the outside world. This makes
the MIC4680 not only a very flexible, but a more reliable and cost-
effective solution for the user.
MIC4680: Worlds’ Simplest Surface Mount Switcher .....1
MIC5245: Newest Addition to the µCap™ Family .........2
MIC2778: Power Supervisor IC for Portables .................3
MIC7201: Differential-to-Single-Ended Converter .........3
QwikRadio™ Receivers Update .....................................4
MIC2550: USB Transceiver for Mobile Products............5
MIC39500: For Low Voltage, High Current FPGAs .......5
Application: Single-Cell Li-Ion Battery Charger .............6
MIC5014: Hot Plug Control Circuit ................................8
The MIC4680 At A Glance
◆Simple buck regulator
◆4V to 34V input voltage operating range, 38V abs. max.
◆Over 1A of continuous output current
◆SO-8 package with twice the normal power handling
capabilities
◆Only four external components
◆Replaces larger TO-220 and TO-263 solutions
◆200kHz switching frequency
◆Nearly zero off current in shutdown, typically 2µA
◆Internally compensated with a typical small signal bandwidth
of 20kHz
◆Fixed output voltages of 3.3V and 5V as well as an adjustable
version down to 1.25V
◆Full current and thermal limit
◆Operation temp of -40°C to +125°C
Up to
34VIN
<5µA Shutdown Current
200KHz
ON/OFF >1A
68µH100µF
• SO-8 with the normal jA (63°C/W)
• Runs cool
• More reliable
• Dissipates excess heat into ground plane
1
/
2
θ
MIC4680
SO-8
MIC4680
SO-8
The Infinite Bandwidth Company
TEL: 1.800.401.9572 FAX: 408.474.0159 HTTP:// www.micrel.com/analogsolutions.html
2
V
IN
OFF ON
1 – 10µF
10nF
2.7V to 6.5V
Totem Pole Output
for Fast Transient Response
Ceramic or
Tantalum Output
Caps
Noise bypass for ultra-low noise
Near zero
off current
MIC5245
The
Clever
Stuff
The World’s Best LDO, the MIC5245
The MIC5245 is a world-class CMOS LDO and the latest
addition to Micrel’s family of µCap low-dropout regulators. It excels
above and beyond its competitors in dropout voltage (100mV @
100mA), ground current (100µA over full load), and noise
(30µV rms). The MIC5245 also has a unique push-pull output stage,
allowing for extremely fast transient response. This output stage
allows the regulator to sink and source current, which increases
transient response speed significantly over traditional source-only
LDOs. The lower dropout and noise, coupled with the fast transient
response and fast turn-on time make the MIC5245 ideal for all
cellular phone technologies.
Key Features
◆Stable with any capacitor, either ceramic or tantalum
◆Output noise: 30µVrms
◆Dropout voltage: 100mV @ 100mA
◆Quiescent current: 100µA (constant over load)
◆Fast transient response: totem-pole output
◆Fast turn-on time: 50µs (C
OUT
= 10µF, C
BYP
= 10nF)
◆Active shutdown clamp: fast turn-off time
MIC5205-3.0 VCO Phase Noise MIC5245-3.0 VCO Phase Noise
10dB!
MIC5205
The Standard Low Noise LDO
for the Past 5 Years
MIC5245
The New Standard
10dB!
Better
Noise
Performance
Better
Noise
Performance
Micrel Semiconductor 1849 FORTUNE DRIVE SAN JOSE, CA 95131 U.S.A. 3
Micrel’s new MIC2778 voltage supervisor is the first supervisor
optimized for tasks like low battery detection in portable devices.
External resistors control the high and low trip points independently,
making hysteresis completely adjustable. No more chattering, no
more waiting for factory trimmed parts.
Unlike most supervisors, the MIC2778 has a separate V
DD
pin, and the inputs and output can be pulled above V
DD
without
adverse effects such as latch-up or excessive current draw.
A built-in 140ms delay generator automatically de-glitches the
output, which can be wire-OR’d with other signals.
Voltage Supervisor Eliminates Low Battery Headaches
Differential to Single-Ended Conversion Made Simple
Key Features
◆IttyBitty™ SOT23-5 packaging
◆No external components required
Key Specs
◆1MHz gain-bandwidth
◆2.8V to 15V supply voltage
◆0.5mA supply current
MIC7201
Differential Single-Ended
V
S
2
IN+ OUT
50k 100k
V+
50k
50k
100k
IN–
V–
MIC7201
1
2
3
4
5
The MIC7201 combines a high
performance rail-to-rail op amp with
precision on-board resistors, creating a
differential-to-single-ended converter all in
Micrel’s IttyBitty™ SOT23-5 package.
