A7431
DC-DC CONVERTER BUCK (STEP-DOWN)
42V 3A CC/CV
AiT Semiconductor Inc.
www.ait-ic.com
DETAILED INFORMATION
Functional Description
CV/CC Loop Regulation
As seen in Functional Block Diagram, the A7431 is a peak current mode pulse width modulation (PWM)
converter with CC and CV control. The converter operates as follows:
A switching cycle starts when the rising edge of the Oscillator clock output causes the High-Side Power
Switch to turn on and the Low-Side Power Switch to turn off. With the SW side of the inductor now connected
to VIN, the inductor current ramps up to store energy in the magnetic field. The inductor current level is
measured by the Current Sense Amplifier and added to the Oscillator ramp signal. If the resulting summation
is higher than the COMP voltage, the output of the PWM Comparator goes high. When this happens or when
Oscillator clock output goes low, the High-Side Power Switch turns off.
At this point, the SW side of the inductor swings to a diode voltage below ground, causing the inductor current
to decrease and magnetic energy to be transferred to output. This state continues until the cycle starts again.
The High-Side Power Switch is driven by logic using BS as the positive rail. This pin is charged to VSW + 5V
when the Low-Side Power Switch turns on. The COMP voltage is the integration of the error between FB input
and the internal 0.808V reference. If FB is lower than the reference voltage, COMP tends to go higher to
increase current to the output. Output current will increase until it reaches the CC limit set by the ISET resistor.
At this point, the device will transition from regulating output voltage to regulating output current, and the
output voltage will drop with increasing load.
The Oscillator normally switches at 125kHz. However, if FB voltage is less than 0.3V, then the switching
frequency decreases to 50kHz.
Over Voltage Protection
The A7431 has an OVP pin. If the voltage at this pin exceeds 0.8V, the IC shuts down high side switch.
Thermal Shutdown
The A7431 disables switching when its junction temperature exceeds 160°C and resumes when the
temperature has dropped by 40°C.
REV1.1
- JAN 2016 RELEASED, SEP 2016 UPDATED -
- 6 -
AITSEMI [ AiT Semiconductor ]
