MB3778P Fujitsu Microelectronics, Inc., MB3778P Datasheet - Page 5

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MB3778P

Manufacturer Part Number
MB3778P
Description
Switching Regulator Controller
Manufacturer
Fujitsu Microelectronics, Inc.
Datasheet

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1. Reference voltage circuit
2. Triangular wave oscillator
3. Error amplifiers (Error Amp.)
4. Timer latch short circuit protection circuit
5. Under voltage lock-out circuit
6. PWM comparator unit
7. Output drive transistor
8. Power control unit
OPERATION DESCRIPTION
The reference voltage circuit generates a temperature-compensated reference voltage ( : = 2.46 V) from V
9) . The reference voltage is used as an operation power supply for internal circuit.
The reference is obtained from the V
Triangular waveforms can be generated at any frequency by connecting a timing capacitor and resistor to the
C
The amplitude of this waveform is from 1.3 V to 1.9 V. These waveforms are connected to the non-inverting
inputs of the PWM comparator and can be output through the C
The error amplifier detects the output voltage of the switching regulator and outputs PWM control signals.The
in-phase input voltage range is from 1.05 V to 1.45 V.The reference voltage obtained by dividing the reference
voltage output (recommended value : V
input. The V
Any loop gain can be chosen by connecting the feedback resistor and capacitor to the inverting input terminal
from the output terminal of the error amplifier.Stable phase compensation is possible.
This circuit detects the output levels of each error amplifier. If the output level of one or both of the error amplifiers
is 2.1 V or higher, 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 idle period to 100 .
The transition state at power-on or a momentary drops in supply voltage may cause the control IC to malfunction,
which may adversely affect or even destroy the system. The under voltage lockout circuit monitors V
reference to the internal reference voltage and resets the latch circuit to turn the output drive transistor off. The
idle period is set to 100 . It also pulls the SCP terminal (pin 15) “Low”.
Each PWM comparator has one inverting input and two non-inverting inputs. This voltage-to-pulse-width con-
verter controls the turning on time of the output pulse according to the input voltage.
The PWM comparator turns the output drive transistor on while triangular waveforms from the oscillator are
lower than the error amplifier output and the DTC terminal voltage.
The output drive transistors have open collector outputs with common source supply and common grounds
independent of V
The power control terminal (pin 14) controls power on/off modes(the power supply current in stand-by mode is
10 A or lower).
T
terminal (pin 1) and to the R
REF
/2 voltage is internally connected to non-inverting input of the other error amplifier.
CC
and signal ground. The output drive transistors for switching can sink or source up to 50 mA.
T
terminal (pin 2) .
REF
REF
terminal (pin 16).
/2) or the R
BE
( : = 0.65 V), the latch circuit turns the output drive transistor off
T
terminal voltage (1.23 V) is supplied to the non-inverting
T
terminal.
MB3778
CC
CC
with
(pin
5

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