OPA2673 datasheet(30/40 Pages) TI

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Power Control Operation

THERMAL ANALYSIS

A0orA1

1.4V

Control

GND

OPA2673

SBOS382A – JUNE 2008 – REVISED OCTOBER 2008..................................................................................................................................................... www.ti.com

The

shutdown

feature

for

the

OPA2673

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

the

–VS 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.

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

maximum desired junction temperature sets the

100% bias

maximum

allowed

internal

power

dissipation,

75% bias

described below. In no case should the maximum

50% bias

junction temperature be allowed to exceed +150°C.

Shutdown

Operating junction temperature (TJ) is given by TA +

PD × θJA. The total internal power dissipation (PD) is

The 100% bias mode is used for normal operating

the sum of quiescent power (PDQ) and additional

conditions. The 75% bias mode brings the quiescent

power dissipation in the output stage (PDL) 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. PDL depends on the required output signal

quiescent power (5.5mA).

and load; for a grounded resistive load, however, PDL

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, PDL = VS

2/(4 × R

L),

To change the power mode, the control pins (either

where RL 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 TJ

using an OPA2673 QFN-16 in the circuit of Figure 76

operating

the

maximum

specified

ambient

temperature of +85°C with both outputs driving a

grounded 20

Ω load to +2.5V.

PD = 12V × 32mA + 2 × [5

2/(4 × [20Ω

535

Ω])] =

1.03W

Maximum TJ = +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.

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