HA16114P/PJ/FP/FPJ, HA16120FP/FPJ

Rev.2.0, Sep.18.2003, page 13 of 37

5. Voltage Reference (Vref = 2.5 V)

5.1 Voltage Reference

A bandgap reference built into the IC (see figure 5.1) outputs 2.5 V ± 50 mV. The sawtooth oscillator,

PWM comparator, latch, and other internal circuits are powered by this 2.5 V and an internally-generated

voltage of approximately 3.2 V.

The voltage reference section shut downs when the IC is turned off at the ON/

OFF pin as described later,

saving current when the IC is not used and when it operates in intermittent mode during overcurrent.

ON/

OFF

+

−

1.25 V

1.25 V

25 k

Ω

25 k

Ω

Vref

2.5 V

3.2 V

ADJ

Sub bandgap circuit

Main bandgap circuit

Figure 5.1 Vref Reference Circuit

5.2 Trimming the Reference Voltage (Vref and ADJ pins)

Figure 5.2 shows a simplified circuit equivalent to figure 5.1. The ADJ pin in this circuit is provided for

trimming the reference voltage (Vref). The output at the ADJ pin is a voltage V

generated by the bandgap circuit. Vref is determined by V

follows:

The design values of R

If trimming is not performed, the ADJ pin open can be left open.

−

+

Vref

ADJ

25 k

Ω

(typ)

25 k

Ω

(typ)

1.25 V (typ)

Figure 5.2 Simplified Diagram of Voltage Reference Circuit