A7525
AiT Semiconductor Inc.
www.ait-ic.com
DC-DC CONVERTER BOOST(STEP-UP)
1.2MHz, MICROPOWER SYNCHRONOUS
DETAILED INFORMATION
Operation
The A7525 is 1.2MHz, synchronous boost converter housed in a 6-lead SOT package. Able to operate from
an input voltage 1V, the device features fixed frequency, current mode PWM control for exceptional line and
load regulation. With its low RDS (ON) and gate charge internal MOSFET switches, the device maintains high
efficiency over a wide range of load current. Detailed descriptions of the operating modes follow. Operation
can be best understood by referring to the Block Diagram.
Synchronous Rectification
The A7525 integrates a synchronous rectifier to improve efficiency as well as to eliminate the external
Schottky diode. The synchronous rectifier is used to reduce the conduction loss contributed by the forward
voltage of Schottky diode. The synchronous rectifier is realized by a P-ch MOSFET with gate control circuitry
that incorporates relatively complicated timing concerns.
Low Noise Fixed Frequency Operation
Oscillator: The frequency of operation is internally set to 1.2MHz. Error Amp: The error amplifier is an
internally compensated trans-conductance type (current output) with a trans-conductance (gm) = 33
micro-siemens. The internal 1.23V reference voltage is compared to the voltage at the FB pin to generate an
error signal at the output of the error amplifier. A volt-age divider from Vout to ground programs the output
voltage via FB from 2.5V to 5V using the equation:
VOUT = 1.23V x [1 + (R1/R2)]
Current Sensing: A signal representing NMOS switch current is summed with the slope compensator.
The summed signal is compared to the error amplifier output to provide a peak current control command for
the PWM. Peak switch current is limited to approximately 850mA independent of input or output voltage. The
current signal is blanked for 40ns to enhance noise rejection.
Zero Current Comparator: The zero current comparator monitors the inductor current to the output and shuts
off the synchronous rectifier once this current reduces to approximately 20mA. This prevents the inductor
current from reversing in polarity improving efficiency at light loads.
Antiringing Control: The antiringing control circuitry pre-vents high frequency ringing of the LX pin as the
inductor current goes to zero by damping the resonant circuit formed by L and CLX (capacitance on LX pin).
REV1.1
- JAN 2012 RELEASED, SEP 2017 UPDATED -
- 8 -
AITSEMI [ AiT Semiconductor ]
