AIC1577COTR 查看數據表（PDF） - Analog Intergrations

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AIC1577COTR

External NMOS Step-Down PWM Controller

Analog Intergrations 

AIC1577

PIN DESCRIPTIONS

PIN 1: CS

- Current sense comparator invert-

ing input, not to exceed VIN volt-

age. Built in offsets between the

CS and VIN pins in conjunction

with RSENSE set the current trip

thresholds.

PIN 2:

ITH/RUN -Combination of error amplifier

compensation point and run con-

trol inputs. The current compara-

tor threshold increases with this

control voltage. Forcing this pin

below 0.8V causes the device to

be shutdown.

PIN 3: FB

- Feedback error amplifier input, to

compare the feedback voltage

with the internal reference voltage.

Connecting a resistor R2 to con-

verter output node and a resistor

R1 to ground yields the output

voltage:

VOUT=0.8 x (R1+R2)/ R1

PIN4: GND - Singal GND for IC. All voltage lev-

els are measured with respect to

this pin.

PIN 5: SW

- Switch node connection to induc-

tor. In buck converter applications

the voltage swing at this pin is

from a schottky diode voltage

drop below ground to VIN

PIN 6: DRI

- External high-side N-MOSFET

gate drive pin. Connect DRI to

gate of the external high-side N-

MOSFET.

PIN 7: BOOST- Supply to high-side floating

driver. The bootstrap capacitor C3

is returned to this pin.

PIN 8: VIN

- The chip power supply pin. It also

provides the gate bias charge for

all the MOSFETs controlled by

the IC. Recommend supply volt-

age is 4.5V~24V.

APPLICATION INFORMATION

Introduction

AIC1577 is a current mode switching regulator con-

troller that drives external N-channel power

MOSFET with constant frequency architecture. It

uses external divider to adjust output voltage with

excellent line regulation and load regulation. A

maximum high duty cycle limit of 95% provides low

dropout operation, which extends operating time in

battery-operated system.

Wide input voltage ranges from 4.5V to 24V, and

switching frequency (500KHz) allows smaller sized

filter components. The operating current level is

user-programmable via an external current sense

resistor and it automatically enters PFM operation

at low output current to boost circuit efficiency.

A multifunction pin (ITH/RUN) allows external

compensation plus shutdown. A built-in soft start

can properly provide sequence supplies. Available

packages are in SOP8 and MSOP8 for SMD.

Principle of Operation

AIC1577 uses a current mode with a constant fre-

quency architecture. Normally high-side MOSFET

turns on each cycle when oscillator sets RS latch

and it turns off when internal current comparator re-

sets RS latch. Voltage on ITH/RUN pin, which is the

output voltage of voltage error amplifier, will control

peak inductor current. The output voltage feeds

back to VFB pin so that the error amplifier receives

a voltage through external resistor divider. When

load current increases, it causes a slight decrease

8

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