Texas Instruments | Split Supply Positive and Negative Dual Voltage Monitoring Solution | Application notes | Texas Instruments Split Supply Positive and Negative Dual Voltage Monitoring Solution Application notes

Texas Instruments Split Supply Positive and Negative Dual Voltage Monitoring Solution Application notes
Application Report
SBVA062 – October 2019
TPS3700 Split Supply Positive and Negative Dual Voltage
Monitoring Solution
Trailokya Rai, Michael DeSando
ABSTRACT
The TPS3700 is a 18-V undervoltage (UV) and overvoltage (OV) supervisor used for window voltage
monitoring. The TI application note SLVA600 shows how this device can be used to monitor negative rails.
This application note describes using the TPS3700 for dual-voltage monitoring applications that require
UV and OV monitoring on a positive and negative voltage rail, such as:
• The dual-rail on operational amplifiers
• Multiplexers
• Demultiplexers
• DACs
• ADCs
• Other high-precision analog circuitry that may need UV or OV protection
1
2
3
4
5
6
7
8
Contents
Introduction ...................................................................................................................
TPS3700 Dual Rail OV and UV Monitoring Solution Overview ........................................................
Setting the Overvoltage and Undervoltage Threshold ..................................................................
Designing the TPS3700 Output Circuit for Overvoltage and Undervoltage Monitoring ............................
Wired OR Configuration for Window Mode (Undervoltage + Overvoltage Monitoring) .............................
Design Example..............................................................................................................
Summary ......................................................................................................................
References ...................................................................................................................
2
2
2
3
4
5
8
8
List of Figures
1
2
3
4
5
6
7
......................................
Undervoltage (OUTA) Monitor Circuit Configuration .................................................................
Window Supervisor for Dual-Rail Using TPS3700 ......................................................................
Window Voltage Monitor Design Example Circuit .......................................................................
Overvoltage Fault on +VDD Supply (Blue Trace: VDD, Red Trace: Output) ........................................
Undervoltage Fault on -VSS Supply (Green Trace: VSS, Red Trace: Output) ......................................
TPS3700 Dual Voltage Rail (+VDD and -VSS) OV and UV Monitor Circuit
(1)
(2)
2
3
5
5
6
7
Window Voltage Monitoring with Overvoltage Faults on Both Supplies (Blue Trace: VDD, Green Trace:
VSS, Red Trace: Output) ................................................................................................... 7
List of Tables
(1)
(2)
1
Design Specifications ....................................................................................................... 6
2
Results from Simulation ..................................................................................................... 8
Both the positive VDD rail and negative VSS rail have independent overvoltage and undervoltage monitoring.
Overvoltage (OUTB) monitor circuit is configured the same way.
SBVA062 – October 2019
Submit Documentation Feedback
TPS3700 Split Supply Positive and Negative Dual Voltage Monitoring
Solution
Copyright © 2019, Texas Instruments Incorporated
1
Introduction
www.ti.com
Trademarks
All trademarks are the property of their respective owners.
1
Introduction
This application note describes how to configure the TPS3700 into a positive and negative voltage rail
monitoring solution for undervoltage and overvoltage. This solution only requires two TPS3700 devices to
accomplish dual-rail window voltage monitoring. This solution is useful in applications where positive and
negative voltage rails are common. Several analog devices, such as operational amplifiers, data
converters, and multiplexers require both positive and negative voltage rails. Any application that uses
such analog devices, and needs both rails to be monitored, would benefit from this application note. Most
applications that require specific voltage rails need solutions to monitor the voltage rails to make sure they
are in the expected operating range for correct system operation. The TPS3700 devices have VDD(max)
= 18 V and are available in automotive grade and the TPS3701 devices have VDD(max) = 36 V. Both
devices are available in a very small WSON package (1.5 mm x 1.5 mm).
2
TPS3700 Dual Rail OV and UV Monitoring Solution Overview
VPU_UV
PUA1
VDD
OUTPUT_UV
0.1 …F
PUB1
R1
INA+
OUTA
OUTA
INB-
OUTB
INA+
TPS3700
(-VSS monitor)
TPS3700
(+VDD monitor)
R2
R4
VDD
PUC1
VDD
OUTB
VPU_OV
R5
INBR6
R3
GND
GND
PUA2
VSS
OUTPUT_OV
0.1 …F
PUB2
PUC2
Figure 1. TPS3700 Dual Voltage Rail (+VDD and -VSS) OV and UV Monitor Circuit
3
(3)
Setting the Overvoltage and Undervoltage Threshold
For negative rail monitoring, VSS represents the negative potential with respect to GND, similar to VDD
representing the positive voltage with respect to GND. The calculation of sense ladder resistor (R1, R2,
R3, and R4, R5, R6) is the same for both +VDD and –VSS rail.
