Datasheet

OPA548
12
SBOS070B
www.ti.com
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 8 provides an example of how to
implement this function using a single supply. Figure 9 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.
Output Disable and Thermal Shutdown Status
As mentioned earlier, the OPA548’s output can be disabled
and the disable status can be monitored simultaneously.
Figures 12 and 13 provide examples interfacing to the E/S
pin while using a single supply and dual supplies, respec-
tively.
OUTPUT STAGE COMPENSATION
The complex load impedances common in power op amp
applications can cause output stage instability. For normal
operation output compensation circuitry is typically not re-
quired. However, if the OPA548 is intended to be driven into
current limit, an R/C network may be required. See Figure 14
for an output series R/C compensation (snubber) network
which generally provides excellent stability.
A snubber circuit may also enhance stability when driving
large capacitive loads (> 1000pF) or inductive loads (motors,
loads separated from the amplifier by long cables). Typically
3Ω to 10Ω in series with 0.01µF to 0.1µF is adequate. Some
variations in circuit value may be required with certain loads.
OUTPUT PROTECTION
Reactive and EMF-generating loads can return load cur-
rent to the amplifier, causing the output voltage to exceed
the power-supply voltage. This damaging condition can be
FIGURE 11. Thermal Shutdown Status with Dual Supplies.
FIGURE 10. Thermal Shutdown Status with a Single Supply.
OPA548
V+
E/S
V–
1kΩ
5V
22kΩ
470Ω
2N3906
Zetex
ZVN3310
OPA548
V+
E/S
V–
CMOS or TTL
OPA548
V+
E/S
HCT
OR
TTL
2.49kΩ
Zetex
ZVN3310
5V
V–
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 10 gives an example of monitoring shutdown in a
single-supply application. Figure 11 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 16.
FIGURE 9. Output Disable with Dual Supplies.
OPA548
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 8. Output Disable with a Single Supply.