US1261
PIN DESCRIPTIONS
PIN #
PIN SYMBOL
PIN DESCRIPTION
2
Vout2
The output #2 (high current) of the regulator. A minimum of 100uF capacitor
must be connected from this pin to ground to insure stability.
5
4
Vout1
Vin
The output #1 (low current) of the regulator. A minimum of 100uF capacitor
must be connected from this pin to ground to insure stability.
The power input pin of the regulator. Typically a large storage capacitor is
connected from this pin to ground to insure that the input voltage does not sag
below the minimum drop out voltage during the load transient response. This
pin must always be higher than both Vout pins by the amount of the dropout
voltage(see datasheet) in order for the device to regulate properly.
This pin is connected to GND. It is also the TAB of the package.
The control input pin of the regulator. This pin via a 10W resistor is connected
to the 5V supply to provide the base current for the pass transistor of both
regulators. This allows the regulator to have very low dropout voltage
which allows one to generate a well regulated 2.5V supply from the 3.3V input.
A high frequency, 1 uF capacitor is connected between this pin and Vin pin to
insure stability.
3
1
Gnd
Vctrl
BLOCK DIAGRAM
Vin 4
5 Vout1
Vctrl
1
THERMAL
SHUTDOWN
3 Gnd
+
1.20V
1261blk1-1.1
2 Vout2
Figure 1 - Simplified block diagram of the US1261
Rev. 1.7
3/22/99
3-3
UNISEM [ UNISEM ]
