AAT1152IKS-1.2-T1 View Datasheet(PDF) - Analog Technology Inc
Part Name
Description
MFG CO.
'AAT1152IKS-1.2-T1' PDF : 18 Pages View PDF
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 2.55kΩ.
R3 = (VO - 1) ⋅ R4 = 0.25 ⋅ 10.0kΩ = 2.55kΩ
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)
⋅
VO
+ RDSON(L)
VIN
⋅
(VIN - VO))
+
tsw ⋅ F ⋅ IO ⋅ VIN + IQ ⋅ VIN
Once the total losses have been determined the junction temperature can be derived from the ΘJA 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 ⋅
VO
VINMAX
⋅
1-
VO
VINMAX
=
IO
2
=
0.5ARMS
P = ESRCOUT ⋅ IRMS2 = 5mΩ ⋅ 0.52 A = 1.25mW
14
1152.2003.01.0.9
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