Datasheet > ADP1173AR-33

ADP1173AR-33

更新时间： 2022-11-25 18:37:48

品牌	Logo	应用领域
亚德诺 - ADI		转换器
页数	文件大小	规格书
16页	480K
描述
Micropower DC-DC Converter

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ADP1173AR-33 数据手册

ADP1173

+5V

The internal structure of the I_LIMcircuit is shown in Figure 21.

Q1 is the ADP1173’s internal power switch, which is paralleled

by sense transistor Q2. The relative sizes of Q1 and Q2 are

scaled so that I_Q2is 0.5% of I_Q1. Current flows to Q2 through an

internal 80 Ω resistor and through the R_LIMresistor. These two

resistors parallel the base-emitter junction of the oscillator-

disable transistor, Q3. When the voltage across R1 and R_LIM

exceeds 0.6 V, Q3 turns on and terminates the output pulse. If

only the 80 Ω internal resistor is used (i.e., the I_LIMpin is con-

nected directly to V_IN), the maximum switch current will be

1.5 A. Figures 4 and 5 gives R_LIMvalues for lower current-limit

values.

ADP1173

1.245V

100kΩ

PROCESSOR

REF

SET

BAT

GND

–1.245V

12.5µA

= BATTERY TRIP POINT

R1 =

R2 = 100kΩ

Figure 22. Setting the Low Battery Detector Trip Point

Figure 22 shows the gain block configured as a low battery

monitor. Resistors R1 and R2 should be set to high values to

reduce quiescent current, but not so high that bias current in the

SET input causes large errors. A value of 100 kΩ for R2 is a

good compromise. The value for R1 is then calculated from the

formula:

LIM

(EXTERNAL)

80Ω

(INTERNAL)

SW1

V_LOBATT− 1.245V

R1=

DRIVER

1.245V

OSCILLATOR

SW2

where V_LOBATTis the desired low battery trip point. Since the

gain block output is an open-collector NPN, a pull-up resistor

should be connected to the positive logic power supply.

Figure 21. Current Limit Operation

The delay through the current limiting circuit is approximately

2 µs. If the switch ON time is reduced to less than 4 µs, accu-

racy of the current trip-point is reduced. Attempting to program

a switch ON time of 2 µs or less will produce spurious responses

in the switch ON time. However, the ADP1173 will still provide

a properly regulated output voltage.

ADP1173

1.245mV

47kΩ

PROCESSOR

REF

SET

BAT

GND

PROGRAMMING THE GAIN BLOCK

The gain block of the ADP1173 can be used as a low-battery

detector, error amplifier or linear post regulator. The gain block

consists of an op amp with PNP inputs and an open-collector

NPN output. The inverting input is internally connected to the

ADP1173’s 1.245 V reference, while the noninverting input is

available at the SET pin. The NPN output transistor will sink

about 100 µA.

1.6MΩ

Figure 23. Adding Hysteresis to the Low Battery Detector

REV. 0

–11–

1...8 9 101112 13 14...16

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