1
OPA548
OPA548
V
IN
V
IN
+
V+
E/S
R
CL
R
CL
sets the current limit
value from 0 to 5A.
(1/4W Resistor)
I
LIM
V
O
V
International Airport Industrial Park Mailing Address: PO Box 11400, Tucson, AZ 85734 Street Address: 6730 S. Tucson Blvd., Tucson, AZ 85706 Tel: (520) 746-1111 Twx: 910-952-1111
Internet: http://www.burr-brown.com/ FAXLine: (800) 548-6133 (US/Canada Only) Cable: BBRCORP Telex: 066-6491 FAX: (520) 889-1510 Immediate Product Info: (800) 548-6132
OPA548
High-Voltage, High-Current
OPERATIONAL AMPLIFIER
DESCRIPTION
The OPA548 is a low cost, high-voltage/high-current
operational amplifier ideal for driving a wide variety
of loads. A laser-trimmed monolithic integrated cir-
cuit provides excellent low-level signal accuracy and
high output voltage and current.
The OPA548 operates from either single or dual sup-
plies for design flexibility. In single supply operation,
the input common-mode range extends below ground.
The OPA548 is internally protected against over-
temperature conditions and current overloads. In addi-
tion, the OPA548 was designed to provide an accurate,
user-selected current limit. Unlike other designs which
use a "power" resistor in series with the output current
path, the OPA548 senses the load indirectly. This
allows the current limit to be adjusted from 0 to 5A
with a resistor/potentiometer or controlled digitally
with a voltage-out or current-out DAC.
The Enable/Status (E/S) pin provides two functions.
An input on the pin not only disables the output stage
to effectively disconnect the load but also reduces the
quiescent current to conserve power. The E/S pin
output can be monitored to determine if the OPA548
is in thermal shutdown.
The OPA548 is available in an industry-standard
7-lead staggered TO-220 package and a 7-lead DDPAK
surface-mount plastic power package. The copper tab
allows easy mounting to a heat sink or circuit board
for excellent thermal performance. It is specified for
operation over the extended industrial temperature
range, 40
C to +85
C. A SPICE macromodel is
available for design analysis.
FEATURES
q
WIDE SUPPLY RANGE
Single Supply: +8V to +60V
Dual Supply:
4V to
30V
q
HIGH OUTPUT CURRENT:
3A Continuous
5A Peak
q
WIDE OUTPUT VOLTAGE SWING
q
FULLY PROTECTED:
Thermal Shutdown
Adjustable Current Limit
q
OUTPUT DISABLE CONTROL
q
THERMAL SHUTDOWN INDICATOR
q
HIGH SLEW RATE: 10V/
s
q
LOW QUIESCENT CURRENT
q
PACKAGES:
7-Lead TO-220
7-Lead DDPAK Surface-Mount
OPA548
OPA548
www.burr-brown.com/databook/OPA548.html
1997 Burr-Brown Corporation
PDS-1389B
Printed in U.S.A. October, 1997
APPLICATIONS
q
VALVE, ACTUATOR DRIVER
q
SYNCHRO, SERVO DRIVER
q
POWER SUPPLIES
q
TEST EQUIPMENT
q
TRANSDUCER EXCITATION
q
AUDIO AMPLIFIER
2
OPA548
SPECIFICATIONS
At T
CASE
= +25
C, V
S
=
30V and E/S pin open, unless otherwise noted.
OPA548T, F
PARAMETER
CONDITION
MIN
TYP
MAX
UNITS
OFFSET VOLTAGE
Input Offset Voltage
V
CM
= 0, I
O
= 0
2
10
mV
vs Temperature
T
A
= 40
C to +85
C
30
V/
C
vs Power Supply
V
S
=
4V to
30V
30
100
V/V
INPUT BIAS CURRENT
(1)
Input Bias Current
(2)
V
CM
= 0V
100
500
nA
vs Temperature
T
A
= 40
C to +85
C
0.5
nA/
C
Input Offset Current
V
CM
= 0V
5
50
nA
NOISE
Input Voltage Noise Density, f = 1kHz
90
nV/
Hz
Current Noise Density, f = 1kHz
200
fA/
Hz
INPUT VOLTAGE RANGE
Common-Mode Voltage Range: Positive
Linear Operation
(V+) 3
(V+) 2.3
V
Negative
Linear Operation
(V) 0.1
(V) 0.2
V
Common-Mode Rejection
V
CM
= (V) 0.1V to (V+) 3V
80
95
dB
INPUT IMPEDANCE
Differential
10
7
|| 6
|| pF
Common-Mode
10
9
|| 4
|| pF
OPEN-LOOP GAIN
Open-Loop Voltage Gain
V
O
=
25V, R
L
= 1k
90
98
dB
V
O
=
25V, R
L
= 8
90
dB
FREQUENCY RESPONSE
Gain-Bandwidth Product
R
L
= 8
1
MHz
Slew Rate
G = 1, 50Vp-p, R
L
= 8
10
V/
s
Full Power Bandwidth
See Typical Curve
kHz
Settling Time:
0.1%
G = 10, 50V Step
15
s
Total Harmonic Distortion + Noise, f = 1kHz
R
L
= 8
, G = +3, Power = 10W
0.02
(3)
%
OUTPUT
Voltage Output, Positive
I
O
= 3A
(V+) 4.1
(V+) 3.7
V
Negative
I
O
= 3A
(V) +3.7
(V) +3.3
V
