Document Number: MC34670
Rev. 3.0, 12/2006
Freescale Semiconductor
Advance Information
* This document contains certain information on a new product.
Specifications and information herein are subject to change without notice.
© Freescale Semiconductor, Inc., 2006. All rights reserved.
IEEE 802.3af PD With Current
Mode Switching Regulator
The 34670 combines a Power Interface Port for IEEE 802.3af
Powered Devices (PD) and a high performance current mode
switching regulator. It allows a designer to build PDs with a minimum
of external components by means of integrating the required IEEE
802.3af functions and all functions necessary to build a high
efficiency DC/DC converter.
On the PD side the 34670 fully supports the IEEE802.3af standard
and provides complete signature and power classification functions.
It controls inrush current limiting and incorporates adjustable
undervoltage lockout. The switching regulator provides excellent line
and load regulation. It drives an external Power MOSFET with sense
resistor.
Features
• Integrated IEEE 802.3af Compliant Interface
• Signature Detection and Classification Functionality
• Integrated Isolation Switch
• Programmable Inrush Current Limiting Control
• Adjustable Undervoltage Lockout
• Input Voltage Range up to 80 V
• Current Mode Control
• Adjustable Oscillator
• Leading Edge Blanking
• Internal Slope Compensation Circuitry
• Input Overvoltage Protection
• 50% Duty Cycle Limitation
• Pb-Free Packaging Designated by Suffix Code EG
Figure 1. 34670 Simplified Application Diagram
POWER OVER ETHERNET
EG SUFFIX (PB-FREE)
98ASB42343B
20-PIN SOICW
34670
ORDERING INFORMATION
Device Temperature
Range (TA)Package
MCZ34670EG/R2 -40°C to 85°C 20 SOICW
PHY PHY
PSE HUB OR SWITCH
TX
RX
HOST PSE POWER
CONTROLLER
48 V POWER
SUPPLY
-48V
GND
CAT 5
SWITCH
RJ-45
PROCESSOR
ETHERNET APPLIANCE (PD)
RX
TX
HOST
PD POWER
CONTROLLER
DC/DC
-48V
CONTROLLER
CABLE
ISOLATION SWITCH
34670
Analog Integrated Circuit Device Data
2Freescale Semiconductor
34670
INTERNAL BLOCK DIAGRAM
INTERNAL BLOCK DIAGRAM
Figure 2. 34670 Simplified Internal Block Diagram
+
+
+
2.5V
0.8R
R
INTERNAL
SUPPLY
HIGH VOLTAGE
REGULATOR
POR OSC
EN
UV or UVLO
CONTROL LOGIC
UNDERVOLTAGE
LOCKOUT
OVERVOLTAGE
DETECTION
250mV
CURRENT
LIMITATION GATE
DRIVE
TEMP
SENSOR
UV or UVLO
R
S
R
Q
8V
5.7V
3.5V
5
µ
A
S
R
Q
0.3V
PWM
COMPARATOR
4.5V
5k
Ω
1.4V
3
REG
DETECT
BLANK
0.4V
0.6V
1.2V
SLOPE
COMP
0.6 - 2.6V
RESET
GATE
VDD
SS
CS
COMP
FB
VOUT
FREQ
VPWR
RCLA
ILIM
UVLO
VIN
RSENSE
Analog Integrated Circuit Device Data
Freescale Semiconductor 3
34670
PIN CONNECTIONS
PIN CONNECTIONS
Figure 3. 34670 Pin Connections
Table 1. 34670 Pin Definitions
Pin Number Pin Name Formal Name Definition
1, 2 VPWR Positive Supply
Voltage Input
This is the most positive power supply input. The load connects between this pin
and the VOUT pin.
3RCLA Classification Resistor Connect a resistor between RCLA and VIN to select the class of the PD.
4UVLO Undervoltage Lookout Used to adjust the undervoltage lookout threshold voltage, connected to VIN to use
the default threshold voltage.
5TEST1 Test pins Connect to VIN in application mode.
6TEST2
7FREQ Frequency Adjustment Adjusts the internal oscillator frequency by connecting a resistor between FREQ
and VIN.
8ILIM Inrush Current Limit Used to adjust the inrush current limit of the isolation switch, add a resistor
between ILIM and VIN.
9VIN Negative Supply Voltage This is the most negative power supply input.
10 VIN
11, 12 VOUT Output Voltage This pin is the drain of the internal Power MOSFET (high current path).
13 VOUT Output Voltage This pin is the drain of the internal Power MOSFET (low current path).
14 RESET RESET Output
(active low)
This is an active-low RESET output signal. This pin is referenced to VOUT.
15 SS Soft Start Input Connect an external capacitor to SS. The internal current source charges the
capacitor and generates a soft-start ramp.
16 COMP Compensation Pin COMP is the output of the error amplifier and is available for feedback
compensation. COMP is pulled-up by an internal 5.0 kΩ resistor to 5.0 V.
17 FB Feedback Input This is the inverting input of the error amplifier. In non-isolated applications it’s
connected to the secondary output through a resistor divider.
18 CS Current Sense The current sense pin CS senses a voltage that is proportional to the current
through the sense resistor.
19 GATE Gate Driver Output GATE drives the gate of the external power MOSFET. GATE sources and sinks
up to 1.0 A.
