www.fairchildsemi.com
FAN7585
Intelligent Voltage Mode PWM IC
Features
Complete PWM Control and House Keeping Circuitry
Few External Components
Precision Voltage Reference Trimmed to 2%
Dual Output for Push-Pull Operation
Each Output TR for 200mA Sink Current
Variable Duty Cycle by Dead Time Control
Soft Start Capability by Using Dead Time Control
Double Pulse Suppression Logic
Over Voltage Protection for 3.3V/5V/12V
Under Voltage Protection for 3.3V/5V/12V
Over Current Protection for 3.3V/5V/12V
One More External Input for Various Protection (PT)
Remote On/Off Control Function (PS-ON)
Latch Function Controlled by Remote and Protection
Input
• Power Good Signal Generator with Hysteresis
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Description
The FAN7585 is a fixed frequency improved performance
pulse width modulation control circuit with complete house-
keeping circuitry for use in the secondary side of SMPS
(Switched Mode Power Supply). It contains various func-
tions, which are overvoltage protection, undervoltage protec-
tion, over current protection, remote on/off control, power
good signal generator, etc.
OVP (Over Voltage Protection) Section
It has OVP functions for +3.3V,+5V,+12V outputs and PT.
The circuit is made up of a comparator with four detecting
inputs and without hysteresis voltage. Especially, PT (Pin19)
is prepared for an extra OVP input or another protection
signal.
UVP (Under Voltage Protection) Section
It also has UVP functions for +3.3V, +5V, +12V outputs. The
block is made up of a comparator with three detecting inputs
and without hysteresis voltage.
Typical Application
• PC Power Supply
OCP (Over Current Protection) Section
It has precision OCP functions for +3.3V, +5V, +12V out-
puts. The block is made up of three comparators with current
source setting function. Two inputs of each OCP comparator
are connected to both sides of current sensing inductor that is
located in the secondary output of SMPS.
Remote On/Off Section
The remote on/off section is used to control SMPS exter-
nally. If a high signal or open state is supplied to the remote
on/off input, PWM signal becomes a high state and all sec-
ondary outputs are grounded. The remote on/off signal is
transferred with some on-delay and off-delay time of 8ms,
24ms respectively.
24-SDIP
Precision Reference Section
1
The reference voltage is trimmed to
±2%.
(4.9V
≤
Vref
≤
5.1V)
PG (Power Good Signal Generator) Section
The power good signal generator is to monitor the voltage
level of power supply for safe operation of a microprocessor
having some delay time at turn-on. The power good output
should be low state before the output voltatge is out of regu-
lation at turn-off.
Rev. 1.0.0
©2003 Fairchild Semiconductor Corporation
FAN7585
Pin Function
Pin Number Pin Name
1
2
3
4
5
V
CC
COMP
E/A(-)
E/A(+)
T
REM
Pin Function Description
Supply voltage. Operating range is 15V~30V. Test condition : V
CC
=20V, Ta=25°C.
Error amplifier output. It is connected to non-inverting input of pulse width modulator
comparator.
Error amplifier inverting input. Its reference voltage is always 1.25V.
Error amplifier non-inverting input feedback voltage. This pin may be used to sense
power supply output voltages.
Remote On/Off delay. Ton/Toff=8ms/24ms (Typ.) with C=0.1uF. Its High/Low threshold
voltages are 1.8V/0.6V.
Remote On/Off input. It is TTL operation and its threshold voltage is 1.4V. Voltage at
this pin can reach normal 4.6V, with absolute maximum voltage, 5.25V.
If REM =
“Low”,
PWM =
“Low”,
that means the main SMPS is operational.
when REM =
“High”,
then PWM =
“High”
and the main SMPS is turned-off.
Oscillation frequency setting R, C.(Test condition R
T
=10kΩ)
OCP current setting pin. You can fix the OCP reference current (Iref1) by using RI
resistor.
AC input under voltage detection pin. Its threshold voltage is 1.25V Typ.
PG delay. Td =260ms (Typ.) with C
TPG
= 2.2uF. The High/Low threshold voltages are
1.8V/0.6V and the voltage of Pin10 is clamped to 2.9V for noise margin.
Power Good output signal. PG =
“High”
means that the power is
“Good”
for operation
and PG =
“Low”
means
“Power
fail”.
Precision voltage reference is trimmed to
±2%
(Typical Value = 5V).
Current sense input for +3.3V output. This pin is connected to the current sensing
resistor or inductor. You can define OCP offset voltage for +3.3V by using RI resistor
externally. If you connect 62kΩ at pin 8 to ground, the reference current(Iref1) should be
20uA. After that , you can make a constant OCP offset voltage(V
offset
=R
offset
*5*20uA).
In case the voltage drop(I
O.33
*Rs) of the sense resistor or inductor is larger than offset
voltage, after OCP delay time the main SMPS is turned off. So the over current level is
determined by the following equation. I
O.33
=V
offset
/Rs.
OVP, UVP input for +3.3V output (Typical Value = 4.1V/2.3V).
Current sense input for +5V output. You can make +5V OCP function as the previous
method in IS5(pin15).
OVP, UVP input for +5V output (Typical Value = 6.4V/4.0V).
Current sense input for +12V output. You can make +12V OCP function as the previous
method in IS12(pin17).
OVP, UVP input for 12V output (Typical Value = 14.2V/10V).
This is prepared for an extra OVP input or another protection signal (Typical Value =
1.25V).
Timing delay pin for under voltage protection and over current protection. Its threshold
voltage is 1.8V and clamped to 2.9V after full charging. Target of delay time is 38ms and
it is realized through external capacitor (C
TUVP
= 0.47uF).
Deadtime control input. The deadtime control comparator has an effective 120mV input
offset which limits the minimum output dead time. Dead time may be imposed on the
output by setting the dead time control input to a fixed voltage, ranging from 0V to 3.3V.
Output drive pin for push-pull operation.
Ground.
Output drive pin for push-pull operation.
6
7
8
9
10
11
12
REM
R
T
/C
T
RI
DET
T
PG
PG
Vref
13
IS33
14
15
16
17
18
19
20
V33
IS5
V5
IS12
V12
PT
T
UVP
21
22
23
24
DTC
C2
GND
C1
4
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