NCP5661, NCV5661
www.onsemi.com
8
V
in
= 4.0 V
V
out
= 0.9 V
C
in
= 150 mF
C
out
= 150 mF
T
J
= 25°C
I
out
= 10 mA to 1.0 A
I
out
0.5 A/Div
V
out
10 mV/Div
TIME (1.0 ms/Div)
I
out
0.5 A/Div
V
out
10 mV/Div
TIME (1.0 ms/Div)
V
in
= 4.0 V
V
out
= 0.9 V
C
in
= 150 mF
C
out
= 150 mF
T
J
= 25°C
I
out
= 1.0 A to 10 mA
Figure 15. Load Transient Response
Figure 16. Load Transient Response
APPLICATION INFORMATION
The NCP5661 is a high performance low dropout 1.0 A
linear regulator suitable for high power applications,
featuring an ultra−fast response time and low noise without
a bypass capacitor. It is offered in both fixed and adjustable
output versions with voltages as low as 0.9 V. Additional
features, such as Enable and Error Flag (fixed output
version) increase the utility of the NCP5661. It is thermally
robust and includes the safety features necessary during a
fault condition, which provide for an attractive high current
LDO solution for server, ASIC power supplies, networking
equipment applications, and many others.
Input Capacitor
The recommended input capacitor value is a 150 mF
OSCON with an Equivalent Series Resistance (ESR) of
50 mW. It is especially required if the power source is
located more than a few inches from the NCP5661. This
capacitor will reduce device sensitivity and enhance the
output transient response time. The PCB layout is very
important and in order to obtain the optimal solution, the Vin
and GND traces should be sufficiently wide to minimize
noise and unstable operation.
Output Capacitor
Proper output capacitor selection is required to maintain
stability. The NCP5661 is guaranteed to be stable at an
output capacitance of C
out
> 10 mF. In the case of using
electrolytic capacitors, low ESR type (ESR < 300 mW)
should be used to maintain device stability. Multilayer
ceramic capacitors can also be used with this device. For
PCB layout considerations, place the recommended ceramic
capacitor close to the output pin and keep the leads short.
This should help ensure ultra−fast transient response times.
Adjustable Output Operation
The application circuit for the adjustable output version is
shown in Figure 1. The reference voltage is 0.9 V and the
adjustable pin current is typically 40 nA. A resistor divider
network, R1 and R2, is calculated using the following
formula:
R1 + R2
ǒ
V
out
V
ref
* 1
Ǔ
C
in
C
out
Input
Output
NCP5661
Enable
ON
OFF
V
in
V
out
EN
ADJ
V
out
= 0.9 V
GND
Figure 17. To achieve the minimum output voltage,
ADJ to V
out
has to be connected together
Current Limit Operation
As the peak output current increases beyond its limitation,
the device is internally clampled to 1.5 A, thus causing the
output voltage to decrease and go out of regulation. This
allows the device never to exceed the maximum power
dissipation.
Error Flag Operation
The Error Flag pin on the NCP5661 will produce a logic
Low when it drops below the nominal output voltage. Refer
to the electrical characteristics for the threshold values at
which point the Error Flag goes Low. When the NCP5661
is above the nominal output voltage, the Error Flag will
remain at logic High.
The external pullup resistor needs to be connected
between V
in
(Pin 1) and the Error Flag pin (Pin 5). A resistor
of approximately 100 kW is recommended to minimize the
current consumption. No pullup resistor is required if the
Error Flag output is not being used.
