A7122A
DC-DC CONVERTER BUCK (STEP-DOWN)
5.5V 2A 1.3MHz SYNCHRONOUS
AiT Semiconductor Inc.
www.ait-ic.com
DETAILED INFORMATION
Operation Description
The A7122A high-efficiency switching regulator is a small, simple, DC-to-DC step-down converter capable of
delivering up to 2A of output current. The device operates in pulse-width modulation (PWM) at 1.3MHz from a
2.5V to 5.5V input voltage and provides an output voltage from 0.6V on, making the A7122A ideal for
on-board post-regulation applications. An internal synchronous rectifier improves efficiency and eliminates the
typical Schottky free-wheeling diode. Using the on resistance of the internal high-side MOSFET to sense
switching currents eliminates current-sense resistors, further improving efficiency and cost.
Loop Operation
A7122A uses a PWM current-mode control scheme. An open-loop comparator compares the integrated
voltage-feedback signal against the sum of the amplified current-sense signal and the slope compensation
ramp. At each rising edge of the internal clock, the internal high-side MOSFET turns on until the PWM
comparator terminates the on cycle. During this on-time, current ramps up through the inductor, sourcing
current to the output and storing energy in the inductor. The current mode feedback system regulates the
peak inductor current as a function of the output voltage error signal. During the off cycle, the internal
high-side P-channel MOSFET turns off, and the internal low-side N-channel MOSFET turns on. The inductor
releases the stored energy as its current ramps down while still providing current to the output.
Current Sense
An internal current-sense amplifier senses the current through the high-side MOSFET during on time and
produces a proportional current signal, which is used to sum with the slope compensation signal. The
summed signal then is compared with the error amplifier output by the PWM comparator to terminate the on
cycle.
Current Limit
There is a cycle-by-cycle current limit on the high-side MOSFET of 2.5A. When the current flowing out of SW
exceeds this limit, the high-side MOSFET turns off and the synchronous rectifier turns on. A7122A utilizes a
frequency fold-back mode to prevent overheating during short-circuit output conditions. The device enters
frequency fold-back mode when the FB voltage drops below 200mV, limiting the current to 2.5A and reducing
power dissipation. Normal operation resumes upon removal of the short-circuit condition.
REV1.0
- MAY 2016 RELEASED -
- 8 -
AITSEMI [ AiT Semiconductor ]
