4. Totem Pole Output Stage Circuit and Power MOS FET Driving Method
The output stage of this IC series is configured of totem pole circuits, allowing direct connection to a power
MOS FET as an external switching device, so long as VIN is below the gate breakdown voltage.
If there is a possibility that VIN will exceed the gate breakdown voltage of the power MOS FET, a Zener
diode circuit like that shown figure 4.1 or other protective measures should be used. The figure 4.1 shows
an example using a P-channel power MOS FET.
E.g.: VIN = 18 V
Zener diode for
Figure 4.1 P-channel Power MOS FET (example)
5. Vref Undervoltage Error Prevention (UVL) and Overvoltage Protection (OVP) Functions
5.1 Operation Principles
The reference voltage circuit is equipped with UVL and OVP functions.
In normal operation the Vref output voltage is fixed at 2.5 V. If VIN is lower than normal, the UVL
circuit detects the Vref output voltage with a hysteresis of 1.7 V and 2.0 V, and shuts off the PWM
output if Vref falls below this level, in order to prevent malfunction.
The OVP circuit protects the IC from inadvertent application of a high voltage from outside, such as if
VIN is shorted. A Zener diode (5.6 V) and resistor are used between Vref and GND for overvoltage
detection. PWM output is shut off if Vref exceeds approximately 7.0 V.
Note that the PWM output pulse logic and the precision of the switching regulator output voltage are not
guaranteed at an applied voltage of 2.5 V to 7 V.
Rev.2.0, Sep.18.2003, page 13 of 33