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>

5

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.

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 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 6.)

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 XC9106/9107 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. As the PFM circuit

generates pulses based on outputs from the PWM Comparator, shifting between modes occurs smoothly. 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.

Externally Applied Reference Voltage (Vref)

XC9106 / 07 Series

PWM Control, PWM/PFM Switching Control,

Step-up DC/DC Converters

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)