MB3825APFV データシートの表示（PDF） - Fujitsu

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MB3825APFV

6-ch DC/DC Converter IC With Synchronous Rectifier

Fujitsu 

MB3825A

s FUNCTIONAL DESCRIPTION

1. Switching Regulator Function

(1) Reference voltage circuit

The reference voltage circuit generates a temperature-compensated reference voltage ( 1.500 V) using the

voltage supplied from the power supply terminal (pin 28) . This voltage is used as the reference voltage for the

internal circuits of the IC. The reference voltage of up to 1 mA can also be supplied to an external device from

the VREF terminal (pin 27) .

(2) Triangular-wave oscillator circuit

By connecting a timing capacitor and a resistor to the CT (pin 22) and the RT (pin 21) terminals, it is possible to

generate any desired triangular oscillator waveform (CT : amplitude 1.0 V to 1.4 V, CT1 : amplitude 0.65 V to

1.35 V in phase with CT1, and CT2 : amplitude 0.65 V to 1.35 V in inverse phase with CT) . The triangular wave

is input to CT1, CT2 and the PWM comparator within the IC.

(3) Error amplifier

This amplifier detects the output voltage of the switching regulator and outputs a PWM control signal accordingly.

It has a wide common-mode input voltage range from 0 V to VCC − 0.9 V on channels 5 and 6 allows easy setting

from an external power supply, making the system suitable for DC motor speed control.

By connecting a feedback resistor and capacitor from the error amplifier output terminal to the inverted input

terminal, you can form any desired loop gain, for stable phase compensation.

(4) PWM comparator

The PWM comparators in these channels are a voltage comparator with one inverted input and one non-inverted

input (channels 1, 2, 4, 5, 6) as well as one inverted input and two non-inverted inputs (channel 3) , and voltage

pulse width modifier to control output duty according to input voltage.

In the interval when the error amplifier output voltage is higher than the triangular waveform, the output transistor

is turned on (channels 1, 2, 4, 5, 6) .

In the interval when the error amplifier output voltage is lower than the triangular waveform, the output transistor

is turned on (channel 1, 4 synchronous rectifier side) .

In the interval when the error amplifier output voltage and DTC3 voltage are higher than the triangular waveform,

the output transistor is switched on (channel 3) .

(5) Output circuit

The output circuits is comprised of a totem-pole configuration on both the main side and synchronous rectifier

side, and can drive an external PNP transistor (main side) or N-ch MOSFET (synchronous rectifier side) .

Sink current (on the main side) can be set up to 20 mA depending on the resistance of the VB terminal.

2. Channel Control Function

Channel on and off levels are dependent on the voltage levels of the CTL1 terminal (pin 30) and CTL 2 terminal

(pin 29) .

Table 1 Channel by Channel On/Off Setting Conditions.

CTL terminal

voltage level

CTL1 CTL2

L

X

L

H

H

On/Off state of channel

Power supply

circuit

Channel 1

Channel 2

Channel 4 Channel 5

Channel 6

Channel 3

OFF (standby mode) *

OFF

ON

ON

* : The power supply current in standby mode is 10 µA or less.

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