Positive
I
O
= 0.6A
(V+) 2.4
(V+) 2.1
V
Negative
I
O
= 0.6A
(V) +1.3
(V) +1.0
V
Maximum Continuous Current Output: dc
3
A
ac
3
Arms
Leakage Current, Output Disabled, dc
See Typical Curve
Output Current Limit
Current Limit Range
0 to
5
A
Current Limit Equation
I
LIM
= (15000)(4.75)/(13750
+ R
CL
)
A
Current Limit Tolerance
(1)
R
CL
= 14.8k
(I
LIM
=
2.5A),
100
250
mA
R
L
= 8
Capacitive Load Drive
See Typical Curve
(4)
OUTPUT ENABLE /STATUS (E/S) PIN
Shutdown Input Mode
V
E/S
High (output enabled)
E/S Pin Open or Forced High
(V) +2.4
V
V
E/S
Low (output disabled)
E/S Pin Forced Low
(V) +0.8
V
I
E/S
High (output enabled)
E/S Pin High
65
A
I
E/S
Low (output disabled)
E/S Pin Low
70
A
Output Disable Time
1
s
Output Enable Time
3
s
Thermal Shutdown Status Output
Normal Operation
Sourcing 20
A
(V) +2.4
(V) +3.5
V
Thermally Shutdown
Sinking 5
A, T
J
> 160
C
(V) +0.35
(V) +0.8
V
Junction Temperature, Shutdown
+160
C
Reset from Shutdown
+140
C
POWER SUPPLY
Specified Voltage
30
V
Operating Voltage Range
4
30
V
Quiescent Current
I
LIM
Connected to V, I
O
= 0
17
20
mA
Quiescent Current, Shutdown Mode
I
LIM
Connected to V, I
O
= 0
6
mA
TEMPERATURE RANGE
Specified Range
40
+85
C
Operating Range
40
+125
C
Storage Range
55
+125
C
Thermal Resistance,
JC
7-Lead DDPAK, 7-Lead TO-220
f > 50Hz
2
C/W
7-Lead DDPAK, 7-Lead TO-220
dc
2.5
C/W
Thermal Resistance,
JA
7-Lead DDPAK, 7-Lead TO-220
No Heat Sink
65
C/W
NOTES: (1) High-speed test at T
J
= +25
C. (2) Positive conventional current flows into the input terminals. (3) See "Total Harmonic Distortion+Noise vs Frequency" in
the Typical Performance Curves section for additional power levels. (4) See "Small-Signal Overshoot vs Load Capacitance" in the Typical Performance Curves section.
3
OPA548
ABSOLUTE MAXIMUM RATINGS
(1)
Output Current ................................................................. See SOA Curve
Supply Voltage, V+ to V ................................................................... 60V
Input Voltage ....................................................... (V)0.5V to (V+)+0.5V
Input Shutdown Voltage ........................................................................ V+
Operating Temperature ................................................. 40
C to +125
C
Storage Temperature ..................................................... 55
C to +125
C
Junction Temperature ...................................................................... 150
C
Lead Temperature (soldering 10s)
(2) .................................................................
300
C
Top Front View
CONNECTION DIAGRAMS
NOTE: (1) Stresses above these ratings may cause permanent damage.
(2) Vapor-phase or IR reflow techniques are recommended for soldering the
OPA548F surface mount package. Wave soldering is not recommended due to
excessive thermal shock and "shadowing" of nearby devices.
The information provided herein is believed to be reliable; however, BURR-BROWN assumes no responsibility for inaccuracies or omissions. BURR-BROWN assumes no responsibility
for the use of this information, and all use of such information shall be entirely at the user's own risk. Prices and specifications are subject to change without notice. No patent rights or
licenses to any of the circuits described herein are implied or granted to any third party. BURR-BROWN does not authorize or warrant any BURR-BROWN product for use in life support
devices and/or systems.
7-Lead
Stagger-Formed
TO-220
NOTE: Tabs are electrically connected to V supply.
I
LIM
V
V
O
V+
V
IN
V
IN
1 2 3 4 5 6
E/S
7
7-Lead
DDPAK
Surface-Mount
+
I
LIM
V
V
O
V+
V
IN
V
IN
1 2 3 4 5 6
E/S
7
+
PACKAGE/ORDERING INFORMATION
PACKAGE
DRAWING TEMPERATURE
PRODUCT
PACKAGE
NUMBER
(1)
RANGE
OPA548T
7-Lead Stagger-Formed TO-220
327
40
C to +85
C
OPA548F
(2)
7-Lead DDPAK Surface-Mount
328
40
C to +85
C
NOTE: (1) For detailed drawing and dimension table, please see end of data
sheet, or Appendix C of Burr-Brown IC Data Book. (2) Available on Tape and
Reel.