20 VDD VDD Output VDD mainly supplies the gate of the external power MOSFET. Connect a capacitor
from VDD to VOUT.
1
2
3
5
4
6
7
8
9
10
20
11
12
13
14
15
16
17
18
19
VPWR
VPWR
RCLA
UVLO
TEST1
TEST2
FREQ
ILIM
VIN
VIN
VDD
GATE
CS
FB
COMP
SS
RESET
VOUT
VOUT
VOUT
Analog Integrated Circuit Device Data
4Freescale Semiconductor
34670
ELECTRICAL CHARACTERISTICS
MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS
MAXIMUM RATINGS
Table 2. Maximum Ratings
All voltages are with respect to VIN unless otherwise noted. Exceeding these ratings may cause a malfunction or permanent
damage to the device.
Ratings Symbol Value Unit
ELECTRICAL RATINGS
Power Supply Voltage VPWR -0.3 to 80 V
Supply Current IPWR 18 mA
VOUT Pins Voltage VOUT -0.3 to (VPWR + 0.3) V
UVLO Voltage VUVLO -0.3 to 10 V
RCLA Voltage VRCLA -0.3 to 5.0 V
ILIM Voltage VILIM -0.3 to 5.0 V
FREQ Voltage VFREQ -0.3 to 5.0 V
With respect to:
VOUT(2) VIN(3)
FB, COMP Voltage VFB, VCOMP -0.3 to 5.0 -0.3 to 80 V
SS Voltage VSS -0.3 to 5.0 -0.3 to 80 V
VDD Voltage VDD -0.3 to 16 -0.3 to 80 V
GATE Voltage VGATE -0.3 to (VDD + 0.3) -0.3 to 80 V
CS Voltage VCS -0.3 to 5.0 -0.3 to 80 V
RESET Voltage VRESET -0.3 to 15 -0.3 to 80
ESD Voltage (1)
Human Body Model
Machine Model
VESD1
VESD2 ± 2000
±200
V
Output Clamp Energy ECL 12 mJ
NotesNotes
1. ESD1 testing is performed in accordance with the Human Body Model (CZAP = 100 pF, RZAP = 1500 Ω). ESD2 testing is performed in
accordance with the Machine Model (CZAP = 200 pF, RZAP = 0 Ω).
2. Measured value relative to VOUT
3. Measured value relative to VIN
Analog Integrated Circuit Device Data
Freescale Semiconductor 5
34670
ELECTRICAL CHARACTERISTICS
MAXIMUM RATINGS
THERMAL RATINGS
Operating Temperature
Ambient (4)
Junction (8), (9)
TA
TJ
-40 to 85
120
°C
Storage Temperature TSTG -65 to 150 °C
Power Dissipation (TA = 25 °C) (7) PD800 mW
Thermal Resistance
Junction to Ambient
20LD SOIC W/B Package (9)
RθJA
RθJB
103
47
°C/W
Peak Package Reflow Temperature During Reflow (5), (6) TPPRT Note 6 °C
Thermal Shutdown Temperature TSHUT 180 °C
Thermal Shutdown Recovery Temperature THYST 150 °C
NotesNotes
4. The limiting factor is junction temperature; taking into account the power dissipation, thermal resistance, and heat sinking.
5. Pin soldering temperature limit is for 10 seconds maximum duration. Not designed for immersion soldering. Exceeding these limits may
cause malfunction or permanent damage to the device.
6. Freescale’s Package Reflow capability meets Pb-free requirements for JEDEC standard J-STD-020C. For Peak Package Reflow
Temperature and Moisture Sensitivity Levels (MSL),
Go to www.freescale.com, search by part number [e.g. remove prefixes/suffixes and enter the core ID to view all orderable parts. (i.e.
MC33xxxD enter 33xxx), and review parametrics.
7. Maximum power dissipation at indicated ambient temperature in free air with no heatsink used.
8. For TA = 85°C and PD = 700 mW and RθJB = 47°C/W.
9. Measured with 4 layers 2s2p JEDEC std. PCB.
Table 2. Maximum Ratings (continued)
All voltages are with respect to VIN unless otherwise noted. Exceeding these ratings may cause a malfunction or permanent
damage to the device.
Ratings Symbol Value Unit
Analog Integrated Circuit Device Data
6Freescale Semiconductor
34670
ELECTRICAL CHARACTERISTICS
STATIC ELECTRICAL CHARACTERISTICS
STATIC ELECTRICAL CHARACTERISTICS
Table 3. Static Electrical Characteristics
Characteristics noted under conditions 30 V ≤ VPWR ≤ 60 V, - 40°C ≤ TA ≤ 85°C, VIN = 0 V unless otherwise noted. Typical
values noted reflect the approximate parameter means at TA = 25°C under nominal conditions unless otherwise noted.
