參數(shù)資料
型號: LT1117IST-2.85
元件分類: 基準電壓源/電流源
英文描述: THREE-TERMINAL POSITIVE FIXED VOLTAGE REGULATORS
中文描述: 三端固定電壓調(diào)節(jié)器
文件頁數(shù): 6/12頁
文件大?。?/td> 196K
代理商: LT1117IST-2.85
6
LT1117/LT1117-2.85
LT1117-3.3/LT1117-5
The adjust pin can be driven, on a transient basis,
±
25V
with respect to the output without any device degradation.
Diodes between input and output are not usually needed.
The internal diode between the output and input pins of the
device can withstand microsecond surge currents of 10A
to 20A. Normal power supply cycling can not generate
currents of this magnitude. Only with extremely large
output capacitors, such as 1000
μ
F and larger, and with the
input pin instantaneously shorted to ground can damage
occur. A crowbar circuit at the input of the LT1117 in
combination with a large output capacitor could generate
currents large enough to cause damage. In this case a
diode from output to input is recommended, as shown in
Figure 1.
to set the overall output voltage. Normally this current is
chosen to be the specified minimum load current of 10mA.
Because I
ADJ
is very small and constant when compared
to the current through R1, it represents a small error and
can usually be ignored. For fixed voltage devices R1 and
R2 are included in the device.
Load Regulation
Because the LT1117 is a 3-terminal device, it is not
possible to provide true remote load sensing. Load regu-
lation will be limited by the resistance of the wire connect-
ing the regulator to the load. The data sheet specification
for load regulation is measured at the output pin of the
device. Negative side sensing is a true Kelvin connection,
with the bottom of the output divider returned to the
negative side of the load. Although it may not be immedi-
ately obvious, best load regulation is obtained when the
top of the resistor divider (R1) is returned directly to the
output pin of the device, not to the load. This is illustrated
in Figure 3. Connected as shown, R
P
is not multiplied by
the divider ratio. If R1 were connected to the load, the
effective resistance between the regulator and the load
would be:
R
R
R
R
R
P
P
×
+
=
2
1
1
,
Parasitic Line Resistance
Figure 2. Basic Adjustable Regulator
Output Voltage
The LT1117 develops a 1.25V reference voltage between
the output and the adjust terminal (see Figure 2). By
placing a resistor between these two terminals, a constant
current is caused to flow through R1 and down through R2
Figure 1
LT1117 TA02
+
+
D1
1N4002
(OPTIONAL)
C
ADJ
10
μ
F
R2
R1
C
OUT
150
μ
F
V
OUT
V
IN
LT1117
IN
ADJ
OUT
LT1117 TA03
R2
R1
V
OUT
V
IN
V
REF
I
ADJ
50
A
LT1117
IN
ADJ
OUT
V
OUT
= V
REF
1 + R1
ADJ
R2
(
)
+
Figure 3. Connections for Best Load Regulation
LT1117 TA04
R2
R1
V
IN
R
P
PARASITIC
LINE RESISTANCE
R
L
CONNECT
R1 TO CASE
CONNECT
R2 TO LOAD
LT1117
IN
ADJ
OUT
For fixed voltage devices the top of R1 is internally Kelvin
connected, and the ground pin can be used for negative
side sensing.
APPLICATIOU
U
相關(guān)PDF資料
PDF描述
LT1117IST-3.3 THREE-TERMINAL POSITIVE FIXED VOLTAGE REGULATORS
LT1117IST-5 THREE-TERMINAL POSITIVE FIXED VOLTAGE REGULATORS
LT1118CST8-2.5 Analog IC
LT1118CST8-2.85 Analog IC
LT1118CST8-5 Analog IC
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