LT1794 datasheet(8/20 Pages) LINER

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LT1794

outputs are in a high impedance state. Part to part varia-

tions however, will cause inconsistent control of the qui-

escent current if direct voltage drive of the SHDN pin is used.

Using a single external resistor, RBIAS, connected in one of

two ways provides a much more predictable control of the

quiescent supply current. Figure 2 illustrates the effect on

supply current per amplifier with RBIAS connected be-

tween the SHDN pin and the 12V V+ supply of the LT1794

and the approximate design equations. Figure 3 illustrates

the same control with RBIAS connected between the

SHDNREF pin and ground while the SHDN pin is tied to V+.

Either approach is equally effective.

APPLICATIO S I FOR ATIO

Figure 1. Internal Current Biasing Circuitry

SHDN

SHDNREF

START-UP

CIRCUITRY

1794 F01

IBIAS

TO AMPLIFIERS

BIAS CIRCUITRY

IBIAS =

ISUPPLY PER AMPLIFIER (mA) = 64 • IBIAS

ISHDN = ISHDNREF

RBIAS (kΩ)

1794 F02

100

130

160

190

VS = ±12V

V+ = 12V

RBIAS

SHDN

SHDNREF

RBIAS =

• 25.6 – 2k

V+ – 1.2V

IS PER AMPLIFIER (mA)

• 25.6

V+ – 1.2V

RBIAS + 2k

≈

RBIAS (kΩ)

130

170

210

250

100

150

190

230

270 290

1794 F03

VS = ±12V

V+ = 12V

RBIAS

SHDN

SHDNREF

RBIAS =

• 64 – 5k

V+ – 1.2V

IS PER AMPLIFIER (mA)

• 64

V+ – 1.2V

RBIAS + 5k

≈

Figure 2. RBIAS to V+ Current Control

Figure 3. RBIAS to Ground Current Control

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