ELECTROSTATIC
DISCHARGE SENSITIVITY
This integrated circuit can be damaged by ESD. Burr-Brown
recommends that all integrated circuits be handled with
appropriate precautions. Failure to observe proper handling
and installation procedures can cause damage.
ESD damage can range from subtle performance degrada-
tion to complete device failure. Precision integrated circuits
may be more susceptible to damage because very small
parametric changes could cause the device not to meet its
published specifications.
4
OPA548
TYPICAL PERFORMANCE CURVES
At T
CASE
= +25
C, V
S
=
30V and E/S pin open, unless otherwise noted.
1
10
100
1k
10k
100k
1M
10M
100
80
60
40
20
0
20
Gain (dB)
0
45
90
135
180
Phase ()
Frequency (Hz)
OPEN-LOOP GAIN AND PHASE
vs FREQUENCY
G
No
Load
R
L
= 8
R
L
= 8
No Load
0
5
10
15
20
25
30
5
4
3
2
1
0
Current Limit (A)
Supply Voltage (V)
CURRENT LIMIT vs SUPPLY VOLTAGE
R
CL
= 4.02k
R
CL
= 14.7k
R
CL
= 57.6k
75
50
25
0
25
50
75
100
125
20
18
16
14
12
10
8
6
4
Quiescent Current (mA)
Temperature (C)
QUIESCENT CURRENT vs TEMPERATURE
I
Q
Shutdown
V
S
= 30V
V
S
= 5V
I
Q
V
S
= 30V
V
S
= 5V
75
50
25
0
25
50
75
100
125
5
4
3
2
1
0
Current Limit (A)
Temperature (C)
CURRENT LIMIT vs TEMPERATURE
R
CL
= 4.02k
+I
LIM
I
LIM
R
CL
= 14.7k
R
CL
= 57.6k
75
50
25
0
25
50
75
100
125
160
140
120
100
80
60
40
Input Bias Current (nA)
Temperature (C)
INPUT BIAS CURRENT vs TEMPERATURE
V
S
= 5V
V
S
= 30V
30
20
10
0
10
20
30
200
150
100
50
0
Input Bias Current (nA)
Common-Mode Voltage (V)
INPUT BIAS CURRENT
vs COMMON-MODE VOLTAGE
5
OPA548
TYPICAL PERFORMANCE CURVES
(CONT)
At T
CASE
= +25
C, V
S
=
30V and E/S pin open, unless otherwise noted.
10
100
1k
10k
100k
1M
100
80
60
40
20
0
Power Supply Rejection (dB)
Frequency (Hz)
POWER SUPPLY REJECTION
vs FREQUENCY
+PSRR
PSRR
10
100
1k
10k
100k
1M
100
80
60
40
20
0
Common-Mode Rejection (dB)
Frequency (Hz)
COMMON-MODE REJECTION vs FREQUENCY
75
50
25
0
25
50
75
100
A
OL
125
100
95
90
85
80
A
OL
, PSRR (dB)
110
105
100
95
90
CMRR (dB)
Temperature (C)
OPEN-LOOP GAIN, COMMON-MODE REJECTION,
AND POWER SUPPLY REJECTION vs TEMPERATURE
CMRR
PSRR
75
50
25
0
25
50
75
100
125
1.25
1
0.75
0.5
0.25
0
13
12
11
10
9
8
Gain-Bandwidth Product (MHz)
Slew Rate (V/s)
Temperature (C)
GAIN-BANDWIDTH PRODUCT AND
SLEW RATE vs TEMPERATURE
SR+
SR
GBW
1
10
100
1k
10k
100k
1M
500
400
300
200
100
0
Voltage Noise (nV/
Hz)
Frequency (Hz)
VOLTAGE NOISE DENSITY vs FREQUENCY
20
100
1k
10k
20k
1
0.1
0.01
0.001
THD+N (%)
Frequency (Hz)
TOTAL HARMONIC DISTORTION+NOISE
vs FREQUENCY
G = +3
R
L
= 8
0.1W
1W
10W
20W
6
OPA548
TYPICAL PERFORMANCE CURVES
(CONT)
At T
CASE
= +25
C, V
S
=
30V and E/S pin open, unless otherwise noted.
