HA16114P Datasheet, PDF (14/38 Pages) Hitachi Semiconductor – Switching Regulator for Chopper Type DC/DC Converter

HA16114P/PJ/FP/FPJ, HA16120FP/FPJ
The relation between Vref and the ADJ pin enables Vref to be trimmed by inserting one external resistor
!
 (R3)betweentheVrefandADJpinsandanother(R4)betweentheADJpinandground,tochangethe
resistance ratio. Vref is then determined by the combined resistance ratio of the internal R₁ and R₂ and
external R₃ and R₄.
Vref
=
V_ADJ
×
R_A + R_B
R_B
Where, R_A: parallel resistance of R₁ and R₃
R_B: parallel resistance of R₂ and R₄
Although Vref can be trimmed by R₃ or R₄ alone, to decrease the temperature dependence of Vref it is
better to use two resistors having identical temperature coefficients. Vref can be trimmed in the range of
2.5 V ± 0.2 V. Outside this range, the bandgap circuit will not operate and the IC may shut down.
Vref
External
resistors
R_{3 ADJ}
R₄
R₁
Internal
resistors
R₂
R_A =
R₁ R₃
R₁ + R₃
R_B =
R₂ R₄
R₂ + R₄
Figure 5.3 Trimming of Reference Voltage
5.3 Vref Undervoltage Lockout and Overvoltage Protection
The undervoltage lockout (UVL) function turns off PWM pulse output when the input voltage (V_IN) is low.
In these ICs, this is done by monitoring the Vref voltage, which normally stays constant at approximately
2.5 V. The UVL circuit operates with hysteresis: it shuts PWM output off when Vref falls below 1.7 V,
and turns PWM output back on when Vref rises above 2.0 V. Undervoltage lockout also provides
protection in the event that Vref is shorted to ground.
The overvoltage protection circuit shuts PWM output off when Vref goes above 6.8 V. This provides
protection in case the Vref pin is shorted to V_IN or another high-voltage source.
PWM
output
PWM
output
off
PWM output on
PWM output off
1.7 2.0 2.5
5.0 6.8 10
Vref (V)
Figure 5.4 Vref Undervoltage Lockout and Overvoltage Protection
UVL Voltage
V_H
V_L
Vref (V typ)
2.0 V
1.7 V
V_IN (V typ)
3.6 V
3.3 V
Description
V_IN increasing: UVL releases; PWM output starts
V_IN decreasing: undervoltage lockout; PWM output stops
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