GS9215 datasheet(13/18 Pages) NIKOSEM

13 / 18 page

Rev.:0P12 (Preliminary Specification)

Aug-12

GStek series

NIKO-SEM

GStek series

High Performance Single Synchronous

Buck Converter

GS9215

Application Information

The GS9215 is small size chip with a relative

constant on-time synchronous buck Converter

suitable for applications in notebook computers

and other battery operated portable devices.

Features include very wide input voltage range,

high efficiency and a fast dynamic response with

internal fast response scheme.

System Clock Generator and PWM Control

The on-time of GS9215 can be set by an external

setting resistor from external Battery input voltage to

TON pin and a sampled output voltage. The

controller maintains the duty-circle as loop feedback

path exists between the GS9215 controller, the

integrated power MOSFET, low pass filter and

voltage divider. For a given VIN to given VOUT buck

application, the feedback maintains the constant

duty-cycle. Due to the constant resistor, battery

voltage and relative constant sampled output voltage,

the GS9215 based buck converter has the relative

constant frequency. Moreover, the GS9215 can

increase the duty-cycle automatically as battery

voltage falls down. Because of the constant on-time

in each switching period, the controller maintains the

relative frequency when the battery input voltage

changes.

At the beginning of each switching cycle, upper

power MOSFET is turned on, after typical fixed

on-time, the upper MOSFET is turned off, and then

lower power MOSFET is turned on after internal

dead time. The upper MOSFET will not be turned on

at the beginning of next cycle until output voltage falls

down below the preset voltage and the dead time

passes. The same events repeat the following

switching cycles. To avoid the surge inductor current

during large load transient, a minimum Off-time is

added. Typical minimum off-time is around 420ns.

High Side Switch On-Time Count

The on-time is decided by the external setting resistor,

battery input voltage and output voltage. Looking at the

TON pin, the battery input voltage is converted to

current which is inversely proportional to itself by

dividing the external setting resistor. Simultaneously,

the sample and hold module inside the chip samples

the output voltage at each switching cycle. The input

voltage-proportional current is used to charge an

internal capacitor from zero volts. When the voltage

between two terminals of the capacitor reaches to the

sampled output voltage, on-time one-shot pulse is

generated, and then upper power MOSFET is turned off

and lower power MOSFET is turned on.

We can count the on-time and switching frequency

according to the equations below:

TON=8.22p×RTON×VOUT/ (VIN-0.8)

Here, the VOUT is the sampled output voltage of VOUT

PIN.For output voltalge VOUT<2.5V, the VOUT Voltage

connects to VOUT PIN directly(refers to Figure 1a), the

VOUT = VOUT(0.7~2.5). For output voltalge VOUT >2.5V,

the VOUT Voltage connects to VOUT PIN through the

dividing resistors RVO1 and RVO2(refers to Figure 1b),

the typical VOUT is set to 2.5V, choose the RVO1 and

RVO2 as follows: VOUT=Vout*RVO2/(RVO1+RVO2).

Then, the switching frequency is:

Fsw=VOUT/ (VIN×TON)

RTON is a resistor connected from the input supply

(VIN) to the TON pin.

For heavy load (more than 10A) application, due to

ground bounced and the high impedance of RTON, the

TON pin should always be bypassed to GND using a

several nF-order ceramic capacitor for reliable system

operation.

EN/DEM,

DEM

Mode

and

Shutdown

Soft-Discharge

The EN/DEM pin enables the power supply. When

GS9215 Datasheet(PDF) 13 Page - NIKO SEMICONDUCTOR CO., LTD.

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