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| 型号： | LT1580IT7-2.5#PBF |
| 厂商： | Linear Technology |
| 文件页数： | 9/16页 |
| 文件大小： | 0K |
| 描述： | IC LDO REGULATOR 7A 2.5V TO220-7 |
| 产品培训模块： | More Information on LDOs |
| 标准包装： | 50 |
| 应用： | 转换器，Intel Pentium? |
| 输入电压： | 1.79 V ~ 6 V |
| 输出数： | 1 |
| 输出电压： | 2.5V |
| 工作温度： | -40°C ~ 125°C |
| 安装类型： | 通孔 |
| 封装/外壳： | TO-220-7 成形引线 |
| 供应商设备封装： | TO-220-7 |
| 包装： | 管件 |
LT1580/LT1580-2.5
APPLICATIO N S I N FOR M ATIO N
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 .
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 μ 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.
V CONTROL
+
V CONTROL
V POWER
+
V POWER
V OUT
+
V OUT
ESR
EFFECTS
LT1580
SENSE
ESL
EFFECTS
CAPACITANCE
EFFECTS
ADJ
V REF
R1
1580 F04
( )
V OUT = V REF 1 + + I ADJ (R2)
SLOPE,
V
t
= ? I
C
POINT AT WHICH REGULATOR
TAKES CONTROL
R2
R1
I ADJ = 50 μ A
R2
1580 F05
Figure 4
Figure 5. Setting Output Voltage
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.
Protection Diodes
In normal operation the LT1580 does not require protec-
tion diodes. Older 3-terminal regulators require protection
diodes between the V OUT pin and the Input pin or between
the ADJ pin and the V OUT pin to prevent die overstress.
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.
9
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