AAT1130 Datasheet, PDF (11/19 Pages) Advanced Analogic Technologies – 2.5MHz 500mA Step-Down DC/DC Converter

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Functional Block Diagram
PRODUCT DATASHEET
AAT1130
2.5MHz 500mA Step-Down DC/DC Converter
VP
VCC
EN
Control and
FET Driver
Logic Circuitry
Current
Limit
Comparator
Error
Comparator
Shoot
Through
LX
Protection
VILIM
Current
Sense
Amplifier
PGND
[Fixed Only]
VOUT
Soft-Start
+ _VREF
-
FB
[Adj Only]
GND
Functional Description
The AAT1130 is a high performance 500mA 2.5MHz
(maximum switching frequency during steady-state
operation) monolithic step-down converter. It minimizes
external component size, enabling the use of a tiny 0603
inductor that is only 1mm tall, and optimizes efficiency
over the complete load range. Apart from the small
bypass input capacitor, only a small L-C filter is required
at the output. Typically, a 1μH inductor and a 4.7μF
ceramic capacitor are recommended for <1.2V output
voltage applications (see table of values).
Only three external power components (C_IN, C_OUT, and L)
are required, for fixed output voltage options. Output
voltage is programmed with external feedback resistors,
ranging from 0.6V to 1.8V. An additional feed-forward
capacitor can also be added to the external feedback to
provide improved transient response (see Figure 1).
The input voltage range is 2.7V to 5.5V. The converter
efficiency has been optimized for all load conditions,
ranging from no load to 500mA.
The internal error comparator and incorporated compen-
sation provide excellent transient response, load, and line
regulation. Soft-start eliminates any output voltage over-
shoot when the enable or the input voltage is applied.
Control Loop
The AAT1130 uses a current-mode control scheme that
allows it to operate at very high switching frequencies.
The current-mode control scheme operates with a fixed
on-time for a given input voltage. The on-time varies
inversely proportional to the input voltage and propor-
tional to the output voltage giving the regulator a fixed
switching frequency when in steady-state. This allows
the use of very small external inductor and capacitor.
The small size coupled with the low quiescent current
and automatic transition to variable switching frequency
mode makes it ideal for small battery operated applica-
tions.
Light Load Operation
The AAT1130 monitors the synchronous rectifier current
and when the current drops to zero, it turns off the syn-
chronous rectifier to emulate an actual rectifier. This
allows the regulator to operate in discontinuous conduc-
1130.2008.08.1.1
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