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FAN7685/FAN7686/FAN7687
PC Power Supply Output Monitoring IC
Features
* * * * * * * * * * * * * PC Power Supply Outputs Supervisory Circuitry Few External Components Over Voltage Protection for 3.3V, 5V and 12V Outputs Under Voltage Protection for 3.3V, 5V and 12V Outputs Over Current Protection for 3.3V, 5V and 12V Outputs Dual Over Current Portection for 12V Outputs(FAN7687) Fault Protection Output With Open Drain Output Open Drain Power Good Output 300ms Power Good Delay 38ms PSON On/Off Delay 73us Debounce 2.3ms PSON to FPO Turn Off Delay Latch Function Controlled by PSON
Description
The FAN7685/FAN7686/FAN7687 is a complete output supervisory circuitry intended for use in the secondary side of the switched mode power supply. It provides overvoltage protection (OVP), undervoltage protection(UVP), overcurrent protection (OCP), and power good signal generator to monitor and control the outputs of the switching power supply system. Remote on/off(PSON) control and some precision protection features are also implemented. It directly senses all the output rails for OVP, UVP, and OCP without external divider resistors. As for output control, power good output(PGO) and fault protection output(FPO) are included. The FAN7685/FAN7686/FAN7687 offers a simple and cost effective solution with minimum number of external components and greatly reduces PCB board space for power supply.
14DIP
Typical Application
* PC Switching Mode Power Supply
1
14SOP
1
Rev. 1.1.0
(c)2004 Fairchild Semiconductor Corporation
FAN7685/FAN7686/FAN7687
Internal Block Diagrams
Vcc 13
Vcc
REF. Start-up POR
3.6V Vref
PSON clr Delay 2.3ms
CLK
Oscillator
Reset
CLK
VS12 10 VS5 12 VS33 11
(9)
UVP L L H
Delay 75ms CLK
R R L
Debounce 73us
R L S Q L
L H FPO
L
3
FPO
CLK
L PWR
clr L PGI_O OVP L L L Vref 3.6V H Q L L L PSON L Debounce 38ms R
CLK
L
R
Vcc
150uA 3.6V
L
L
4 PSON
14 PGO 2
GND
IS33 9
(8)
H
IS5 8
L UVP H L L L
8*Iref 8*Iref 8*Iref
H H
(7)
Vcc
Iref
R H
CLK
L H Short Detector
when AC ON
IS12 5
Debounce 73us
H Delay clr 300ms
CLK
1.2V
Vref PSON
6
1
FAN7685 (FAN7686)
RI
PGI
VCC12 13
Vcc
REF. Start-up POR
Power On Reset
3.6V Vref
PSON clr Delay 2.3ms
CLK
Oscillator
Reset
CLK
R
L L Q L H FPO
UVP Block VS12 10 VS5 12
UVP
L
3 FPO
L H
Delay 75ms CLK
R L
Debounce 73us
R L S
CLK
clr
L
L PGI_O
R
Vcc
150uA 3.6V
VS33 11
OVP Block
OVP
L
PSON L
Debounce 38ms R
CLK
L
L
4 PSON
3.6V H
14 PGO 2 GND
IS33 9
Q
L L L
IS5 8 OCP COMPs
Vcc Iref H H L L H Short Detector
when AC ON
IS12 5
UVP R H
CLK
H H
ISVCC12 7
8*Iref
L L L Vref PSON
Debounce 73us
1.2V
H Delay clr 300ms
CLK
6
1
RI
PGI
FAN7687 FAN7687A
2
FAN7685/FAN7686/FAN7687
Pin Assignments
PGI 1 GND 2
14 PGO 13 VCC
PGI 1 GND 2
14 PGO 13 VCC
PGI GND FPO
1 2
14 PGO 13 VCC12
F A N 7687 FAN7687A
F A N 7 685
F A N 7 686
FPO 3 PSON 4 IS12 5 RI 6 NC 7
12 VS5 11 VS33 10 VS12 9 IS33 8 IS5
FPO 3 PSON 4 IS12 5 RI 6 IS5 7
12 VS5 11 VS33 10 NC 9 VS12 8 IS33
3
