PRODUCT DATASHEET
AAT1162
SwitchRegTM
12V, 1.5A Step-Down DC/DC Converter
High efficiency is maintained under light load conditions
by automatically switching to variable frequency Light
Load control. In this condition, transition losses are
reduced by operating at a lower frequency at light
loads.
Applications Information
Setting the Output Voltage
Figure 1 shows the basic application circuit for the
AAT1162 and output setting resistors. Resistors R1 and
R2 program the output to regulate at a voltage higher
than 0.6V. To limit the bias current required for the
external feedback resistor string while maintaining good
noise immunity, the minimum suggested value for R2 is
5.9kΩ. Although a larger value will further reduce quies-
cent current, it will also increase the impedance of the
feedback node, making it more sensitive to external
noise and interference. Table 1 summarizes the resistor
values for various output voltages with R2 set to either
5.9kΩ for good noise immunity or 59kΩ for reduced no
load input current.
Short-Circuit Protection
The AAT1162 uses a cycle-by-cycle current limit to pro-
tect itself and the load from an external fault condition.
When the inductor current reaches the internally set
3.0A current limit, the P-channel MOSFET switch turns
off and the N-channel synchronous rectifier is turned on,
limiting the inductor and the load current.
During an overload condition, when the output voltage
drops below 50% of the regulation voltage (0.3V at FB),
the AAT1162 switching frequency drops by a factor of 4.
This gives the inductor current ample time to reset dur-
ing the off time to prevent the inductor current from
rising uncontrolled in a short-circuit condition.
L1
EP2
VOUT
VIN 4.5V- 13.2V
R4
C6
10μF
3.8μH
5V, 1.5A
LX
3
4
1
2
LX
LX
EN
IN
C1
100pF
R3
10Ω
5
7
C3
22μF
C2
0.1μF
432kΩ
IN
9
AAT1162
FB
AIN
Thermal Protection
10
11
C8
1μF
R6
COMP
AGND
59kΩ
6
13
16
R5
24kΩ
DGND
DGND
PGND
The AAT1162 includes thermal protection that disables
the regulator when the die temperature reaches 140ºC.
It automatically restarts when the temperature decreas-
es by 25ºC or more.
14
8
DGND
LDO
DGND
EP1
C7
330pF
C9
1μF
Figure 1: Typical Application Circuit.
The adjustable feedback resistors, combined with an
external feed forward capacitor (C1 in Figure 1), deliver
enhanced transient response for extreme pulsed load
applications. The addition of the feed forward capacitor
typically requires a larger output capacitor C3 for stabil-
ity. Larger C1 values reduce overshoot and undershoot
during startup and load changes. However, do not
exceed 470pF to maintain stable operation.
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1162.2008.01.1.3
ANALOGICTECH [ ADVANCED ANALOGIC TECHNOLOGIES ]
