Datasheet

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SBOS206E − DECEMBER 2001 − REVISED FEBRUARY 2007
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7
APPLICATIONS INFORMATION
Figure 1 shows the OPA561 connected as a basic
noninverting amplifier. However, the OPA561 can be used
in virtually any op amp configuration.
Power-supply terminals should be bypassed with low
series impedance capacitors. The technique of using a
ceramic and tantalum type in parallel is recommended.
Power-supply wiring should have low series impedance.
402k
Ω
(3)
47
µ
F
0.1
µ
F
47µF
0.1
µ
F
V
IN
V
O
V−
R
CL
(1)
E/S
(2)
(I
MAX
= 200
µ
A)
I
LIM
V+
NOTES: (1) R
CL
sets the current limit value
from 0.2A to 1.2A. (2) E/S Pin

Forced
LOW: Output Disable; Indicates LOW:
Thermal Shutdown. (3) 402kΩresistor
permanently enables the OPA561.
OPA561
Figure 1. Basic Circuit Connections
POWER SUPPLIES
The OPA561 operates from single (+7V to +15V) or dual
(±3.5V to ±7.5V) supplies with excellent performance.
Power-supply voltages do not need to be equal. For
example, the positive supply could be set to 10V with the
negative supply at –5V, or vice-versa. Most behaviors
remain unchanged throughout the operating voltage
range. Parameters that vary significantly with operating
voltage are shown in the typical characteristics.
ADJUSTABLE CURRENT LIMIT
The OPA561’s accurate, user-defined, current limit can be
set from 0.2A to 1.2A by controlling the input to the I
LIM
pin.
Unlike other designs that use a power resistor in series
with the output current path, the OPA561 senses the load
internally. This allows the current limit to be set with
low-power components. In contrast, other designs require
one or two expensive power resistors that can handle the
full output current (1.2A in this case).
Current Limit Accuracy
Separate circuits monitor the positive and negative
currents. Each output is compared to a single internal
reference that is set by the external current limit resistor (or
voltage). The OPA561 employs a patented circuit
technique to achieve an accurate and stable current limit.
The output current limit has an accuracy of up to 5% on the
1A current limit. Due to internal matching limitations, the
positive and negative current limits can be slightly
different. However, the values are typically within 10% of
each other.
Setting the Current Limit
Leaving the I
LIM
pin open could damage the part.
Connecting I
LIM
directly to V− programs the maximum
output current limit, typically 1.2A. The simplest method for
adjusting the current limit (I
LIM
) uses a resistor or
potentiometer connected between the I
LIM
pin and V−
according to Equation 1:
I
LIM
+
ǒ
1.2V
R
CL
) 10kW
Ǔ
10, 000
This external resistor determines a small internal current
which sets the desired output current limit. Alternatively,
the output current limit can be set by applying a voltage to
the I
LIM
pin. Figure 2 shows a simplified schematic of the
OPA561’s current limit.
R
CL
0.01
µ
F
(optional, for noisy
environments)
1.2V 10k
Ω
V−
I
LIM
=
Max I
O
=I
LIM
1.2V
R
CL
+10kΩ
()
×
10k
Figure 2. Adjustable Current Limit—Resistor
Method
(1)