Characteristic Symbol Min Typ Max Unit
SIGNATURE DETECTION
Input Offset Current (1.4 V ≤ VPORT ≤ 9.5 V) IOFFSET — — 10 µA
Differential Input Resistance (1.4 V ≤ VPORT ≤ 9.5 V) RDIFF 600 — — kΩ
CLASSIFICATION
Classification Current (13.5 V ≤ VPORT ≤ 20 V)
Class 0: RCLASS = 4.42 kΩ
Class 1: RCLASS = 475 Ω
Class 2: RCLASS = 261 Ω
Class 3: RCLASS = 169 Ω
Class 4: RCLASS = 113 Ω
ICLASS
0
9.0
17
26
36
—
—
—
—
—
4.0
12
20
30
44
mA
Classification Current Limit ICLASS(LIM) — — 50 mA
RCLA Reference Voltage (13.5 V ≤ VPORT ≤ 20 V) VRCLA 4.0 4.5 5.0 V
INRUSH CURRENT LIMITATION (37 V ≤ VPORT ≤ 60 V) (RLIM)
Input Inrush Current, ILIM connected to VIN IINRUSH — — 350 mA
Input Inrush Current, ILIM connected via resistor RILIM to VIN
RILIM = 12.1 kΩ
RILIM = 42.2 kΩ
RILIM = 191 kΩ
IINRUSH
130
70
30
180
110
65
250
165
100
NORMAL OPERATION (VPWR, UVLO)
Supply Voltage VPWR — — 60 V
Supply Current (10) IPWR —4.5 7.3 mA
Default Turn-On Voltage (UVLO = VIN)VUVLO(ON) — — 40 V
Default Turn-Off Voltage (UVLO = VIN)VUVLO(OFF) 30 — — V
UVLO Hysteresis when set internally VHYST(INT) 6.0 — — V
External UVLO Programming Range VUVLO(PR) 25 —50 V
UVLO Reference Voltage VUVLO(REF) 1.96 2.0 2.04 V
UVLO Hysteresis when set externally VHYST(EXT) —15 — %
UVLO Bias Current IUVLO(B) — — 1.0 µA
ISOLATION SWITCH (ILIM)
On-Resistance (VPORT = 48 V, IPORT = 350 mA) (11) RDS(ON) — — 500 mΩ
Isolation Switch Current Limit in Normal Operation Mode ILIM 380 —700 mA
Notes
10. GATE pin open, PWM controller running.
11. Measured across VIN and VOUT.
Analog Integrated Circuit Device Data
Freescale Semiconductor 7
34670
ELECTRICAL CHARACTERISTICS
STATIC ELECTRICAL CHARACTERISTICS
PWM COMPARATOR (COMP)
COMP Control Voltage Range VCOMP 1.3 —4.0 V
COMP Input Bias Current ICOMP(B) — — 1.8 mA
HIGH VOLTAGE REGULATOR
Regulator Output Voltage VDDREG 8.0 9.0 10 V
Regulator Turn-Off Voltage (12) VREG(OFF) VDDReg
+0.5
— V
Regulator Current Limitation (13) IREGLIM 7.0 —15 mA
Regulator Continuous Current IREGDC — — 5.0 mA
GATE DRIVER (UVLO)
Gate Driver UVLO, Rising VGATE(R) VDD-0.5 — — V
Gate Driver UVLO, Falling VGATE(F) — — 6.5 V
CURRENT LIMIT (CS)
CS Threshold Voltage VCS 320 400 480 mV
CS Bias Current ICS(B) — — 30 µA
ERROR AMPLIFIER
Reference Voltage VREF 1.164 1.2 1.236 V
OVERVOLTAGE SHUTDOWN
OVLO Threshold, Rising VOV(R) 66 —72 V
OVLO Threshold, Falling VOV(F) 63 —69 V
OVLO Hysteresis VOV(HYS) —3.0 — V
SOFT-START (SS)
SS Output Voltage VSS —2.0 — V
SS Source Current ISS(OUT) 3.25 5.0 6.75 µA
SS Sink Current ISS(IN) —2.0 2.25 mA
Shutdown Threshold Voltages VSS(R)
VSS(F)
0.48
0.24
0.6
0.3
0.72
0.40
V
THERMAL SHUTDOWN
Thermal Shutdown Temperature TSHUTDOWN 150 165 180 °C
Thermal Hysteresis THYS —30 —°C
Notes
12. An external voltage has to be applied.
13. Thermal limitations of the device might derate usable current range.
Table 3. Static Electrical Characteristics(continued)
Characteristics noted under conditions 30 V ≤ VPWR ≤ 60 V, - 40°C ≤ TA ≤ 85°C, VIN = 0 V unless otherwise noted. Typical
values noted reflect the approximate parameter means at TA = 25°C under nominal conditions unless otherwise noted.
Characteristic Symbol Min Typ Max Unit
Analog Integrated Circuit Device Data
8Freescale Semiconductor
34670
ELECTRICAL CHARACTERISTICS
DYNAMIC ELECTRICAL CHARACTERISTICS
DYNAMIC ELECTRICAL CHARACTERISTICS
Table 4. Dynamic Electrical Characteristics
Characteristics noted under conditions 30 V ≤ VPWR ≤ 60 V, - 40°C ≤ TA ≤ 85°C, VIN = 0 V unless otherwise noted. Typical
values noted reflect the approximate parameter means at TA = 25°C under nominal conditions unless otherwise noted.
