μPD168807

Chapter Title

R03DS0001EJ0200 Rev.2.00

Page 11 of 30

Mar 18, 2011

7. Operation of Each Block (Overview)

Reference Voltage Block

The reference voltage block outputs a reference voltage (2.0 V TYP) that has been temperature-compensated by the

voltage supplied from the internal power supply block (3.3 V TYP). This reference voltage is used as the reference

voltage for all the internal circuits and a current of up to 1 mA can be output to an external circuit from the VREF pin

(pin 28).

Internal power supply block

The internal power supply block generates 3.3 V (TYP.) from analog power supply through AVDD pin (34 pin). This

block provides internal circuits with electric sources; however, not supposed to be used externally.

Oscillator block

The oscillator block spontaneously oscillates when a timing capacitance and a timing resistance are respectively

connected to the CT pin (pin 26) and RT pin (pin 25), and outputs a symmetrical triangular wave with an amplitude of

0.4 to 0.8 V (TYP.) to the CT pin.

E/A block (error amplifier)

The circuit configuration of all error amplifiers E/A1, E/A2, E/A3 and E/A4 is identical. All E/As have an internal

phase compensator. Pin II inputs an inverted signal to the E/A block. The input threshold voltages of the E/A block are

about 0.8 V for E/A1, E/A2 and E/A4 (CTL = L, when step-down), 1.0 V (TYP.) for E/A3 and 0.4 V (TYP.) for E/A4

(CTL = H, when inverting).

Output control block

The output control block controls the output ON duty by using the E/A output signal and the signal output from the

current detection amplifier. The maximum duty is 100% (TYP) when ch1 and ch2 operate, and ch3 (step-down) and ch4

(step-down, CTL = L) operate, and 85% (TYP) when ch3 (step-up) operates and ch4 operates as the inverting circuit

(CTL = H).

Output circuit block

The output circuit block of ch1 to ch3 includes a power MOSFET. The output current capacity of ch1 is 1.6 A (MAX)

when a switching pulse is output and 1.2 A (MAX) when DC is output. The output current capacity of ch2 is 1.9 A

(MAX) when a switching pulse is output and 1.5 A (MAX) when DC is output. The output current capacity of ch3 is

1.6 A (MAX) when a switching pulse is output and 1.2 A (MAX) when DC is output. The output circuit block of ch4

has a push-pull configuration and can directly drive the power MOSFET. The output current capacity of ch4 is 400 mA

(MAX) when a pulse is output and 30 mA (MAX) when DC is output.

ON/OFF control block

This circuit can turn on/off the output voltage of each channel by using the SHDNB1 pin to SHDNB4 pin and an

external signal. When the SHDNB1 to SHDNB4 pins are made low, a shut-down circuit operates, shutting down the

output of each channel. When the SHDNB1 to SHDNB4 pins are made high, the shut-down circuit stops, ch1 to ch4

are soft-started and their output voltage rises.