US3033 UNISEM, US3033 Datasheet - Page 3

• Manufacturer Part Number: US3033
• Description: PWM SWITCHER & LINEAR CONTROLLER IC
• Manufacturer: UNISEM

BLOCK DIAGRAM
BLOCK DIAGRAM
PIN DESCRIPTIONS
PIN DESCRIPTIONS
PIN #
Rev. 1.5
1/14/99
1
3
6
7
5
4
2
8
PIN SYMBOL
Drv 1
Gnd
1
5
Drv1
V
V
Drv2
Gnd
V
V
V
12SW
12
FB1
FB2
HYST
V12sw
2
A resistor divider from this pin to the output of the switching regulator and ground sets the
Core supply voltage.
The feedback pin of the linear regulator. A resistor divider from this pin to the output of the
linear regulator and ground sets the I/O supply voltage.
The drive pin of the linear regulator. This pin controls the base of a transistor or the gate
of a MOSFET acting as the series pass element for the linear regulator.
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 biasing for the chip and drive for the linear regulator controller. It
isconnected to 12V supply. A 10 ohm resistor in series from this pin to the 12V supply
and a 1uF, high frequency capacitor connected from this pin to Gnd is required to filter
the switching noise of the switching regulator.
PIN DESCRIPTION
Vhyst
4
Figure 1 - Simplified block diagram of the US3033
3033blk1-1.0
PWM Control
UVLO
Vfb 1
1.25V
3
Vref
5V Reg
V12
8
FB1
Drv 2
US3033
Vfb2
pin to set the
7
6
4-3