US3036
PIN DESCRIPTIONS
PIN #
3
6
PIN SYMBOL PIN DESCRIPTION
A resistor divider from this pin to the output of the switching regulator and ground sets the
V
FB
Core supply voltage.
This pin is connected to the minus side of the external current sense resistor. An internal
C.S-
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
C.S+
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
Gnd
in the system.
The PWM output of the switching controller. This pin is a totem pole drive that is con-
Drv
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.
This pin supplies the voltage to the PWM drive and hysterises circuitry and it is con-
V
CC
nected to the same supply as the input supply to the switching regulator . A 1 uF, high
frequency capacitor must be connected from this pin to ground to provide the peak cur-
rent 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
S.S
time when the converter goes into current limiting, providing low duty cycle for the catch
diode allowing it to survive during short circuit.
No connect.
N.C
7
5
1
2
8
4
BLOCK DIAGRAM
Vcc
2
NC
4
Vfb
3
5V Reg
UVLO
R
20uA
Drv
1
CS-
6
CS+
7
SS
8
PWM Control
1.25V
R
Vref
Gnd
5
S.S. / Hiccup
Control
3036blk1-1.2
Figure 1 - Simplified block diagram of the US3036
Rev. 1.1
12/4/98
4-3
UNISEM [ UNISEM ]
