AAT1112
1.5A, 1.4MHz Step-Down Converter
Output regulation is maintained until the dropout
voltage, or minimum input voltage, is reached. At
1.5A output load, dropout voltage headroom is
approximately 200mV.
and line conditions. Internal loop compensation ter-
minates the transconductance voltage error amplifi-
er output. The reference voltage is internally set to
program the converter output voltage greater than or
equal to 0.6V.
The AAT1112 typically achieves better than ±0.5%
output regulation across the input voltage and output
load range. A current limit of 2.0A (typical) protects
the IC and system components from short-circuit
damage. Typical no load quiescent current is 42µA.
Soft Start/Enable
Soft start limits the current surge seen at the input
and eliminates output voltage overshoot. When
pulled low, the enable input forces the AAT1112 into
a low-power, non-switching state. The total input
current during shutdown is less than 1µA.
Thermal protection completely disables switching
when the maximum junction temperature is detect-
ed. The junction over-temperature threshold is
140°C with 15°C of hysteresis. Once an over-tem-
perature or over-current fault condition is removed,
the output voltage automatically recovers.
Current Limit and Over-Temperature
Protection
Peak current mode control and optimized internal
compensation provide high loop bandwidth and
excellent response to input voltage and fast load
transient events. Soft start eliminates output volt-
age overshoot when the enable or the input voltage
is applied. Under-voltage lockout prevents spuri-
ous start-up events.
For overload conditions, the peak input current is
limited. To minimize power dissipation and stresses
under current limit and short-circuit conditions,
switching is terminated after entering current limit
for a series of pulses. Switching is terminated for
seven consecutive clock cycles after a current limit
has been sensed for a series of four consecutive
clock cycles.
Control Loop
Thermal protection completely disables switching
when internal dissipation becomes excessive. The
junction over-temperature threshold is 140°C with
15°C of hysteresis. Once an over-temperature or
over-current fault conditions is removed, the output
voltage automatically recovers.
The AAT1112 is a peak current mode step-down
converter. The current through the P-channel
MOSFET (high side) is sensed for current loop
control, as well as short-circuit and overload pro-
tection. A fixed slope compensation signal is added
to the sensed current to maintain stability for duty
cycles greater than 50%. The peak current mode
loop appears as a voltage-programmed current
source in parallel with the output capacitor.
Under-Voltage Lockout
Internal bias of all circuits is controlled via the VIN
input. Under-voltage lockout (UVLO) guarantees
sufficient VIN bias and proper operation of all inter-
nal circuitry prior to activation.
The output of the voltage error amplifier programs
the current mode loop for the necessary peak switch
current to force a constant output voltage for all load
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