VDD: the positive (+VDD) supply voltage rail
VSS: the negative (-VSS) supply voltage rail
VOV: Overvoltage threshold for OUTB to trigger low voltage
VUV: Undervoltage threshold for OUTA to trigger low voltage
(3)
2
Both the positive VDD rail and negative VSS rail have independent overvoltage and undervoltage monitoring.
TPS3700 Split Supply Positive and Negative Dual Voltage Monitoring
Solution
Copyright © 2019, Texas Instruments Incorporated
SBVA062 – October 2019
Submit Documentation Feedback
Designing the TPS3700 Output Circuit for Overvoltage and Undervoltage Monitoring
www.ti.com
VIT+: Positive going input threshold voltage in volts (0.4 V typical for TPS3700)
VIT-: Negative going input threshold voltage in volts (0.395 V typical for TPS3700)
RLadder [Ω] = Max Supply Voltage [V] ÷ Max Current in Resistor Ladder [A]
R3 = R6 [Ω] = VTHP × RLadder ÷ VOV
R2 = R5 [Ω] = VTHP × RLadder ÷ VUV
R1 = R4 [Ω] = RLadder - R2 - R3
4
(1)
(2)
(3)
(4)
Designing the TPS3700 Output Circuit for Overvoltage and Undervoltage Monitoring
Figure 2 shows circuit to set the output voltage at proper VOL and VOH levels. The same resistor ladder
configuration with diode is also used for the OUTB pins on the TPS3700 device for overvoltage
monitoring.
VPU
PUA
OUTPUT_UV
PUB
TPS3700
(+VDD monitor)
PUC
TPS3700
(-VSS monitor)
OUTA
OUTA
Figure 2. Undervoltage (OUTA) Monitor Circuit Configuration
(4)
NOTE: Section 4 describes how to configure undervoltage monitoring using the OUTA pin on two
TPS3700 devices for both +VDD and -VSS supplies. To configure overvoltage monitoring
use the OUTB pins.
Please note the terminology below:
VFB: Forward bias of the diode
VOL: The output voltage at OUTA or OUTB when asserted to logic low due to an undervoltage (OUTA) or
overvoltage (OUTB) fault
IOL: The current into the OUTA or OUTB pin when asserted to logic low due to an undervoltage (OUTA) or
overvoltage (OUTB) fault
The following cases show the possible output configurations:
(4)
Overvoltage (OUTB) monitor circuit is configured the same way.
SBVA062 – October 2019
Submit Documentation Feedback
TPS3700 Split Supply Positive and Negative Dual Voltage Monitoring
Solution
Copyright © 2019, Texas Instruments Incorporated
3
Designing the TPS3700 Output Circuit for Overvoltage and Undervoltage Monitoring
4.1
www.ti.com
Case 1 - No Undervoltage Condition on +VDD or -VSS Supply
When there is no undervotlage condition on either supply, the OUTA pins on each TPS3700 device are
high-impedance, so the Output_UV pulls up to VPU through the resistor ladder. In the case of –VSS supply
monitor, GND is at –VSS potential. The recommended maximum output voltage for OUTA and OUTB pins
with respect to GND is 18 V for TP3700. Equation 5 notes the maximum pullup voltage (VPU) allowed for
TPS3700.
VOUT (max) ≥ |VSS| + VPU for the maximum VSS value while no undervoltage or overvoltage fault
4.2
(5)
Case 2- Undervoltage Condition on -VSS Supply
When an undervoltage condition occurs on the -VSS supply, meaning the negative voltage drops towards
0 V from the negative threshold value, the OUTA of the TPS3700 monitoring the –VSS supply asserts to
VOL level with respect to GND pin connected to -VSS and the diode turns on. The diode is necessary
because, when it turns on during an undervoltage condition on -VSS supply, OUTPUT_UV depends on
the foward bias voltage of the diode (VFB) instead of the VSS supply voltage.
The minimum pullup resistor RPUC when OUTA is logic low is calculated in Equation 6.
RPUC (min) = (VFB + |VSS|) ÷ IOL (max)
(6)
To make sure that the diode turns on, the current through RPUB must be much less than the current
through RPUC. RPUA and RPUB are generally in the range of 10 kΩ to 100 kΩ.
