AAT1162
12V, 1.5A Step-Down DC/DC Converter
Short-Circuit Protection
Applications Information
The AAT1162 uses a cycle-by-cycle current limit to
protect 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 syn-
chronous rectifier is turned on, limiting the inductor
and the load current.
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 volt-
age higher than 0.6V. To limit the bias current
required for the external feedback resistor string
while maintaining good noise immunity, the mini-
mum suggested value for R2 is 5.9kΩ. Although a
larger value will further reduce quiescent 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.
During an overload condition, when the output volt-
age 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 cur-
rent ample time to reset during the off time to pre-
vent the inductor current from rising uncontrolled in
a short-circuit condition.
Thermal Protection
The AAT1162 includes thermal protection that dis-
ables the regulator when the die temperature
reaches 140ºC. It automatically restarts when the
temperature decreases by 25ºC or more.
L1
EP2
VOUT
5V, 2A
VIN 4.5V -13.2V
R4
3.8ꢀH
LX
3
4
1
2
LX
LX
FB
EN
IN
C3
100pF
R1
43.2kΩ
10Ω
5
7
C1
22ꢀF
C2
22ꢀF
C6
0.1ꢀF
IN
9
AAT1162
AIN
10
11
R2
5.9kΩ
C7
1ꢀF
COMP
AGND
6
13
16
R3
50kΩ
DGND
14
8
DGND
PGND
DGND
LDO
DGND
EP1
C4
270pF
C5
1ꢀF
Figure 1: Typical Application Circuit.
The adjustable feedback resistors, combined with
an external feed forward capacitor (C3 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 C2 for stability. Larger C3 values reduce
overshoot and undershoot during startup and load
changes. However, do not exceed 470pF to main-
tain stable operation.
1162.2007.09.1.2
11
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