OPA890IDBV BURR-BROWN [Burr-Brown Corporation], OPA890IDBV Datasheet - Page 23

• Manufacturer Part Number: OPA890IDBV
• Description: Low-Power, Wideband, Voltage-Feedback OPERATIONAL AMPLIFIER with Disable
• Manufacturer: BURR-BROWN [Burr-Brown Corporation]

DISABLE OPERATION
The OPA890 provides an optional disable feature
that may be used either to reduce system power or
to
operation. If the DIS control pin is left unconnected,
the OPA890 operates normally. To disable the
OPA890, the control pin must be asserted low.
Figure 54
disable control feature.
In normal operation, base current to Q1 is provided
through the 2M
through the 80k
is inadequate to turn on the two diodes in the Q1
emitter. As V
pulled through the 80k
on those two diodes ( 15 A). At this point, any
further current pulled out of V
diodes, holding the emitter-base voltage of Q1 at
approximately 0V. This process shuts off the
10kW
Figure 53. DC-Coupled, Inverting Gain of -2V/V,
Figure 54. Simplified Disable Control Circuit
www.ti.com
implement
+5V
-5V
5kW
5kW
V
DIS
shows a simplified internal circuit for the
DIS
V
with Offset Adjustment
0.1 F
I
0.1 F
m
is pulled low, additional current is
a
resistor sets up a voltage drop that
m
resistor, while the emitter current
324W
20kW
R
80kW
200kW
G
simple
226W
resistor, eventually turning
Control
+V
±150mV Output Adjustment
I
S
DIS
S
OPA890
V
channel
V
Q1
+5V
-5V
O
I
=
goes through those
-
Power-supply decoupling
not shown.
R
R
F
G
750W
-
R
= 2
V
F
-
S
2MW
multiplexing
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V
O
collector current out of Q1, turning the amplifier off.
The supply current in the disable mode is only that
required to operate the circuit of
Additional circuitry ensures that turn-on time occurs
faster than turn-off time (make-before-break).
When disabled, the output and input nodes go to a
high-impedance state. If the OPA890 is operating at
a gain of +1V/V, it shows a very high impedance at
the output and exceptional signal isolation. If
operating at a gain greater than +1V/V, the total
feedback network resistance (R
the impedance looking back into the output, but the
circuit still shows very-high forward and reverse
isolation. If configured as an inverting amplifier, the
input and output are connected through the feedback
network resistance (R
very poor, as a result.
THERMAL ANALYSIS
Maximum desired junction temperature sets the
maximum allowed internal power dissipation, as
described below. In no case should the maximum
junction temperature be allowed to exceed +150 C.
Operating junction temperature (T
P
the sum of quiescent power (P
power dissipated in the output stage (P
load power. Quiescent power is simply the specified
no-load supply current times the total supply voltage
across the part. P
signal and load, but for a grounded resistive load is
at a maximum when the output is fixed at a voltage
equal to 1/2 of either supply voltage (for equal
bipolar supplies). Under this condition, P
R
Note that it is the power in the output stage and not
into the load that determines internal power
dissipation.
As a worst-case example, compute the maximum T
using an OPA890IDBV (SOT23-6 package) in the
circuit of
specified ambient temperature of +85 C and driving
a grounded 100
P
79mW
Maximum T
Although this result is still well below the specified
maximum junction temperature, system reliability
considerations may require lower operating junction
temperatures.
dissipation occurs if the load requires current to be
forced into the output for positive output voltages, or
sourced from the output for negative output voltages.
This configuration puts a high current through a large
internal voltage drop in the output transistors.
D
D
L
) where R
= 10V
JA
. The total internal power dissipation (P
Figure 46
J
L
= +85 C + (79W
includes feedback network loading.
1.25mA + 5
The
load.
DL
depends on the required output
F
operating at the maximum
highest
+ R
2
/(4
G
) and the isolation is
150 C/W) = +97 C.
F
DQ
(100
J
possible
+ R
) is given by T
) and additional
SBOS369 – MAY 2007
G
) appears as
DL
DL
Figure
) to deliver
1.5k )) =
= V
OPA890
internal
S
2
/(4
D
) is
54.
A
23
+
J