6. Setting of Intermittent Operation Timing when Overcurrent is Detected
6.1 Operation Principles
The current limiter on this IC detects overcurrent in each output pulse, providing pulse-by-pulse
overcurrent protection by limiting pulse output whenever an overcurrent is detected. If the overcurrent
state continues, the TIM pin and ON/OFF pin can be used to operate the IC intermittently. As a result, a
power supply with sharp vertical characteristics can be configured.
The ON/OFF timing for intermittent operation makes use of the hysteresis in the ON/OFF pin threshold
voltage VON and VOFF, such that VON – VOFF = VBE. Setting method is performed as described on the
following pages. VBE is based-emitter voltage of internal transistor.
When an overcurrent is detected in one channel of this IC but not the other, the pulse-by-pulse
current limiter still goes into operation on both channels. Also, when the intermittent operation
feature is not used, the TIM pin should be set to open state and the ON/OFF pin pulled up to high
level (above VON).
2.2 µF −
Figure 6.1 Connection Diagram (example)
6.2 Intermittent Operation Timing Chart (VON/OFF only)
IC is on
IC is off
a. Continuous overcurrent detected
b. Intermittent operation starts (IC is off)
c. Overcurrent cleared (dotted line)
Note: 1.VBE is the base-emitter voltage in transistors on the IC, and is approximately 0.7 V
(see the figure 7.1).
For details, see the overall waveform timing diagram.
Figure 6.2 Intermittent Operation Timing Chart
Rev.2.0, Sep.18.2003, page 15 of 33