Data Sheet

ADPL42010A

analog.com

Rev. 0

16 of 28

APPLICATIONS INFORMATION

The ADPL42010A series are 1A low dropout regulators optimized for fast transient response. The devices are capable

of supplying 1A at a dropout voltage of 400mV. The low operating quiescent current (1mA) drops to less than 1µA in

shutdown. In addition to the low quiescent current, the ADPL42010A regulators incorporate several protection

features, which make them ideal for use in battery-powered systems. The devices are protected against both reverse

input and reverse output voltages. In battery backup applications where the output can be held up by a backup

battery when the input is pulled to ground, the ADPL42010A acts as it has a diode in series with its output and

prevents reverse current flow. Additionally, 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 20V and still allow the device to start and

operate.

Adjustable Operation

The adjustable version of the ADPL42010A has an output voltage range of 1.21V to 20V. The output voltage is set by

the ratio of two external resistors, as shown in Figure 27. The device serves the output to maintain the voltage at the

ADJ pin at 1.21V referenced to ground. The current in R1 is then equal to 1.21V/R1 and the current in R2 is the current

in R1 plus the ADJ pin bias current. The ADJ pin bias current, 3µA at 25°C, flows through R2 into the ADJ pin. The

output voltage can be calculated using the formula in Figure 27. The value of R1 should be less than 4.17k to minimize

errors in the output voltage caused by the ADJ pin bias current. Note that in shutdown, the output is turned off and

the divider current is zero.

The adjustable device is tested and specified with the ADJ pin connected to the OUT pin for an output voltage of

1.21V. Specifications for output voltages greater than 1.21V are proportional to the ratio of the required output

voltage to 1.21V: VOUT/1.21V. For example, load regulation for an output current change of 1mA to 1A is –3mV typical

at VOUT = 1.21V. At VOUT = 5V, load regulation is:

(5V/1.21V) × (–3mV) = –12.4mV

Output Capacitors and Stability

The ADPL42010A regulator is a feedback circuit. Similar to any feedback circuit, frequency compensation is needed

to make it stable. For the ADPL42010A, the frequency compensation is both internal and external due to the output

capacitor. The size of the output capacitor, the type of the output capacitor, and the ESR of the particular output

capacitor all affect the stability.

Figure 27. Adjustable Operation

In addition to stability, the output capacitor also affects the high frequency transient response. The regulator loop

has a finite bandwidth. For the high-frequency transient loads, recovery from a transient is a combination of the

output capacitor and the bandwidth of the regulator. The ADPL42010A is designed to be easy to use and accept a

wide variety of output capacitors. However, the frequency compensation is affected by the output capacitor and

optimum frequency stability may require some ESR, especially with ceramic capacitors.

IN

R2

OUT

VIN

VOUT

R2

R1

VOUT = 1.21V 1 +

+ (IADJ)(R2)

VADJ = 1.21V

IADJ = 3µA AT 25°C

OUTPUT RANGE = 1.21V TO 20V

ADJ

GND

ADPL42010A

R1

+