AN1154: Remotely Adjustable Voltage Regulators

Remotely Adjustable Voltage Regulators
using XDCPs
®
Application Note
April 21, 2005
AN1154.0
Author: Applications Staff
This note shows how an X9312 can be used to implement a
remote, adjustable regulator. The LM317 is probably the
most common adjustable three- terminal voltage regulator in
use today. Often it would be desirable to adjust these
regulators remotely, but extending the adjustment rheostat
any distance introduces noise and instability. Intersil’s X9312
XDCP can provide a simple solution. By using this XDCP,
the voltage output of the LM317 can be set using a simple 3wire digital interface over practically any distance.
Figure 1 shows the LM317’s usual adjustment resistor
replaced with the 10kΩ version of the X9312. The
pushbutton control circuitry would be located remotely (on a
separate board). The adjustment range can be set remotely
to fit an application by changing R7, just remember not to
exceed the VH or VL maximum limit of +15 volts.
1
The standard formula for output voltage naturally still
applies:
R pot
V out = V ref + V ref ------------ + I adj ( R ref )
R ref
where Vref = 1.25V
Rref = R7
Rpot = 0 to 10kΩ value for U1 in 99 steps.
Iadj = approx. 50µA of current from the
adjustment pin of the LM317
Figure 1 shows the control circuitry connected via a
10-pin connector. This allows an LM317 voltage regulator to
be set and then for the control circuitry to be removed. In this
configuration, it’s a good idea to include a pull-up resistor on
all of the control lines (R9, R10, and R11) to assure that
inadvertant XDCP changes do not occur.
CAUTION: These devices are sensitive to electrostatic discharge; follow proper IC Handling Procedures.
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Copyright Intersil Americas Inc. 2005. All Rights Reserved
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Application Note 1154
VR1
LM31 7T
3. 5mm PL UG
3
VI N
VOUT
1
ADJ
C6
10 0UF
3. 5mm J ACK
1. 25 V T O 1 0V
WALL MOUNTED
12 V TO 1 5V POWER CONVERTER
2
R7
1. 3K
R8
2. 7K
C5
1 0UF
RET URN
HEAT SI NK
U1
+5V
3
5
6
VR2
3
2
I N
OUT
1
VH
VW
VL
I NC
U/ D
CS
1
2
7
+ 5V
X9C103
GND
P1/J1
C7
0 . 1UF
LM7 8L0 5ACZ
1
3
5
7
9
PUSHBUTTON CONTROLLER
R11
10K
R9
10K
+ 5V
+5 V
++
++
++
++
++
2
4
6
8
10
R10
1 0K
J1/P1
+5V
CR1
1N4 148
R4
1 0K
U2B
R5
1 0K
1
3
5
7
9
4
6
5
S1
DECREASE
R2
2 7K
U2A
7 4HC132
C2
1 000 PF
++
++
++
++
++
2
4
6
8
10
1
+5V
3
2
S2
I NCREASE
7 4HC132
CR2
1 N414 8
R6
47 0
U2C
U2D
10
8
C8
0. 1UF
C9
0 . 1UF
DS1
13
9
11
12
R3
2 7K
C3
1 000 PF
LED
74 HC132
7 4HC13 2
C1
1UF
R1
2 20K
FIGURE 1. 1.25V to 10V DC Supply
Intersil Corporation reserves the right to make changes in circuit design, software and/or specifications at any time without notice. Accordingly, the reader is cautioned to
verify that the Application Note or Technical Brief is current before proceeding.
For information regarding Intersil Corporation and its products, see www.intersil.com
2
April 21, 2005
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