HA16114P Datasheet, PDF (13/38 Pages) Hitachi Semiconductor – Switching Regulator for Chopper Type DC/DC Converter

HA16114P/PJ/FP/FPJ, HA16120FP/FPJ
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
Sub bandgap circuit
Main bandgap circuit
V_IN
1.25 V
25 kΩ
25 kΩ
3.2 V
Vref
2.5 V
ADJ
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_ADJ of 1.25 V (Typ)
generated by the bandgap circuit. Vref is determined by V_ADJ and the ratio of internal resistors R₁ and R₂ as
follows:
Vref = V_ADJ ×
R₁ + R₂
R₂
The design values of R₁ and R₂ are 25 kΩ with a tolerance of ±25%.
If trimming is not performed, the ADJ pin open can be left open.
V_IN
Vref
R₁
25 kΩ
(typ)
ADJ
R₂
25 kΩ
(typ)
V_BG (bandgap voltage)
1.25 V (typ)
Figure 5.2 Simplified Diagram of Voltage Reference Circuit
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