FAN1582D25X Fairchild Semiconductor, FAN1582D25X Datasheet - Page 6

• Manufacturer Part Number: FAN1582D25X
• Description: IC REG LDO 3A 2.5V TO-252
• Manufacturer: Fairchild Semiconductor

Specifications of FAN1582D25X

• Regulator Topology: Positive Fixed
• Voltage - Output: 2.5V
• Voltage - Input: Up to 7V
• Voltage - Dropout (typical): 0.4V @ 3A
• Number Of Regulators: 1
• Current - Output: 3A
• Current - Limit (min): 3.1A
• Operating Temperature: -65°C ~ 150°C
• Mounting Type: Surface Mount
• Package / Case: TO-252-2, DPak (2 Leads + Tab), TO-252AA, SC-63
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

FIN1582 Rev. 1.1.4
© 2003 Fairchild Semiconductor Corporation
Detailed Operation
The FAN1582, FAN1582-1.5, and FAN1582-2.5 are
three-terminal regulators optimized for GTL+ V
tion and logic applications. These devices are short-cir-
cuit protected and offer thermal shutdown to turn off the
regulator when the junction temperature exceeds
~150°C. The FAN1582 series provides low dropout volt-
age and fast transient response. Frequency compensa-
tion uses capacitors with low ESR while maintaining
stability. This is critical in addressing the needs of low-
voltage, high-speed microprocessor busses like GTL+.
V
The FAN1582 utilizes a dual-supply approach to maxi-
mize efficiency. The collector of the power device is
brought out to the V
sipation under high-current loads. V
for the control circuitry and the drive for the output NPN
transistor. V
output voltage. Special care was taken to ensure there
are no supply-sequencing problems. The output voltage
does not turn on until both supplies are operating. If the
control voltage comes up first, the output current is typi-
cally limited to about 3.0mA until the power input voltage
comes up. If the power input voltage comes up first, the
output does not turn on until the control voltage comes
up. The output can never come up unregulated.
The FAN1582 can also be used as a single-supply
device with the control and power inputs tied together. In
this mode, the dropout is determined by the minimum
control voltage.
Stability
The FAN1582 series requires an output capacitor as a
part of the frequency compensation. It is recommended to
use a 22µF solid tantalum or a 100µF aluminum electro-
lytic on the output to ensure stability. The frequency com-
pensation of these devices optimizes the frequency
response with low-ESR capacitors. In general, it is sug-
gested to use capacitors with an ESR of <0.3Ω. It is also
recommended to use bypass capacitors, such as a 22µF
tantalum or a 100µF aluminum, on the adjust pin of the
FAN1582 for low ripple and fast transient response. If
these bypassing capacitors are not used at the adjust pin,
smaller values of output capacitors provide equally good
results. A graph showing stability of output capacitance
ESR vs. load current is shown in Figure 16.
Protection Diodes
In normal operation, the FAN1582 series does not require
any protection diodes. For the FAN1582, internal resis-
tors limit internal current paths on the adjust pin. There-
fore, even with bypass capacitors on the adjust pin, no
protection diode is needed to ensure device safety under
short-circuit conditions.
IN
and V
CNTL
CNTL
Functions
should be at least 1.2V higher than the
IN
pin to minimize internal power dis-
CNTL
provides power
TT
termina-
6
A protection diode between the input and output pins is
usually not needed. An internal diode between the input
and the output pins on the FAN1582 series can handle
microsecond surge currents of 50A to 100A. Even with
large value output capacitors, it is difficult to obtain those
values of surge currents in normal operation. Only with
large values of output capacitance, such as 1000µF to
5000µF, and with the input pin instantaneously shorted to
ground, can damage occur. Because a crowbar circuit at
the input can generate those levels of current, a diode from
output to input is recommended, as shown in Figure 16.
Usually, normal power supply cycling or system “hot
plugging and unplugging” does not generate current
large enough to cause damage.
Ripple Rejection
In applications that require improved ripple rejection, a
bypass capacitor from the adjust pin of the FAN1582 to
ground reduces the output ripple by the ratio of V
1.25V. The impedance of the adjust pin capacitor at the
ripple frequency should be less than the value of R1 (typ-
ically in the range of 100Ω to 120Ω) in the feedback
divider network in Figure 17. Therefore, the value of the
required adjust pin capacitor is a function of the input rip-
ple frequency. For example, if R1 equals 100Ω and the rip-
ple frequency equals 120Hz, the adjust pin capacitor
should be 22µF. At 10kHz, only 0.22µF is needed.
V
V
OUT
CNTL
V
V
IN
IN
Figure 17. Optional Protection Diode
+
+
C1
10F
C1
10F
FAN1582 – 1.5, 2.5
V
V
V
V
(OPTIONAL)
CNTL
IN
(OPTIONAL)
CNTL
IN
FAN1582
1N4002
1N4002
Gnd
+
Adj
D1
D1
V
V
SENSE
SENSE
C
V
V
OUT
ADJ
OUT
+
R1
R2
C2
22F
www.fairchildsemi.com
+
C2
22F
V
V
OUT
OUT
OUT
/