" NOTE ON HOW TO USE B TYPE

Please set time constant equal to 10ms by the following equation.

Time constant :

τ (s) = R (Ω) x C (F)

[ Example of Equation ]

R = 100k

Ω, C = 0.1µF

τ (s)

= R (

Ω) x C (F)

= 100k

Ω x 0.1µF = 10ms

" OPERATIONAL DESCRIPTION

The XC9103/04/05 series are step-up DC/DC converter controller ICs with built-in high speed, low ON resistance drivers.

<Error Amp.>

<OSC Generator>

<Ramp Wave Generator>

The Ramp Wave Generator generates a saw-tooth waveform based on outputs from the OSC Generator.

<PWM Comparator>

<PWM/PFM Controller>

<Vref 1 with Soft Start>

<Enable Function>

XC9103/04/05 Series

Ceramic Cap. Compatible

Step-Up DC/DC Converters

Error Amplifier is designed to monitor the output voltage, comparing the feedback voltage (FB) with the reference voltage Vref. In response to feedback

of a voltage lower than the reference voltage Vref, the output voltage of the error amp. decreases.

This circuit generates the internal reference clock.

The PWM comparator compares outputs from the Error Amp. and saw-tooth waveform. When the voltage from the Error Amp's output is low, the

external switch will be set to ON.

This circuit generates PFM pulses.

The PWM/PFM automatic switching mode switches between PWM and PFM automatically depending on the load. The PWM/PFM automatic switching

mode is selected when the voltage of the CE pin is less than VDD - 1.0V, and the control switches between PWM and PFM automatically depending on

the load. PWM/PFM control turns into PFM control when threshold voltage becomes lower than voltage of error amps. PWM control mode is selected

when the voltage of the CE pin is more than VDD - 0.2V. Noise is easily reduced with PWM control since the switching frequency is fixed. The series is

suitable for noise sensitive portable audio equipment as PWM control can suppress noise during operation and PWM/PFM switching control can reduce

consumption current during light load in stand-by.

The reference voltage, Vref (FB pin voltage)=0.9V, is adjusted and fixed by laser trimming (for output voltage settings, please refer to the notes on page

8). To protect against inrush current, when the power is switched on, and also to protect against voltage overshoot, soft-start time is set internally to

10ms. It should be noted, however, that this circuit does not protect the load capacitor (CL) from inrush current. With the Vref voltage limited and

depending upon the input to the error amps, the operation maintains a balance between the two inputs of the error amps and controls the EXT pin's ON

time so that it doesn't increase more than is necessary.

This function controls the operation and shutdown of the IC. When the voltage of the CE pin is 0.2V or less, the mode will be disable, the channel's

operations will stop and the EXT1 pin will be kept at a low level (the external N-type MOSFET will be OFF). When the IC is in a state of disable, current

consumption will be no more than 1.0

µA.

When the CE pin's voltage is 0.65V or more, the mode will be enable and operations will recommence.

When applying voltage to VDD through CE pin with the series' B type product, the

limiter circuit may operate when a power supply is on, and the operation may not

start. In this case, as the right circuit indicates, please connect a resistor and a

capacitor with the CE pin. By the time constant, the CE pin will be chip enable after

VDD rise so that IC will be in the stable condition.

Semiconductor Ltd.

R

CE/PWM

EXT

GND

FB

VDD

C

7