mb3881pff Fujitsu Microelectronics, Inc., mb3881pff Datasheet - Page 17

• Manufacturer Part Number: mb3881pff
• Description: 8-ch Dc/dc Converter Ic With Synchronous Rectifier For Voltage Step-up And Step-down
• Manufacturer: Fujitsu Microelectronics, Inc.

1. DC-DC Converter Functions
(1) Reference voltage generator
(2) Triangular-wave oscillator circuit
(3) Error amplifier (Error Amp.)
(4) PWM comparator (PWM Comp.)
(5) Output circuits
FUNCTIONS
The reference voltage generator generates a temperature-compensated reference voltage (typically : = 2.5 V)
from the voltage supplied from the power supply terminal (pin 27). The voltage is used as the reference voltage
for the IC’s internal circuitry.
The reference voltage can supply a load current of up to 1 mA to an external device through the VREF terminal
(pin 24).
The triangular wave oscillator incorporates a timing capacitor and a timing resistor connected respectively to
the CT terminal (pin 34) and RT terminal (pin 33) to generate triangular oscillation waveform CT (amplitude of
0.3 to 0.8 V), CT1 (amplitude 1.0 to 1.73 V in phase with CT), or CT2 (amplitude 1.0 to 1.73 V in inverse phase
with CT).
CT1 and CT2 are input to the PWM comparator in the IC.
The error amplifier detects the DC/DC converter output voltage and outputs PWM control signals. It supports
a wide range of in-phase input voltages from 0 V to “V
the external power supply.
In addition, an arbitrary loop gain can be set by connecting a feedback resistor and capacitor from the output
pin to inverted input pin of the error amplifier, enabling stable phase compensation to the system.
The PWM comparator is a voltage-to-pulse width converter for controlling the output duty depending on the input
voltage.
Channels 1, 2 main sides, channel 3 to 8
Channels 1, 2 synchronous rectification sides:The comparator keeps the output transistor on while the error
The output circuits on the main side and on the synchronous rectification side are both in the totem pole
configuration, capable of driving an external PNP transistor (channels 1,2 main sides, channels 3 to 7), NPN
transistor (channel 8), and N-channel MOSFET (channels 1,2 synchronous rectification sides).
: The comparator keeps the output transistor on while the
error amplifier output voltage and DTC voltage remain higher than
the triangular wave voltage.
amplifier output voltage remain lower than the triangular wave
voltage.
CC
- 1.8 V” (channels 1 to 7), allowing easy setting from
MB3881
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