AAT1152 Datasheet, PDF(14/18 Page) Advanced Analogic Technologies – 850kHz 1A Synchronous Buck DC/DC Converter

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AAT1152 Datasheet, PDF (14/18 Pages) Advanced Analogic Technologies – 850kHz 1A Synchronous Buck DC/DC Converter

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AAT1152

850kHz 1A Synchronous Buck DC/DC Converter

Adjustable Output

For applications requiring an output other than the

fixed outputs available, the 1V version can be pro-

grammed externally. Resistors R3 and R4 of figure

3 force the output to regulate higher than 1 Volt.

R4 should be 100 times less than the internal 1

MegOhm resistance of the FB pin. Once R4 is

selected R3 can be calculated. For a 1.25V output

with R4 set to 10.0k, R3 is 2.55kâ¦.

R3 = (VO - 1) â R4 = 0.25 â 10.0kâ¦ = 2.55kâ¦

Layout Considerations

Figures 5 and 6 display the suggested PCB layout

for the AAT1152. The most critical aspect of the lay-

out is the placement of the input capacitor C1. For

proper operation C1 must be placed as close as

possible to the AAT1152.

Thermal Calculations

There are two types of losses associated with the

AAT1152 output switching MOSFET, switching

losses and conduction losses. The conduction

losses are associated with the Rds(on) character-

istics of the output switching device. At full load,

assuming continuous conduction mode (CCM), a

simplified form of the total losses is:

PLOSS

IO2

(RDSON(H)

+ RDSON(L)

VIN

(VIN - VO))

tsw â F â IO â VIN + IQ â VIN

Once the total losses have been determined the junction temperature can be derived from the ÎJA for the

MSOP-8 package.

Design Example

Specifications

IOUT = 1.0A

IRIPPLE = 30% of full load at max VIN

VOUT = 1.5V

VIN = 2.7 - 4.2 V (3.6V nominal)

Fs = 830 kHz

Maximum Input Capacitor Ripple:

IRMS = IO â

VINMAX

ï£«ï£1-

VINMAX

ï£¶

ï£¸

0.5ARMS

P = ESRCOUT â IRMS2 = 5mâ¦ â 0.52 A = 1.25mW

1152.2003.01.0.9

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