Datasheet
SLUS430A – APRIL 1999 – REVISED DECEMBER 2000
4
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
electrical characteristics V
DD
= 12 V, RT = 53.3 kΩ, C
VDD
= 1 µF, C
REF
= 0.1 mF, C
SS
= 0.01 µF,
R
OUT
= 4 Ω, C
OUT
= 1 nF and T
A
= T
J
(unless otherwise stated)
PARAMETER TEST CONDITIONS MIN TYP MAX UNITS
Feedback Section (FB)
Input bias current FB = 4.5 V, SS = 0 V 0.4 µA
Negative compliance voltage I
FB
= –100 mA, SS = 0 V –6.8 –7.2 –7.6 V
Delay time, FB–SS to OUT, rising edge FB–SS pulsed = 2 V, FB = SS 40 70 100 ns
Delay time, FB–SS to OUT, falling edge FB–SS pulsed = 2 V, FB = SS 50 85 120 ns
Terminal Functions
TERMINAL
I/O
DESCRIPTION
NAME NO.
I/O
DESCRIPTION
CS 5 I Pulse-by-pulse and shutdown overcurrent sense input pin
FB 2
I
Control input for the signal from a secondary–side PWM
controller
GND 6 Ground for the IC.
OUT 7 O Drive pin for the MOSFET power switch
RT 3 I Sets the free-running startup oscillator frequency.
REF 4 O Output reference
SS 1 I Primary-side soft-start function
VDD 8 Power input connection
detailed descriptions
current sense (CS)
This is the pulse-by-pulse and shutdown overcurrent sense input pin. This current-sense pin triggers a
pulse-by-pulse termination anytime a 1.0-V threshold is exceeded while a signal in excess of 1.375 V on this
pin initiates a complete shutdown. Since the CS pin can be noise sensitive, it is good practice to insert a small
low-pass RC filter between this pin and the current sensor.
feedback (FB)
This is the control input for the signal from a secondary-side PWM controller whose pulse-width command has
been differentiated by the feedback pulse edge transformer (PET) into positive
start
and negative
stop
pulses.
These signals are used to turn on and off the primary power switch and must have an amplitude of at least
V
SS
± 2.0 V (4 V peak-to-peak) for at least 25 ns per pulse and no more than 200 ns per pulse. The maximum
amplitude allowed on this pin is V
SS
± 7.0 V.
output drive (OUT)
This drive pin for the N–channel MOSFET power switch sinks (1.5 A) and sources (0.75 A) fast, high-current
gate drive pulses. During shutdown, this pin is self–biased to an active low state. A minimum of 4 W should
be added in series with the output to ensure that the on-chip driver safe operating area is not exceeded. (Data
from the IRF820/830/840 family of MOSFETs, commonly available in the TO–220 package, is used to derive
this value. The gate charge needed to provide full enhancement was used to establish an equivalent
capacitance of up to 4000 pF.)