12 VS5 11 VS33 10 VS12 9 IS33 8 IS5
PSON 4 IS12 RI
5 6
ISVCC12 7
Pin Definitions
Pin Number 1 2 3 4 5 6 7 Pin Name PGI GND FPO PSON IS12 RI NC IS5* ISVCC12** 8 9 10 11 12 13 14 IS5 IS33* IS33 VS12* VS12 NC* VS33 VS5 Vcc VCC12** PGO I I I I O I I I I I I I I/O I O I I O Power Good Input Ground Fault Protection Output, Open Drain Output Remote On/Off Control Input 12V Over Current Protection Reference Current Setting Resistor No Connection(FAN7685) 5V Over Current Protection(FAN7686) 12V-II Over Current Protection(FAN7687) 5V Over Current Protection(FAN7685/7) 3.3V Over Current Protection(FAN7686) 3.3V Over Current Protection(FAN7685/7) 12V Output Over/Under Voltage Protection(FAN7686) 12V Output Over/Under Voltage Protection(FAN7685/7) No Connection(FAN7686) 3.3V Output Over/Under Voltage Protection 5V Output Over/Under Voltage Protection Supply Voltage(FAN7675/6) Supply Voltage & 12V-II OV/UV Protectioin(FAN7687) Power Good Output, Open Drain Output Pin Function Description
Notes : * : FAN7686 Pin Definitions ** : FAN7687/FAN7687A Pin Definitions
3
FAN7685/FAN7686/FAN7687
Absolute Maximum Ratings
Parameter Supply Voltage Input Voltage Symbol VCC, VCC12 VPSON, VS5, VS33, VPGI, IS5, IS33 VS12, IS12, ISVCC12 Output Voltage Operating Temperature Storage Temperature Power Dissipation VPGO VFPO Topr Tstg PD Value 16 8 16 8 16 -40 ~ 125 -55 ~ 150 1 V C C W Unit V V
*Note : Stresses beyond those listed under "absolute maximum ratings" may cause permanent damage to the device.
Recommended Operating Conditions
Characteristic Supply Voltage Input Voltage VCC, VCC12 VPSON , VS5, VS33, VPGI, IS5, IS33 VS12, IS12, ISVCC12 Output Voltage Output Sink Current Supply Voltage Rising Time, See Note1 Output Current for RI
Note 1. VCC slew rate must be less than 14V/ms.
Min. 4 1 12.5
Typ.
Max. 15
Unit V V V V mA mA ms uA
-
7 15 7 15 30 10 62.5
VPGO VFPO IFPO IPGO tr IO(RI)
4
FAN7685/FAN7686/FAN7687
Electrical Characteristics(VCC = 5V, Ta=25C, unless otherwise specified)
Over Voltage Protection, Under Voltage Protection and FPO Parameter VS33 VS5 VS12, VCC12 VS33 VS5 VS12, VCC12 Ratio of Current Sense Sink Current to Current Sense Setting Pin(RI) Source Current Offset Voltage of OCP Comparator Leakage Current(FPO) Low Level Output Voltage(FPO) PGI and PGO Input Threshold Voltage(PGI) Leakage Current(PGO) Low Level Output Voltage(PGO) PSON Control Input Pull-up Current High-Level Input Voltage Low-Level Input Voltage Total Device Supply Current Switching Characteristics Debounce Time(PSON) Noise Debounce Time PGO Delay Time(PGI to PGO) Internal UVP Delay Time ICC VPSON = 5V 25 50 200 FPO goes low and every time PGI > 1.2 FPO goes low and everytime PGI<1.2 51 200 38 73 300 75 300 1 51 100 410 102 410 mA IPSON VIHPS VILPS VPSON = 0V 2.4 150 1.2 uA V V VPGI ILKG2 VOL2 VPGO = 5V IPGO=10mA 1.16 1.20 1.24 5 0.4 V uA V Test Condition
FAN7687A
Min. 3.9 3.77 5.8
Typ. 4.1 6.1 13.8
Max. 4.3 4.06 6.4 6.16 14.3 14.79 14.5
Unit
