NCP5500, NCV5500, NCP5501, NCV5501
NCP5500
Input
I
in
C
in
10
mF
Enable
I
EN
EN
GND
I
GND
I
Q
NCP5501
Input
I
in
C
in
10
mF
C
in2
100 nF
V
in
NCV5501
V
out
I
out
C
out
Output
ADJ
I
ADJ
C
in2
100 nF
V
in
NCV5500
V
out
I
out
C
out
Output
R
L
R
L
GND
I
GND
I
Q
Figure 21. Measuring Circuits
Circuit Description
The NCP5500/NCP5501/NCV5500/NCV5501 are
integrated linear regulators with a DC load current
capability of 500 mA. The output voltage is regulated by a
PNP pass transistor controlled by an error amplifier and
band gap reference. The choice of a PNP pass element
provides the lowest possible dropout voltage, particularly at
reduced load currents. Pass transistor base drive current is
controlled to prevent oversaturation. The regulator is
internally protected by both current limit and thermal
shutdown. Thermal shutdown occurs when the junction
temperature exceeds 150C. The NCV5500 includes an
enable/shutdown pin to turn off the regulator to a low current
drain standby state.
Regulator
linear regulator: startup delay, load transient response and
loop stability. The capacitor value and type should be based
on cost, availability, size and temperature constraints. Refer
to Typical Operating Characteristics for stability regions.
Enable Input
(NCP5500, NCV5500)
The enable pin is used to turn the regulator on or off. By
holding the pin at a voltage less than 0.4 V, the output of the
regulator will be turned off to a minimal current drain state.
When the voltage at the Enable pin is greater than 2.0 V, the
output of the regulator will be enabled and rise to the
regulated output voltage. The Enable pin may be connected
directly to the input pin to provide a constant enable to the
regulator.
Active Load Protection in Shutdown
(NCP5500,
NCV5500)
The error amplifier compares the reference voltage to a
sample of the output voltage (V
out
) and drives the base of a
PNP series pass transistor via a buffer. The reference is a
bandgap design for enhanced temperature stability.
Saturation control of the PNP pass transistor is a function of
the load current and input voltage. Oversaturation of the
output power device is prevented, and quiescent current in
the ground pin is minimized.
Regulator Stability Considerations
The input capacitor is necessary to stabilize the input
impedance to reduce transient line influences. The output
capacitor helps determine three main characteristics of a
When a linear regulator is disabled (shutdown), the output
(load) voltage should be zero. However, stray PC board
leakage paths, output capacitor dielectric absorption, and
inductively coupled power sources can cause an undesirable
regulator output voltage if load current is low or zero. The
NCV5500 features a load protection network that is active
only during Shutdown mode. This network switches in a
shunt current path (~500
mA)
from V
out
to Ground. This
feature also provides a controlled (“soft”) discharge path for
the output capacitor after a transition from Enable to
Shutdown.
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