Characteristic Symbol Min Typ Max Unit
NORMAL OPERATION
Turn-On Filter Time tFILT(ON) —200 —µs
Turn-Off Filter Time tFILT(OFF) —200 —µs
PWM COMPARATOR
Slope Compensation Ramp as a Function of Switching Frequency
fPWM = 100 kHz
fPWM = 250 kHz
fPWM = 400 kHz
m100
m250
m400
—
—
—
10
25
40
—
—
—
mV/µs
Duty Cycle Limit (14) DMAX — — 48 %
GATE DRIVER
Rise Time (10% - 90%), CLoad = 2.0 nF, VDDREG = 9.0 VtR— — 50 ns
Fall Time (90% - 10%), CLoad = 2.0 nF, VDDREG = 9.0 VtF— — 30 ns
CURRENT LIMIT
Blanking Time (14) tBLANK 40 50 60 ns
PWM OSCILLATOR
Default Clock Frequency (FREQ connected to VIN)fPWM 175 225 325 kHz
Oscillator Frequency Adjusting Resistor Range RFREQ 121 —499 kΩ
Oscillator Frequency Range, RFREQ = 121 kΩfRANGE 320 —480 kHz
Oscillator Frequency Range, RFREQ = 499 kΩfRANGE 80 —120 kHz
ERROR AMPLIFIER
Gain Bandwidth (14) GBW 1.0 — — MHz
DC Open Loop Gain AVOL —80 —dB
RESET OUTPUT
RESET Output Low Voltage (IRESET, SINK = 20 mA) VRESET,LOW — — 0.8 V
RESET Output Filter Time tRESET —20 —µs
Notes
14. Guaranteed by design. Not production tested.
Analog Integrated Circuit Device Data
Freescale Semiconductor 9
34670
ELECTRICAL CHARACTERISTICS
TYPICAL SWITCHING WAVEFORMS
TYPICAL SWITCHING WAVEFORMS
Figure 4. Drain Voltage of Switching MOSFET
Figure 5. Secondary and Output Voltage
Figure 6. Secondary Voltage before Diode
Figure 7. Gate Voltage and Voltage at CS pin
w/o snubber
w/ snubber
w/ snubber
w/o snubber
Analog Integrated Circuit Device Data
10 Freescale Semiconductor
34670
ELECTRICAL CHARACTERISTICS
ELECTRICAL PERFORMANCE CURVES
ELECTRICAL PERFORMANCE CURVES
Figure 8. Efficiency Plot
MC34670 Efficiency Plot: Vo= 5V, w/ bias windin
g
, Coilcraft
DA2362-AL
50.00
55.00
60.00
65.00
70.00
75.00
80.00
85.00
90.00
0.40 0.60 0.80 1.00 1.20 1.40 1.60 1.80 2.00
IO [A]
%
57V
48V
36V
MC34670 Efficiency Plot: Vo= 5V, w/o bias windin
g
, Coilcraft
DA2142-AL
50.00
55.00
60.00
65.00
70.00
75.00
80.00
85.00
90.00
0.40 0.60 0.80 1.00 1.20 1.40 1.60 1.80 2.00
IO [A]
%
57V
48V
36V
Analog Integrated Circuit Device Data
Freescale Semiconductor 11
34670
FUNCTIONAL DESCRIPTION
INTRODUCTION
FUNCTIONAL DESCRIPTION
INTRODUCTION
The 34670 combines a Power Interface Port for IEEE
802.3af Powered Devices (PD) and a high performance
current mode switching regulator. It allows a designer to build
PDs with a minimum of external components by means of
integrating the required IEEE 802.3af functions and all
functions necessary to build a high efficiency DC/DC
converter. Thus 34670 gives the system designer a device
that drastically reduces cost and board space.
On the PD side the 34670 fully supports the IEEE802.3af
standard and provides complete signature detection and
power classification functions. It controls inrush current
limiting and incorporates an adjustable undervoltage lockout.
The 34670 includes thermal protection circuitry to protect the
device in case of high power dissipation.
The 34670 also offers an input overvoltage detection to
protect the external switching MOSFET by disabling the gate
driver in case of input line overvoltage.
The switching regulator provides excellent line and load
regulation. It drives an external power MOSFET with sense
resistor. The switching frequency is adjustable between
100 kHz and 400 kHz. The output voltage feedback
information can be accomplished by an optocoupler, if
isolation is required.
An internal logic control block manages the sequencing of
signature detection, classification and proper turn on and turn
off of the DC/DC converter.
FUNCTIONAL PIN DESCRIPTION
POSITIVE SUPPLY VOLTAGE INPUT (VPWR)
This is the most positive power supply input. The load
connects between this pin and the VOUT pin.
CLASSIFICATION RESISTOR (RCLA)
Connect a resistor between RCLA and VIN to select the
class of the PD.
UNDERVOLTAGE LOOKOUT (UVLO)
Used to adjust the undervoltage lookout threshold voltage,
connected to VIN to use the default threshold voltage.
TEST PINS (TEST1, TEST2)
Connect to VIN in application mode.
FREQUENCY ADJUSTMENT (FREQ)
Adjusts the internal oscillator frequency by connecting a
resistor between FREQ and VIN.
INRUSH CURRENT LIMIT (ILIM)
Used to adjust the inrush current limit of the isolation
switch, add a resistor between ILIM and VIN.
NEGATIVE SUPPLY VOLTAGE (VIN)
This is the most negative power supply input.
OUTPUT VOLTAGE (VOUT)
This pin is the drain of the internal Power MOSFET (high
current path and low current path).
RESET OUTPUT (RESET)
This is an active-low RESET output signal. This pin is
referenced to VOUT.
SOFT START INPUT (SS)
Connect an external capacitor to SS. The internal current
source charges the capacitor and generates a soft-start
ramp.
