Datasheet
R
F
750W
±200mVOutputAdjustment
= = 2- -
Power-supply
decouplingnotshown.
5kW
5kW
250W0.1 Fm
R
G
375W
V
I
20kW
10kW
0.1 Fm
-5V
+5V
1/2
OPA2889
+5V
-5V
V
O
V
O
V
I
R
F
R
G
THERMAL ANALYSIS
DISABLE OPERATION (MSOP-10 Package
150kW 4MW
100kW
I
S
Control
-V
S
+V
S
V
DIS
Q1
OPA2889
SBOS373B – JUNE 2007 – REVISED AUGUST 2008 .......................................................................................................................................................
www.ti.com
inverting input node through resistor values that are In normal operation, base current to Q1 is provided
much larger than the signal path resistors. This through the 4M Ω resistor, while the emitter current
technique ensures that the adjustment circuit has through the 100k Ω resistor sets up a voltage drop
minimal effect on the loop gain and thus, the that is inadequate to turn on the two diodes in the Q1
frequency response. emitter. As V
DIS
is pulled LOW, additional current is
pulled through the 100k Ω resistor, eventually turning
on those two diodes ( ≈ 18 µ A). At this point, any
further current pulled out of V
DIS
goes through those
diodes holding the emitter-base voltage of Q1 at
approximately 0V. This current shuts off the collector
current out of Q1, turning the amplifier off. The supply
currents in the disable mode are only those required
to operate the circuit of Figure 63 . 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 OPA2889 is operating at
a gain of +1V/V, the device 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
F
+ R
G
)
appears as 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
F
+ R
G
) and the
Figure 62. DC-Coupled, Inverting Gain of – 2V/V,
isolation will be very poor as a result.
with Offset Adjustment
Maximum desired junction temperature sets the
Only)
maximum allowed internal power dissipation as
described below. In no case should the maximum
The OPA2889IDGS provides an optional disable
junction temperature be allowed to exceed +150 ° C.
feature that can be used either to reduce system
power or to implement a simple channel multiplexing
Operating junction temperature (T
J
) is given by T
A
+
operation. If the DIS control pin is left unconnected,
P
D
× θ
JA
. The total internal power dissipation (P
D
) is
the OPA2889IDGS operates normally. To disable, the
the sum of quiescent power (P
DQ
) and additional
control pin must be asserted LOW. Figure 63 shows
power dissipated in the output stage (P
DL
) to deliver
a simplified internal circuit for the disable control
load power. Quiescent power is simply the specified
feature.
no-load supply current times the total supply voltage
across the part. P
DL
depends on the required output
signal and load; for a grounded resistive load, P
DL
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
DL
= V
S
2
/(4 × R
L
),
where R
L
includes feedback network loading.
Note that it is the power in the output stage and not
into the load that determines internal power
dissipation.
Figure 63. Simplified Disable Control Circuit
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