MB3881 Datasheet, PDF (17/40 Pages) Fujitsu Component Limited. – 8-ch DC/DC Converter IC with Synchronous Rectifier for Voltage Step-up and Step-down

MB3881
s FUNCTIONS
1. DC-DC Converter Functions
(1) Reference voltage generator
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).
(2) Triangular-wave oscillator circuit
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.
(3) Error amplifier (Error Amp.)
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 “VCC - 1.8 V” (channels 1 to 7), allowing easy setting from
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.
(4) PWM comparator (PWM Comp.)
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
: The comparator keeps the output transistor on while the
error amplifier output voltage and DTC voltage remain higher than
the triangular wave voltage.
Channels 1, 2 synchronous rectification sides:The comparator keeps the output transistor on while the error
amplifier output voltage remain lower than the triangular wave
voltage.
(5) Output circuits
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).
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