MB3817_03 Datasheet, PDF (11/28 Pages) Fujitsu Component Limited. – Switching Regulator Controller

MB3817
s FUNCTIONAL DESCRIPTION
1. Switching Regulator Functions
(1) Reference voltage circuit (Ref)
The reference voltage circuit generates a temperature-compensated stable voltage ( =: 1.50 V) . This reference
voltage is used as the reference voltage and bias level for the power control unit.
(2) Triangular-wave oscillator circuit
By connecting a timing capacitor and a resistor to the CT (pin1) and the RT (pin2) terminals, it is possible to
generate any desired triangular oscillation waveform.
(3) Error amplifier
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 − 0.9 V provides easy setting from
external power supplies and enables use with applications such as DC motor speed control systems.
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 terminal (FB terminal
(pin 5) ) and the inverse input terminal (−IN terminal (pin 4) ) .
(4) PWM comparator (PWM Comp.)
This is a voltage comparator with one inverted input and three non-inverted inputs, and operates as a voltage-
pulse width modulator controlling output duty in relation to input voltage.
The output transistor is turned on during the interval in which the triangular waveform is lower than any of three
voltages : the error amp. output voltage (FB terminal (pin 5) ) , soft start set voltage (CS terminal (pin 13) ) , or
dwell time setting voltage (DTC terminal (pin 6) ) .
(5) Output circuits (OUT)
The output circuit has totem pole type configuration, and can drive an external PNP transistor.
The on current value can be set up to a maximum of 30 mA using the resistance (RE) connected to the VE
terminal (pin 11) .
The off current is set by connecting a bootstrap capacitor CB between the CP1 terminal (pin 7) and CP2 terminal
(pin 8) .
2. Power Supply Control Functions
The output is switched on and off according to the voltage level at the CTL terminal (pin 15) .
CTL terminal voltage level
Channel on/off status
L ( ≤ 0.7 V)
H ( ≥ 2.1 V)
Standby mode*
Operating mode
* : Supply current in standby mode is 10 µA or less.
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