mb3775pfv Fujitsu Microelectronics, Inc., mb3775pfv Datasheet - Page 3

• Manufacturer Part Number: mb3775pfv
• Description: Switching Regulator Controller
• Manufacturer: Fujitsu Microelectronics, Inc.

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OPERATION DESCRIPTION
The reference voltage circuit generates a stable, temperature-compensated 2.5 V reference from Vcc (pin 9) for
use by internal circuits.
A reference voltage of temperature compensated 1/2 Vref can be obtained to external circuit by Vref terminal
(pin 16).
A triangular waveform of any frequency is obtained by connecting an external capacitor and resistor to the C
(pin 1) and R
The amplitude of this waveform is from 1.3 V to 1.9 V. The oscillator is internally connected to the non-inverting
inputs of the PWM comparators. The oscillator waveform is available at the C
The error amplifier detects the output voltage of the switching regulator.
The common-mode input voltage range is 0.2 V to 1.45 V, so the input reference voltage can be set the V
and GND levels. Error amplifiers can be used as either inverting and non-inverting amplifiers.
The voltage gain is fixed. Phase compensation is possible by connecting a capacitor to the FB terminals (pins
5 and 12) of the error amplifiers.
The error amplifier output are internally connected to the inverting inputs of the PWM comparators and also to
the short protection circuit.
The timer latch short protection circuit detects the output levels of the error amplifiers. If one or both error amplifier
outputs are 1.1 V or lower, the timer circuit begins charging the externally connected protection enable capacitor.
If the output level of the error amplifier does not drop below the normal voltage range before the capacitor voltage
reaches the transistor base-emitter voltage V
and sets the dead time to 100 %.
An ambiguous transition state at power-on or a momentary fluctuation in the supply line may result in loss of
control and may adversely affect or even destroy the system. The under voltage lockout protection circuit com-
pares the internal reference voltage level with the supply voltage level. If the supply voltage level falls below the
reference level the latch circuit is reset the output drive transistor is turned off and the dead time is set to 100
%. The protection enable terminal (pin 15) is pulled “Low”.
Each PWM comparator has two inverting inputs and one non-inverting input. This voltage-to-pulse-width con-
verter controls the output pulse width according to the input voltage.
The PWM comparator turns the output drive transistor on when the oscillator triangular waveform is higher than
the error amplifier output and the dead time control terminal voltage.
The open-collector output-drive transistors provide common-emitter output of 18 V dielectric capability. The
output drive transistors can source up to 50 mA of drive current to the switching power transistor.
Reference voltage
Oscillator
Timer latch short protection circuit
Under voltage lockout protection circuit
PWM comparator
Output drive transistor
Error amplifiers
T
terminals (pin 2).
BE
(
0.65 V), the latch circuit turns the output drive transistor off
T
terminal.
MB3775
REF
T
3