No additional external components are
required, and the output is biased to mid-
supply.
Key Features
◆Optimized for battery voltage monitoring
◆Separate trip points for adjustable hysteresis
◆140ms (min.) delay generator de-glitches output
◆Separate V
DD
input
◆Active-low, open-drain output
◆Inputs and output can be pulled above V
DD
◆Ultra-low supply current, 1.0µA (typ.)
◆Micrel’s IttyBitty™ SOT23-5 package
Competition
1
BAT_LOW
0
VBATT
VHIGH
VLOW
TIME
Low Battery Detected;
System Shuts Down
Adequate Hysteresis
Prevents Chatter
as Battery Voltage
Recovers
1
BAT_LOW
0
VBATT
VLOW
TIME
Low Battery Detected;
System Shuts Down
(But Not For Long!)
Inadequate Hysteresis
Causes Chatter as Battery
Voltage Recovers
(Drives Users Crazy!)
VHYST
Micrel
Micrel Doesn’t ChatterOthers Chatter at Low Battery
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4
QwikRadio™ Receivers Enable Wireless Applications
Micrel’s QwikRadio receivers provide wireless capability for previously wired
applications by addressing the key drawbacks of RF — cost and complexity
QwikRadio — Easy to Use
In the past, RF receiver design was quite complex, requiring
many external components and manual tuning. QwikRadio
simplifies receiver design. Most of these requirements are now
integrated on the chip, eliminating the need for manual tuning. This
reduces the number external components down to just the antenna,
a low-cost ceramic resonator, a couple of capacitors, and a power
supply.
QwikRadio — No Trimming
QwikRadio receivers are true single-chip receivers taking RF-
in and producing digital data-out with no trim-pots and just three
external components. Production trimming adds cost and introduces
quality concerns. Trim-pots drift over time, impacting reliability
and range.
QwikRadio — Low Power
Micrel’ s all-CMOS integrated design of fers significant power
savings over bipolar or discrete implementations. Power savings
can be further optimized on the MICRF002 and MICRF003, which
are ideally suited to duty-cycling. In addition, both feature a
“WAKE” function which can be used to enable the receiving system
upon detection of incoming data.
QwikRadio — Low Cost
QwikRadio combines low component count with much lower
manufacturing cost (no production trimming) and competitive
pricing.
Key Specs
◆400MHz and 900MHz bands
◆Data rate up to 20kbps
◆Low power
– 2.4mA continuous operation
– 240µA polled (10% duty cycle)
Target Applications
◆Remote Switching — lights, ceiling fans
◆Remote Control — set-top boxes
◆Security Systems — remote keyless entry , garage door openers
◆Wireless Data — utility metering, wireless keyboard and
mouse, game controllers
Part Number Operating Frequency Data Rate Package
300 - 440MHz 800 - 1000MHz 8-pin SOIC 8-pin DIP 14-pin SOIC 14-pin DIP 16-pin SOIC 16-pin DIP
MICRF001 X 4.8kbps X X
MICRF011 X 10kbps X X
MICRF002 X 10kbps X X
MICRF022 X 10kbps X X
MICRF003 X 20kbps X
MICRF033 X 20kbps X
SHUTDOWN DATA OUT
RF INPUT
900 MHz
5V
RF Input
No
Inductors
No Trim
Pots
Digital
Output
MICRF003
Micrel Semiconductor 1849 FORTUNE DRIVE SAN JOSE, CA 95131 U.S.A. 5
World’s Only USB Transceiver for Mobile Products
If you are planning to add USB communications to your next
design, Micrel’s MIC2550 saves you time and money! The
MIC2550 employs a unique dual supply voltage design which
allows it to operate down to 2.5V on the system side, and connect
directly to the 5V USB voltage bus. With the MIC2550, you can
operate your embedded controller or ASIC down to 2.5V without
any additional voltage translation circuitry or special I/O cells, which
would normally be necessary to support 3.3V USB signalling.
In addition, the MIC2550 takes its operating power directly
from the USB voltage bus, which decreases the power consumed
from your system’s battery. The MIC2550 will draw no more
than 1µA from your battery, enhancing battery life in today’s
mobile products.
