Figure 5. Block diagram of a typical circuit and its function.

Figure 6. VBATT valid and protected window from damage.

Spare battery

Battery backup is possible via the LTC4079, which has a multi-chemical charger that allows flexible battery voltage to be used. The reference design circuit uses a charging voltage of about 4.2 V. To avoid recharging the battery, the LTC4079 also has the option of stopping charging with a C / 10 detector or a set charging timer of about 2 hours and 30 minutes .

Automatic switching between VBATT and VBACKUP is possible via the LTC4412 PowerPath controller. This feature allows the LT8603 to support the output voltage of VOUT4, having a VIN drawing from VBATT or VBACKUP. In the event of a disconnection of the VBATT or error detection, the controller allows current to flow from the VBACKUP to the VIN of the LT8603. When no error is detected, the LTC4412 will block the path connecting the VBACKUP to the VIN of the LT8603. Figure 7 shows the waveform of the power switching event.

384948-fig-07 (1)

Figure 7. Cold crank power switch event.

In the case of a cold crank, VBATT decreases from 12 V to 2 V. VBATT the road is interrupted, and VRESERVE now serves as VIN of the amplifier converter to maintain the 8 V output of the VOUT4. When VBATT increases to ~ 5 V, it will again serve as VIN for the amplifier converter. VOUT4 will continue to be maintained at 8 V to VBATT reaches 8 V. As VBATT is restored to its initial voltage of 12 V, VOUT4 then the voltage of V will followBATT. Small voltage drop of VOUT4 due to the voltage of the diode. Switching the power supply allows VOUT1INOUT2and BOUT3 to maintain its regulation.

Quadruple output regulator

LT8603 has a gain regulator, VOUT4with two high voltage stabilizers, VOUT1 and BOUT2and low voltage regulator, VOUT3. The boost regulator is able to provide power to the booster regulators. LT8603 provides good regulation of input and output loads at different input voltage levels. Figure 8 shows the output regulation of the LT8603.

384948-fig-08 (1)

Figure 8. LT8603 output adjustment.

The possibility of high output peak current at one of the outputs of the step-down regulator, VOUT2, the LT8603 is used for applications that include a communication module. A typical output voltage of 3.6 V to 4 V and an output peak current of 0.6 ms for a period of 4.6 ms are required for a communication module. Under the tested conditions shown in Figure 9, the transient behavior of the system is observed. VOUT2 is characterized by good transient characteristics with minimal voltage reduction and overshoot.

384948-fig-09 (1)

Figure 9. High output peak current of VOUT2.

Charging Disposal Response

Input protection protection and the reference design power switching function allow the LT8603 to operate even though it is in a load drop event. Figure 10 shows a simulated waveform of a load ejection state, where VBATT reaches 100 V and the gain response, VOUT4and one of the downsizing regulators, VOUT3. During overrun due to load shedding, 36 VVBATT the limit is reached and LTC4367 terminates the connection connecting VBATT to BIN. VOUT4 now its sources VIN by BRESERVE to maintain the regulated level of 8 V. As BBATT restores to its original level, VOUT4 then V will followBATT

384948-figure 10 (1)

Figure 10. Load ejection response.

Variations and realizations of the chain

The flexibility of the schematic design allows variations in the way the scheme can be applied. The reference design board has “Do not install” components and path connectors that allow the user to configure the board with topology 1 or topology 2. This also allows the configuration of an amplifier or SEPIC converter of VOUT4 depending on the application. On the LTC4367, an additional circuit option can be implemented for additional protection against input damage for 150 V transient conditions. More details about the configuration are shown in the circuit board diagram for reference design.

The circuit configuration shown in Figure 5 is topology 1 having a minimum of VRESERVE voltage 2.5 V, one EMI filter after VIN, and it is possible to switch the power supply via LTC4412HV. ININ the amplifier controller receives its power supply from VBATT or inRESERVE. During the BBATT valid window, VOUT4 maintains a regulated voltage level via the amplifier converter or follows VBATT as shown in Figure 6. Outside VBATT valid window, VOUT4 sources from BRESERVE in order to maintain a regulated set level.

Topology 2 addresses the need for a lower VRESERVE voltage application, such as 1.5 V. When there is no input error, VBATT is directly related to VOUT4 while BRESERVE is VIN to the amplifier controller. Additional filters at the input of the step-down regulators are needed for better noise filtering and EMI performance. Power switching is achieved without problems when VBATT falls below or exceeds its valid window. The minimum VBATT the voltage level of the valid window is set to the regulated V levelOUT4. During the BBATT valid window, VOUT4 follows BBATT. Outside VBATT valid window, VRESERVE is used to maintain a regulated set level.

384948-fig.11 (1)

Figure 11. Variations of the circuit.

Table 1. Comparison between topology 1 and 2
Topology 1 Topology 2
Used ICs LT8603, LTC4412HV, LTC4367, LTC4079 LT8603, LTC4367, LTC4079
Working with a spare battery VRESERVE works up to 2.5 V VRESERVE works up to 1.5 V
EMI input filtering Connected before the amplifier regulator Connected before the input of the boost and downspout regulator
Minimum VBATT Valid window VBATT can fall as low as VRESERVE level VBATT must be equal to VOUT4 regulated set level


The ever-increasing advancement of automotive applications requires more reliability and safety considerations. Standards set by international organizations have played a significant role for designers who focus on what contributes to voltage transients that can be harmful or cause the electronic system to deteriorate. In conclusion, the reference design with four output powers has proven its ability when exposed to simulated test conditions of overvoltage, undervoltage and reverse voltage operations. In addition, the different circuit variants allow flexibility in terms of backup battery operation, minimum battery voltage level, EMI input filtering and number of components. For more information on the Reference Design Dashboard, contact the authors or your local ADI representative.

ICs and reference design files

Here are the schematics, PCB Gerber files and the material specification (Topology 1) of the quadruple output controller. Contact the authors or your local ADI representative for the scoreboard.


Eddleman, Dan. “Stop at low overvoltage at rest: stable protection of the car power supply in accordance with ISO 7637-2 and ISO 16750-2.” Analog Devices, Inc., January 2017.

Eddleman, Dan. “LTspice: Transition Models ISO 7637-2 and ISO 16750-2.” Analog Devices, Inc.

ISO 16750-2: 2012: Road vehicles – Environmental conditions and testing of electrical and electronic equipment – Part 2: Electrical loads. International Organization for Standardization, November 2012

Wu, Bin and Zhongming Ye. “Comprehensive designs for heavy-duty automotive power systems consume minimal space, conserve battery power, and have low EMI.” Analog Dialogue, no. 53, issue 3, August 2019

Quad Output Power Reference Design with Input Fault Protection for Automotive Applications

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