A7506
AiT Semiconductor Inc.
www.ait-ic.com
DC-DC CONVERTER BOOST(STEP-UP)
1.2MHz CONSTANT FREQUENCY SYNCHRONUS
DETAILED INFORMATION
Operation
The A7506 is 1.2MHz, synchronous boost converter housed in a 6-lead SOT package. Able to operate from
an input voltage below 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 A7506 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 Voltage Start-Up
The A7506 will start up at a typical VIN volt-age of 0.85V or higher. The low voltage start-up circuitry controls
the internal NMOS switch up to a maximum peak inductor current of 850mA (typical), with an
approximate1.5us off-time during start-up, allowing the devices to start up into an output load. Once VOUT
exceeds 2.3V, the start-up circuitry is disabled and normal fixed frequency PWM operation is initiated. In this
mode, the A7506 operate independent of VIN, allowing extended operating time as the battery can droop to
several tenths of a volt without affecting output voltage regulation. The limiting factor for the application
becomes the ability of the battery to supply sufficient energy to the output.
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 • [1 + (R1/R2)]
REV1.1
- APR 2009 RELEASED, MAY 2017 UPDATED -
- 8 -
AITSEMI [ AiT Semiconductor ]