Key Features
◆Bidirectional differential-to-single-ended data conversion
◆Integrated 3.3V LDO for termination
◆Fully compliant to USB specification 1.1
◆Operates down to 2.5V
◆Unique dual supply voltage design
◆2µA quiescent current
◆Low speed (1.5Mbps) and high speed (12Mbps) support
◆Low power suspend mode
◆Low height TSSOP package
VIF
RCV
VP
VM
SUS
SPD
OE#
D–
D+
VTRM
D–
D+Embedded
Controller
or
ASIC GND
VBUS V
BUS
V
CC
MIC2550
MIC2550 interface runs from same supply as ASIC,
making input and output signals fully compliant
Built-in LDO saves
cost and space for
providing 3.3V
termination
Transceiver supply current is direct from USB, not
system supply, saving power consumption
2.5V – 5.25V
MIC39500 — Powering Today’s Low Voltage, High
Current FPGAs
Key Features
◆5A, 2.5V LDO has guaranteed 500mV dropout
◆3-pin, 500mV dropout at full load and temperature
◆82% efficiency when operating off of 3V supply
◆Only output capacitor required for operation
◆Fast transient response
◆±1% tolerance
◆Fully protected with current limit, thermal shutdown
and reversed lead insertion
◆For lower current output, see the MIC39300 (3A),
MIC39150 (1.5A) or MIC39100 (1A).
47µF
3.3V I/O Voltage
V
OUT
= 2.5V
V
IN
= 3.0V
Only
500mV
Drop
Altera is a trademark of Altera Corporation. Xilinx is a trademark of Xilinx, Inc.
®
TEL: 1.800.401.9572 FAX: 408.474.0159 HTTP:// www.micrel.com/analogsolutions.html
6
Introduction
The Micrel MIC2179 is a current-mode, 200kHz, synchronous,
buck (step-down) regulator. In this application, the MIC2179 is
configured to provide both constant-current and constant-voltage
for a 1-cell lithium battery charger. The current is sensed on the
high side to avoid ground-bounce noise and the associated problems
usually found in ground referenced circuits. Voltage is sensed using
a simple voltage controller to reduce the parts count and provide a
0.5% voltage tolerance. The MIC2179 operates from a 4.5V to
16.5V input and has the following value-added features: dual-mode
(skip-mode, PWM-mode) operation for high efficiency (up to 96%),
low quiescent current (1.0mA in PWM mode, 600µA in skip mode),
internal current limit, thermal shutdown, undervoltage lockout
(4.35V), low dropout (100% duty cycle) and simplified loop
compensation (current-mode control).
Lithium-Ion Charge States
The three charge states for a lithium-ion battery are trickle
charge, bulk-charge, and overcharge. Starting with a fully discharged
battery , a lithium battery charger needs to change modes sequentially
through these different charge states.
Trickle charge—a constant-current mode used to bring a
battery up to the cutoff voltage (V
CUTOFF
). The battery could be in
deep discharge (2.5V to 2.7V per cell) for many reasons such as
low state of charge, low ambient temperature, shorted cells, or high
internal leakage.
Bulkcharge—occurs while in constant-current mode and the
charger is delivering the maximum allowable current to the battery
(see manufacturer’s specification). This method replaces a majority
of the battery’s charge as quickly as possible until the overcharge
voltage threshold is reached.
Float Charge— maintain a constant voltage on an already
charged cell. Not recommended for li-ion batteries.
Overcharge—is a constant-voltage mode function that occurs
consecutively after bulk charge. As the li-ion battery nears full
capacity, the current decreases, and the battery’s terminal voltage
increases until it reaches its terminal voltage, typically 4.2V. When
the current becomes low enough, less than trickle-charge normally ,
the charging cycle is complete. Li-ion cells should not be float
charged. After the charge cycle is complete, the char ger should be
shut down.
Theory of Operation
The lithium-ion battery charger can be divided in to four blocks:
a constant-current source, constant-voltage source, a switching
regulator and an end-of-charge circuit.
Constant-Current Block
To analyze this block, assume the constant-voltage block (U3
and supporting circuitry) is inactive. Starting with a discharged
battery connected to the charger, the circuit acts like a constant-
current source. An MIC2179 synchronous buck regulator provides
the regulated power. The constant-current source’s feedback loop
consists of R7 (current-sense resistor), U2 (MIC621 1 op amp), Q3
(VN2222 N-channel MOSFET), and the internal 1.24V feedback
of U1 (MIC2179 synchronous buck regulator).
