US3034CS UNISEM, US3034CS Datasheet - Page 3

• Manufacturer Part Number: US3034CS
• Description: 8 PIN PWM SWITCHER CONTROLLER IC
• Manufacturer: UNISEM

BLOCK DIAGRAM
BLOCK DIAGRAM
PIN DESCRIPTIONS
PIN DESCRIPTIONS
PIN #
Rev. 1.8
1/13/99
1
3
6
7
5
4
2
8
PIN SYMBOL
Gnd
Drv
Drv
1
5
V
C.S-
C.S+
Gnd
V
V
S.S
12
FB
HYST
V12
2
A resistor divider from this pin to the output of the switching regulator and ground sets the
Core supply voltage.
This pin is connected to the minus side of the external current sense resistor. An internal
current source together with an external resistor in series with this pin programs the
current limit threshold voltage. This voltage divided by the external current sense resistor
sets the current limit threshold.
This pin is connected to the plus side of the external current sense resistor. A resistor in
series with this pin and a capacitor connected between this pin and pin 6 provides a high
frequency filtering for the noise spikes of turn on and turn off switching.
This pin is connected to the IC substrate and must be connected to the lowest potential
in the system.
The PWM output of the switching controller. This pin is a totem pole drive that is con-
nected to the gate of the power MOSFET. A resistor may be placed from this pin to the
gate in order to reduce switching noise.
A resistor and a 10pF capacitor is connected from this pin to the V
output ripple voltage for the switching regulator.
This pin supplies the voltage to the PWM drive and hysterises circuitry and it is con-
nected to the 12V supply. A 1 uF, high frequency capacitor must be connected from this
pin to ground to provide the peak current for charging and discharging of the MOSFET.
This pin provides the soft start for the regulator during power up. It also sets a long off
time when the converter goes into current limiting, providing low duty cycle for the catch
diode allowing it to survive during short circuit.
PIN DESCRIPTION
Vhyst
4
Figure 1 - Simplified block diagram of the US3034
PWM Control
S.S. / Hiccup
UVLO
Control
Vfb
3
1.25V
R
3R
5V Reg
Vref
3034blk1-1.1
20uA
CS+
CS-
FB1
SS
6
7
8
US3034
pin to set the
4-3