COMPENSATION PIN (COMP)
COMP is the output of the error amplifier and is available
for feedback compensation. COMP is pulled-up by an
internal 5.0 kΩ resistor to 5.0 V.
FEEDBACK INPUT (FB)
This is the inverting input of the error amplifier. In non-
isolated applications it’s connected to the secondary output
through a resistor divider.
CURRENT SENSE (CS)
The current sense pin CS senses a voltage that is
proportional to the current through the sense resistor.
GATE DRIVER OUTPUT (GATE)
GATE drives the gate of the external power MOSFET.
GATE sources and sinks up to 1.0 A.
VDD OUTPUT (VDD)
VDD mainly supplies the gate of the external power
MOSFET. Connect a capacitor from VDD to VOUT.
Analog Integrated Circuit Device Data
12 Freescale Semiconductor
34670
FUNCTIONAL DEVICE OPERATION
OPERATIONAL MODES
FUNCTIONAL DEVICE OPERATION
OPERATIONAL MODES
POWER DEVICES (PD) INTERFACE
The PD interface of the 34670 has been designed to
comply with the requirements of the IEEE standard 802.3af.
The device operates in three different modes, depending on
the input voltage.
PD OPERATING MODES
The IEEE 802.3af standard defines three operating modes
in general. These modes are summarized in Table 5.
SIGNATURE RESISTOR DETECTION
A PD shall present a valid detection signature at the PD
input connector to get properly detected as a power over LAN
enabled pin. Valid and non-valid detection signature regions
are separated by guard bands. See Figure 9 for valid and
non-valid signature regions.
Figure 9. Signature Resistance Guard Bands
The effective resistance across the input pins is calculated
by two subsequent voltage-current measurements made
during the detection process by the PSE.
VALID PD DETECTION SIGNATURE
CHARACTERISTICS
During signature detection phase the Power Sourcing
Equipment (PSE) applies a voltage in the range 2.7 V -
10.1 V on the PI connector and looks for the 25 kΩ signature
resistor. Since the PD circuitry includes bridge rectifiers, the
PD has to compensate for the voltage drop across the diodes
and the diodes serial resistance. The effective signature
resistance dR is obtained by the V-I-Slope measurement of
the PSE (Figure 10).
It can be seen in Figure 11, that a signature resistor of
25 kΩ as defined in IEEE 802.3af and two diodes in series
would lead to an effective resistance out of the valid region
specified in Figure 9. At low voltages the effective resistance
is above the maximum allowed value of 26.25 kΩ, as
illustrated in Figure 11. Therefore one has to adjust the
signature resistor RSIG (R1 and R2, see UVLO Adjustment
on page 13) to a value below 25 kΩ to stay within the valid
region.
Figure 11. dR at Low Input Voltages
Table 5. PD Operating Modes
Operating Mode Voltage at PD Input Connector
Signature Resistor Detection 2.7 V - 10.1 V
Classification 14.5 V - 20.5 V
Normal Operation Mode 37 V - 57 V
Signature [kΩ]
non-valid region
12 23.75 26.25 45
non-valid region
valid region
I
V
I1
I2
V1V2
RdV2V1
–
I2I1
–
---------------------=
Figure 10. dR Measurement
Analog Integrated Circuit Device Data
Freescale Semiconductor 13
34670
FUNCTIONAL DEVICE OPERATION
OPERATIONAL MODES
CLASSIFICATION
A PD may optionally be classified by the PSE. The intent
of classification is to provide a method for more efficient
power allocation through the PSE. The PD classification
allows the PSE to identify four different (power) classes
depending on the required power that the PD will draw during
normal operation. The classes and the corresponding
maximum power drawn by the PD is shown in Table 6.
Table 6. PD Classes
PD CLASSES
During classification probing by the PSE, the PD applies
the appropriate load current onto the line. The PSE measures
the load current and can determine the classification as
described in Table 7.
.
CLASSIFICATION SIGNATURE LOAD CURRENT
The implementation for the classification circuitry is shown
in Figure 12.
Figure 12. Classification Circuitry
A constant voltage is applied at pin RCLA and depending
on the resistor RCLASS, a current from +VPORT to -VPORT is
flowing with the following relation:
ICLASS is the classification current that is measured by the
PSE. The values for the RCLASS resistor corresponding to the
appropriate class are listed in Table 8.
UVLO ADJUSTMENT
The 34670 has default UVLO settings that corresponds to
the IEEE 802.3af standard. Nevertheless the user can adjust
the UVLO by an external resistor divider as sketched in
Figure 13. Since the UVLO resistor divider replaces the
Class Usage Maximum Power
[W]
0Default 0.44 - 12.95
1Optional 0.44 - 3.84
2Optional 3.84 - 6.49
3Optional 6.49 - 12.95
4Reserved —
Table 7. PD Class vs. Classification Current
Class
Classification Current [mA]
Condition
Min Max
0 0 4 14.5 - 20.5 Volts
measured at PD
input connector
1 9 12
217 20
326 30
436 44
Table 8. PD Class vs. Classification Resistor RCLASS
Class Classification Current [mA] RCLASS [Ω]
02.0 4.42k
110.5 475
218.5 261
328 169
440 113
+VPORT
-VPORT
RCLASS
RCLA
VPWR
VIN
34670
Vref
-
+
ICLASS
EN
ICLASS
VRCLA
RCLASS
---------------------=
Analog Integrated Circuit Device Data
14 Freescale Semiconductor
34670
FUNCTIONAL DEVICE OPERATION
OPERATIONAL MODES
signature resistor, the total resistance of R1+R2 must equal
25 kΩ.
