Preliminary

" OPERATIONAL DESCRIPTION

<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 Controler>

<Vref 1 with Soft Start>

TSS = 8.65 x Vref + 2.21

[Example Computation]

Vref = 0.9V, TSS = 8.65 x 0.9 + 2.21 = 10.0 ms

<Enable Function>

6

XC9106 / 07 Series

PWM Control, PWM/PFM Switching Control,

Step-up DC/DC Converters

This function controls the operation and shutdown of the IC. When the voltage of the CE pin drops to 0.2V or less, disable mode will be entered, the

IC's operations will stop and the EXT pin will be kept at a low level (the external N-type MOSFET will be OFF) . When the IC is in a state of chip

disable, current consumption will be no more than 1.0

µA.

When the CE pin's voltage rises to 0.65V or more, enable mode will be entered and operations will recommence. The CE pin also doubles with

reference voltage in the XC9106/9107 series, and the range of reference voltage can be varied externally from 0.8V to 2.5V.

The XC9106/9107 series alters soft start times by the setting value of reference voltage in order to protect against voltage overshoot and also to

protect against inrush current. Please determine soft start time by the formula equation.

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. PWM/PFM control turns into

PFM control when threshold voltage becomes lower than voltage of error amps. Noise is easily reduced with PWM control since the switching

frequency is fixed. Because of the function, control suited to the application can easily be selected. The series 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

loads in stand-by.

The reference voltage of the XC9106/9107 series is adjusted and fixed by external applied voltage. (For output voltage settings, please refer to the

output voltage setting on page 7.)

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 error amp, the operation maintains a balance between the two inputs of error amps and controls the EXT pin's ON time

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

The XC9106 / 07 series are reference voltage (Vref) apply external step-up DC/DC Controler ICs. Output voltage will be set with external resistors

(RFB1 and 2) and Vref value. The series make it easy to control output voltage externally and are suited to software applications that need to vary

voltage such as LCD power supply for PDA.

Externally Applied Reference Voltage (Vref)

XC9106 / XC9107D xxx MR

0

5

10

15

20

25

30

0.0

0.5

1.0

1.5

2.0

2.5

3.0

Reference Voltage Vref (V)

Semiconductor Ltd.

Semiconductor Ltd.