Datasheet

4
UC1572
UC2572
UC3572
4
8
7
1
2
6
5
3
R
SLEEP1
56k
R
SLEEP2
33k
R
COMP
R
REF
RV
SENSE
40k
RSLEEP3
1MEG
R
CS
C
IN
10µF
COUT
100µF
VOUT
GND
–12V OUT
D
FLYBACK
L
FLYBACK
M
SWITCH
C
RAMP
680pF
CV
CC
10µF
M
SLEEP
GND
SLEEP
VIN
VCC
3VREF
RAMP
EAINV
EAOUT
GND
CS
OUT
UC1572
C3V
REF
100nF
C
COMP
Figure 2. Typical application: +5V to –12V flyback converter.
UDG-99057
PIN DESCRIPTIONS
3VREF: Precision 3V reference. Bypass with 100nF ca
-
pacitor to GND.
CS: Current limit sense pin. Connect to a ground refer
-
enced current sense resistor in series with the flyback in
-
ductor. OUT will be held high (PMOS switch off) if CS
exceeds 0.2V.
EAINV: Inverting input to error amplifier. Summing junc
-
tion for 3VREF and VOUT sense. The non-inverting input
of the error amplifier is internally connected to GND. This
pin will source a maximum of 1mA.
EAOUT: Output of error amplifier. Use EAOUT and EAINV
for loop compensation components.
GND: Circuit Ground.
OUT: Gate drive for external PMOS switch connected
between V
CC and the flyback inductor. OUT drives the
gate of the PMOS switch between V
CC and GND.
RAMP: Oscillator and ramp for pulse width modulator.
Frequency is set by a capacitor to GND by the equation
F
kC
RAMP
=
•
1
15
Recommended operating frequency range is 10kHz to
200kHz.
VCC: Input voltage supply to chip. Range is 4.75 to 30V.
Bypass with a 1µF capacitor.