0
1
2
3
4
5
4
3
2
1
0
V
SUPPLY
V
OUT
(V)
Output Current (A)
OUTPUT VOLTAGE SWING vs OUTPUT CURRENT
(V+) V
O
(V) V
O
5
4
3
2
1
0
V
SUPPLY
V
OUT
(V)
Temperature (C)
OUTPUT VOLTAGE SWING vs TEMPERATURE
75
50
25
0
25
50
75
100
125
I
O
= +3A
I
O
= 3A
I
O
= +0.6A
I
O
= 0.6A
1k
10k
100k
1M
30
25
20
15
10
5
0
Output Voltage (Vp)
Frequency (Hz)
MAXIMUM OUTPUT VOLTAGE SWING
vs FREQUENCY
Maximum Output
Voltage Without
Slew Rate Induced
Distortion
40
30
20
10
0
10
20
40
30
10
5
0
5
10
Leakage Current (mA)
Output Voltage (V)
OUTPUT LEAKAGE CURRENT
vs APPLIED OUTPUT VOLTAGE
R
L
= 8
Output Disabled
V
E/S
< (V) + 0.8V
R
CL
=
R
CL
= 0
OFFSET VOLTAGE
PRODUCTION DISTRIBUTION
Percent of Amplifiers (%)
Offset Voltage (mV)
10 9 8 7 6 5 4 3 2 1 0 1 2 3 4 5 6 7 8 9 10
20
18
16
14
12
10
8
6
4
2
0
Typical distribution
of packaged units.
OFFSET VOLTAGE DRIFT
PRODUCTION DISTRIBUTION
Percent of Amplifiers (%)
Offset Voltage Drift (V/C)
14
12
10
8
6
4
2
0
Typical production
distribution of
packaged units.
0
10
20
30
40
50
60
70
80
90 100 110 120 130
7
OPA548
TYPICAL PERFORMANCE CURVES
(CONT)
At T
CASE
= +25
C, V
S
=
30V and E/S pin open, unless otherwise noted.
SMALL-SIGNAL STEP RESPONSE
G = 3, C
L
= 1000pF
100mV/div
2
s/div
LARGE-SIGNAL STEP RESPONSE
G = 3, C
L
= 1000pF, R
L
= 8
10V/div
5
s/div
SMALL-SIGNAL STEP RESPONSE
G = 1, C
L
= 1000pF
50mV/div
2
s/div
0
2k
4k
6k
8k
10k
12k
14k
16k
18k
20k
50
40
30
20
10
0
Overshoot (%)
Load Capacitance (pF)
SMALL-SIGNAL OVERSHOOT
vs LOAD CAPACITANCE
G = 1
G = +1
8
OPA548
APPLICATIONS INFORMATION
Figure 1 shows the OPA548 connected as a basic non-
inverting amplifier. The OPA548 can be used in virtually
any op amp configuration.
Power supply terminals should be bypassed with low series
impedance capacitors. The technique shown, using a ce-
ramic and tantalum type in parallel is recommended. In
addition, we recommend a 0.01
F capacitor between V+
and V as close to the OPA548 as possible. Power supply
wiring should have low series impedance.
With the OPA548, the simplest method for adjusting the
current limit uses a resistor or potentiometer connected
between the I
LIM
pin and V according to the equation:
The low level control signal (0 to 330
A) also allows the
current limit to be digitally controlled.
Figure 3 shows a simplified schematic of the internal cir-
cuitry used to set the current limit. Leaving the I
LIM
pin open
programs the output current to zero, while connecting I
LIM
directly to V programs the maximum output current limit,
typically 5A.
SAFE OPERATING AREA
Stress on the output transistors is determined both by the
output current and by the output voltage across the conduct-
ing output transistor, V
S
V
O
. The power dissipated by the
output transistor is equal to the product of the output current
and the voltage across the conducting transistor, V
S
V
O
.
The Safe Operating Area (SOA curve, Figure 2) shows the
permissible range of voltage and current.
FIGURE 1. Basic Circuit Connections.
POWER SUPPLIES
The OPA548 operates from single (+8V to +60V) or dual
(
4V to
30V) supplies with excellent performance. Most
behavior remains unchanged throughout the full operating
voltage range. Parameters which vary significantly with
operating voltage are shown in the typical performance
curves.
Some applications do not require equal positive and negative
output voltage swing. Power supply voltages do not need to
be equal. The OPA548 can operate with as little as 8V
between the supplies and with up to 60V between the
supplies. For example, the positive supply could be set to
55V with the negative supply at 5V, or vice-versa.
ADJUSTABLE CURRENT LIMIT
The OPA548 features an accurate, user-selected current
limit. Current limit is set from 0 to 5A by controlling the
input to the I
LIM
pin. Unlike other designs which use a power
resistor in series with the output current path, the OPA548
senses the load indirectly. This allows the current limit to be
set with a 0 to 330
A control signal. In contrast, other
designs require a limiting resistor to handle the full output
current (5A in this case).
R
CL
=
15000
(
)
4. 75
(
)
I
LIM
13750
FIGURE 2. Safe Operating Area.
The safe output current decreases as V
S
V
O
increases. Out-
put short-circuits are a very demanding case for SOA. A
short-circuit to ground forces the full power supply voltage
(V+ or V) across the conducting transistor. Increasing the
case temperature reduces the safe output current that can be
tolerated without activating the thermal shutdown circuit of
the OPA548. For further insight on SOA, consult Applica-
tion Bulletin AB-039.