Over Voltage Threshold
FAN7687A
5.71 13.3 13.71 13.42 2.55 2.69 4.3 9.3 2.88 4.1 4.37 8.8 10.5 10.21 7.6 -5 8 -
V
FAN7687A(VS12) FAN7687A(VCC12)
2.83 3.02 4.5 4.58 9.8 11.0 10.71 8.4 5 5 0.3 0.7 mV uA V V
FAN7687A
Under Voltage Threshold
FAN7687A
FAN7687A(VS12) FAN7687A(VCC12)
Iref Voffset ILKGI VOLI
Resistor at RI=30k, 0.1% Resistor VPSON=0V VFPO = 5V IFPO=10mA IFPO=30mA
tb1 tb2* td1 td2 td4*
ms us ms ms ms ms
PSON off to FPO Delay Time
td3
tb1+1.6 tb1+2.3 tb1+3.2
* : These parameters although guaranteed over the recommended operating conditions, are not 100% tested in production. 5
FAN7685/FAN7686/FAN7687
Timing Chart
1) AC Input ON/OFF - Normal State
VCC
AC Input Enable
POR
PSON
FPO
tb1
UVP Threshold AC Input Disable
PGI
OUT
PGO
tb2+td1
2) PSON ON/OFF - Normal State
PSON
FPO
td3
tb1
PGI
UVP Threshold
OUT
tb1+tb2
PGO
tb2+td1
6
FAN7685/FAN7686/FAN7687
3) Under Voltage at Normal State
PSON
Latch
FPO
tb2
tb1
UVP Threshold
PGI UVP Threshold
OUT
PGO
tb2+td1
4) Under Voltage at AC Input ON
VCC
AC Input Enable
POR
PSON
Latch
FPO
tb1
tb2+td2
PGI
PGI Threshold
UVP Threshold
OUT
PGO
tb2+td1
7
FAN7685/FAN7686/FAN7687
5) Under Voltage at PSON ON/OFF
PSON
Latch
FPO
td3
tb1
tb2+td2
PGI
PGI Threshold
UVP Threshold
OUT
tb1+tb2
PGO
tb2+td1
6) Over Voltage at PSON ON/OFF
PSON
Latch
FPO
tb2
tb1
PGI OVP Threshold
UVP Threshold
OUT
PGO
tb2+td1
8
FAN7685/FAN7686/FAN7687
Typical Application Circuits
FAN7685 Application Circuit
12V Output
RIS12 RS_12V
5V Coil
RIS5
IS12
RS_5V
VS12 5V Output
PWM
3.3V Coil
RIS33
IS5
RS_3.3V
VS5 3.3V Output
IS33
VS33
5Vsb
1 PGI 2 GND
PGO 14
PGO 5Vsb VS5 VS33 VS12
VCC 13
F A N 7685
3
FPO
VS5 12
PSON
4 PSON 5 IS12 6 RI 7 NC
VS33 11
VS12 10
IS33
9 8
IS5
FAN7687 Application Circuit
12V-I Output
RIS12 RS_12V-I
5V Coil
RIS5
IS12
RS_5V
VS12 5V Output
PWM
3.3V Coil
RIS33
IS5
RS_3.3V
VS5 3.3V Output
12V_II Coil
IS33
RS_12V-II RISVCC12
VS33 12V-II Output
5Vsb
ISVCC12
1 PGI 2 GND 3
PGO 14
PGO 5Vsb VS5 VS33 VS12 IS33 IS5 ISVCC12
VCC12 13
F A N 7687
FPO
VS5 12
PSON IS12
4 PSON 5 IS12 6 RI
VS33 11
VS12 10
IS33
9 8
7 ISVCC12
IS5
9
FAN7685/FAN7686/FAN7687
Application Information
Power Good(PGO) and Power Good Delay
A PC power supply is commonly designed to provide the motherboard with a power good signal, which is defined by the computer manufacturers. If the +3.3V, +5V, and +12V outputs are above the undervoltage threshold limit, the PC power supply makes the power good signal high. At this time the power supply should be able to provide enough power to assure continuous operation within the specification. Conversely, when one of the +3.3V, +5V, or +12V outputs falls below the undervoltage threshold or rises above the overvoltage threshold, or when main power has been turned off for a sufficiently long time so that power supply operation is no longer assured, a PGO signal will be a low state. The AC input, power good(PGO), remote on/off(PSON), and +3.3V/+5V/+12V supply rails are shown in the below figure.
