AT9173AG 查看數據表（PDF） - AME, Inc

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AT9173AG

Bus Termination Regulator

AME, Inc 

AME, Inc.

AT9173

Bus Termination Regulator

n Application Information

VCNTL = 3.3V

VIN = 1.8V

2N7002

EN

R1

VIN

VCNTL

REFEN AT9173 VOUT

R2

CSS

GND

RTT

CIN

CCNTL

COUT

RDUMMY

R1 = R2 = 100KO, RTT = 50O / 33O / 25O

COUT(MIN) = 10uF (Ceramic) + 1000uF under the worst case testing condition

RDUMMY = 1KO as for VOUT discharge when VIN is not presented but VCNTL is presented

CSS = 1uF, CIN = 470uF (Low ESR), CCNTL = 47uF

n Application Circuit

n General Regulator

Typical application circuit is used as a regulator to provide

termination voltage in double data rate (DDR) memory

system. The regulator could source and sink up to 2A peak

current. The output voltage will follow REFEN which

generated by two external dividing resistors down from VIN

or to the desired output voltage set externally by forcing a

voltage level to REFEN pin. To add a shutdown function ,

connect a small transistor to REFEN pin. To perform

shutdown function , put a logic high 5V signal to EN yield a

low (0V) to REFEN pin thus force output voltage to zero

voltage. The capacitor Css is used to softstart the output

voltage since VOUT will follow REFEN.

The AT9173 can be used as a general regulator.

To get a desired output voltage, put a reference

voltage to REFEN pin or dividing resistors down a

input voltage source. To drive inside N-Channel

MOSFET the VCNTL should be larger than VIN to get

enough driving voltage. The minimum dropout

voltage could be IOUT*0.1, where IOUT is the output

current.

n Layout issue

Time constant for this circuit is Css*(R1//R2). The Css

could also used as the bypass capacitor to filter out noise in

REFEN pin. So carefully layout should put Css close to

REFEN pin to maintain noise immunity. The CIN an CCNTL is

used as power decoupling capacitor. COUT is composed of

10uF ceramic plus 1000uF electrolyte capacitors. The first

one is to used as high frequency filter and the second one is

used to reduce voltage drop during load regulating.

Place a bypass capacitor as close as possible to

VIN and VCNTL pin is necessary. A low ESR

capacitor is recommended for this bypass

capacitor. Use wide and short PCB traces to

connect in between VIN power source VOUT to

reduce PCB resistance thus to reduce undesired

power dissipation.

Rev. C.04

7

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