AMPLIFIER MOUNTING
Figure 4 provides recommended solder footprints for both the
TO-220 and DDPAK power packages. The tab of both pack-
ages is electrically connected to the negative supply, V. It
may be desirable to isolate the tab of TO-220 package from its
G = 1+
R
2
R
1
Z
L
E/S
3
7
5
2
1
4
6
R
2
I
LIM
(1)
R
1
0.1F
(2)
10F
OPA548
V
V+
+
+
V
IN
10F
0.1F
(2)
0.01F
(2)
V
O
NOTE: (1) I
LIM
connected to V gives the maximum current
limit, 5A (peak). (2) Connect capacitors directly to package
power supply pins.
1
2
5
10
V
S
V
O
(V)
20
50
100
SAFE OPERATING AREA
10
1
Output Current (A)
0.1
Pulse Operation Only
(Limit rms current to
3A)
Current-Limited
Output current can
be limited to less
than 3A--see text.
T
C
= 125C
T
C
= 85C
T
C
= 25C
PD = 50W
PD = 26W
PD = 10W
9
OPA548
7-Lead DDPAK
(1)
(Package Drawing #328)
7-Lead TO-220
(Package Drawing #327)
NOTE: (1) For improved thermal performance increase footprint area.
See Figure 6, "Thermal Resistance vs Circuit Board Copper Area".
Mean dimensions in inches. Refer to end of data sheet
or Appendix C of Burr-Brown Data Book for tolerances
and detailed package drawings.
0.335
0.15
0.05
0.45
0.51
0.105
0.05
0.035
0.04
0.2
0.085
dissipation. Figure 6 shows typical thermal resistance from
junction-to-ambient as a function of the copper area
POWER DISSIPATION
Power dissipation depends on power supply, signal, and load
conditions. For dc signals, power dissipation is equal to
the product of output current times the voltage across the
mounting surface with a mica (or other film) insulator (see
Figure 5). For lowest overall thermal resistance it is best to
isolate the entire heat sink/OPA548 structure from the mount-
ing surface rather than to use an insulator between the semi-
conductor and heat sink.
For best thermal performance, the tab of the DDPAK sur-
face-mount version should be soldered directly to a circuit
board copper area. Increasing the copper area improves heat
13750
R
CL
0.01F
(optional, for noisy
environments)
3
4
3
4
4.75V
R
CL
=
13750
OPA547 CURRENT LIMIT: 0 to 5A
NOTE: (1) Resistors are nearest standard 1% values.
DESIRED
CURRENT LIMIT
0A
1A
2.5A
3A
4A
5A
RESISTOR
(1)
(R
CL
)
I
LIM
Open
57.6k
14.7k
10k
4.02k
I
LIM
Connected to V
CURRENT
(I
SET
)
0A
67A
167A
200A
267A
333A
VOLTAGE
(V
SET
)
(V) + 4.75V
(V) + 3.8V
(V) + 2.5V
(V) + 2V
(V) + 1.1V
(V)
RESISTOR METHOD
15000 (4.75V)
I
LIM
V
13750
I
SET
= I
LIM
/15000
V
SET
= (V) + 4.75V (13750
) (I
LIM
)/15000
DAC METHOD (Current or Voltage)
V
D/A
I
SET
4.75V
I
LIM
=
Max I
O
= I
LIM
(4.75) (15000)
13750
+ R
CL
Max I
O
= I
LIM
I
LIM
=15000
I
SET
FIGURE 3. Adjustable Current Limit.
FIGURE 4. TO-220 and DDPAK Solder Footprints.
10
OPA548
THERMAL RESISTANCE vs
CIRCUIT BOARD COPPER AREA
50
40
30
20
10
0
Thermal Resistance,
JA
(C/W)
0
1
2
3
4
5
Copper Area (inches
2
)
OPA548F
Surface Mount Package
1oz copper
Circuit Board Copper Area
OPA548
Surface Mount Package
FIGURE 5. TO-220 Thermal Resistance vs Aluminum Plate Area.
FIGURE 6. DDPAK Thermal Resistance vs Circuit Board Copper Area.
conducting output transistor. Power dissipation can be mini-
mized by using the lowest possible power supply voltage
necessary to assure the required output voltage swing.
For resistive loads, the maximum power dissipation occurs
at a dc output voltage of one-half the power supply voltage.
Dissipation with ac signals is lower. Application Bulletin
AB-039 explains how to calculate or measure power dissi-
pation with unusual signals and loads.
THERMAL PROTECTION
Power dissipated in the OPA548 will cause the junction
temperature to rise. The OPA548 has thermal shutdown
circuitry that protects the amplifier from damage. The ther-
mal protection circuitry disables the output when the junc-
tion temperature reaches approximately 160
C, allowing the
device to cool. When the junction temperature cools to
approximately 140
C, the output circuitry is again enabled.
Depending on load and signal conditions, the thermal pro-
tection circuit may cycle on and off. This limits the dissipa-
tion of the amplifier but may have an undesirable effect on
the load.