T1 VAC PSON +12VDC +5VDC +3.3VDC PGO
95% 10%
T5
T3 T2 T4 T6
Although there is no requirement to meet specific timing parameters, the following signal timings are recommended :
-T1(Power On Time) : T1 < 500ms -T2(Rise Time) : 0.1ms T2 20ms -T3(PGO Delay) : 100ms < T3 <500ms -T4(PGO Delay Risetime) : T4 10ms -T5(AC Loss to PGO Hold-Up Time) : T5 16ms -T6(Power Down Warning) : T6 1ms
Furthermore, motherboards should be designed to comply with the above recommended timing range. If timings other than these are implemented or required, that information should be clearly specified. The FAN7685/FAN7686/FAN7687 provide a power good(PGO) signal for the +3.3V, +5V and +12V supply voltage rails and a separate power good input(PGI). An internal delay circuit is used to generate a 300ms power good delay. If voltages at PGI(+1.2V), VS33(+3.3V), VS5(+5V), and VS12(+12V) rise above the undervoltage threshold, the open drain power good output(PGO) will go high after a delay of 300ms. When the PGI voltage or any of +3.3V, +5V, and +12V rails drops below the undervoltage threshold, the PGO signal will be disabled immediately.
Power Supply Remote On/Off(PSON) and Fault Protection Output(FPO)
Since the latest personal computer generation focuses on easy turn on and power saving functions, a PC power supply will require two characteristics. One is a dc power supply remote on/off function; the other is standby power to achieve very low power consumption of the PC power supply. Thus, the main power needs to be shut down. The power supply remote on/off(PSON) is an active-low signal that turns on all of the main power rails including the +3.3V, +5V, and +12V power rails. When this signal is held high by the PC motherboard or left open circuited, the signal of the fault protect output(FPO) also goes high. Thus, the main power rails can not deliver current and are held at 0V. When the FPO signal is held high due to a fault condition, the fault status will be latched and the outputs of the main power rails can not deliver current and are held at 0V. Toggling the PSON input signal from low to high will reset the fault protection latch. During this fault condition only the standby power is not affected. When the PSON input signal goes from high to low or low to high, the 38ms debounce block will be active to avoid that a glitch on the PSON input may disable/enable the FPO output. When the PSON is set low, the undervoltage function is disabled for 75ms to avoid turn-on failure. At turn-off, there is an additional delay of 2.3ms from PSON to FPO. Power should be delivered to the rails only when the PSON signal is held at ground potential, thus the FPO becomes a low 10
FAN7685/FAN7686/FAN7687
state after a debounce of 38ms. The FPO pin can be connected to +5V(or up to +15V) through a pull-up resistor.
Under Voltage Protection
The FAN7685/FAN7686/FAN7687 provide undervoltage protection(UVP) for the +3.3V, +5V, and +12V power rails. When an undervoltage condition appears at one of the VS33(+3.3V), VS5(+5V), or VS12(+12V) input pins for more than 73us, the PGO goes low and FPO output goes high. Also, this fault condition will be latched until the PSON is toggled from low to high or the Vcc falls below a minimum operating voltage. When the power supply is turned on by the AC input or PSON, an internal UVP delay time is 75ms. But at normal state an UVP delay time is only a 73us debounce time. The need for undervoltage protection is often overlooked in off-line switching power supply system design. But it is very important in battery powered or hand-held equipment since the TTL or CMOS logic often malfunctions under UVP condition.
Over Voltage Protection(OVP)
The overvoltage protection(OVP) of the FAN7685/FAN7686/FAN7687 monitor +3.3V, +5V, and +12V. When an overvoltage condition appears at one of the +3.3V, +5V, or +12V input pins for more than 73us, the FPO output goes high and the PGO goes low. Also, this fault condition will be latched until the PSON is toggled from low to high or Vcc drops below a minimum operating voltage. During overvoltage condition, most power supplies have the potential to deliver higher output voltages than those normally specified or required. In unprotected equipment, it is possible for output voltages to be high enough to cause internal or external damage to the system. To protect the system under these abnormal conditions, it is common practice to provide overvoltage protection within the power supply. Because TTL and CMOS circuits are very vulnerable to overvoltage, it is becoming industry standard to provide overvoltage protection on all +3.3V, +5V, and +12V outputs. Therefore, not only the +3.3V and +5V rails for the logic circuits on the motherboard need to be protected, but also the +12V peripheral devices such as the hard disk, flopply disk, and CD-ROM players etc., need to be protected.
