Data Sheet G13567EJ3V0DS00

11

µµµµ PC1934

2.3

Under Voltage Lock-out Circuit

The under voltage lock-out circuit prevents malfunctioning of the internal circuits when the supply voltage is low, such as

when the supply voltage is first applied, or when the power supply is interrupted. When the voltage is low, the two output

transistors are cut off at the same time.

2.4

Error Amplifiers

The circuits of the error amplifiers E/A1 and E/A2 are exactly the same. The first stage of the error amplifier is a P-

channel MOS transistor input. Be careful of the input voltage ranges (the common mode input voltage ranges are all 0 to

0.4 V (TYP.)).

2.5

PWM Comparators

The output ON duty is controlled according to the outputs of the error amplifiers and the voltage input to the Dead Time

Control pin.

A triangular waveform is input to the non-inverted pin, and the error amplifier output and Dead Time Control pin voltage

are input to the inverted pins of the PWM comparators. Therefore, the output transistor ON period is the period when the

triangular waveform is higher than the error amplifier output and Dead Time Control pin voltage (refer to Timing Charts).

2.6

Timer Latch-Method Short Circuit Protection Circuit

When the converter outputs either a channel or both channels drop, the FB outputs of the error amplifiers of those

outputs go low. If the FB output goes lower than the timer latch input detection voltage (VTH = 0.63 V)), then the output of

the SCP comparator goes low, and Q1 goes off.

When Q1 turns OFF, the constant-current supply charges CDLY via the DLY pin. The DLY pin is internally connected to a

flip-flop. When the DLY pin voltage reaches the UV detection voltage (VUV = 0.8 V (TYP.)), the output Q of the flip-flop goes

low, and the output stage of each channel is latched to OFF (refer to Figure 2-1 Block Diagram).

Make the power supply voltage briefly less than the reset voltage (VCCR, 1.0 V TYP.) to reset the latch circuit when the

short-circuit protection circuit has operated.

2.7

Output Circuit

The output circuit has an N-channel open-drain output providing an output withstand voltage of 30 V (absolute maximum

rating), and an output current of 21 mA (absolute maximum rating).