LT1581CT7-2.5 Linear Technology, LT1581CT7-2.5 Datasheet - Page 7

• Manufacturer Part Number: LT1581CT7-2.5
• Description: IC LDO REGULATOR 10A 2.5V TO2207
• Manufacturer: Linear Technology

Specifications of LT1581CT7-2.5

• Applications: Converter, Intel Pentium®
• Voltage - Input: 1.68 ~ 6 V
• Number Of Outputs: 1
• Voltage - Output: 2.5V
• Operating Temperature: 0°C ~ 125°C
• Mounting Type: Through Hole
• Package / Case: TO-220-7 (Bent and Staggered Leads)
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

APPLICATIONS
illustrates the effect on output regulation. It is important to
note that the voltage drops due to R
They will add to the dropout voltage of the regulator
regardless of whether they are inside the loop as in Figure
2 or outside the loop as in Figure 1. This means that the
3.3V
3.3V
Figure 3. Remote Sensing Improves Load Regulation
FIGURE 1
FIGURE 2
Figure 1. Conventional Load Sensing
POWER
POWER
V
V
I
Figure 2. Remote Load Sensing
OUT
OUT
OUT
CONTROL
CONTROL
LT1581
LT1581
U
ADJ
5V
ADJ
5V
( I
R2
R2
OUT
INFORMATION
OUTPUT
OUTPUT
SENSE
U
SENSE
)(R
R1
R1
P
)
TIME
W
P
are not eliminated.
R
R
R
R
P
P
P
P
1581 F03
LOAD
LOAD
U
+
V
–
1581 F01
+
V
–
1581 F02
OUT
OUT
LT1581 can control the voltage at the load as long as the
input/output voltage is greater than the total of the dropout
voltage of the LT1581 plus the voltage drop across R
Stability
The LT1581 requires the use of an output capacitor as part
of the device frequency compensation. The device re-
quires a minimum of 22 F tantalum or 150 F of aluminum
electrolytic to ensure stability. Larger capacitor values
increase stability and improve transient performance.
Many different types of capacitors are available and have
widely varying characteristics. These capacitors differ in
capacitor tolerance (sometimes up to 100%), equivalent
series resistance, equivalent series inductance and ca-
pacitance temperature coefficient. The LT1581 frequency
compensation optimizes frequency response with low
ESR capacitors. In general, use capacitors with an ESR of
less than 1 .
For microprocessor applications larger value capacitors
will be needed to meet the transient requirements of the
processor. Processor manufacturers require tight voltage
tolerances on the power supply. High quality bypass
capacitors must be used to limit the high frequency noise
generated by the processor. Multiple small ceramic ca-
pacitors in addition to high quality bulk tantalum capaci-
tors are typically required to limit parasitic inductance
(ESL) and resistance (ESR) in the capacitors to acceptable
levels. The LT1581 is stable with the type of capacitors
recommended by processor manufacturers.
Bypassing the adjust terminal on the LT1581 improves
ripple rejection and transient response. The ADJUST pin is
brought out on the fixed voltage device specifically to
allow this capability.
Capacitor values on the order of several hundred microfar-
ads are used to ensure good transient response with heavy
load current changes. Output capacitance can increase
without limit and larger values of output capacitance
further improve the stability and transient response of the
LT1581.
Modern microprocessors generate large high frequency
current transients. The load current step contains higher
order frequency components that the output coupling
LT1581/LT1581-2.5
7
P
.