廬
APPLICATION BULLETIN
Mailing Address: PO Box 11400 鈥?Tucson, AZ 85734 鈥?Street Address: 6730 S. Tucson Blvd. 鈥?Tucson, AZ 85706
Tel: (602) 746-1111 鈥?Twx: 910-952-111 鈥?Telex: 066-6491 鈥?FAX (602) 889-1510 鈥?Immediate Product Info: (800) 548-6132
VERY LOW COST ANALOG ISOLATION WITH POWER
By Mark Stitt (602) 746-7445
You can make a low-cost, precision analog isolation ampli-
fier (ISO amp) with power by combining the ISO122 low-
cost ISO amp with the HPR117 low-cost DC/DC converter.
With isolated signal and isolated power in separate pack-
ages, complete application flexibility is assured.
The ISO122 features:
鈥?Unity gain (鹵10V In to
鹵10V
Out):
鹵0.05%
鈥?0.02% max nonlinearity
鈥?5mA quiescent current
鈥?140dB isolation mode rejection at 60Hz
鈥?1500Vrms continuous isolation rating (100% tested)
The HPR117 features:
鈥?V
OUT
= V
IN
,
鹵5%
(V
IN
= 13.5V to 16.5V, I
OUT
= 25mA)
鈥?I
OUT
= 25mA (750mW) continuous at 85擄C
鈥?8mA quiescent current, no load
鈥?80% efficiency, full load
鈥?Low output ripple
鈥?750VDC isolation rating
OUTPUT-SIDE POWERED ISO AMP
The most commonly used ISO amp configuration is shown
in Figure 1. Both the ISO amp and the DC/DC converter are
powered at the output side of the ISO amp. The HPR117 is
connected to +15V and ground. The ISO122 is connected to
鹵15V
and ground. The power-supply connections for the
input side of the ISO amp are connected directly to the
HPR117 output. No bypass capacitors are needed. The
HPR117 has built-in 0.33碌F bypass capacitors on both the
input and outputs.
The isolated
鹵15V
power output from the HPR117 can also
be used for ancillary input-side circuitry such as input
amplifiers and references. The ISO122 input section con-
sumes about
鹵5mA.
An additional
鹵20mA
is available for
other circuitry.
INPUT-SIDE POWERED ISO AMP
Some applications call for output-side isolation as shown in
Figure 2. Isolated
鹵15V,
20mA auxiliary power is available
on the output side for ancillary circuitry.
HPR117
6
5
4
2
1
+15V
V
IN
Input
Gnd
16
15
10
V鈥?/div>
ISO122P
9
V+
Gnd V
IN
INPUT
SECTION
Auxiliary
Isolated
Power
Output
+15V, 20mA
V+
1
V鈥?/div>
2
鈥?5V
OUTPUT
SECTION
V
O
Gnd
8
Output
Gnd
V
O
7
鈥?5V, 20mA
FIGURE 1. Output-Side Powered ISO Amp.
漏
1991 Burr-Brown Corporation
AB-024
Printed in U.S.A. March, 1991
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