Datasheet LT1795 (Analog Devices) - 7
| Hersteller | Analog Devices |
| Beschreibung | Dual 500mA/50MHz Current Feedback Line Driver Amplifier |
| Seiten / Seite | 12 / 7 — APPLICATIO S I FOR ATIO. SHUTDOWN/CURRENT SET. If the shutdown/current … |
| Dateiformat / Größe | PDF / 158 Kb |
| Dokumentensprache | Englisch |
APPLICATIO S I FOR ATIO. SHUTDOWN/CURRENT SET. If the shutdown/current set feature is not used, connect
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LT1795
U U W U APPLICATIO S I FOR ATIO
The LT1795 is a dual current feedback amplifier with high When VSHDN = VSHDNREF, the device is shut down. The output current drive capability. The amplifier is designed device will interface directly with 3V or 5V CMOS logic to drive low impedance loads such as twisted-pair trans- when SHDNREF is grounded and the control signal is mission lines with excellent linearity. applied to the SHDN pin. Switching time between the active and shutdown states is about 1.5µs.
SHUTDOWN/CURRENT SET
Figures 1 to 4 illustrate how the SHDN and SHDNREF pins
If the shutdown/current set feature is not used, connect
can be used to reduce the amplifier quiescent current. In
SHDN to V+ and SHDNREF to ground.
both cases, an external resistor is used to set the current. The two approaches are equivalent, however the required The SHDN and SHDNREF pins control the biasing of the resistor values are different. The quiescent current will be two amplifiers. The pins can be used to either turn off the approximately 115 times the current in the SHDN pin and amplifiers completely, reducing the quiescent current to 230 times the current in the SHDNREF pin. The voltage less then 200µA, or to control the quiescent current in across the resistor in either condition is V+ – 1.5V. For normal operation. example, a 50k resistor between V+ and SHDN will set the V+ V+ 10 SHDN RSHDN 11 SHDNREF 10 SHDN RSHDNREF 11 SHDNREF 1795 F03 1795 F01
Figure 1. RSHDN Connected Between V + and SHDN (Pin 10); Figure 3. RSHDNREF Connected Between SHDNREF (Pin 11) SHDNREF (Pin 11) = GND. See Figure 2 and GND; SHDN (Pin 10) = V +. See Figure 4
80 80 TA = 25°C TA = 25°C 70 VS = ±15V 70 VS = ±15V 60 60 50 50 40 40 30 30 – mA (BOTH AMPLIFIERS) 20 – mA (BOTH AMPLIFIERS) 20 AMPLIFIER SUPPLY CURRENT, I SY AMPLIFIER SUPPLY CURRENT, I SY 10 10 0 0 0 25 50 75 100 125 150 175 200 225 50 100 150 200 250 300 350 400 450 500 RSHDN (kΩ) RSHDNREF (kΩ) 1795 F02 1795 F04
Figure 2. LT1795 Amplifier Supply Current vs RSHDN. RSHDN Figure 4. LT1795 Amplifier Supply Current vs RSHDNREF. Connected Between V+ and SHDN, SHDNREF = GND (See RSHDNREF Connected Between SHDNREF and GND, Figure 1) SHDN = V+ (See Figure 3)
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U U W U APPLICATIO S I FOR ATIO
The LT1795 is a dual current feedback amplifier with high When VSHDN = VSHDNREF, the device is shut down. The output current drive capability. The amplifier is designed device will interface directly with 3V or 5V CMOS logic to drive low impedance loads such as twisted-pair trans- when SHDNREF is grounded and the control signal is mission lines with excellent linearity. applied to the SHDN pin. Switching time between the active and shutdown states is about 1.5µs.
SHUTDOWN/CURRENT SET
Figures 1 to 4 illustrate how the SHDN and SHDNREF pins
If the shutdown/current set feature is not used, connect
can be used to reduce the amplifier quiescent current. In
SHDN to V+ and SHDNREF to ground.
both cases, an external resistor is used to set the current. The two approaches are equivalent, however the required The SHDN and SHDNREF pins control the biasing of the resistor values are different. The quiescent current will be two amplifiers. The pins can be used to either turn off the approximately 115 times the current in the SHDN pin and amplifiers completely, reducing the quiescent current to 230 times the current in the SHDNREF pin. The voltage less then 200µA, or to control the quiescent current in across the resistor in either condition is V+ – 1.5V. For normal operation. example, a 50k resistor between V+ and SHDN will set the V+ V+ 10 SHDN RSHDN 11 SHDNREF 10 SHDN RSHDNREF 11 SHDNREF 1795 F03 1795 F01
Figure 1. RSHDN Connected Between V + and SHDN (Pin 10); Figure 3. RSHDNREF Connected Between SHDNREF (Pin 11) SHDNREF (Pin 11) = GND. See Figure 2 and GND; SHDN (Pin 10) = V +. See Figure 4
80 80 TA = 25°C TA = 25°C 70 VS = ±15V 70 VS = ±15V 60 60 50 50 40 40 30 30 – mA (BOTH AMPLIFIERS) 20 – mA (BOTH AMPLIFIERS) 20 AMPLIFIER SUPPLY CURRENT, I SY AMPLIFIER SUPPLY CURRENT, I SY 10 10 0 0 0 25 50 75 100 125 150 175 200 225 50 100 150 200 250 300 350 400 450 500 RSHDN (kΩ) RSHDNREF (kΩ) 1795 F02 1795 F04
Figure 2. LT1795 Amplifier Supply Current vs RSHDN. RSHDN Figure 4. LT1795 Amplifier Supply Current vs RSHDNREF. Connected Between V+ and SHDN, SHDNREF = GND (See RSHDNREF Connected Between SHDNREF and GND, Figure 1) SHDN = V+ (See Figure 3)
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