HM6313 datasheet(8/11 Pages) HMSEMI

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High Efficiency Low Voltage Synchronous

Step-up DC/DC Converter

HM6313

Functional Description

1) General Description

The HM6313 is a synchronous step-up DC-DC converter.

It utilizes internal MOSFET switches to achieve high

efficiency over full load current range. It operates at a

fixed switching frequency of 1.2MHz, and uses the

slope compensated peak current mode pulse width

modulation (PWM) architecture. The device can

operate with an input voltage below 1V and the

minimum start-up voltage is 0.85V.

2) Current Mode Operation

The HM6313 is based on a slope compensated peak

current mode PWM control topology. It operates at a

fixed frequency of 1.2MHz. At the beginning of each

clock cycle, the main switch (NMOS) is turned on and

the inductor current starts to ramp. After the maximum

duty cycle or the sense current signal equals the error

amplifier output, the main switch is turned off and the

synchronous switch (PMOS) is turned on. This control

topology features cycle-by-cycle current limiting which

can prevent the main switch from overstress and the

external inductor from saturating.

3) Synchronous Rectification

The HM6313 integrates a synchronous rectifier to

improve efficiency as well as to eliminate the need for

an external Schottky diode. The synchronous rectifier is

used to reduce the loss condition contributed by the

forward voltage of an external Schottky diode. The

synchronous rectifier is realized by a P-channel MOS

(PMOS) with gate control circuitry that incorporates

relatively complicated timing concerns.

4) Low voltage Start-up

The HM6313 can start-up with input voltage down to

0.85V. During start-up, the internal low voltage start-up

circuitry controls the internal NMOS switch. The

HM6313 leaves the start-up mode once output voltage

exceeds 2V. An internal comparator monitors the output

voltage and place the chip into normal operation once

output voltage exceeds 2V. The supply voltage of

control circuit is biased by input voltage in start-up

mode and biased by output voltage in normal mode.

When output voltage exceeds 2V, the HM6313 is

independent of input voltage.

5) Pulse Frequency Modulation Operation

At very light load, the HM6313 automatically enters

pulse frequency modulation (PFM) Mode to improve

efficiency. During this mode, the PFM control will skip

some pulses to maintain regulation. If the load

increases and output voltage drops, the device will

automatically switch back to normal PWM mode and

maintain regulation.

6) Anti-Ringing Control

An anti-ringing circuitry is included to remove the high

frequency ringing that appears on the SW pin when the

inductor current goes to zero. In this case, a ringing on

the SW pin is induced due to remaining energy stored

in parasitic components of switch and inductor. The

anti-ringing circuitry clamps the voltage internally to

the preset voltage and therefore dampens this ringing.

Page 8

Shenzhen H&M Semiconductor Co.Ltd

http：//www.hmsemi.com

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