Datasheet LT6559 (Analog Devices) - 9
| Manufacturer | Analog Devices |
| Description | Low Cost 5V/±5V 300MHz Triple Video Amplifier in 3mm x 3mm QFN |
| Pages / Page | 16 / 9 — APPLICATIONS INFORMATION. Enable/Disable. Figure 2. Amplifi er Enable … |
| File Format / Size | PDF / 451 Kb |
| Document Language | English |
APPLICATIONS INFORMATION. Enable/Disable. Figure 2. Amplifi er Enable Time, AV = 2. Figure 3. Amplifi er Disable Time, AV = 2
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LT6559
APPLICATIONS INFORMATION
internal capacitance. At a gain of 2 with 301Ω feedback The enable/disable times are very fast when driven from and gain resistors and ±5V supplies, the output slew rate standard 5V CMOS logic. Each amplifi er enables in about is typically 800V/µs. Larger feedback resistors will reduce 30ns (50% point to 50% point) while operating on ±5V the slew rate as will lower supply voltages. supplies (Figure 2). Likewise, the disable time is approxi- mately 40ns (50% point to 50% point) (Figure 3).
Enable/Disable
Each amplifi er of the LT6559 has a unique high imped- ance, zero supply current mode which is controlled by its 2V own ⎯E⎯N pin. These amplifi ers are designed to operate with OUTPUT CMOS logic; the amplifi ers draw 0.1µA of current when 0V these pins are high or fl oated. To activate each amplifi er, its ⎯E⎯N pin is normally pulled to a logic low. However, sup- ply current will vary as the voltage between the V+ supply 5V and ⎯E⎯N is varied. As seen in Figure 1, +IS does vary with EN (V+ – V 0V ⎯E⎯N), particularly when the voltage difference is less than 3V. For normal operation, it is important to keep the 6559 F02 VS = ±5V RF = 301Ω RL = 100Ω ⎯E⎯N pin at least 3V below the V+ supply. If a V+ of less than VIN = 1V RG = 301Ω 3V is used, for the amplifi er to remain enabled at all times
Figure 2. Amplifi er Enable Time, AV = 2
the ⎯E⎯N pin should be tied to the V– supply. The enable pin current is approximately 30µA when activated. If using CMOS open-drain logic, an external 1k pull-up resistor is recommended to ensure that the LT6559 remains disabled regardless of any CMOS drain-leakage currents. 2V OUTPUT 0V 5.0 TA = 25°C 4.5 V + = 5V 4.0 V – = 0V 3.5 3.0 V – = – 5V 5V (mA) 2.5 EN S+I 0V 2.0 6559 F03 VS = ±5V RF = 301Ω RL = 100Ω V R 1.5 IN = 1V G = 301Ω 1.0
Figure 3. Amplifi er Disable Time, AV = 2
0.5 0 0 1 2 3 4 5 6 7 V + – VEN (V)
Differential Input Signal Swing
6559 F01 To avoid any breakdown condition on the input transis-
Figure 1. +IS vs (V+ – V
⎯
E
⎯
N)
tors, the differential input swing must be limited to ±5V. In normal operation, the differential voltage between the input pins is small, so the ±5V limit is not an issue. In the disabled mode however, the differential swing can be the same as the input swing, and there is a risk of device breakdown if the input voltage range has not been properly considered. 6559f 9
APPLICATIONS INFORMATION
internal capacitance. At a gain of 2 with 301Ω feedback The enable/disable times are very fast when driven from and gain resistors and ±5V supplies, the output slew rate standard 5V CMOS logic. Each amplifi er enables in about is typically 800V/µs. Larger feedback resistors will reduce 30ns (50% point to 50% point) while operating on ±5V the slew rate as will lower supply voltages. supplies (Figure 2). Likewise, the disable time is approxi- mately 40ns (50% point to 50% point) (Figure 3).
Enable/Disable
Each amplifi er of the LT6559 has a unique high imped- ance, zero supply current mode which is controlled by its 2V own ⎯E⎯N pin. These amplifi ers are designed to operate with OUTPUT CMOS logic; the amplifi ers draw 0.1µA of current when 0V these pins are high or fl oated. To activate each amplifi er, its ⎯E⎯N pin is normally pulled to a logic low. However, sup- ply current will vary as the voltage between the V+ supply 5V and ⎯E⎯N is varied. As seen in Figure 1, +IS does vary with EN (V+ – V 0V ⎯E⎯N), particularly when the voltage difference is less than 3V. For normal operation, it is important to keep the 6559 F02 VS = ±5V RF = 301Ω RL = 100Ω ⎯E⎯N pin at least 3V below the V+ supply. If a V+ of less than VIN = 1V RG = 301Ω 3V is used, for the amplifi er to remain enabled at all times
Figure 2. Amplifi er Enable Time, AV = 2
the ⎯E⎯N pin should be tied to the V– supply. The enable pin current is approximately 30µA when activated. If using CMOS open-drain logic, an external 1k pull-up resistor is recommended to ensure that the LT6559 remains disabled regardless of any CMOS drain-leakage currents. 2V OUTPUT 0V 5.0 TA = 25°C 4.5 V + = 5V 4.0 V – = 0V 3.5 3.0 V – = – 5V 5V (mA) 2.5 EN S+I 0V 2.0 6559 F03 VS = ±5V RF = 301Ω RL = 100Ω V R 1.5 IN = 1V G = 301Ω 1.0
Figure 3. Amplifi er Disable Time, AV = 2
0.5 0 0 1 2 3 4 5 6 7 V + – VEN (V)
Differential Input Signal Swing
6559 F01 To avoid any breakdown condition on the input transis-
Figure 1. +IS vs (V+ – V
⎯
E
⎯
N)
tors, the differential input swing must be limited to ±5V. In normal operation, the differential voltage between the input pins is small, so the ±5V limit is not an issue. In the disabled mode however, the differential swing can be the same as the input swing, and there is a risk of device breakdown if the input voltage range has not been properly considered. 6559f 9