Over Current Protection
In bridge or forward type, off-line switching power supplies, usually designed from medium to large power, the overload protection design needs to be very precise. Most of these types of power supplies are sensing the output current for an overload condition. The trigger point needs to be set higher than the maximum load in order to prevent false turn-on. During safety testing the power supply might have tied the output voltage direct to ground. If this happens during the nomal operating, this is called a short-circuit or over current condition. When it happens before the power supply turns on, this is called a short-circuit power supply turn-on. It can happen during the design period, in the production line, at quality control inspection or at the end user. The FAN7685/FAN7686/FAN7687 provide an UVP and OCP with a 75ms delay after PSON is set low. The FAN7685/FAN7686/FAN7687 provide overcurrent protection(OCP) for the 3.3V, 5V, and 12V rails. When an overcurrent condition appears at the OCP comparator input pins for more than 73us, the FPO output goes high and PGO goes low. Also, this fault condition will be latched until PSON is toggled from low to high or Vcc is removed. The resistor connected between the RI pin and the GND pin will introduce an accurate IO(RI) for the OCP function. Of course, a more accurate resistor tolerance will be better. The formula for choosing the RI resistor is VRI/IO(RI). The IO(RI) range is from 12.5uA to 62.5uA. Four OCP comparators and the IO(RI) section are supplied by VS12. Current drawn from the VS12pin is less than 1mA. Following is an example on calculating OCP for the 12V rail :
V RI 1.2VRI = ------------- = ------------- = 60k I O ( RI ) 20uA I O ( RI ) x K x R ( IS12 ) = R ( sense ) x I ( OCP - Trip ) I ( OCP - Trip ) = 20u x 8 x 560 ( 0.01 ) = 9.2A
11
FAN7685/FAN7686/FAN7687
Mechanical Dimensions
Package Dimensions in millimeters/inches
14-DIP
12
FAN7685/FAN7686/FAN7687
Mechanical Dimensions
Package Dimensions in millimeters/inches
14-SOP
13
FAN7685/FAN7686/FAN7687
Ordering Information
Product Number FAN7685N FAN7686N FAN7687N FAN7687AN FAN7685M FAN7686M FAN7687M FAN7687AM FAN7685MX FAN7686MX FAN7687MX FAN7687AMX 14SOP -40 ~ 125C Tape & Reel 14SOP -40 ~ 125C Tube 14DIP -40 ~ 125C Tube Package Operating Temperature Packing
DISCLAIMER FAIRCHILD SEMICONDUCTOR RESERVES THE RIGHT TO MAKE CHANGES WITHOUT FURTHER NOTICE TO ANY PRODUCTS HEREIN TO IMPROVE RELIABILITY, FUNCTION OR DESIGN. FAIRCHILD DOES NOT ASSUME ANY LIABILITY ARISING OUT OF THE APPLICATION OR USE OF ANY PRODUCT OR CIRCUIT DESCRIBED HEREIN; NEITHER DOES IT CONVEY ANY LICENSE UNDER ITS PATENT RIGHTS, NOR THE RIGHTS OF OTHERS. LIFE SUPPORT POLICY FAIRCHILD'S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT OF FAIRCHILD SEMICONDUCTOR CORPORATION. As used herein: 1. Life support devices or systems are devices or systems which, (a) are intended for surgical implant into the body, or (b) support or sustain life, and (c) whose failure to perform when properly used in accordance with instructions for use provided in the labeling, can be reasonably expected to result in a significant injury of the user.
www.fairchildsemi.com 3/9/04 0.0m 001 Stock#DSxxxxxxxx 2004 Fairchild Semiconductor Corporation
2. A critical component in any component of a life support device or system whose failure to perform can be reasonably expected to cause the failure of the life support device or system, or to affect its safety or effectiveness.

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