7.2 Adjusting UVL Voltage (when intermittent operation is not used)
The UVL voltage setting in this IC series can be adjusted externally as shown below.
Using the relationships shown in the figure, the UVL voltage in relation to VIN can be adjusted by changing
the relative values of VTH and VTL.
When the IC is operating, transistor Q4 is off, so VON = 3VBE ≈ 2.1 V. Accordingly, by connecting resistors
RC and RD, the voltage at which UVL is cancelled is as follows.
VIN = 2.1 V ×
RC + RD
This VIN is simply the supply voltage at which the UVL stops functioning, so in this state Vref is still below
2.5 V. In order to restore Vref to 2.5 V, a VIN of approximately 4.3 V should be applied.
With this IC series, VON/OFF makes use of the VBE of internal transistors, so when designing a power supply
system it should be noted that VON has a temperature dependency of around –6 mV/°C.
To other circuitry
On/off hysteresis circuit
VIN ≥ 4.5 V
Figure 7.2 Adjusting UVL Voltage
Rev.2.0, Sep.18.2003, page 19 of 33