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AAT1142

800mA Voltage-Scaling Step-Down Converter

Advanced Analogic Technologies 

SwitchRegTM

PRODUCT DATASHEET

AAT1142

800mA Voltage-Scaling Step-Down Converter

tion. Output regulation is maintained until the dropout

voltage, or minimum input voltage, is reached.

The AAT1142 achieves better than ±0.5% output regula-

tion across the input voltage and output load range.

Maximum continuous load is 800mA. A current limit of

1A (typical) protects the IC and system components

from short-circuit damage. Typical no load quiescent cur-

rent is 35μA.

Thermal protection completely disables switching when

the maximum junction temperature is detected. The

junction over-temperature threshold is 140°C with 15°C

of hysteresis. Once an over-temperature or over-current

fault condition is removed, the output voltage automati-

cally recovers.

Peak current mode control and optimized internal com-

pensation provide high loop bandwidth and excellent

response to input voltage and fast load transient events.

The output voltage is stable across all operating condi-

tions, ensuring fast transitions with no overshoot or ring-

ing. Soft start eliminates output voltage overshoot when

the enable or the input voltage is applied. Under-voltage

lockout prevents spurious start-up events.

Control Loop

The AAT1142 is a peak current mode step-down con-

verter. The current through the P-channel MOSFET (high

side) is sensed for current loop control, as well as short-

circuit and overload protection. A fixed slope compensa-

tion signal is added to the sensed current to maintain

stability for duty cycles greater than 50%. The peak cur-

rent mode loop appears as a voltage-programmed cur-

rent source in parallel with the output capacitor.

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 and line

conditions. Internal loop compensation terminates the

transconductance voltage error amplifier output. Loop

stability and fast transient response are maintained

across the entire input and output voltage range with a

small 2.2μH output inductor and 10μF output capacitor.

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 AAT1142 into a low-power,

non-switching state. The total input current during shut-

down is less than 1μA. The turn-on time from EN to

output regulation is 100μs (typical).

Alternatively, the EN/SET pin serves as the input for

S2Cwire single line control. Details of S2Cwire operation

and timing diagrams are provided in the Applications

Information section of this datasheet.

Current Limit and

Over-Temperature Protection

Switching is terminated after entering current limit for a

series of pulses to minimize power dissipation and

stresses under overload and short-circuit conditions.

Switching is terminated for seven consecutive clock

cycles after a current limit has been sensed for a series

of four consecutive clock cycles.

Thermal protection completely disables switching when

internal dissipation becomes excessive. The junction

over-temperature threshold is 140°C with 15°C of hys-

teresis. Once an over-temperature or over-current fault

condition is removed, the output voltage automatically

recovers.

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 internal circuitry prior to

activation.

1142.2009.08.1.1

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