Any tendency to activate the thermal protection circuit
indicates excessive power dissipation or an inadequate heat
sink. For reliable operation, junction temperature should be
limited to 125
C, maximum. To estimate the margin of
safety in a complete design (including heat sink) increase the
ambient temperature until the thermal protection is trig-
gered. Use worst-case load and signal conditions. For good
reliability, thermal protection should trigger more than 35
C
above the maximum expected ambient condition of your
application. This produces a junction temperature of 125
C
at the maximum expected ambient condition.
The internal protection circuitry of the OPA548 was de-
signed to protect against overload conditions. It was not
intended to replace proper heat sinking. Continuously run-
ning the OPA548 into thermal shutdown will degrade reli-
ability.
0
1
2
3
4
5
6
7
8
18
16
14
12
10
8
Thermal Resistance
JA
(C/W)
Aluminum Plate Area (inches
2
)
THERMAL RESISTANCE
vs ALUMINUM PLATE AREA
Aluminum Plate Area
Flat, Rectangular
Aluminum Plate
OPA548
TO-220 Package
0.030in Al
0.062in Al
0.050in Al
Vertically Mounted
in Free Air
Optional mica or film insulator
for electrical isolation. Adds
approximately 1C/W.
Aluminum
Plate Thickness
11
OPA548
HEAT SINKING
Most applications require a heat sink to assure that the
maximum operating junction temperature (125
C) is not
exceeded. In addition, the junction temperature should be
kept as low as possible for increased reliability. Junction
temperature can be determined according to the equation:
T
J
= T
A
+ P
D
JA
(1)
where,
JA
=
JC
+
CH
+
HA
(2)
T
J
= Junction Temperature (
C)
T
A
= Ambient Temperature (
C)
P
D
= Power Dissipated (W)
JC
= Junction-to-Case Thermal Resistance (
C/W)
CH
= Case-to-Heat Sink Thermal Resistance (
C/W)
HA
= Heat Sink-to-Ambient Thermal Resistance (
C/W)
JA
= Junction-to-Air Thermal Resistance (
C/W)
Figure 7 shows maximum power dissipation versus ambient
temperature with and without the use of a heat sink. Using
a heat sink significantly increases the maximum power
dissipation at a given ambient temperature as shown.
The difficulty in selecting the heat sink required lies in
determining the power dissipated by the OPA548. For dc
output into a purely resistive load, power dissipation is
simply the load current times the voltage developed across
the conducting output transistor, P
D
= I
L
(V
s
V
O
). Other
loads are not as simple. Consult Application Bulletin AB-
039 for further insight on calculating power dissipation.
Once power dissipation for an application is known, the
proper heat sink can be selected.
Combining equations (1) and (2) gives:
T
J
= T
A
+ P
D
(
JC
+
CH
+
HA
)
(3)
T
J
, T
A
, and P
D
are given.
JC
is provided in the specification
table, 2.5
C/W (dc).
CH
can be obtained from the heat sink
manufacturer. Its value depends on heat sink size, area, and
material used. Semiconductor package type, mounting screw
torque, insulating material used (if any), and thermal
joint compound used (if any) also affect
CH
. A typical
CH
for a TO-220 mounted package is 1
C/W. Now we can solve
for
HA
:
To maintain junction temperature below 125
C, the heat
sink selected must have a
HA
less than 14
C/W. In other
words, the heat sink temperature rise above ambient must be
less than 67.5
C (13.5
C/W x 5W). For example, at 5 Watts
Thermalloy model number 6030B has a heat sink
temperature rise of 66
C above ambient (
HA
= 66
C/5W =
13.2
C/W), which is below the 67.5
C required in this
example. Figure 7 shows power dissipation versus ambient
temperature for a TO-220 package with a 6030B heat sink.
Another variable to consider is natural convection vs forced
convection air flow. Forced-air cooling by a small fan can
lower
CA
(
CH
+
HA
) dramatically. Heat sink manufactures
provide thermal data for both of these cases. For additional
information on determining heat sink requirements, consult
Application Bulletin AB-038.
As mentioned earlier, once a heat sink has been selected the
complete design should be tested under worst-case load and
signal conditions to ensure proper thermal protection.
ENABLE/STATUS (E/S) PIN
The Enable/Status Pin provides two functions: forcing this
pin low disables the output stage, or, E/S can be monitored
to determine if the OPA548 is in thermal shutdown. One or
both of these functions can be utilized on the same device
using single or dual supplies. For normal operation (output
enabled), the E/S pin can be left open or pulled high (at least
2.4V above the negative rail). A small value capacitor
connected between the E/S pin and V may be required for
noisy applications.
Output Disable
A unique feature of the OPA548 is its output disable capa-
bility. This function not only conserves power during idle
periods (quiescent current drops to approximately 6mA) but
also allows multiplexing in low frequency (f<20kHz), mul-
tichannel applications. Signals greater than 20kHz may
cause leakage current to increase in devices that are shut-
down. Figure 18 shows the two OPA548s in a switched
amplifier configuration. The on/off state of the two amplifi-
ers is controlled by the voltage on the E/S pin.