4.3
Case 3- Undervoltage Condition on +VDD Supply
When an undervoltage condition occurs on the +VDD supply, the OUTA of the TPS3700 monitoring the
+VDD supply asserts to logic low of VOL, thus OUTPUT_UV is logic low indicating an undervoltage fault.
The OUTA pin on the TPS3700 monitoring the -VSS rail is high-impedance, so there is no current flowing
through RPUB and RPUC. The diode is off and has no effect in this case. Select RPUA using Equation 7 such
that the current into OUTA is within the recommended operating conditions given in the TPS3700 data
sheet.
RPUA (min) = VPU ÷ IOUTA (max)
4.4
(7)
Case 4- Undervoltage on Both +VDD and -VSS Supplies
Using similar reasoning for Case 3, when there is an undervoltage on both +VDD and -VSS supplies, the
OUTPUT_UV asserts to logic low because the OUTA pin of the TPS3700 monitoring the +VDD supply
asserts to VOL. The OUTA for the TPS3700 device monitoring the -VSS supply is at -VSS so the diode
turns on and supplies IOL to this OUTA pin.
5
Wired OR Configuration for Window Mode (Undervoltage + Overvoltage Monitoring)
The TPS3700 devices can also be used in wired OR configuration to monitor both undervoltage and
overvoltage for dual rails since these devices have open-drain output topology. Figure 3 shows both of the
open-drain outputs tied together with a single resistor network to monitor both UV and OV on both +VDD
and -VSS supplies. Using similar reasoning to the cases above, OUTPUT_UV+OV asserts to logic low if
either +VDD or -VSS is out of the voltage window configured by the resistor ladders on INA+ and INB- for
both TPS3700 devices. When both of the supplies are within the voltage window, all OUTA and OUTB
pins are high-impedance and OUTPUT_UV+OV pull up to logic high = VPU_UV+OV.
4
TPS3700 Split Supply Positive and Negative Dual Voltage Monitoring
Solution
Copyright © 2019, Texas Instruments Incorporated
SBVA062 – October 2019
Submit Documentation Feedback
Design Example
www.ti.com
VPU_UV+OV
VDD
0.1 …F
PUA
OUTPUT_UV+OV
PUB
R1
VDD
INA+
PUC
OUTA
OUTA
TPS3700
(+VDD monitor)
R2
INB-
R4
VDD
INA+
TPS3700
(-VSS monitor)
OUTB
R4
INB-
OUTB
R5
R3
GND
GND
VSS
0.1 …F
Figure 3. Window Supervisor for Dual-Rail Using TPS3700
6
Design Example
This section shows a window voltage monitor design example using two TPS3700 devices, as shown in
Figure 4.
VPU
VDD
0.1 …F
100 kŸ
Output
20 kŸ
192 kŸ
VDD
INA+
192 kŸ
VDD
OUTA
3 kŸ
OUTA
INA+
2.1 kŸ
2.1 kŸ
TPS3700
INB-
TPS3700
OUTB
OUTB
INB6.7 kŸ
6.7 kŸ
GND
GND
VSS
0.1 …F
Figure 4. Window Voltage Monitor Design Example Circuit
SBVA062 – October 2019
Submit Documentation Feedback
TPS3700 Split Supply Positive and Negative Dual Voltage Monitoring
Solution
Copyright © 2019, Texas Instruments Incorporated
5
Design Example
6.1
www.ti.com
Detailed Design Procedure
For this design example, the voltage threshold values and window voltage specifications for this design
example is shown in Table 1.
Table 1. Design Specifications
POSITIVE RAIL (+VDD)
6.2
NEGATIVE RAIL (-VSS)
UV
9V
-9 V
OV
12 V
-12 V
Inside the window
9 V ≤ VSS ≤ 12 V
-12 V ≤ VSS ≤ -9 V
Outside of the window
VDD < 9 V or VDD > 12 V
VSS > -9 V, VSS < -12 V
Monitoring +VDD Positive Voltage Supply
Figure 5 shows the results for the positive +VDD supply = [10 V, 12.5 V] only to show an overvoltage fault
on the +VDD supply.
Figure 5. Overvoltage Fault on +VDD Supply (Blue Trace: VDD, Red Trace: Output)
6
TPS3700 Split Supply Positive and Negative Dual Voltage Monitoring
Solution
Copyright © 2019, Texas Instruments Incorporated
SBVA062 – October 2019
Submit Documentation Feedback
Design Example
www.ti.com
6.3
Monitoring -VSS Negative Voltage Supply
Figure 6 shows the results for the negative -VSS supply = [-7 V, -10 V] only to show an undervoltage fault
on the -VSS supply.
