ADM7171ACPZ-R7 Просмотр технического описания (PDF) - Analog Devices

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ADM7171ACPZ-R7

6.5 V, 1 A, Ultralow Noise, High PSRR, Fast Transient Response CMOS LDO

Analog Devices 

ADM7171

THEORY OF OPERATION

The ADM7171 is a low quiescent current, low dropout linear

regulator that operates from 2.3 V to 6.5 V and provides up to

1 A of load current. Drawing a low 4.0 mA of quiescent current

(typical) at full load makes the ADM7171 ideal for portable

equipment. Typical shutdown current consumption is 0.25 μA

at room temperature.

Optimized for use with small 4.7 µF ceramic capacitors, the

ADM7171 provides excellent transient performance.

VIN

GND

CURRENT-LIMIT,

THERMAL

PROTECT

VOUT

SENSE

REFERENCE

EN

SHUTDOWN

SOFT START

SS

Figure 54. Internal Block Diagram

Internally, the ADM7171 consists of a reference, an error

amplifier, a feedback voltage divider, and a PMOS pass transistor.

Output current is delivered via the PMOS pass device, which is

controlled by the error amplifier. The error amplifier compares

the reference voltage with the feedback voltage from the output

and amplifies the difference. When the feedback voltage is

lower than the reference voltage, the gate of the PMOS device is

pulled lower, allowing more current to pass and increasing the

output voltage. When the feedback voltage is higher than the

reference voltage, the gate of the PMOS device is pulled higher,

allowing less current to pass and decreasing the output voltage.

Data Sheet

The ADM7171 is available in 17 fixed output voltage options,

ranging from 1.2 V to 5 V. The ADM7171 architecture allows

any fixed output voltage to be set to a higher voltage with an

external voltage divider. For example, a fixed 5 V output

ADM7171 can be set to a 6 V output according to the following

equation:

VOUT = 5 V(1 + R1/R2)

VIN = 6.5V

CIN

4.7µF

ADM7171

VIN

VOUT

VIN

VOUT

SENSE

ON

OFF

EN GND SS

VOUT = 6.0V

R1

2kΩ

R2

10kΩ

COUT

4.7µF

CSS

1nF

Figure 55. Typical Adjustable Output Voltage Application Schematic

Use a value of less than 200 kΩ for R2 to minimize errors in the

output voltage caused by the SENSE pin input current. For

example, when R1 and R2 each equal 200 kΩ and the default

output voltage is 1.2 V, the adjusted output voltage is 2.4 V. The

output voltage error introduced by the SENSE pin input current is

0.1 mV or 0.004%, assuming a typical SENSE pin input bias

current of 1 nA at 25°C.

The ADM7171 uses the EN pin to enable and disable the VOUT

pins under normal operating conditions. When EN is high,

VOUT turns on, when EN is low, VOUT turns off. For automatic

startup, tie EN to VIN (Pin 7 or Pin 8).

Rev. A | Page 16 of 23

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