Heat Sink Selection Example
A TO-220 package is dissipating 5 Watts. The maximum
expected ambient temperature is 40
C. Find the proper heat
sink to keep the junction temperature below 125
C (150
C
minus 25
C safety margin).
FIGURE 7. Maximum Power Dissipation vs Ambient
Temperature.
HA
=
T
J
T
A
P
D
JC
+
CH
(
)
HA
=
125
C 40
C
5W
2. 5
C/ W
+
1
C/ W
(
)
=
13. 5
C/ W
10
8
6
4
2
0
Power Dissipation (Watts)
0
25
50
75
100
125
Ambient Temperature (C)
MAXIMUM POWER DISSIPATION
vs AMBIENT TEMPERATURE
TO-220 with Thermalloy
6030B Heat Sink
JA
= 16.7C/W
P
D
= (T
J
(max) T
A
)
/
JA
T
J
(max) = 150C
With infinite heat sink
(
JA
= 2.5C/W),
max P
D
= 50W at T
A
= 25C.
DDPAK
JA
= 26C/W
(3 in
2
one oz
copper mounting pad)
DDPAK or TO-220
JA
= 65C/W (no heat sink)
12
OPA548
To disable the output, the E/S pin is pulled low, no greater
than 0.8V above the negative rail. Typically the output is
shutdown in 1
s. Figure 8 provides an example of how to
implement this function using a single supply. Figure 9 gives
a circuit for dual supply applications. To return the output to
an enabled state, the E/S pin should be disconnected (open) or
pulled to at least (V) + 2.4V. It should be noted that pulling
the E/S pin high (output enabled) does not disable internal
thermal shutdown.
Output Disable and Thermal Shutdown Status
As mentioned earlier, the OPA548's output can be disabled
and the disable status can be monitored simultaneously.
Figures 12 and 13 provide examples interfacing to the E/S
pin while using a single supply and dual supplies, respec-
tively.
OUTPUT STAGE COMPENSATION
The complex load impedances common in power op amp
applications can cause output stage instability. For normal
operation output compensation circuitry is typically not
required. However, if the OPA548 is intended to be
driven into current limit, an R/C network may be required.
Figure 14 shows an output series R/C compensation (snub-
ber) network which generally provides excellent stability.
A snubber circuit may also enhance stability when driving
large capacitive loads (>1000pF) or inductive loads (motors,
loads separated from the amplifier by long cables). Typi-
cally 3
to 10
in series with 0.01
F to 0.1
F is adequate.
Some variations in circuit value may be required with
certain loads.
OUTPUT PROTECTION
Reactive and EMF-generating loads can return load cur-
rent to the amplifier, causing the output voltage to exceed
the power supply voltage. This damaging condition can
FIGURE 11. Thermal Shutdown Status with Dual Supplies.
FIGURE 10. Thermal Shutdown Status with a Single Supply.
OPA548
V+
E/S
V
1k
5V
22k
470
2N3906
Zetex
ZVN3310
OPA548
V+
E/S
V
CMOS or TTL
OPA548
V+
E/S
HCT
OR
TTL
2.49k
Zetex
ZVN3310
5V
V
Thermal Shutdown Status
Internal thermal shutdown circuitry shuts down the output
when the die temperature reaches approximately 160
C, reset-
ting when the die has cooled to 140
C. The E/S pin can be
monitored to determine if shutdown has occurred. During
normal operation the voltage on the E/S pin is typically 3.5V
above the negative rail. Once shutdown has occurred this
voltage drops to approximately 350mV above the negative rail.
Figure 10 gives an example of monitoring shutdown in a
single supply application. Figure 11 provides a circuit for
dual supplies. External logic circuitry or an LED could be
used to indicate if the output has been thermally shutdown,
see Figure 16.
FIGURE 9. Output Disable with Dual Supplies.
OPA548
V+
E/S
V
NOTE: (1) Optional--may be required to limit leakage
current of optocoupler at high temperatures.
(1)
6
1
1
4N38
Optocoupler
5
4
HCT or TTL In
5V
FIGURE 8. Output Disable with a Single Supply.
13
OPA548
be avoided with clamp diodes from the output terminal to
the power supplies as shown in Figure 14. Schottky
rectifier diodes with a 5A or greater continuous rating are
recommended.
VOLTAGE SOURCE APPLICATION
Figure 15 illustrates how to use the OPA548 to provide an
accurate voltage source with only three external resistors.
First, the current limit resistor, R
CL
, is chosen according to
the desired output current. The resulting voltage at the I
LIM
pin is constant and stable over temperature. This voltage,
V
CL
, is connected to the noninverting input of the op amp
and used as a voltage reference, thus eliminating the need for
an external reference. The feedback resistors are selected to
gain V
CL
to the desired output voltage level.
PROGRAMMABLE POWER SUPPLY
A programmable source/sink power supply can easily be
built using the OPA548. Both the output voltage and output
current are user-controlled. Figure 16 shows a circuit using
potentiometers to adjust the output voltage and current while
Figure 17 uses digital-to-analog converters. An LED tied to
the E/S pin through a logic gate indicates if the OPA548 is
in thermal shutdown.