Figure 13. UVLO Adjustment by External
Resistor Divider
To use the default settings for UVLO, the pin UVLO must
be connected to VIN. In this case, a valid signature resistor
has to be placed between -VPORT and +VPORT. This
configuration can be seen in Figure 14.
Figure 14. Default UVLO Settings
To calculate the values for R1 and R2 the following
equations should be used:
where VUVLO(ON) is the desired turn-on voltage threshold and
VUVLO(ref) the UVLO reference voltage.
The typical turn-off voltage VUVLO(OFF) is 85% of the turn
on voltage VUVLO(ON).
INRUSH CURRENT LIMITATION
The 34670 has been designed to interface also with legacy
PoE-PSEs which do not meet the inrush current requirement
of the IEEE 802.3af specification. By setting the initial inrush
current limit to a low level, a PD using the 34670 minimizes
the current drawn from the PSE during start-up. The
maximum inrush current level can be set by connecting a
resistor from ILIM to VIN as illustrated in Figure 15.
Figure 15. Inrush Current Limitation by External
Resistor RILIM
The following table shows the selectable current limits and
the corresponding resistor value that has to be connected
between pins ILIM and VIN:
After powering up, the 34670 switches to the high level
current limit, thereby allowing the PD to consume up to
12.95 W if a 802.3af PSE is present.
PULSE WITH MODULATOR CONTROLLER
CURRENT-MODE CONTROL OPERATION
The 34670 offers current-mode control operation with
leading-edge blanking. The current-limit comparator monitors
the CS pin at all times and provides cycle-by-cycle current
limit.
The CS signal contains a leading-edge spike that is the
result of the MOSFET gate charge current, capacitive and
diode reverse recovery current of the power circuit. The
leading-edge blanking of the CS signal prevents the PWM
comparator from premature termination of the on cycle.
The 34670 limits the duty cycle to 50%. This is
advantageous for applications which are not allowed to
exceed an on-time of 50 % of the switching period TS. Beside
the duty-cycle limit, slope compensation is provided to
stabilize the inner current loop and avoid oscillations for
R2
R1
-VPORT
+VPORT
RCLA
VPWR
UVLO
ILIM
VIN
RSIG
25kΩ
-VPORT
+VPORT
RCLA
VPWR
UVLO
ILIM
VIN
R1R2
+R
SIG
=
R2
VUVLO REF()
VUVLO ON()
----------------------------------RSIG
⋅=
Table 9. Inrush Current Limit vs. RILIM
Inrush Current Limit [mA] RILIM Value [kΩ]
180 12.1
110 42.2
65 191
R1RSIG R2
–=
VUVLO OFF()
VUVLO ON()
0.85⋅=
RSIG
25kΩ
-VPORT
+VPORT
RCLA
VPWR
UVLO
ILIM
VIN
RILIM
RCLASS
Analog Integrated Circuit Device Data
Freescale Semiconductor 15
34670
FUNCTIONAL DEVICE OPERATION
OPERATIONAL MODES
converters running in continuos conduction mode (CCM).
The value of the slope compensation depends on the
switching frequency. See Table 10.
ISOLATED OPTOCOUPLER FEEDBACK
Isolated voltage feedback can be accomplished by using
an optocoupler and a shunt regulator (see Figure 19). The
output voltage accuracy is a function of the accuracy of the
shunt regulator and feedback resistor divider tolerance,
therefore the feedback resistors should have an appropriate
accuracy.
Since the error amplifier function is implemented on the
secondary side by the optocoupler and a 3-pin adjustable
shunt regulator, the internal error amplifier of the 34670 is not
used. The FB pin is connected to VOUT, thus disabling the
internal open-drain error amplifier.
The bias voltage for the optocoupler is accomplished
through the internal 5.0 kΩ pull-up resistor between COMP
and an internal 5.0 V reference.
When a TL431 or TLV431 shunt regulator is used for
output voltage regulation, the output voltage is set by the ratio
of resistors R1 and R2, see Figure 16 for details. The output
voltage is given by the following equation:
where VREF = 1.24 V for the TLV431 (VREF = 2.5 V for the
TL431).
Figure 16. Isolated Optocoupler Feedback
ISOLATED PRIMARY CONTROL FEEDBACK
Another option to accomplish isolated feedback is the use
of a tertiary winding (see Figure 21). The advantage of this
solution without optocoupler and shunt regulator is clearly the
cost effectiveness. Nevertheless the line and load regulation
is worse than with optocoupler feedback.
When isolated primary feedback is used, the loop
compensation components are connected between pins
COMP and FB.
INTERNAL REGULATORS
The internal high voltage regulator of the 34670 regulates
from the input voltage across VPWR and VIN down to the
VDD voltage. During start-up the high voltage regulator
provides the necessary voltage for the internal gate driver to
commence switching. If the external MOSFET gate drive
pulls less than 3.0 mA under all circumstances, an auxiliary
transformer winding that usually provides the bias voltage for
the chip and the gate driver is not required.
