A7534
AiT Semiconductor Inc.
DC-DC CONVERTER/BOOST(STEP-UP)
0.9V STARTUP, 1MHZ, 300MA IOUT, LOW IQ, SYNCHRONOUS
BOOST CONVERTER
www.ait-ic.com
DETAILED INFORMATION
A7534 is a low input voltage start up, current mode DC-DC step up converter. It’s operation can be best
understood by referring to the block diagram. Upon starting up, the low voltage startup circuitry drives SW
with on-off cycles, transferring energy from input to OUT by storing energy in the inductor during on-time and
releasing it to the output during off-time. When OUT reaches 2V, the startup circuit turns off and the main
controller takes over. The main control loop consists of a reference, a GM error amplifier, a PWM controller, a
current sense amplifier, an oscillator, a PWM logic control, and it is power stage including its driver. The main
control loop is a classic current mode control loop. The GM stage integrates the error between FB and REF,
and its output is used to compare with a triangular wave which the summing result of the current sense
amplifier output and a slope compensation voltage. The output of the comparator is used to drive the power
stage to reach regulation.
Application Information
Inductor selection
With switching frequency up to 1MHz, small surface mount inductors can be used with values from 2.2uH to
4.7uH. For a given chosen inductor value and application conditions make sure the peak inductor current
does not exceed the maximum current rating of the selected vendor's inductor.
Input and output capacitor selection
The A7534's bootstrap architecture allows the use of very small input capacitor. For applications that only
need to drive small output load current, the input capacitor is optional, because once output is started up, the
IC's is powered by OUT, a quiet power supply.
The output capacitor is used to stabilize the loop and provide ac current to the load. A low ESR ceramic cap
with values from 2.2uF to 22uF can be used. Smaller value capacitors are generally cheaper with small
footprints, while larger capacitor provides lower ripples and better transient load responses. Also, when
extreme low startup voltage is needed, larger output capacitors are needed for the part to startup under heavy
load condition.
REV1.1
- JAN 2015 RELEASED, JUL 2016 UPDATED -
- 7 -
AITSEMI [ AiT Semiconductor ]