Figure 6. Undervoltage Fault on -VSS Supply (Green Trace: VSS, Red Trace: Output)
6.4
Monitoring Both +VDD and -VSS Supplies
Figure 7 shows the results for both +VDD = [10 V, 12.5 V] and -VSS = [-12 V, -15 V] supplies to show an
overvoltage fault on the +VDD supply and an overvoltage fault on the -VSS supply.
Figure 7. Window Voltage Monitoring with Overvoltage Faults on Both Supplies (Blue Trace: VDD, Green
Trace: VSS, Red Trace: Output)
SBVA062 – October 2019
Submit Documentation Feedback
TPS3700 Split Supply Positive and Negative Dual Voltage Monitoring
Solution
Copyright © 2019, Texas Instruments Incorporated
7
Design Example
6.5
www.ti.com
Design Simulation Results
Table 2 shows the output voltage values during each of the possible voltage monitoring scenarios.
Table 2. Results from Simulation
7
CASE
+VDD SUPPLY
-VSS SUPPLY
OUTPUT (mV)
1
Out of window
In the Window
10-15
2
Out of window
Out of window
10-15
3
In the window
Out of window
250
4
In the window
In the window
5000
Summary
This application report demonstrates a dual voltage rail (+VDD and -VSS) window voltage (UV and OV)
monitoring solution using two TPS3700 devices. The voltage thresholds are adjustable thorough the
resistor ladder values and the TPS3700 allows for wide Vin voltage monitoring with high accuracy (0.25%
typical) not accounting for component tolerance.
8
References
The following references provide additional information and resources related to this application note.
• Texas Instruments, Using the TPS3700 as a Negative Rail Over- and Undervoltage Detector
Application Report
• Texas Instruments, TPS3700 High voltage (18V) window voltage detector with internal reference for
over and undervoltage monitoring Data Sheet
• Texas Instruments, RAD-TOLERANT SPACE GRADE DIE, PRECISION PROGRAMMABLE
REFERENCE Data Sheet
• Texas Instruments, TPS3701 High voltage (36V) window voltage detector with internal reference for
over and undervoltage monitoring Data Sheet
8
TPS3700 Split Supply Positive and Negative Dual Voltage Monitoring
Solution
Copyright © 2019, Texas Instruments Incorporated
SBVA062 – October 2019
Submit Documentation Feedback
IMPORTANT NOTICE AND DISCLAIMER
TI PROVIDES TECHNICAL AND RELIABILITY DATA (INCLUDING DATASHEETS), DESIGN RESOURCES (INCLUDING REFERENCE
DESIGNS), APPLICATION OR OTHER DESIGN ADVICE, WEB TOOLS, SAFETY INFORMATION, AND OTHER RESOURCES “AS IS”
AND WITH ALL FAULTS, AND DISCLAIMS ALL WARRANTIES, EXPRESS AND IMPLIED, INCLUDING WITHOUT LIMITATION ANY
IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE OR NON-INFRINGEMENT OF THIRD
PARTY INTELLECTUAL PROPERTY RIGHTS.
These resources are intended for skilled developers designing with TI products. You are solely responsible for (1) selecting the appropriate
TI products for your application, (2) designing, validating and testing your application, and (3) ensuring your application meets applicable
standards, and any other safety, security, or other requirements. These resources are subject to change without notice. TI grants you
permission to use these resources only for development of an application that uses the TI products described in the resource. Other
reproduction and display of these resources is prohibited. No license is granted to any other TI intellectual property right or to any third
party intellectual property right. TI disclaims responsibility for, and you will fully indemnify TI and its representatives against, any claims,
damages, costs, losses, and liabilities arising out of your use of these resources.
TI’s products are provided subject to TI’s Terms of Sale (www.ti.com/legal/termsofsale.html) or other applicable terms available either on
ti.com or provided in conjunction with such TI products. TI’s provision of these resources does not expand or otherwise alter TI’s applicable
warranties or warranty disclaimers for TI products.
Mailing Address: Texas Instruments, Post Office Box 655303, Dallas, Texas 75265
Copyright © 2019, Texas Instruments Incorporated
Was this manual useful for you? yes no
Thank you for your participation!

* Your assessment is very important for improving the work of artificial intelligence, which forms the content of this project

Related manuals

Download PDF

advertising