In cases where the external MOSFET gate drive pulls
more than 5.0 mA, an auxiliary winding is needed to reduce
the power dissipation in the internal high voltage LDO. See
Figure 18 for an application drawing. It is recommended to
add a 0.1 µF ceramic capacitor in parallel with the existing
load capacitor. This reduces noise at the VDD pin caused by
the auxiliary winding.
The high voltage regulator is disabled when the VDD pin is
forced by an external voltage above the VDD regulation point.
Table 10. Slope Compensation Values
Switching Frequency [kHz] Slope Compensation [mV/µs]
100 10
250 25
400 50
VOVREF 1
R1
R2
-------+
⎝⎠
⎜⎟
⎛⎞
⋅=
T1
NPNS
RV
R1
TLV431
R2
Analog Integrated Circuit Device Data
16 Freescale Semiconductor
34670
FUNCTIONAL DEVICE OPERATION
OPERATIONAL MODES
This reduces power dissipation in the device and improves
overall efficiency.
Figure 17. VDD and MOSFET Driver Output Behavior
A load capacitor connected to VDD ensures a proper
filtering of the VDD voltage. The minimum capacitance value
for this load capacitor should be at least 10 µF. An electrolytic
type capacitor is sufficient.
Please refer to application note A/N3279 for further
information about the size of the capacitor.
If VDD falls below the UVLO threshold, the voltage
regulator is disabled and the MOSFET driver output (GATE)
is held low.
PWM CONTROLLER UVLO, SOFT-START, AND
SHUTDOWN FUNCTION
The soft-start function provided by the 34670 allows the
output voltage to ramp up in a controlled way, thus
eliminating output voltage overshoot.
While the PWM controller is in undervoltage lockout, the
capacitor CSS connected to the SS pin is fully discharged.
After coming out of undervoltage lockout, an internal current
source starts charging the capacitor CSS to initiate soft-start.
When VSS has reached 0.6 V, the gate driver is enabled and
PWM operation begins. The duty cycle during soft-start is
primarily controlled by the internal sawtooth voltage and the
voltage at the SS pin. If the voltage at the SS pin is above
2.6 V, the regular PWM control through pins CS, COMP, and
FB takes over and soft-start is finished.
The following equation calculates the total soft-start time:
OVERVOLTAGE SHUTDOWN
The 34670 includes an overvoltage protection (OVP)
feature that turns off the external MOSFET when the input
voltage exceeds the overvoltage threshold.
When the overvoltage protection is triggered
(VPWR > VOV(R)), the gate driver is immediately disabled. At
the same time, the slow discharge of CSS is initiated. While
the soft-start capacitor is discharging, the gate driver remains
disabled. Once VSS = 0.3 V and the overvoltage
(VPWR < VOV(F)) condition disappears, operation resumes
through a regular soft-start.
CURRENT-SENSE COMPARATOR
The current-sense (CS) comparators and its associated
circuitry limits the peak current through the MOSFET. Current
is sensed at CS pin as a voltage across the sense resistor
RCS between the source of the MOSFET and VOUT.
The CS input has two voltage trip levels, a 600mV high
limit and a 400 mV low limit. When the voltage on CS
produced by a current through the current sense resistor
exceeds the high limit threshold, the current ON-cycle is
immediately terminated and the GATE output is pulled low.
If the low limit threshold is exceeded for longer than 50 ns
(typical blanking time), the current ON-cycle is also
terminated. The blanking time ensures a false termination of
the switching cycle caused by the leading-edge spike on the
sense waveform.
The current-sense resistor RCS is selected according to
the following equation:
where ILIM(primary) is the maximum peak primary-side
current.
In case of an overcurrent in the external MOSFET the
current switching cycle is terminated and GATE is pulled low.
The soft-start capacitor CSS is discharged and after removal
of the faulty condition the PWM is re-started through a regular
soft start.
PWM OSCILLATOR
A default 250 kHz oscillator sets the switching frequency
of the PWM controller. The frequency of the oscillator can be
adjusted between 100 kHz and 400 kHz by an optional
external resistor RFREQ connected from the FREQ pin of the
integrated circuit to VIN.
The appropriate switching frequency fPWM can be
calculated as shown below:
where fPWM is the PWM switching frequency and RFREQ is the
frequency adjusting resistor.
To use the default frequency of 250 kHz the FREQ pin can
be connected to VIN or can be left open.
RESET OUTPUT
The RESET pin is an open drain output. The reset control
circuit supervises the FB voltage and recognizes if the output
HVReg enable
GATE enable
10
2
4
6
8
VGATE( R)
VREG(OFF)
12
VGATE( F)
VDD
t
tSS ms[]0.4 CSS nF[]⋅=
RCS
400mV
ILIM primary()
----------------------------------------=
fPWM kHz[] 47920
RFREQ kΩ[]
------------------------------------4+=
Analog Integrated Circuit Device Data
Freescale Semiconductor 17
34670
FUNCTIONAL DEVICE OPERATION
OPERATIONAL MODES
voltage is out of regulation. In this case the RESET pin is
pulled low.
The RESET output can only be used in non-isolated
applications.
There is a 20 µs delay filter preventing erroneous RESET
output pulses. During soft-start, RESET is held low. RESET
is released when the PWM controller is in regulation.
N-CHANNEL MOSFET GATE DRIVER
GATE drives an N-channel MOSFET. GATE sources and
sinks large transient currents up to 1.0 A to charge and
discharge the MOSFET gate. The GATE output is supplied
by the internal generated VDD voltage, which is internally set
to approximately 9.0 V.
