MB3827 Datasheet, PDF (20/41 Pages) Fujitsu Component Limited. – 6-ch DC/DC Converter IC With Synchronous Rectification for voltage step-up and step-down

MB3827
s FUNCTIONAL DESCRIPTION
1. Switching Regulator Function
(1) Reference voltage circuit
The reference voltage circuit generates a temperature-compensated reference voltage ( =: 2.50 V) using the
voltage supplied from the power supply terminal (pin 26). This voltage is used as the reference voltage for the
internal circuits of the IC. The reference voltage of up to 1mA can also be supplied to an external device from
the VREF terminal (pin 24).
(2) Triangular-wave oscillator circuit
By connecting a timing capacitor and a resistor to the CT (pin 34) and the RT (pin 33) terminals, it is possible
to generate any desired triangular oscillation waveform (CT : amplitude 0.3V to 0.8V, CT1 : amplitude 1.1V to
1.8V in phase with CT, and CT2 : amplitude 1.1V to 1.8V in inverse phase with CT). The triangular wave is input
to CT1, CT2 and the PWM comparator within the IC.
(3) Error amplifier (Error Amp.)
The error amp. is an amplifier circuit that detects the output voltage from the switching regulator and produces
the PWM control signal. The broad in-phase input voltage range of 0 V to Vcc − 1.8 V (1-6 ch) and 0 V to Vcc
− 0.9 V (channel 7) provides easy setting from external power supplies.
Also, it is possible to provide stable phase compensation for a system by setting up any desired level of loop
gain, by connecting feedback resistance and a capacitor between the error amp. output pin and the inverse input
pin.
(4) Inverter amplifier (Inv. Amp.)
The inverter amplifier detects the output voltage (negative voltage) from the switching regulator, and outputs a
control signal to the error amplifier.
(5) PWM comparator (PWM Comp.)
The voltage-pulse width modulator controls the output duty according to the input voltage.
(Channel 1 to 2, main side, and channel 3 to 7)
During the interval that the error amplifier output voltage and DTC are higher than the triangular wave,
the output transistor is turned on.
(Channel 1 step-down synchronous rectifier side)
During the interval when the error amplifier output voltage is lower than the triangular wave, the output
transistor is turned on.
(Channel 1 step-up synchronous rectifier side)
During the interval when the error amplifier output voltage and DTC3 voltage are lower than the triangular
wave, the output transistor is turned on.
(6) 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 NPN transistor (channel 1 step-up main side,
channel 7) or N-ch MOSFET (synchronous rectifier side).
20