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LT3022

1A, 0.9V to 10V, Very Low Dropout Linear Regulator

Linear Technology 

LT3022/LT3022-1.2

LT3022-1.5/LT3022-1.8

APPLICATIONS INFORMATION

The LT3022 very low dropout linear regulator is capable of

0.9V input supply operation. It supplies 1A output current

and dropout voltage is typically 145mV. Quiescent current

is typically 400µA and drops to 7.5µA in shutdown. The

LT3022 incorporates several protection features, making

it ideal for use in battery-powered systems. The device

protects itself against reverse-input and reverse-output

voltages. If the output is held up by a backup battery when

the input is pulled to ground in a battery backup application,

the LT3022 behaves as if a diode is in series with its output,

preventing reverse current flow. In dual supply applications

where the regulator load is returned to a negative supply,

pulling the output below ground by as much as 10V does

not affect start-up or normal operation.

Adjustable Operation

The LT3022’s output voltage range is 0.2V to 9.5V. Figure 1

shows that the external resistor ratio sets output voltage.

The device regulates the output to maintain ADJ at 200mV

referred to ground. R1’s current equals 200mV/R1. R2’s

current is R1’s current minus the ADJ pin bias current.

The 30nA ADJ pin bias current flows out of the pin. Use

Figure 1’s formula to calculate output voltage. Given the

LT3022’s 1mA minimum load current requirement, Linear

Technology recommends choosing resistor divider values

to satisfy this requirement. A 200Ω R1 value sets a 1mA

resistor divider current. In shutdown, the output is 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 (VOUT/200mV). For example, load regulation for

an output current change of 1mA to 1A is typically 100µV

at VADJ = 200mV. At VOUT = 1.5V, load regulation is:

1.5V • 100µV =750µV

200mV

Table 1 shows 1% resistor divider values for some common

output voltages with a resistor divider current equaling or

about 1mA.

Table 1

VOUT (V)

0.9

1.0

1.2

1.5

1.8

2.5

3.3

R1 (Ω)

200

187

200

200

187

187

200

R2 (Ω)

698

750

1000

1300

1500

2150

3090

+

VIN

IN

OUT

LT3022

R2

SHDN ADJ

GND

R1

VOUT

3022 F01

VOUT: 200mV • (1 + R2/R1) – (IADJ • R2)

VADJ: 200mV

IADJ: 30nA AT 25°C

OUTPUT RANGE: 0.2V TO 9.5V

Figure 1. Adjustable Operation

Output Capacitance and Transient Response

The LT3022’s design is stable with a wide range of output

capacitors, but is optimized for low ESR ceramic capacitors.

The output capacitor’s ESR affects stability, most notably

with small value capacitors. Use a minimum output

capacitor of 10µF with an ESR of less than 0.1Ω to prevent

oscillations. The LT3022 is a low voltage device and output

load transient response is a function of output capacitance.

Larger values of output capacitance decrease the peak

deviations and provide improved transient response for

large load current changes.

Ceramic capacitors require extra consideration. Manufac­

turers make ceramic capacitors with a variety of dielectrics;

each with a different behavior across temperature and

applied voltage. The most common dielectrics are Z5U,

Y5V, X5R and X7R. Z5U and Y5V dielectrics provide

high C-V products in a small package at low cost, but

exhibit strong voltage and temperature coefficients. X5R

and X7R dielectrics yield highly stable characteristics

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