Datasheet

+V
S
A0orA1
1.4V
Control
GND
OPA2673
SBOS382F –JUNE 2008–REVISED MAY 2010 www.ti.com
Power Control Operation
The shutdown feature for the OPA2673 is a
ground-supply referenced, current-controlled
The OPA2673 provides a power control feature that
interface. For voltage output logic interfaces, the
may be used to reduce system power. The four
on/off voltage levels described in the Electrical
modes of operation for this power control feature are
Characteristics apply only for either the ground pin
100% bias, 75% bias, 50% bias, and power
RGV package or the –V
S
pin used for the
shutdown. These four operating modes are set
single-supply specifications.
through two logic lines A0 and A1. Table 3 shows the
different modes of operation.
THERMAL ANALYSIS
Table 3. Operating Modes
As a result of the high output power capability of the
OPA2673, heat-sinking or forced airflow may be
MODE OF
required under extreme operating conditions. The
OPERATION A1 A0
maximum desired junction temperature sets the
100% bias 0 0
maximum allowed internal power dissipation,
75% bias 0 1
described below. In no case should the maximum
50% bias 1 0
junction temperature be allowed to exceed +150°C.
Shutdown 1 1
Operating junction temperature (T
J
) is given by T
A
+
P
D
× q
JA
. The total internal power dissipation (P
D
) is
The 100% bias mode is used for normal operating
the sum of quiescent power (P
DQ
) and additional
conditions. The 75% bias mode brings the quiescent
power dissipation in the output stage (P
DL
) to deliver
power to 24mA. The 50% bias mode brings the
load power. Quiescent power is the specified no-load
quiescent power to 16mA. The shutdown mode has a
supply current times the total supply voltage across
high output impedance as well as the lowest
the part. P
DL
depends on the required output signal
quiescent power (5.5mA).
and load; for a grounded resistive load, however, P
DL
If the A0 and A1 pins are left unconnected, the
is at a maximum when the output is fixed at a voltage
OPA2673 operates normally (100% bias).
equal to 1/2 of either supply voltage (for equal bipolar
supplies). Under this condition, P
DL
= V
S
2
/(4 × R
L
),
To change the power mode, the control pins (either
where R
L
includes feedback network loading.
A0 or A1) must be asserted low. This logic control is
referenced to the ground supply, as shown in the
Note that it is the power in the output stage and not
simplified circuit of Figure 86.
into the load that determines internal power
dissipation.
As a worst-case example, compute the maximum T
J
using an OPA2673 QFN-16 in the circuit of Figure 76
operating at the maximum specified ambient
temperature of +85°C with both outputs driving a
grounded 20Ω load to +2.5V.
P
D
= 12V × 32mA + 2 × [5
2
/(4 × [20Ω 535Ω])]
= 1.03W
Maximum T
J
= +85°C + (1.03 × 45°C/W) = 131°C
Although this value is still well below the specified
maximum junction temperature, system, reliability
considerations may require lower tested junction
temperatures.The highest possible internal dissipation
occurs if the load requires current to be forced into
Figure 86. Supply Power Control Circuit
the output for positive output voltages, or sourced
from the output for negative output voltages. This
space
condition puts a high current through a large internal
drop in the output transistors. The output V-I plot in
space
the Typical Characteristics (Figure 6) includes a
boundary for 2W maximum internal power dissipation
under these conditions.
30 Submit Documentation Feedback Copyright © 2008–2010, Texas Instruments Incorporated
Product Folder Link(s): OPA2673