OPA548F datasheet(12/24 Pages) TI

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OPA548

SBOS070B

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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 1

µs. 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

Ω 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–

Ω

22k

Ω

470

Ω

2N3906

Zetex

ZVN3310

OPA548

V+

E/S

V–

CMOS or TTL

OPA548

V+

E/S

HCT

TTL

2.49k

Ω

Zetex

ZVN3310

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)

4N38

Optocoupler

HCT or TTL In

FIGURE 8. Output Disable with a Single Supply.

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