A7115
AiT Semiconductor Inc.
DC-DC CONVERTER
www.ait-ic.com
1.5MHZ, 1.5A SYNCHRONOUS STEP-DOWN CONVERTER
DETAILED INFORMATION
Operation
A7115 is a monolithic switching mode Step-Down DC-DC converter. It utilizes internal MOSFETs to achieve
high efficiency and can generate very low output voltage by using internal reference at 0.6V. It operates at a
fixed switching frequency, and uses the slope compensated current mode architecture. This Step-Down
DC-DC Converter supplies 1500mA output current at VOUT = 1.8V with input voltage range from 2.5V to 6.5V.
Current Mode PWM Control
Slope compensated current mode PWM control provides stable switching and cycle-by-cycle current limit for
excellent load and line responses and protection of the internal main switch (P-Ch MOSFET) and
synchronous rectifier (N-CH MOSFET). During normal operation, the internal P-Ch MOSFET is turned on for
a certain time to ramp the inductor current at each rising edge of the internal oscillator, and switched off when
the peak inductor current is above the error voltage. The current comparator, ICOMP limits the peak inductor
current. When the main switch is off, the synchronous rectifier will be turned on immediately and stay on until
either the inductor current starts to reverse, as indicated by the current reversal comparator, IZERO, or the
beginning of the next clock cycle. The OVDET comparator controls output transient overshoots by turning the
main switch off and keeping it off until the fault is no longer present.
Idle Mode Operation
At very light loads, the A7115 automatically enters pulse skipping Mode. In the pulse skipping Mode, the
inductor current may reach zero or reverse on each pulse. The PWM control loop will automatically skip
pulses to maintain output regulation. The bottom MOSFET is turned off by the current reversal comparator,
IZERO and the switch voltage will ring. This is discontinuous mode operation, and is normal behavior for the
switching regulator.
Dropout Operation
When the input voltage decreases toward the value of the output voltage, the A7115 allows the main switch to
NOTE4
remain on for more than one switching cycle and increases the duty cycle
until it reaches 100%. The
output voltage then is the input voltage minus the voltage drop across the main switch and the inductor. At low
input supply voltage, the RDS(ON) of the P-Channel MOSFET increases, and the efficiency of the converter
decreases. Caution must be exercised to ensure the heat dissipated not to exceed the maximum junction
temperature of the IC.
REV1.0
- APR 2013 RELEASED, NOV 2014 UPDATED -
- 7 -
AITSEMI [ AiT Semiconductor ]
