TPS38 datasheet(29/53 Pages) TI

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9.3.1.1 Design Requirements

This design requires voltage supervision on a 12-V power supply voltage rail with possibility of the 12-V rail rising

up as high as 42 V. The undervoltage fault occurs when the power supply voltage drops below 7.7 V.

PARAMETER

DESIGN REQUIREMENT

DESIGN RESULT

Power Rail Voltage Supervision

Monitor 12 V power supply for undervoltage

condition, trigger a undervoltage fault at 7.7 V.

TPS38-Q1 provides voltage monitoring with

1.5% max accuracy with adjustable/non-adjustable

variations.

Maximum Input Power

Operate with power supply input up to 42 V.

The TPS38-Q1 can support a VDD of up to 65 V.

Output logic voltage

Open-Drain Output Topology

An open-drain output is recommended to provide

the correct reset signal, but a push-pull can also be

used.

Maximum system current

consumption

2 µA max when power supply is at 12 V typical

TPS38-Q1 allows for IQ to remain low with support

of up to 65 V. This allows for no external resistor

divider to be required.

Voltage Monitor Accuracy

Maximum voltage monitor accuracy of 1.5%.

The TPS38-Q1 has 1.5% maximum voltage

monitor accuracy.

Delay when returning from fault

condition

RESET delay of at least 420 ms when returning

from a undervoltage fault.

CCTR = 0.33 µF sets 422 ms delay

9.3.1.2 Detailed Design Procedure

The primary advantage of this application is being able to directly monitor a voltage on an automotive battery

without needing external resistor dividers on the SENSEx inputs. This keeps the overall IQ of the design low

while still achieving the desired rail monitoring.

As shown in Figure 9-4, rail monitoring is done by connecting SENSE1 and SENSE2 inputs directly to the

battery rail after the TVS protection diodes. The TPS38-Q1 that is being used in this example is a fixed voltage

variant where SENSE1 and SENSE 2 threshold voltages have been set internally by the factory. Word of

caution, the TVS protection diodes must be chosen such that the transient voltages on the monitored rails do not

exceed the absolute max limit listed in Section 7.1.

To use this configuration, the specific voltage threshold variation of the device must be chosen according to the

application. In this configuration, the '77' variation must be chosen for 7.7 V as shown in Table 12-1.

The device being able to handle 65 V on VDD means the monitored voltage rail can go as high as 42 V for the

application transients and not violate the recommended maximum for the supervisor as it usually would. This

is useful when monitoring a voltage rail that has a wide range that may go much higher than the nominal rail

voltage such as in this case. Good design practice recommends using a 0.1 µF capacitor on the VDD pin and

this capacitance may need to increase if using an adjustable version with a resistor divider.

www.ti.com

TPS38-Q1

SNVSBI8C – AUGUST 2020 – REVISED DECEMBER 2021

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