HA16107P Datasheet, PDF (9/40 Pages) Hitachi Semiconductor – PWM Switching Regulator for High-performance Voltage Mode Control

HA16107P/FP, HA16108P/FP
Vref Protection Functions: Overvoltage and Undervoltage
Vref overvoltage and undervoltage conditions are detected by the overvoltage detection circuit and UVL2 circuit.
PWM output shuts down when Vref ≥ 8 V. UVL2 detects undervoltage with hysteresis between approximately 4 V and
5 V. PWM output also shuts down below these voltages. It follows that PWM output will shut off whenever the Vref
pin is shorted to the power supply (V_IN) or ground (GND). PWM output also shuts off when V_IN is turned on or off.
The following diagram shows how these protection functions operate when power comes on and goes off (Vref < 6.45
V), and when a high external voltage is applied to the Vref pin (Vref > 6.45 V).
PWM
OUT
PWM output shut-
down region
Power-off,
or shorted
to ground
Power-up
PWM output
operating region
Shorted to
power supply
PWM output
shut-down region
Vref
0
4 V 5 V 6.45 V 8 V 10 V
UVL2
Vref
OVP
1. Current-Limiter Circuit
The current limiter pin (CL) is connected to the emitter of an npn transistor, as shown in the block diagram. The
threshold voltage is 240 mV typ. The switching speed of this circuit is approximately 100 ns from detection of
overcurrent to shut-down of PWM output. Switching speed increases with the strength of the signal input to the CL
pin.
Instead of simple pulse-by-pulse current limiting, in these ICs the current limiting circuit is linked to the timer-and-
latch or ON/OFF timer circuit, and also detects the degree of overcurrent. The overcurrent value is determined from
the point at which current limiting is triggered in the ON-duty cycle. With a large overcurrent (causing current
limiting to operate even at a small ON-duty), the IC automatically shortens the timer time.
Rev.4.00 Jun 15, 2005 page 9 of 39