Datasheet

OPA547
10
SBOS056F
www.ti.com
THERMAL PROTECTION
The OPA547 has thermal shutdown that protects the ampli-
fier from damage. Activation of the thermal shutdown circuit
during normal operation is an indication of excessive power
dissipation or an inadequate heat sink. Depending on load
and signal conditions, the thermal protection circuit may
cycle on and off. This limits the dissipation of the amplifier but
may have an undesirable effect on the load.
The thermal protection activates at a junction temperature of
approximately 160°C. However, for reliable operation, junc-
tion temperature should be limited to 150°C. To estimate the
margin of safety in a complete design (including heat sink),
increase the ambient temperature until the thermal protection
is activated. Use worst-case load and signal conditions. For
good reliability, the thermal protection should trigger more
than 35°C above the maximum expected ambient condition of
the application. This produces a junction temperature of
125°C at the maximum expected ambient condition.
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 OPA547 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 en-
abled), the E/S pin can be left open or pulled high (at least
+2.4V above the negative rail).
Output Disable
A unique feature of the OPA547 is its output disable capabil-
ity. This function not only conserves power during idle peri-
ods (quiescent current drops to approximately 4mA), but also
allows multiplexing in low frequency (f<10kHz), multichannel
applications. Signals that are greater than 10kHz may cause
leakage current to increase in devices that are shutdown.
Figure 15 shows the two OPA547s in a switched amplifier
configuration. The on/off state of the two amplifiers is con-
trolled by the voltage on the E/S pin.
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 1µs. Figure 5 provides an example of how to implement this
function using a single supply. Figure 6 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.
OPA547
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 6. Output Disable with Dual Supplies.
Thermal Shutdown Status
Internal thermal shutdown circuitry shuts down the output when
the die temperature reaches approximately 160°C, resetting
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 7 gives an example of monitoring shutdown in a
single-supply application. Figure 8 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 13.
FIGURE 7. Thermal Shutdown Status with a Single Supply.
FIGURE 8. Thermal Shutdown Status with Dual Supplies.
FIGURE 5. Output Disable with a Single Supply.
OPA547
V+
E/S
HCT
OR
TTL
2.49kΩ
Zetex
ZVN3310
5V
V–
OPA547
V+
E/S
V–
1kΩ
5V
22kΩ
470Ω
2N3906
Zetex
ZVN3310
OPA547
V+
E/S
V–
CMOS or TTL