FIGURE 13. Output Disable and Thermal Shutdown Status with Dual Supplies.
FIGURE 12. Output Disable and Thermal Shutdown Status
with a Single Supply.
FIGURE 14. Motor Drive Circuit.
OPA548
V+
E/S
Open Drain
(Output Disable)
HCT
(Thermal Status
Shutdown)
V
OPA548
V+
E/S
NOTE: (1) Optional--may be required to limit leakage
current of optocoupler at high temperatures.
V
(1)
6
1
2
4N38
Optocoupler
5
4
HCT or TTL In
5V
6
2
1
4N38
Optocoupler
5
4
Zetex
ZVN3310
TTL Out
7.5k
1W
5V
G = = 4
R
2
R
1
10
(Carbon)
0.01F
R
2
20k
R
1
5k
OPA548
V
V+
V
IN
Motor
D
1
D
2
D
1
, D
2
: Motorola MUR410.
14
OPA548
G = 1 + = 10
9k
1k
9k
1k
OPA548
+30V
+5V
+5V
0.12V to 2.5V
0V to 4.75V
Output
Adjust
V+
5
6
Thermal
Shutdown Status
NOTES: (1) For V
O
0V, V
1V.
(2) Optional: Improves noise
immunity.
(LED)
74HCT04
R
250
E/S
V
O
= 1.2V to 25V
(1)
I
O
= 0 to 5A
7
4
3
1
2
V
I
LIM
10.5k
499
10k
Current
Limit
Adjust
1k
20k
0.01F
(2)
V
13750
R
CL
I
LIM
0.01F
(Optional, for noisy
environments)
4.75V
I
O
=
15000 (4.75V)
13750
+ R
CL
V
O
= V
CL
(1 + R
2
/R
1
)
V
V+
V
CL
V
CL
= = 2V
Desired V
O
= 20V,
R
1
= 1k
and R
2
= 9k
G = = 10
20
2
For Example:
10k
4.75V
(10k
+ 13750
)
If I
LIM
= 3A, R
CL
=
10k
R
2
R
1
Uses voltage developed at I
LIM
pin
as a moderately accurate reference
voltage.
FIGURE 16. Resistor-Controlled Programmable Power Supply.
FIGURE 15. Voltage Source.
15
OPA548
( )
E/S
R
2
R
1
V
IN1
AMP1
V
O
E/S
R
4
R
3
V
E/S
> (V) +2.4V: Amp 1 is on, Amp 2 if off
V
O
= V
IN1
R
2
R
1
V
E/S
V
IN2
AMP2
( )
V
E/S
< (V) +2.4V: Amp 2 is on, Amp 1 if off
V
O
= V
IN2
R
4
R
3
OPA548
R
CL2
R
CL1
Close for high current
(Could be open drain
output of a logic gate).
I
LIM
V
FIGURE 19. Multiple Current Limit Values.
FIGURE 20. Single Quadrant V I Limiting.
FIGURE 17. Digitally-Controlled Programmable Power Supply.
OPA548
V
O
I
LIM
R
CL
As V
O
increases,
I
LIM
decreases.
FIGURE 18. Switched Amplifier.
DAC B
1/2 DAC7800/1/2
(3)
1/2 DAC7800/1/2
(3)
10pF
I
OUT B
R
FB B
AGND B
0.01F
(2)
I
LIM
Thermal
Shutdown Status
(LED)
74HCT04
R
250
9k
1k
V
O
= 0.8 to 25V
(1)
I
O
= 0 to 5A
G = 10
V
E/S
DAC A
+5V
+5V
V
REF B
DGND
10pF
I
OUT A
R
FB A
OUTPUT ADJUST
OPA548
CURRENT LIMIT ADJUST
AGND A
+30V
V
REF A
NOTES: (1) For V
O
0V, V
1V. (2) Optional, improves noise immunity. (3) Chose DAC780X based on
digital interface: DAC7800 - 12-bit interface, DAC7801 - 8-bit interface + 4 bits, DAC7802 - serial interface.
(4) Can use OPA2237, I
O
= 100mA to 5A.
1/2
OPA2336
1/2
OPA2336
V
REF
5V
16
OPA548
I
LIM
V
V+
R
1
1k
R
2
4k
OPA548
OPA548
V
O
I
O
= 10A (peak)
(2)
G
= 1 + = 5
(1)
V
IN
800
800
0.25
4k
1k
0.25
NOTES: (1) Works well for G < 10. Input offset causes output current to flow between amplifiers
with G > 10. Gains (resistor ratios) of the two amplifiers should be carefully matched to ensure
equal current sharing. (2) As configured (I
LIM
connected to V) output current limit is set to 10A
(peak). Each amplifier is limited to 5A (peak). Other current limit values may be obtained, see
Figure 3, "Adjustable Current Limit".
I
LIM
V
V+
R
3
1k
R
4
4k
FIGURE 21. Parallel Output for Increased Output Current.
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