Datasheet LT1413 (Analog Devices) - 7
| Manufacturer | Analog Devices |
| Description | Single Supply, Dual Precision Op Amp |
| Pages / Page | 8 / 7 — APPLICATIONS INFORMATION. Single Supply Operation. Gain 100 Amplifier. … |
| File Format / Size | PDF / 254 Kb |
| Document Language | English |
APPLICATIONS INFORMATION. Single Supply Operation. Gain 100 Amplifier. Voltage Follower. Figure 1. Comparator Applications
Model Line for this Datasheet
Text Version of Document
LT1413
U U W U APPLICATIONS INFORMATION Single Supply Operation
other amplifier out of negative saturation for the phase reversal protection to function properly. The LT1413 is fully specified for single supply operation, i.e., when the negative supply is 0V. Input common-mode Since the output of the LT1413 cannot go exactly to range includes ground; the output swings within a few ground, but can only approach ground to within a few millivolts of ground. millivolts, care should be exercised to ensure that the output is not saturated. For example, a 1mV input signal If the input is more than a few hundred millivolts below will cause the amplifier to set up in its linear region ground, two distinct problems can occur on previous in the gain 100 configuration shown below, but is not single supply designs, such as the LM124, LM158, OP-21 enough to make the amplifier function properly in the and OP-221. voltage-follower mode. a) When the input is more than a diode drop below
Gain 100 Amplifier Voltage Follower
ground, unlimited current will flow from the substrate (V– terminal) to the input. This can destroy the unit. On 5V 5V the LT1413, the 400Ω resistors, in series with the input R 99R – – (see Schematic Diagram), protect the devices even when OUTPUT 100mV SATURATED the input is 5V below ground. ≈ 15mV 1mV + 1mV + b) When the input is more than 400mV below ground LT1413 • 27 (at 25°C), the input stage saturates (transistors Q3 and
Figure 1.
Q4) and phase reversal occurs at the output. This can
Comparator Applications
cause lock-up in servo systems. Due to a unique phase reversal protection circuitry (Q21, Q22, Q27, Q28), the The single supply operation of the LT1413 lends itself to LT1413 outputs do not reverse, as illustrated below, its use as a precision comparator with TTL compatible even when the inputs are at –1.5V. Keep the output of the output; the response time is shown below.
Voltage Follower with Input Exceeding the Negative Common-Mode Range
4V 4V 4V 2V 2V 2V 0V 0V 0V 6VP-P INPUT, –1.5V TO 4.5V LM324, LM358, OP-221 LT1413 LT1413 • TA21 EXHIBIT OUTPUT PHASE REVERSAL NO PHASE REVERSAL LT1413 • TA22 LT1413 • TA23
Comparator Rise Response Time Comparator Fall Response Time 10mV, 5mV, 2mV Overdrives to 10mV, 5mV, 2mV Overdrives
4 4 2 2 OUTPUT (V) OUTPUT (V) 0 0 0 100 INPUT (mV) INPUT (mV) –100 0 V V S = 5V, 0V 50µs/DIV S = 5V, 0V 50µs/DIV LT1413 • TA24 LT1413 • TA25 Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen- tation that the interconnection of its circuits as described herein will not infringe on existing patent rights. 7
U U W U APPLICATIONS INFORMATION Single Supply Operation
other amplifier out of negative saturation for the phase reversal protection to function properly. The LT1413 is fully specified for single supply operation, i.e., when the negative supply is 0V. Input common-mode Since the output of the LT1413 cannot go exactly to range includes ground; the output swings within a few ground, but can only approach ground to within a few millivolts of ground. millivolts, care should be exercised to ensure that the output is not saturated. For example, a 1mV input signal If the input is more than a few hundred millivolts below will cause the amplifier to set up in its linear region ground, two distinct problems can occur on previous in the gain 100 configuration shown below, but is not single supply designs, such as the LM124, LM158, OP-21 enough to make the amplifier function properly in the and OP-221. voltage-follower mode. a) When the input is more than a diode drop below
Gain 100 Amplifier Voltage Follower
ground, unlimited current will flow from the substrate (V– terminal) to the input. This can destroy the unit. On 5V 5V the LT1413, the 400Ω resistors, in series with the input R 99R – – (see Schematic Diagram), protect the devices even when OUTPUT 100mV SATURATED the input is 5V below ground. ≈ 15mV 1mV + 1mV + b) When the input is more than 400mV below ground LT1413 • 27 (at 25°C), the input stage saturates (transistors Q3 and
Figure 1.
Q4) and phase reversal occurs at the output. This can
Comparator Applications
cause lock-up in servo systems. Due to a unique phase reversal protection circuitry (Q21, Q22, Q27, Q28), the The single supply operation of the LT1413 lends itself to LT1413 outputs do not reverse, as illustrated below, its use as a precision comparator with TTL compatible even when the inputs are at –1.5V. Keep the output of the output; the response time is shown below.
Voltage Follower with Input Exceeding the Negative Common-Mode Range
4V 4V 4V 2V 2V 2V 0V 0V 0V 6VP-P INPUT, –1.5V TO 4.5V LM324, LM358, OP-221 LT1413 LT1413 • TA21 EXHIBIT OUTPUT PHASE REVERSAL NO PHASE REVERSAL LT1413 • TA22 LT1413 • TA23
Comparator Rise Response Time Comparator Fall Response Time 10mV, 5mV, 2mV Overdrives to 10mV, 5mV, 2mV Overdrives
4 4 2 2 OUTPUT (V) OUTPUT (V) 0 0 0 100 INPUT (mV) INPUT (mV) –100 0 V V S = 5V, 0V 50µs/DIV S = 5V, 0V 50µs/DIV LT1413 • TA24 LT1413 • TA25 Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen- tation that the interconnection of its circuits as described herein will not infringe on existing patent rights. 7
