Texas Instruments | Why Users Should Consider Upgrading Their LMV324, LMV358, and LMV321 Devices | Application notes | Texas Instruments Why Users Should Consider Upgrading Their LMV324, LMV358, and LMV321 Devices Application notes

Texas Instruments Why Users Should Consider Upgrading Their LMV324, LMV358, and LMV321 Devices Application notes
Application Report
SBOA368 – October 2019
Why Users Should Consider Upgrading Their LMV324,
LMV358, and LMV321 Devices
Ronald Michallick
ABSTRACT
This app note provides guidance as to why a designer should consider upgrading their designs from
legacy LMV324, LMV358, and LMV321 (LMV) devices to the modern LMV324A, LMV358A, and LMV321A
(LMVA) device family, which are more robust and can be used as a drop-in replacement for LMV devices.
LMVA devices also have overall better performance while staying within same design budget. While the
legacy LMV devices are fabricated by multiple semiconductor manufacturers and found in many designs,
the devices are not necessarily interchangeable across manufacturers. For example, some devices not
produced by Texas Instruments have higher current when used in comparator mode. Also, some LMV
devices, including those produced by Texas Instruments, may exhibit phase reversal when common-mode
recommended voltage range violations occur. TI’s modern LMVA devices do not have phase reversal and
can be used in comparator mode, which yields a more robust design.
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2
3
Contents
Phase Reversal .............................................................................................................. 1
Better Performance Within Design Budget ............................................................................... 3
Summary ...................................................................................................................... 4
List of Figures
1
Maximum Input Common-Mode Range (Supply is 5 V) ................................................................ 2
2
Output Voltage Versus Negative Input Current (Non-Inverting Input) for Texas Instruments’ Samples ......... 2
3
Output Voltage Versus Negative Input Current (Non-Inverting Input) for *Other Manufacturers' Samples ...... 3
4
Change in Supply Current for Output in VOL and VOH state Versus Supply Voltage for Texas
Instruments’ Samples ....................................................................................................... 4
5
Change in Supply Current for Output in VOL and VOH State Versus Supply Voltage for *Other
Manufacturers' Samples ................................................................................................... 4
List of Tables
Trademarks
All trademarks are the property of their respective owners.
1
Phase Reversal
When the input common mode is in the recommended operating range, the output is the correct phase for
all devices tested. When both inputs are above the common-mode range, LMV devices from multiple
manufacturers have input stages where the transistors are in cutoff, so the output tries to either go to VOH
(positive supply rail) or VOL (negative supply rail). In normal (negative feedback) operation, VOL-going
samples clamp the output to keep input at the maximum common-mode voltage, the point where inversion
stops. LMVA devices do not exhibit phase reversal and provide the desired output voltage.
Figure 1 is sample data for maximum input common mode range with supply voltage set to 5 V. If the
input common-mode voltage exceeds the chart value, the input stage goes into cut off. Therefore, the
output is no longer controlled by the input voltage.
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Why Users Should Consider Upgrading Their LMV324, LMV358, and
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1
Phase Reversal
www.ti.com
5
Upper Common-Mode Range
4.9
4.8
4.7
4.6
4.5
4.4
4.3
4.2
4.1
4
LMV358 LMV358-NLMV358A Other 1* Other 2* Other 3*
D001
Figure 1. Maximum Input Common-Mode Range (Supply is 5 V)
For a negative input voltage on either input, LMV devices from multiple manufacturers, including Texas
Instruments, exhibited phase reversal. The output voltage went to the incorrect supply rail for at least one
of the inputs. LMVA samples tested did not invert with current up to -10mA. Avoiding negative voltages
altogether is the preferred design practice.
However, good design practice limits the maximum input current to -1mA. Figure 2 and Figure 3 show the
output voltage for a unity gain buffer application where negative input current flows due to a negative input
voltage. Ideally, the output must be low. Output voltage going high indicates phase reversal.
6
Output Voltage (V)
5
LMV358
LMV358-N
LMV358A
4
3
2
1
0
-1
0.001
0.01
0.1
1
Negative Input Current (mA)
10
D002
Figure 2. Output Voltage Versus Negative Input Current (Non-Inverting Input) for Texas Instruments’
Samples
2
Why Users Should Consider Upgrading Their LMV324, LMV358, and
LMV321 Devices
Copyright © 2019, Texas Instruments Incorporated
SBOA368 – October 2019
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Better Performance Within Design Budget
www.ti.com
6
Output Voltage (V)
5
Other 1*
Other 2*
Other 3*
4
3
2
1
0
-1
0.001
0.01
0.1
1
Negative Input Current (mA)
10
D003
Figure 3. Output Voltage Versus Negative Input Current (Non-Inverting Input) for *Other Manufacturers'
Samples
2
Better Performance Within Design Budget
As of the publication of this document, LMVA device specifications are better and 1 ku web pricing is
lower. This quick comparison link has up-to-date 1 ku product page pricing.
The comparison highlights the improvements in input offset error and quiescent current. There is also
significant improvement in common mode rejection (13 dB higher) and power supply rejection (28 dB
higher). Slew rate is also increased by 70%.
In general, op amps must not be used as comparators. However, these general purpose op amps are
often used as comparators in some applications. Comparator applications spend most of the time in VOL
or VOH output state. Some LMV devices tested had an elevated quiescent current when the output was
VOL or VOH. Texas Instruments LMV and LMVA products do not have increased quiescent current when
the output is VOL or VOH. Also important for comparator usage is overload recovery time; this parameter
is analogous to propagation delay in a dedicated comparator. Overload recovery for LMVA is typically 0.9
us. After overload recovery time, slew rate controls the output rise and fall times.
Figure 4 and Figure 5 show changes in supply current and quiescent current when the output is driven
into VOL and VOH states. Greater changes in VOL or VOH are charted in Figure 4 and Figure 5.
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LMV321 Devices
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3
Summary
www.ti.com
Change in Supply Current (PA/CH)
50
LMV358
LMV358-N
LMV358A
45
40
35
30
25
20
15
10
5
0
2.5
3
3.5
4
4.5
Supply Voltage (V)
5
5.5
D004
Figure 4. Change in Supply Current for Output in VOL and VOH state Versus Supply Voltage for Texas
Instruments’ Samples
Change in Supply Current (PA/CH)
2000
1800
1600
1400
1200
1000
800
600
400
200
0
2.5
3
3.5
4
4.5
Supply Voltage (V)
5
5.5
D005
Figure 5. Change in Supply Current for Output in VOL and VOH State Versus Supply Voltage for *Other
Manufacturers' Samples
3
Summary
This document has outlined a number of reasons why designers should consider upgrading their designs
from legacy LMV324, LMV358, and LMV321 (LMV) devices to the modern LMV324A, LMV358A, and
LMV321A (LMVA) device families. They yield better performance (comparator mode, no phase reversal)
without sacrificing design budget.
4
Why Users Should Consider Upgrading Their LMV324, LMV358, and
LMV321 Devices
Copyright © 2019, Texas Instruments Incorporated
SBOA368 – October 2019
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