NCV8509_08 Datasheet, PDF (12/18 Pages) ON Semiconductor – Sequenced Linear Dual-Voltage Regulator

NCV8509 Series
CIRCUIT DESCRIPTION
V_IN
V_OUT1
RESET
Reset Delay
Power Up
Reset Delay Reset Delay
Short on
V_OUT1
V_IN1 Fast
Turn Off
RESET
Output Peak
Figure 41. Dual Drive RESET Valid
RESET
The RESET function gets its drive from both the input
(V_IN1) and the output (V_OUT1). Because of this, it is able to
maintain a more reliable reset valid signal. Most regulators
maintain a valid reset signal down to 1 V on the output
voltage. The reset on the NCV8509 is valid down to 0 V on
the output voltage V_OUT1 (power is provided via V_IN1) and
the reset on the NCV8509 is valid down to 0 V on the input
voltage V_IN1 (power is provided via V_OUT1). Refer to
Figure 41 for operation timing diagrams.
Delay Function
The reset delay circuit provides a programmable (by
external capacitor) delay on the RESET output lead.
The delay lead provides source current (typically 6.0 μA)
to the external delay capacitor during the following
proceedings:
1. During power up (once the regulation threshold
has been verified);
2. After a reset event has occurred and the device is
back in regulation.
The delay capacitor is discharged when the regulation
(RESET threshold) has been violated. This is a latched
incident. The capacitor will fully discharge and wait for the
device to regulate before going through the delay time event
again.
Power Shunt
R_EX routes some of the current used in the V_OUT2 to a
second input pin (V_IN2). This is accomplished by using an
internal shunt. A simplified version of this shunt is shown in
Figure 42. This has the effect of reducing the amount of
power dissipated on chip. The effects of choosing the
external resistor value are shown in Figure 43.
Selection of the optimum Rex resistor value can be done
using the following equation:
(Vin(max) * 4.5)
Iout2(max)
When not using the power shunt, short V_IN1 to V_IN2.
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