Datasheet LT1794 (Analog Devices) - 8
| Hersteller | Analog Devices |
| Beschreibung | Dual 500mA, 200MHz xDSL Line Driver Amplifier |
| Seiten / Seite | 20 / 8 — APPLICATIO S I FOR ATIO. Figure 1. Internal Current Biasing Circuitry. … |
| Dateiformat / Größe | PDF / 287 Kb |
| Dokumentensprache | Englisch |
APPLICATIO S I FOR ATIO. Figure 1. Internal Current Biasing Circuitry. Figure 2. RBIAS to V+ Current Control
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LT1794
U U W U APPLICATIO S I FOR ATIO
SHDN outputs are in a high impedance state. Part to part varia- tions however, will cause inconsistent control of the qui- 5I 2k escent current if direct voltage drive of the SHDN pin is used. I 2I 2I 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 1k supply current per amplifier with R TO BIAS connected be- START-UP tween the SHDN pin and the 12V V+ supply of the LT1794 CIRCUITRY IBIAS TO AMPLIFIERS and the approximate design equations. Figure 3 illustrates BIAS CIRCUITRY SHDNREF 1794 F01 the same control with RBIAS connected between the 2 IBIAS = ISHDN = ISHDNREF SHDNREF pin and ground while the SHDN pin is tied to V+. 5 ISUPPLY PER AMPLIFIER (mA) = 64 • IBIAS Either approach is equally effective.
Figure 1. Internal Current Biasing Circuitry
30 VS = ±12V V+ = 12V 25 RBIAS SHDN 20 V+ – 1.2V IS PER AMPLIFIER (mA) ≈ • 25.6 RBIAS + 2k 15 R V+ – 1.2V PER AMPLIFIER (mA) BIAS = • 25.6 – 2k I 10 S PER AMPLIFIER (mA) SHDNREF I SUPPLY 5 0 7 10 40 70 100 130 160 190 RBIAS (kΩ) 1794 F02
Figure 2. RBIAS to V+ Current Control
45 VS = ±12V V+ = 12V 40 SHDN 35 V+ – 1.2V I ≈ S PER AMPLIFIER (mA) • 64 R 30 BIAS + 5k 25 R V+ – 1.2V BIAS = • 64 – 5k 20 IS PER AMPLIFIER (mA) PER AMPLIFIER (mA) SHDNREF 15 RBIAS I SUPPLY 10 5 0 4 7 10 30 50 70 90 100 130 150 170 190 210 230 250 270 290 RBIAS (kΩ) 1794 F03
Figure 3. RBIAS to Ground Current Control
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U U W U APPLICATIO S I FOR ATIO
SHDN outputs are in a high impedance state. Part to part varia- tions however, will cause inconsistent control of the qui- 5I 2k escent current if direct voltage drive of the SHDN pin is used. I 2I 2I 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 1k supply current per amplifier with R TO BIAS connected be- START-UP tween the SHDN pin and the 12V V+ supply of the LT1794 CIRCUITRY IBIAS TO AMPLIFIERS and the approximate design equations. Figure 3 illustrates BIAS CIRCUITRY SHDNREF 1794 F01 the same control with RBIAS connected between the 2 IBIAS = ISHDN = ISHDNREF SHDNREF pin and ground while the SHDN pin is tied to V+. 5 ISUPPLY PER AMPLIFIER (mA) = 64 • IBIAS Either approach is equally effective.
Figure 1. Internal Current Biasing Circuitry
30 VS = ±12V V+ = 12V 25 RBIAS SHDN 20 V+ – 1.2V IS PER AMPLIFIER (mA) ≈ • 25.6 RBIAS + 2k 15 R V+ – 1.2V PER AMPLIFIER (mA) BIAS = • 25.6 – 2k I 10 S PER AMPLIFIER (mA) SHDNREF I SUPPLY 5 0 7 10 40 70 100 130 160 190 RBIAS (kΩ) 1794 F02
Figure 2. RBIAS to V+ Current Control
45 VS = ±12V V+ = 12V 40 SHDN 35 V+ – 1.2V I ≈ S PER AMPLIFIER (mA) • 64 R 30 BIAS + 5k 25 R V+ – 1.2V BIAS = • 64 – 5k 20 IS PER AMPLIFIER (mA) PER AMPLIFIER (mA) SHDNREF 15 RBIAS I SUPPLY 10 5 0 4 7 10 30 50 70 90 100 130 150 170 190 210 230 250 270 290 RBIAS (kΩ) 1794 F03
Figure 3. RBIAS to Ground Current Control
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