Modern cars are equipped with sensors throughout the body of a vehicle. Sensors offer a variety of purposes such as measuring temperature, determining rotor position in motors, and detecting pressure.

Depending on the parameter being sensed, the sensor location can be in remote areas, away from the control module. Such ‘off-board’ sensors are often powered via wire harness and find applications in sectors like powertrain, body/zonal control modules, traction inverters and passive safety.

The harsh nature of the automotive environment places the wire harness at a high risk of exposure to various fault conditions. These fault conditions could result in short-to-ground or short-to-battery situations on the power supply line. It is critical therefore for the power supply IC’s to have integrated protection features against such fault conditions, and possibly to be able to also detect them quickly.

Tracking LDOs are ideal for powering ratio metric sensors and off board loads, because they come with a range of integrated protection features and a tight tracking tolerance of ±5-6mV. This tight tolerance ensures that the error between the ADC full scale reference and the sensor supply is minimal for achieving high-quality data acquisition.

TI Tracking LDOs have integrated protection features against fault conditions such as short-to-battery, short-to-ground, reverse polarity, reverse current and over temperature which reduce the risk of system failures and alleviate system complexity. For example, the integrated reverse current protection feature eliminates the use of an external diode, thus reducing the number of components in the design. This is depicted in Figure 1.

The tracking LDO can also act as a protective buffer while providing power supply as shown in Figure 2.

TI offers a wide range of products in this family. Table 1 depicts the latest Tracking LDOs.

Enable/Adj and Feedback

Tracking LDOs featuring a feedback pin generate an output voltage larger than the reference voltage at ADJ/EN pin. This can be achieved by simply connecting a resistor divider at the FB pin and V_OUT is calculated by Equation 2. This implementation is illustrated in Figure 5 taking an example of TPS7B4258-Q1.

Independent Enable and Power Good

TPS7B4259-Q1 and TPS7B4261-Q1 offer an independent enable and power good feature. Having a PG pin helps to detect both undervoltage and overvoltage fault conditions at the tracking LDO output.

Typically, at the end of the device start up or because of variations in line/load, the output voltage could overshoot or undershoot from the nominal value and the PG pin helps inform when the output voltage has stabilized to its nominal value. A logic high on the PG pin signifies that the tracking LDO output is within the accepted range. Therefore, apart from fault detection, the PG signal can also help in signal sequencing, by informing the MCU when the power supply to the sensor is stabilized, so the sampling of the sensor output may begin. An implementation of using the PG functionality for output voltage monitoring is shown in Figure 6.

Table 2 lists the part numbers for the latest TI tracking LDOs. TI offers these devices in different output current ratings – 70mA, 150mA, 300mA and various packages. The higher current Tracking LDOs are often used to power up multiple off board sensors having a common sensor voltage. The different packages allow for greater flexibility in the device selection for thermally sensitive applications.

Learn more

• Watch the Application of tracking LDOs and implementation in systems
• Automotive off-board sensor power considerations
• Fundamentals of designing with LDOs in automotive battery direct connect applications
• Various Applications of Voltage Tracking LDOs

Evaluate the Design:

• TPS7B4255-Q1: TPS7B4255EVM-062
• TPS7B4256/58/60-Q1: TRKRLDOEVM-119
• TPS7B4259/61-Q1: TPS7B4261EVM-151
• Leverage existing simulation models available in PSpice for TI

For additional assistance, ask questions to TI engineers on the TI E2E™ Power Management Support Forum.