First, the lithium-ion battery charger starts up in trickle-charge
Constant Current and Voltage for a Single-Cell Lithium-
Ion Battery Charger
by Jeff Dixon, Senior Applications Engineer
C6
0.01µF
U3
LM3420M5-4.2
4.2V Voltage Controller
IN
COMP
GND
Single
Li-Ion
Cell
Q4
VN2222
D2
SS12
1
OUT
MIC6211
U2 3
4
1
5
2
C5
0.01µF
R5
100Ω
0.5%
C4
0.01µF
Q3
VN2222
BIASSGND
PWRGD
COMP
PGND
FB
SW
VIN L1
68µH
C2
6.8nF C3
0.01µF
MIC2179
PWM
SYNC
EN
R1
100k
1%
R2
10k
1%
C1
68µF
20V U1
15
6
5
13
89-12 14
7
1,2,
19,20
3, 4
16,17
D1
MBRS140 1.1M
MIC6270
U4
200k
3
4
1
5
2
MIC6211
U5
4
3
1
5
R11
75k
R9
100k
2
R6
976Ω
1%
R8
976Ω
1%
R10
100k
10k
1%
R7
0.1Ω
1%
Trickle Charge
Resistor (120mA)
R4
1.15k
0.5%
R3
10.2k
0.5%
Fast
Charge
Resistor
(1.2A)
Q2
VN2222
HIGH = FAST CHARGE
LOW = TRICKLE CHARGE
Charge
Current
Shutdown
HIGH = SHUTDOWN
LOW = ENABLE
VIN
6.5V to 16.5V
Q1
VN2222
R12
100k 1%
100k
C7
VOUT
4.2V/1.2A
C2
68µF
20V
End Charge
D3
1N4148
1.24V
TTL Logic Levels
IOUT ≥ 120mA
IOUT ≤ 120mA
R13
4.2k
Micrel Semiconductor 1849 FORTUNE DRIVE SAN JOSE, CA 95131 U.S.A. 7
mode. In trickle mode, the output of U2 (MIC6211) is on, biasing
Q2 on, allowing the output of the MIC2179 to source 121mA of
charging current to the battery. The intelligent system or
microprocessor senses the low logic level at the output of U4 and
places the charger into the bulk-mode charging state (1.2A).
Sequencing from trickle mode to bulk mode is accomplished by
applying a logic high on Q2’s gate. In bulk-mode, current ramps
up to 1.20A (for a 1-cell lithium application) through sense-resistor
R7 (100mΩ) creating a 120mV drop.
Initially, the inverting input of U2 is lower than the non-
inverting input causing the output to go higher , increasing drive to
Q3. This increases the current through the parallel combination of
R3 and R4 until 1.24V is developed across them. The MIC2179
feedback pin senses the 1.24V and compares it to the internal 1.24V
bandgap reference and reduces output duty cycle until 120mV is
maintained across resistor R7. Finally , there is 120mV at both inputs
of the MIC621 1 (op amp), completing the negative feedback loop.
Trickle charge and bulk charge is calculated using:
Trickle Charge Current 1.24V
R3 R5
R7 121mA=
=
Bulk Charge Current 1.24V
R3|| R4 R5
R7 1.20A=
=
Constant-Voltage Source
Once the battery’s terminal reaches the 4.2V (1-cell lithium-
ion battery overcharge threshold), the constant-current source circuit
is biased off. As the output voltage of the charger tries to go higher
than 4.2V, the output of U3 (open-emitter configuration) biases D3
on. The feedback pin of the MIC2179 is now pulled-up toward the
4.2V V
OUT
rail, reducing duty cycle and maintaining output voltage
regulation. The constant voltage feedback loop consists of U3
(LM3420A), D3, U1 (MIC2179), L1, R7, D2, and Q4.
Because overvoltage conditions greatly reduce the life span
of a lithium battery, an LM3420A was chosen for the voltage
feedback loop to help maintain terminal voltage to 0.5%.
In this charger design when the input supply is disconnected,
diode D2 is reverse biased to prevent battery discharge. Q4 is
bifunctional: it prevents the battery from being discharged when
the input supply is removed; and it alleviates a race condition
between the LM3420 and the start-up of the MIC2179 switching
regulator. The LM3420 must be on before the output of the
MIC2179 comes up.
End-of-Charge Circuit
The end-of-charge circuit is used to signal the microprocessor
or another subsystem when the lithium-ion battery pack has reached
the overcharge threshold. Again, in this 1-cell lithium-ion
application, the overcharge threshold is 4.2V.
Starting with a discharged battery and the charger in bulk-
charge mode, the constant-current is decreasing and the voltage
across the battery is increasing over time. The change in current
versus voltage is a function of the changing internal impedance of
the lithium-ion battery under charge.
U5 is being used as a differential amplifier to monitor the output
current by sensing the I·R drop across sense resistor R7. The gain
of U5 is set to 102.5. The gain of U5 is set to maintain greater than
1.24V at its output down to a I
OUT
of greater than 120mA. U4
compares the output of U5 against the 1.24V bandgap reference on
its non-inverting pin generated by the internal bandgap reference
of MIC2179. In bulk-charge mode, the output of U5 is always higher
than U4’s reference voltage, thus maintaining a logic level low at
the end-of-charge pin.
