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PJ3800

Low Voltage Switching Regulator Controller

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PJ3800

Low Voltage Switching Regulator Controller

PJ3800

PJ3800

1. Switching Regulator Function

(1) Reference voltage circuit

The reference voltage circuit generates a temperature-compensated reference voltage (@1.25V) from voltage supplied from the

power supply pin. In addition to providing the reference voltage for the switching regulator, the circuit also sets the idle period.

(2) Saw tooth wave oscillator

The saw tooth oscillator generates a saw tooth wave (up to 1 MHz) that is stable with respect to the supply voltage and

temperature. The capacitor and resistor that set the oscillation frequency are connected to the OSC pin (pin 7).

(3) Error amplifier (Error Amp.)

The error amplifier detects the output voltage of the switching regulator and outputs the PWM control signal. The voltage gain is

fixed, and connecting a phase compensation capacitor to the FB pin (pin 8) provides stable phase

compensation for the system.

(4) PWM comparator (PWM Comp.)

The voltage comparator has one inverting and three non-inverting inputs. The comparator is a voltage/pulse width converter that

controls the ON time of the output pulse depending on the input voltage. The output level is high (H) when the saw tooth wave is

lower than the error amplifier output voltage, soft start setting voltage, and idle period setting voltage.

(5) Output circuit

The output circuit has a totem pole type configuration and can drive an external NPN transistor directly. The value of the ON/OFF

current can be set by a resistor connected to the BR/CTL pin .

2. Power Supply Control Function

Stand-by mode (supply current 1 mA or less) can be set by connecting the BR/CTL pin to VCC or by making the pin open circuit.

6-8

2003/04.rev.A

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