HA16114P Datasheet, PDF (15/38 Pages) Hitachi Semiconductor – Switching Regulator for Chopper Type DC/DC Converter

HA16114P/PJ/FP/FPJ, HA16120FP/FPJ
6. Usage of ON/OFF Pin
This pin is used for the following purposes:
• To shut down the IC while its input power remains on (power management)
• To externally alter the UVL release voltage
• With the timer (TM) pin, to operate in intermittent mode during overcurrent (see next section)
6.1 Shutdown by ON/OFF Pin Control
The IC can be shut down safely by bringing the voltage at the ON/OFF pin below about 0.7 V (the internal
VBE value). This feature can be used in power supply systems to save power. When shut down, the
HA16114 draws a maximum current (I_OFF) of 10 µA, while the HA16120 draws a maximum 150 µA. The
ON/OFF pin sinks 290 µA (Typ) at 5 V, so it can be driven by TTL and other logic ICs. If intermittent
mode will also be employed, use a logic IC with an open-collector or open-drain output.
External logic IC
I_IN
R_A
V_IN
Off On
R_B
Switch
+
C_{ON/OFF −}
TM
To latch
Q₁
10 kΩ
ON/OFF
3V_BE
Q₂
GND
HA16114,
HA16120
V_IN
To other circuitry
Vref
reference
Vref
output
Q₃
On/off hysteresis circuit
Figure 6.1 Shutdown by ON/OFF Pin Control
6.2 Adjustment of UVL Voltages (when not using intermittent mode)
These ICs permit external adjustment of the undervoltage lockout voltages. The adjustment is made by
changing the undervoltage lockout thresholds V_TH and V_TL relative to V_IN, using the relationships shown in
the accompanying diagrams.
When the IC is powered up, transistor Q₃ is off, so V_ON is 2V_BE, or about 1.4 V. Connection of resistors R_C
and R_D in the diagram makes undervoltage lockout release at:
V_IN
=
1.4
V
×
R_C + R_D
R_D
This V_IN is the supply voltage at which undervoltage lockout is released. At the release point Vref is still
below 2.5 V. To obtain Vref = 2.5 V, V_IN must be at least about 4.3 V.
Since V_ON/OFF operates in relation to the base-emitter voltage of internal transistors, V_ON has a temperature
coefficient of approximately –4 mV/°C. Keep this in mind when designing the power supply unit.
When undervoltage lockout and intermittent mode are both used, the intermittent-mode time constant is
shortened, so the constants of external components may have to be altered.
15