Once R7 has less than a 12mV drop across it, the output of U5
can no longer sustain greater than 1.24V at its output. Now U4 has
1.24V on both its inputs.
Next, the I
OUT
drawn by the battery reduces even further due
to charging. Now the voltage at U4’ s inverting pin is lower than the
1.24V reference producing a logic level high at the output of U4,
signaling an end-of-charge.
The present industry-standard variable used to determine
lithium-ion battery end-of-charge is the current draw at about 90%
charge (see graph below). The end-of-charge current is typically
about C/10. A simple countdown timer circuit (not shown) is usually
started upon reaching the end-of-charge state. Based on the
individual manufacture specification, this completes the charge
cycle.
End-of-charge output current is calculated using a 1.24V reference:
IR7
R9
R6 1.24V
OUT
≤×
()
=
End-of-Charge Theshold
1.24V is the reference for U4 pin 3 which is the end-of-charge
comparator.
Note: This circuit uses 120mA as an end-of-charge threshold. At
the end of charge, the charging circuit should be shut down. It is
not recommended to float charge li-ion cells for long periods of
time.
0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
0 0.5 1.0 1.5 2.0 2.5 3.0
CELL VOLTAGE (V)
CHARGE CURRENT (A)
TIME (HRS)
Current
Cell Voltage
Typical lithium cell voltage vs. charging current
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8
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1849 Fortune Drive
San Jose, CA 95131 USA
Tel: (408) 944-0800
Fax: (408) 944-0970
Eastern US Sales Office
93 Branch Street
Medford, NJ 08055 USA
Tel: (609) 654-0078
Fax: (609) 654-0989
Central US Sales Office, including
Mexico, Central & South America
Suite 450C-199
120 South Denton Tap
Coppell, TX 75019 USA
Tel: (972) 393-3603
Fax: (972) 393-9186
Contact Micrel Semiconductor
Western US Sales Office
3250 Scott Boulevard
Santa Clara, CA 95054 USA
Tel: (408) 914-7670
Fax: (408) 914-7878
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Clere House
21 Old Newtown Road
Newbury RG14 7DP UK
Tel: +44 (1635) 524455
Fax: +44 (1635) 524466
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826-14, Yeoksam-dong
Kangnam-ku
Seoul 135-080 Korea
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Worldwide Web
http://www.micrel.com
Literature Requests
USA: 1-800-401-9572
Outside the U.S.: Contact sales office
Hot-Plug Control Circuit Handles 60V Power Rail
The MIC5014 high-side FET driver can be used to perform
all the necessary control and protection features for a hot-plug
controller. This simple circuit may be added to a circuit board that
is designed to hot-plug into a powered backplane. It enables the
supply voltage slowly, preventing current surges that might
propagate backward through the backplane and affect global power
supply regulation. Additionally, it further protects the backplane
by protecting against short-circuited cards.
Key Features
◆Adjustable output rise time
◆Adjustable current limit
◆High voltage operation
◆Hot-swap compatible
◆Fast reaction to short circuits (<10µs)
Circuit Operation
The MIC5014 High Side N-Channel MOSFET driver provides
a supervoltage (output voltage higher than the input voltage) suitable
for fully enhancing the gate of the FET. When power is applied,
and/or the Shutdown input is released, the MIC5014 charges the
gate of the FET through R3. Overcurrent protection is provided by
R2, Q2, and Q3. When excessive output current flows, the resulting
voltage drop across R2 turns on Q2, which then switches on Q3,
the gate clamp transistor. Q3 discharges the MOSFET gate, disabling
the hot-plug controller output. Q3 also provides the shutdown
function.
Although the MIC5014 is rated to 30V maximum operating
voltage, it may be used in this configuration to well over 60V. Its
supply voltage is clamped by the 15V (nominal) zener diode, which
is current limited by R1. The power dissipated by the zener must
be considered.
High Voltage “Hot Swap” circuit schematic. When power is suddenly applied to VIN, the output is
enabled slowly to prevent current surges and their resulting voltage transients
VIN
20V to 60V 15Q1
Q2
47k
47k
Q3
OUTPUT
3
4
SHUTDOWN
2
10µ
10µ
1N4002
15V
R1
2.7k
MIC5014
VIN
IN
VIN SOURCE
GATE
R3
22Ω
R2
330k
ON OFF
MIC5014
P
ZENER
=V
IN
(max) – 15V
R
1
R
1
=
R
2
=
V
IN
(min) – 15V
10mA
0.44
I
LIM
