LT3020IMS8 Datasheet, PDF (9/16 Pages) Linear Technology – 100mA, Low Voltage, Very Low Dropout Linear Regulator

BLOCK DIAGRA
SHDN
(5)
SHUTDOWN
BIAS CURRENT
AND
REFERENCE
GENERATOR
200mV
212mV
LT3020/LT3020-1.2/
LT3020-1.5/LT3020-1.8
THERMAL
SHUTDOWN
–
ERROR AMP
+
CURRENT
GAIN
–
NO-LOAD
RECOVERY
+
IN
(7, 8)
R3
D1
Q3
Q1
D2
Q2
R2
25k
OUT
(1, 2)
OUT SENSE
(3)
ADJ
(3)
NOTE:
FOR LT3020 ADJUST PIN 3 IS CONNECTED TO
THE ADJUST PIN, R1 AND R2 ARE EXTERNAL.
FOR LT3020-1.X PIN 3 IS CONNECTED TO THE
OUTPUT SENSE PIN, R1 AND R2 ARE INTERNAL.
FIXED
V_OUT
1.2V
1.5V
1.8V
R1 R2
20k 100k
20k 130k
20k 160k
R1
3020 BD
GND
(4,9)
APPLICATIO S I FOR ATIO
The LT3020 is a very low dropout linear regulator capable
of 0.9V input supply operation. Devices supply 100mA of
output current and dropout voltage is typically 150mV.
Quiescent current is typically 120µA and drops to 3µA in
shutdown. The LT3020 incorporates several protection
features, making it ideal for use in battery-powered sys-
tems. The device protects itself against reverse-input and
reverse-output voltages. In battery backup applications
where the output is held up by a backup battery when the
input is pulled to ground, the LT3020 acts as if a diode is
in series with its output which prevents reverse current
flow. In dual supply applications where the regulator load
is returned to a negative supply, the output can be pulled
below ground by as much as 10V without affecting start-
up or normal operation.
Adjustable Operation
The LT3020’s output voltage range is 0.2V to 9.5V. Figure
1 shows that the output voltage is set by the ratio of two
external resistors. The device regulates the output to
maintain the ADJ pin voltage at 200mV referenced to
ground. The current in R1 equals 200mV/R1 and the
current in R2 is the current in R1 minus the ADJ pin bias
current. The ADJ pin bias current of 20nA flows out of the
pin. Use the formula in Figure 1 to calculate output voltage.
An R1 value of 20k sets the resistor divider current to
10µA. Note that in shutdown the output is turned off and
the divider current is zero. Curves of ADJ Pin Voltage vs
Temperature and ADJ Pin Bias Current vs Temperature
appear in the Typical Performance Characteristics section.
Specifications for output voltages greater than 200mV are
proportional to the ratio of desired output voltage to
200mV; (V_OUT/200mV). For example, load regulation for
V_IN
IN
OUT
LT3020-ADJ
+
R2
V_OUT
SHDN ADJ
GND
R1
3020 F01
( ) ^VOUT ^{= 200mV}
1 + ^R2
R1
– I_ADJ (R2)
V_ADJ = 200mV
I_ADJ = 20nA AT 25°C
OUTPUT RANGE = 0.2V TO 9.5V
Figure 1. Adjustable Operation
3020fc
9