US1205
Note 1 :
Low duty cycle pulse testing with Kelvin con-
nections are required in order to maintain accurate data.
Note 2 :
Drop-out voltage is defined as the minimum
differential voltage between Vin and Vout required to main-
tain regulation at Vout. It is measured when the output
voltage drops 1% below its nominal value.
Note 3
: Ground current is the the regulator quiescent
current plus the pass transistor current. The total cur-
rent from the supply is the sum of the load current plus
the ground pin current.
Note 4
: The specification applies for the junction tem-
perature of 0 to +125°C.
Pin DescRIPTIONS
PIN #
4
4
5
PIN SYMBOL
Adj
(Adjustable only)
Byp
(Fixed output only)
Vout
PIN DESCRIPTION
A resistor divider from this pin to the Vout pin and ground sets
the output voltage.
A 470 to 1000pF bypass capacitor connected to this pin re-
duces the output noise.
The output of the regulator .A minimum of 2.2uF with max
ESR of 1 ohm capacitor must be connected from this pin to
ground to insure stability.
Ground pin. This pin must be connected to the lowest poten-
tial in the system & all other pins must be at higher potential
with respect to this pin.
Enable pin. A low signal or left open on this pin shuts down the
output.This pin must be tied HI or to Vin for normal operation.
The 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 minimumdrop out voltage dur-
ing the load transient response. This pin must always be higher
than Vout by at least the amount of the dropout voltage and
some margin in order for the device to regulate properly.
2
GND
3
1
En
Vin
5 LEAD
SOT 23
US1205
US1205-25
US1205-30
US1205-33
US1205-36
Output
Voltage
1.242V
2.5 V
3.0 V
3.3 V
3.6 V
The output voltage of the adjustable device can be set using:
Vo=1.242
X
(1+R1/R2)
Where;
R1=Resistor connected from output to the Adj pin
R2=Resistor connected from Adj pin to GND
Table 1- Nominal output voltage v.s. part number
BLOCK DIAGRAM
Vin
Vout
Vin
Vout
Adj
THERMAL
SHUTDOWN
Byp
1.242V
+
1.242V
+
THERMAL
SHUTDOWN
Gnd
1205blk1-1.1
En
Gnd
1205blk2-1.0
En
Figure 1- US1205 Adjustable block diagram
Rev. 1.4
9/25/00
Figure 2- US1205 Fixed output block diagram
2-3
UNISEM [ UNISEM ]
