AAT1142 View Datasheet(PDF) - Advanced Analogic Technologies
Part Name
Description
MFG CO.
'AAT1142' PDF : 21 Pages View PDF
SwitchRegTM
PRODUCT DATASHEET
AAT1142
800mA Voltage-Scaling Step-Down Converter
IQ is the step-down converter quiescent current. The
term tsw is used to estimate the full load step-down con-
verter switching losses.
For the condition where the step-down converter is in
dropout at 100% duty cycle, the total device dissipation
reduces to:
PTOTAL = IO2 · RDS(ON)H + IQ · VIN
Since RDS(ON), quiescent current, and switching losses all
vary with input voltage, the total losses should be inves-
tigated over the complete input voltage range.
Given the total losses, the maximum junction tempera-
ture can be derived from the θJA for the TSOPJW-12
package which is 160°C/W.
TJ(MAX) = PTOTAL · ΘJA + TAMB
Layout
The suggested PCB layout for the AAT1142 in a
TSOPJW-12 package is shown in Figures 7 and 8. The
following guidelines should be used to help ensure a
proper layout.
1. The input capacitor (C2) should connect as closely as
possible to VIN (Pin 12) and PGND (Pin 2).
2. C1 and L1 should be connected as closely as possi-
ble. The connection of L1 to the LX pin (Pin 1) should
be as short as possible.
3. The feedback pin (Pin 7) should be separate from
any power trace and connected close to the VOUT ter-
minal. Sensing along a high-current load trace will
degrade VOUT load regulation.
4. The resistance of the trace from the GND terminal to
PGND (Pin 2) should be kept to a minimum. This will
help to minimize any error in DC regulation due to
differences in the potential of the internal signal
ground and the power ground.
5. Connect unused signal pins to ground to avoid
unwanted noise coupling. When using S2Cwire, con-
nect SDA and SCL to ground to disable I2C function-
ality.
6. When using the TDFN33-12 package, connect the
exposed paddle (EP) to the GND plane.
Figure 7: AAT1142 Evaluation Board
Top Side Layout (TSOPJW-12 Package).
Figure 8: AAT1142 Evaluation Board
Bottom Side Layout (TSOPJW-12 Package).
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1142.2009.08.1.1
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