廬
APPLICATION BULLETIN
鈥?Mailing Address: PO Box 11400 Tucson, AZ 85734
鈥?Tel: (602) 746-1111
鈥?FAX: (602) 746-7401
Burr-Brown Corporation
BOOST ISO120 BANDWIDTH TO MORE THAN 100kHz
By R. Mark Stitt and Rod Burt (602) 746-7445
There has been considerable demand for high-bandwidth
isolation amplifiers. The highest bandwidth Burr-Brown
ISO amps are the ISO100 and the ISO120/121/122 family
with bandwidths of about 50kHz. The ISO120/121 bandwidth
can be boosted to more than 100kHz by adding gain in the
feedback.
Adding gain in the feedback of the ISO120/121 increases
bandwidth and decreases phase margin鈥攕ee Figure 4. The
ISO120 was designed with approximately 70擄 phase margin
in the output stage for maximally flat magnitude response
and a f
鈥?dB
bandwidth of approximately 50kHz. With a gain
of 2.4V/V in the feedback as shown in Figure 1, phase
margin is decreased to an acceptable 45擄. Due to gain
peaking, the actual f
鈥?dB
bandwidth is increased to almost
150kHz. With the addition of an input filter as shown in
Figure 2, flat magnitude response with a bandwidth of
greater than 100kHz is obtained. Since the added gain is
within the ISO120 feedback loop, the overall gain of the
isolation amplifier is unchanged (gain = 1).
To verify the phase margin, analyze the step response of the
Figure 1 circuit (shown in the Scope Photo 1). The 25%
overshoot translates to a damping factor of 0.4 and 45擄 phase
margin.
If the ISO120 is used in the clocked mode, maximum
bandwidth is determined by the clock frequency. For 150kHz
bandwidth and 45擄 phase margin with a gain of 2.4V/V in
the ISO120 feedback, the clock frequency should be 500kHz.
Lower clock frequencies will result in reduced phase margin
and possible instability. Higher clock frequencies will result
in better phase margin, but clock frequencies above 700kHz
are not recommended.
+4.5V to +18V
R
1
7.5k
鈩?/div>
23
3
In
15
11
ISO120
21
Com
22
Gnd
24
4
10
12
OPA602
R
5
470
鈩?/div>
R
2
10.5k
鈩?/div>
+15V
V
IN
V
OUT
= V
IN
9
16
5.1V
1N4689
5.1V
1N4689
鈥?5V
Step response of Figure 1 circuit showing 25% overshoot
which translates into 45擄 phase-margin.
鈥?.5V to 鈥?8V
FIGURE 1. ISO120 with f
鈥?dB
Bandwidth Boosted to Approximately 150kHz.
+4.5V to +18V
R
4
10k
鈩?/div>
R
1
R
3
10k
鈩?/div>
V
IN
C
1
200pF
ISO120
21
Com
22
Gnd
24
4
23
3
In
15
11
10
12
OPA602
R
5
470
鈩?/div>
V
OUT
= V
IN
7.5k
鈩?/div>
R
2
10.5k
鈩?/div>
+15V
9
16
5.1V
1N4689
5.1V
1N4689
Step response of Figure 2 circuit.
鈥?5V
鈥?.5V to 鈥?8V
FIGURE 2. ISO120 with Flat Magnitude Response and f
鈥?dB
Bandwidth Boosted to More Than 100kHz.
漏
1990 Burr-Brown Corporation
AB-012A
Printed in U.S.A. September, 1990
AB-012相關(guān)型號PDF文件下載
-
型號
版本
描述
廠商
下載
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英文版
AB-001 - INCREASING INA117 DIFFERENTIAL INPUT RANGE
ETC
-
英文版
AB-002 - MAKE A PRECISION CURRENT SOURCE OR CURRENT SINK
ETC
-
英文版
AB-003 - VOLTAGE-REFERENCE FILTERS
ETC
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英文版
AB-004 - MAKE A PRECISION -10V REFERENCE
ETC
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英文版
AB-005 - Make A Precision -10V Reference
ETC
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英文版
AB-006 - Make a -10V to +10V Adjustable Precision Voltage So...
ETC
-
英文版
AB-007 - CLASSICAL OP AMP OR CURRENT-FEEDBACK OP AMP?
ETC
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英文版
AB-008 - AC COUPLING INSTRUMENTATION AND DIFFERENCE AMPLIFIE...
ETC
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英文版
AB-009 - SINGLE-SUPPLY OPERATION OF ISOLATION AMPLIFIERS
ETC
-
英文版
AB-010 - -200V DIFFERENCE AMPLIFIER WITH COMMON-MODE VOLTAGE...
ETC
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英文版
AB-011 - LOW POWER SUPPLY VOLTAGE OPERATION OF REF102 10.0V ...
ETC
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英文版
AB-012 - BOOST ISO120 BANDWIDTH TO MORE THAN 100kHz
ETC
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英文版
AB-013 - INCREASING ADC603 INPUT RANGE
ETC
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英文版
AB-014 - INPUT OVERLOAD PROTECTION FOR THE RCV420 4-20mA CUR...
ETC
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英文版
AB-015 - EXTENDING THE COMMON-MODE RANGE OF DIFFERENCE AMPLI...
ETC
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英文版
AB-016 - BOOST AMPLIFIER OUTPUT SWING WITH SIMPLE MODIFICATI...
ETC
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英文版
AB-017 - Sallen-Key Low-Pass Filter Design Program
ETC
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英文版
AB-018 - 0 TO 20mA RECEIVER USING RCV420
ETC
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英文版
AB-019 - USING THE ADS7800 12 BIT ADC WITH UNIPOLAR INPUT SI...
ETC
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英文版
AB-020 - BURR-BROWN SPICE BASED MACROMODELS. REV. F
ETC
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