SNVAA62 September 2023 TPS37 , TPS37-Q1 , TPS3760 , TPS3760-Q1 , TPS38 , TPS38-Q1
3 Common Applications and Use Cases
This section describes common applications for wide VIN supervisors. Each use case details the type of supervisor being used, how to implement, device recommendations, and application-based documents to consider.
Direct Battery Monitoring
Due to the large capacitive delays present in most power supply designs, monitoring the source power rail directly can provide an earlier fault warning than monitoring a downstream rail. This presents a challenge for battery powered applications, as a supervisor directly connected to the battery constantly draws power. A low Iq supervisor with fixed thresholds minimizes total power draw. The TPS37 handles battery voltage transients up 65 V. The pullup resistor RP1 can be set to a standard value of 10 kΩ.
Device shown: TPS37-Q1 fixed threshold variants
Adjustable Window Monitoring
TPS37 is capable of monitoring a power rail for both OV and UV faults simultaneously. Reset signals for OV and UV faults can be tied together on an open drain bus as shown by the dashed line, or connected to the rest of the system independently. The voltage thresholds of the TPS37A010122DSKR are set with resistive voltage dividers R1, R2 and R3, R4. The linked online calculator below can be used to calculate the sense input resistors or refer to section 10.1 in the data sheet linked below for more information. Pullup resistors RP1 and RP2 can be set to a standard value of 10 kΩ.
Device shown: TPS37A010122DSKR adjustable threshold variant
Additional resources: TPS37 data sheet section 10.1
Monitoring Downstream Power Rails
Many types of end equipment power several downstream power rails using a source high voltage rail. For maximum fault tolerance, a supervisor monitoring the downstream rails must be powered by the source high voltage supply, so that the supervisor continues to function even if downstream power supplies fail. The linked online calculator below can be used to calculate the sense input resistors or refer to section 8.3.7 in the data sheet linked below for more information. Pullup resistors RP1 and RP2 can be set to a standard value of 10 kΩ.
Device shown: TPS38A010122DSKRQ1 adjustable threshold variant
Additional resources: TPS38 data sheet section 8.3.7
Battery Backup Management
A supervisor is used to start up a battery backup system when the primary voltage input falls below an operating threshold. The supervisor draws power directly from the battery backup, making sure that the supervisor is always on and monitoring the primary power rail. The linked online calculator below can be used to calculate the sense input resistors or refer to section 10.1 in the data sheet linked below for more information. Pullup resistors RP1 and RP2 can be set to a standard value of 10 kΩ.
Device shown: TPS37A010122DSKR adjustable threshold variant
Additional resources: TPS37 data sheet section 10.1
Low Current Load Switch Controller
Large OV transients can cause damage to downstream devices. An OV supervisor can be used to detect these transients and shut off a MOS device or load switch to disconnect downstream devices, protecting them from damage. The linked online calculator below can be used to calculate the sense input resistors or refer to section 10.1 in the data sheet linked below for more information. Pullup resistors RP1 and RP2 can be set to a standard value of 10 kΩ.
Device shown: TPS37A010122DSKR adjustable threshold variant
Additional resources: Monitoring 12V automotive battery systems technical article
Monitoring Rails With Known Transients
Adjusting the sense and reset delays on a supervisor allows for known transients to be accounted for by the design. If there are transients on a monitored rail which will cause unwanted behavior in downstream devices, then the sense delay can be set to make sure that reset is not asserted when these transients are encountered. The linked online calculator below can be used to calculate the delay capacitors or refer to sections 8.3.4 and 8.3.5 in the data sheet linked below for more information. Pullup resistors RP1 and RP2 can be set to a standard value of 10 kΩ.
Device shown: TPS37A010122DSKR adjustable threshold variant or TPS38A010122DSKRQ1 adjustable threshold variant
Additional resources: TPS37 data sheet section 8.3.4
Adjustable Hysteresis
For applications which require large hysteresis values, or different values of hysteresis for each channel, the hysteresis of the supervisor can be adjusted using external resistors as shown in the diagram below. Adjustable hysteresis requires an open drain active low output topology for UV channels and an open drain active high output high output topology for OV channels. The linked online calculator below can be used to calculate both RHYS and the sense input resistors. Pullup resistor RP1 can be set to a standard value of 10 kΩ.
Device shown: TPS3760A012DYYR adjustable threshold variant
Additional resources: TPS3760 online design calculator
Power Sequencing
One or more supervisors can be used to enable/disable downstream LDOs or DC/DC converters in a desired order. The sense and reset delays of the supervisor/s can be used to set the timing of the sequence and make sure that successive power rails are not brought up until the previous rail has stabilized. R1 and R2 set the enable voltage of the sequence. C1 and C2 set the power down sequence. C3 and C4 set the power up sequence. The linked online calculator below can be used to calculate the delay capacitors or refer to sections 8.3.4 and 8.3.5 in the data sheet linked below for more information. Pullup resistors RP1 and RP2 can be set to a standard value of 10 kΩ.
Device shown: TPS38A010122DSKRQ1 adjustable threshold variant
Additional resources: TPS38 data sheet section 8.3.4
PWM Duty Cycle Monitoring
The duty cycle of a PWM signal is monitored using the sense pins of a window supervisor along with the sense and reset delays. When the duty cycle of the PWM signal is above threshold, a pulsing output is observed on the OV reset output. When the duty cycle of the PWM signal is below threshold, a pulsing output is observed on the UV reset output. Capacitors C1-C4 set the pulse width. The linked online calculator below can be used to calculate the delay capacitors or refer to sections 8.3.4 and 8.3.5 in the data sheet linked below for more information. Pullup resistors RP1 and RP2 can be set to a standard value of 10 kΩ.
Device shown: TPS37A010122DSKR adjustable threshold variant
Additional resources: TPS37 data sheet section 8.3.4
Tri-state Pin Decoding
In this application, the voltage sensing pins on a supervisor are used alongside a resistor divider to decode a tri-state sensor input into a 2-bit binary value which can be read using standard digital I/O pins. The SENSE pins on TPS38 are 65 V tolerant, ensuring robustness to transients introduced by a sensor connector. Pullup resistors RP1 and RP2 can be set to a standard value of 10 kΩ.
Device shown: TPS38J010155DSKRQ1 adjustable threshold variant
Negative Voltage Monitoring
With the addition of an external reference and resistor divider, a wide VIN supervisor can be modified to monitor negative voltage rails. The resistor divider values for a specific threshold voltage can be calculated using the equation 0.8V = (R1*Vref + R2*Vth) / (R1+R2) More detailed instructions and calculations can be found at the link below. Pullup resistor RP1 can be set to a standard value of 10 kΩ.
Device shown: TPS3760A012DYYR adjustable threshold variant
Additional resources: Voltage Supervisor and Reset ICs: Tips, Tricks and Basics E-book