For Power-over-Ethernet applications, the used MOSFET
must be able to withstand a DC level of ~60 V plus the
reflected voltage at the primary side of the transformer. This
requires a MOSFET rated at 150 V or 200 V.
Analog Integrated Circuit Device Data
18 Freescale Semiconductor
34670
TYPICAL APPLICATIONS
TYPICAL APPLICATIONS
Please refer to application note AN3279 for further information of PD design and layout recommendations.
Figure 18. Isolated Flyback Converter with Bias Winding
Figure 19. Isolated Flyback Converter without Bias Winding
3
6
1
2
4
5
8
7
RX
TX
CPORT
RCLASS
M1
RCS
T1
VOUT = 5V@2A
R2
R1
NPNS
NAUX
-VPORT
+VPORT
CSS
CIN
RV
CDD 0.1 F
SS
VPWR
RCLA
UVLO
ILIM
VIN VOUTFB
CS
GATE
VDD
FREQ
RESET
COMP
34670
3
6
1
2
4
5
8
7
RX
TX
CPORT
RCLASS
M1
RCS
T1 VOUT = 5V@2A
R2
R1
CDD
D1
NPNS
RV
-VPORT
+VPORT
CSS
CIN
RX+
RX-
TX+
TX-
SPARE+
SPARE-
VPORT
SS
VPWR
RCLA
UVLO
ILIM
VIN VOUTFB
CS
GATE
VDD
FREQ
RESET
COMP
34670
Analog Integrated Circuit Device Data
Freescale Semiconductor 19
34670
TYPICAL APPLICATIONS
Figure 20. Isolated Forward Converter
Figure 21. Isolated Flyback with Primary Control
3
6
1
2
4
5
8
7
RX
TX
CPORT
RCLASS
M1
RCS
T1
R2
R1
CDD
NPNS
RV
Rv1
-VPORT
+VPORT
Rv2
CSS
CIN
NR
SS
VPWR
RCLA
UVLO
ILIM
VIN VOUTFB
CS
GATE
VDD
FREQ
RESET
COMP
34670
3
6
1
2
4
5
8
7
RX
TX
CPORT
RCLASS
M1
RCS
T1
VOUT = 5V@2A
R2
R1
CDD
NPNS
NAUX
-VPORT
+VPORT
CSS
CIN
C2
C1
R2
CAUX
SS
VPWR
RCLA
UVLO
ILIM
VIN VOUTFB
CS
GATE
VDD
FREQ
RESET
COMP
34670
Analog Integrated Circuit Device Data
20 Freescale Semiconductor
34670
TYPICAL APPLICATIONS
Figure 22. Non-Isolated Flyback Converter
3
6
1
2
4
5
8
7
RX
TX
CPORT
RCLASS
M1
RCS
T1
CO
VOUT = 5V@2A
R4
R3
CDD
D1
NPNS
R1
-VPORT
+VPORT
Rb
CSS
CIN
C2
C1
R2
SS
VPWR
RCLA
UVLO
ILIM
VIN VOUTFB
CS
GATE
VDD
FREQ
RESET
COMP
34670
Analog Integrated Circuit Device Data
Freescale Semiconductor 21
34670
REFERENCE DOCUMENTS
REFERENCE DOCUMENTS
Table 11. Reference Documents
Title LIterature Order Number Publication Date
IEEE Std 802.3af™-2003 IEEE Std 802.3af™-2003 18 June 2003
MC34670 Usage and Configuration AN3279
Analog Integrated Circuit Device Data
22 Freescale Semiconductor
34670
PACKAGING
PACKAGE DIMENSIONS
PACKAGING
PACKAGE DIMENSIONS
For the most current package revision, visit www.freescale.com and perform a keyword search using the “98A” listed below.
EG SUFFIX (PB-FREE)
20-PIN
PLASTIC PACKAGE
98ASB42343B
ISSUE J
Analog Integrated Circuit Device Data
Freescale Semiconductor 23
34670
REVISION HISTORY
REVISION HISTORY
Revision Date Description of Changes
1.0 8/2006 • Initial release
2.0 9/2006 • Change to UVLO Hysteresis when set internally on page 6, Regulator Current Limitation
(13) on page 7, OVLO Threshold, Rising on page 7, OVLO Threshold, Falling on page 7,
Shutdown Threshold Voltages on page 7, and Default Clock Frequency (FREQ
connected to VIN) on page 8
• Changed Data Sheet category to “Advanced Information*”
3.0 12/2006 • Typ and Max change to RCLA Reference Voltage (13.5 V ≤ VPORT ≤ 20 V) on page 6
• Deleted Oscillator Frequency Adjusting Resistor Range in Static Electrical
Characteristics
• Split Oscillator Frequent Range into two parameters, Oscillator Frequency Range,
RFREQ = 121 kΩ on page 8 and Oscillator Frequency Range, RFREQ = 499 kΩ on page 8
• Added note to Duty Cycle Limit (14) on page 8, Blanking Time (14) on page 8, and Gain
Bandwidth (14) on page 8
• Changed nomenclature for Peak Package Reflow Temperature During Reflow (5), (6) on
page 5
• Changed name and value for Thermal Shutdown Recovery Temperature on page 5
MC34670
Rev. 3.0
12/2006
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