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.
V+
5V
OPA548
2.49kΩ
E/S
TTL
V–
Zetex
ZVN3310
OR
HCT
V+
FIGURE 10. Thermal Shutdown Status with a Single Supply.
OPA548
E/S
5V
V+
V–
CMOS or TTL
1kΩ
OPA548
2N3906
FIGURE 8. Output Disable with a Single Supply.
E/S
22kΩ
470Ω
Zetex
ZVN3310
V+
V–
5V
FIGURE 11. Thermal Shutdown Status with Dual Supplies.
OPA548
E/S
1
6
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.
5
(1)
HCT or TTL In
1
4
4N38
Optocoupler
V–
OUTPUT STAGE COMPENSATION
NOTE: (1) Optional—may be required to limit leakage
current of optocoupler at high temperatures.
The complex load impedances common in power op amp
applications can cause output stage instability. For normal
operation output compensation circuitry is typically not
required. However, if the OPA548 is intended to be
driven into current limit, an R/C network may be required.
Figure 14 shows an output series R/C compensation (snub-
ber) network which generally provides excellent stability.
FIGURE 9. Output Disable with Dual Supplies.
Thermal Shutdown Status
Internal thermal shutdown circuitry shuts down the output
when the die temperature reaches approximately 160°C, reset-
ting 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.
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). Typi-
cally 3Ω to 10Ω in series with 0.01µF to 0.1µF is adequate.
Some variations in circuit value may be required with
certain loads.
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.
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
®
OPA548
12
BB [ BURR-BROWN CORPORATION ]
