MB3825A Fujitsu Microelectronics, Inc., MB3825A Datasheet - Page 18

• Manufacturer Part Number: MB3825A
• Description: 6-ch DC/DC Converter ic With Synchronous Rectifier
• Manufacturer: Fujitsu Microelectronics, Inc.

18
MB3825A
1. Switching Regulator Function
2. Channel Control Function
* : The power supply current in standby mode is 10 A or less.
(1) Reference voltage circuit
(2) Triangular-wave oscillator circuit
(3) Error amplifier
(4) PWM comparator
(5) Output circuit
CTL1
CTL terminal
voltage level
FUNCTIONAL DESCRIPTION
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) .
By connecting a timing capacitor and a resistor to the C
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.
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 V
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.
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) .
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.
Channel on and off levels are dependent on the voltage levels of the CTL1 terminal (pin 30) and CTL 2 terminal
(pin 29) .
H
L
CTL2
X
H
L
Power supply
circuit
Table 1 Channel by Channel On/Off Setting Conditions.
Channel 1 Channel 2 Channel 4 Channel 5 Channel 6 Channel 3
On/Off state of channel
OFF (standby mode) *
ON
T
(pin 22) and the R
CC
0.9 V on channels 5 and 6 allows easy setting
T
(pin 21) terminals, it is possible to
OFF
ON