NCP1086ST-ADJT3G ON Semiconductor, NCP1086ST-ADJT3G Datasheet - Page 6

• Manufacturer Part Number: NCP1086ST-ADJT3G
• Description: IC REG 1.5A ADJ VOLTAGE SOT223
• Manufacturer: ON Semiconductor

Specifications of NCP1086ST-ADJT3G

• Regulator Topology: Positive Adjustable
• Voltage - Output: 1.25 ~ 5.5 V
• Voltage - Input: Up to 7V
• Voltage - Dropout (typical): 1.05V @ 1.5A
• Number Of Regulators: 1
• Current - Output: 1.5A
• Current - Limit (min): 1.6A
• Operating Temperature: 0°C ~ 70°C
• Mounting Type: Surface Mount
• Package / Case: SOT-223 (3 leads + Tab), SC-73, TO-261
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: NCP1086ST-ADJT3GOS

2.0 mA. R1 and R2 should be the same type, e.g. metal film
for best tracking over temperature.
maximum specification of 7.0 V for the voltage difference
between V
regulate voltages in excess of 7.0 V. The main
considerations in such a design are powerup and short circuit
capability.
is fairly slow, typically on the order of several tens of
milliseconds, while the regulator responds in less than one
microsecond. In this case, the linear regulator begins
charging the load as soon as the V
large enough that the pass transistor conducts current. The
load at this point is essentially at ground, and the supply
voltage is on the order of several hundred mV, with the result
that the pass transistor is in dropout. As the supply to V
increases, the pass transistor will remain in dropout, and
current is passed to the load until V
which the IC is in regulation. Further increase in the supply
voltage brings the pass transistor out of dropout. The result
is that the output voltage follows the power supply ramp−up,
staying in dropout until the regulation point is reached. In
this manner, any output voltage may be regulated. There is
no theoretical limit to the regulated voltage as long as the
V
circuit condition is very real for this type of design. Short
circuit conditions will result in the immediate operation of
the pass transistor outside of its safe operating area.
Overvoltage stresses will then cause destruction of the pass
transistor before overcurrent or thermal shutdown circuitry
can become active. Additional circuitry may be required to
clamp the V
fail−safe operation is required. One possible clamp circuit is
illustrated in Figure 16; however, the design of clamp
circuitry must be done on an application by application
basis. Care must be taken to ensure the clamp actually
protects the design. Components used in the clamp design
V
IN
IN
R1 is chosen so that the minimum load current is at least
The adjustable output linear regulator has an absolute
In most applications, ramp−up of the power supply to V
However, the possibility of destroying the IC in a short
to V
C
1
OUT
Figure 15. Resistor Divider Scheme
IN
IN
differential of 7.0 V is not exceeded.
and V
V
to V
IN
NCP1086
OUT
OUT
Adj
. However, the IC may be used to
differential to less than 7.0 V if
V
OUT
I
Adj
V
IN
REF
OUT
to V
reaches the point at
OUT
R
R
1
2
differential is
C
2
http://onsemi.com
V
OUT
IN
IN
6
must be able to withstand the short circuit condition
indefinitely while protecting the IC.
Stability Considerations
three main characteristics of a linear regulator: startup delay,
load transient response and loop stability.
size and temperature constraints. A tantalum or aluminum
electrolytic capacitor is best, since a film or ceramic
capacitor with almost zero ESR can cause instability. The
aluminum electrolytic capacitor is the least expensive
solution. However, when the circuit operates at low
temperatures, both the value and ESR of the capacitor will
vary considerably. The capacitor manufacturers’ data sheet
provides this information.
applications, but with high current regulators such as the
NCP1086 series the transient response and stability improve
with higher values of capacitance. The majority of
applications for this regulator involve large changes in load
current, so the output capacitor must supply the
instantaneous load current. The ESR of the output capacitor
causes an immediate drop in output voltage given by:
output capacitor network consisting of several tantalum and
ceramic capacitors in parallel. This reduces the overall ESR
and reduces the instantaneous output voltage drop under
load transient conditions. The output capacitor network
should be as close as possible to the load for the best results.
The output or compensation capacitor helps determine
The capacitor value and type is based on cost, availability,
A 22 mF tantalum capacitor will work for most
For microprocessor applications it is customary to use an
Figure 16. Short Circuit Protection Circuit for High
V
EXTERNAL
IN
SUPPLY
NCP1086
Voltage Application
Adj
DV + DI
V
OUT
ESR
V
OUT