LT1580CR-2.5 Linear Technology, LT1580CR-2.5 Datasheet - Page 9

• Manufacturer Part Number: LT1580CR-2.5
• Description: IC LDO REGULATOR 7A 2.5V DDPAK-7
• Manufacturer: Linear Technology

Specifications of LT1580CR-2.5

• Applications: Converter, Intel Pentium®
• Voltage - Input: 1.79 ~ 6 V
• Number Of Outputs: 1
• Voltage - Output: 2.5V
• Operating Temperature: 0°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: D²Pak, TO-263 (7 leads + tab)
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

APPLICATIONS
load current changes. Output capacitance can increase
without limit and larger values of output capacitance
further improve the stability and transient response of the
LT1580.
Modern microprocessors generate large high frequency
current transients. The load current step contains higher
order frequency components that the output coupling
network must handle until the regulator throttles to the
load current level. Capacitors are not ideal elements and
contain parasitic resistance and inductance. These para-
sitic elements dominate the change in output voltage at the
beginning of a transient load step change. The ESR of the
output capacitors produces an instantaneous step in out-
put voltage ( V = I)(ESR). The ESL of the output capaci-
tors produces a droop proportional to the rate of change
of the output current (V = L)( I/ t). The output capaci-
tance produces a change in output voltage proportional to
the time until the regulator can respond ( V = t)( I/ C).
These transient effects are illustrated in Figure 4 .
The use of capacitors with low ESR, low ESL and good
high frequency characteristics is critical in meeting the
output voltage tolerances of these high speed micropro-
cessors. These requirements dictate a combination of
high quality, surface mount, tantalum and ceramic capaci-
tors. The location of the decoupling network is critical to
transient performance. Place the decoupling network as
close to the processor pins as possible because trace runs
from the decoupling capacitors to the processor pins are
inductive. The ideal location for the decoupling network is
actually inside the microprocessor socket cavity. In addi-
tion, use large power and ground plane areas to minimize
distribution drops.
ESR
EFFECTS
ESL
EFFECTS
SLOPE,
V
t
=
C
I
U
Figure 4
INFORMATION
POINT AT WHICH REGULATOR
U
TAKES CONTROL
W
U
CAPACITANCE
EFFECTS
1580 F04
Output Voltage
The adjustable version of the LT1580 develops a 1.25V
reference voltage between the SENSE pin and the ADJ pin
(see Figure 5). Placing a resistor R1 between these two
terminals causes a constant current to flow through R1
and down through R2 to set the overall output voltage.
Normally R1 is chosen so that this current is the specified
minimum load current of 10mA. The current out of the ADJ
pin adds to the current from R1. The ADJ pin current is
small, typically 50 A. The output voltage contribution of
the ADJ pin current is small and only needs to be consid-
ered when very precise output voltage setting is required.
Note that the top of the resistor divider should be con-
nected directly to the SENSE pin for best regulation. See
the section on grounding and Kelvin sensing above.
Protection Diodes
In normal operation the LT1580 does not require protec-
tion diodes. Older 3-terminal regulators require protection
diodes between the V
the ADJ pin and the V
On the LT1580, internal resistors limit internal current
paths on the ADJ pin. Therefore even with bypass capaci-
tors on the ADJ pin, no protection diode is needed to
ensure device safety under short-circuit conditions. The
ADJ pin can be driven on a transient basis 7V with
respect to the output without any device degradation.
V
V
POWER
OUT
= V
REF
+
+
1 +
R2
R1
Figure 5. Setting Output Voltage
V
+ I
POWER
ADJ
(R2)
I
OUT
V
V
ADJ
OUT
CONTROL
CONTROL
LT1580
LT1580/LT1580-2.5
ADJ
= 50 A
pin and the Input pin or between
pin to prevent die overstress.
SENSE
V
OUT
V
REF
R2
R1
+
1580 F05
V
OUT
9