MB3883 Datasheet, PDF (18/39 Pages) Fujitsu Component Limited. – 6-ch DC/DC Converter IC With Synchronous Rectification for voltage step-up and step-down

MB3883
s FUNCTIONS
1. DC-DC Converter Functions
(1) Reference voltage block
The reference voltage circuit generates a temperature-compensated reference voltage (typically =: 2.49 V) from
the voltage supplied from the power supply terminal (pin 19). 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 16).
(2) Triangular-wave oscillator block
The triangular wave oscillator incorporates a timing capacitor and a timing resistor connected respectively to
the CT terminal (pin 26) and RT terminal (pin 25) to generate triangular oscillation waveform CT (amplitude of
0.3 V to 0.8 V), CT1 (amplitude 1.1 V to 1.8 V in phase with CT), or CT2 (amplitude 1.1 V to 1.8 V in inverse
phase with CT).
CT1 and CT2 are input to the PWM comparator in the IC.
(3) Error amplifier (Error Amp.) block
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 5), or 0 V to “Vcc-0.9 V”(channel6)
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) Inverting amplifier (Inv Amp.) block
The inverting amplifier detects the DC/DC converter output voltage (as a negative voltage) and outputs a control
signal to the error amp.
(5) PWM comparator (PWM Comp.) block
The PWM comparator is a voltage-to-pulse width converter for controlling the output duty depending on the input
voltage.
Channels 1, 2, and 5 main sides,channel 3,4, and 6 : The comparator keeps the output transistor on while the
error amplifier output voltage and DTC voltageremain
higher than the triangular wave voltage.
Channels 1, 2, and 5 synchronous rectification sides : The comparator keeps the output transistor on while the
error amplifier output voltage remain lower than the tri-
angular wave voltage.
(6) Output block
The output block on the main side and on the synchronous rectification side is both in the totem pole configuration,
capable of driving an external P-channel MOS FET (channels 1, 2 main sides, channel 5 synchronous rectification
side), NPN transistor (channel 6), and N-channel MOS FET (channels 3, 4, channel 5 main side, channels 1, 2
synchronous rectification sides).
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