Automotive camera modules

• Compact units directly connected to 12V battery
• Compact units connected to 8V secondarly rail
• Automotive camera modules

There are two possible cases for automotive camera modules: directly connected to 12V battery, or supplied by a primary power supply output of roughly 8V.
Examples of solutions suitable for automotive camera modules, whose miniaturization is continuing to advance, are presented.

Solution Overview

A large number of camera modules are now used in automobiles, with requirements for their power supplies to have even smaller sizes, higher efficiency, lower noise, and lower power consumption.

Primary step-down DC/DC

These generally have a structure where the voltage is decreased to the common voltage at the first stage, and then decreased further at the second stage to the individual required voltages to be supplied. These are referred to as the primary power supply and secondary power supply respectively.
For primary DC/DC, use a switching frequency of 2MHz or greater in consideration for EMI.
If a light load condition will be experienced for a long time, and a decrease in frequency during that time is allowed, select the PWM/PFM automatic switching type. If it is desired to keep the operating frequency constant regardless of the load condition, select the PWM fixed type.

Also, starting from conditions such as cold cranks or idling stops, or elements such as long harnesses, will cause the power supply line voltage to decrease significantly, so the Pch SW type, which supports a duty ratio of 100% and can easily maintain the output voltage even when there is a drop in input voltage, is suitable in such cases.

Step-down DC/DCs, 36V operation(Absolute maximum rating of 40V, and 46V ≦ 400ms)

XDL605: Inductor built-in PWM

XDL606: Inductor built-in PWM/PFM

XD9267: PWM

XD9268: PWM/PFM

Step-down DC/DCs, 18V operation(Absolute maximum rating of 20V)

XDL603: Inductor built-in PWM

XDL604: Inductor built-in PWM/PFM

XD9263: PWM

XD9264: PWM/PFM

Use the PG (Power Good) pin and soft-start time settings of the primary DC/DC for the rise-up sequence. After sufficient rise-up of the primary DC/DC, the CE is driven by the PG pin to perform rise-up of the secondary DC/DC, to prevent malfunctions of the ECU.

Also, in order to suppress spike noise from the primary input or radiation noise from the connected harness, it is common to use surge clamps or EMI filters at the primary DC/DC input. For information on the filter which is compatible with CISPR 25 of XDL605, refer to the noise data at the following link.

※CISPR25_Class5 Noise Data
XDL605-CISPR25_Class5.pdf[2.6MB]

Step-down DC/DC for ISP and CMOS sensor

DC/DCs with compact sizes, high-speed response, and low noise are recommended for each secondary power supply rail.

Step-down DC/DCs

XDL601: Integrated coil type PWM, high-speed transient response, low EMI

XDL602: Integrated coil type PWM/PFM, high-speed transient response, low EMI

XD9260: PWM, High-speed transient response

XD9261: PWM/PFM, High-speed transient response

Although it is common to use a value of 2MHz or greater for the DC/DC switching frequency, since it is not directly connected to the exterior using a harness as with a primary DC/DC, a relatively lower frequency may be used in some cases for greater efficiency. The XD9260 and XD9261 include both 3.0MHz and 1.2MHz types for this reason.

Also, if the rise-up / rise-down sequences for each voltage rail are specified, set them in the CE of each DC/DC with delays which use CR.

RESET IC for input voltage monitoring

Voltage detector with a separated sense (VSEN) pin is used for monitoring the input voltage on the primary side.
Monitoring the input Voltage to helps to ensure stable operation and is useful for power sequencing (when implementing start-up and shut-down sequences).

The VSEN pin uses divider resistors which are connected to the primary side input Voltage supply. The divider circuit allows the Voltage Detector to monitor voltages that exceed the absolute maximum voltage range of the IC. The VIN supply for the Voltage Detector is connected to the output side of the primary DC/DC (5.0V in our example circuit).

Voltage detector

XD6132: sense isolation, HYS (hysteresis) external adjustment, External Cd for release / detect delays, Sense pin surge voltage protection circuit

The operation indicated in the above diagram together with this voltage detector is as shown below.
Example: Case where primary V_IN: 12V directly from battery, V_OUT of primary DC/DC: 5V, Detection voltage of voltage detector: 7V, release voltage: 9V

(a) During application of input voltage, during recovery after cold crank
When the 12V directly from the battery rises up and the primary DC/DC rises up so that the output voltage reaches 5V, PG becomes "H".
This causes the secondary stage CE to go "H" and the secondary DC/DC starts-up and supplies voltage to the ECU.
If the Voltage Detector input voltage exceeds the release voltage of 9V, RESETB becomes "H" and the ISP is notified that the input voltage is normal.

(b) During input Voltage drop or cut-off
If the input voltage falls below the detect voltage of 7V, RESETB becomes "L" and the ISP is notified of the voltage drop.
In response to this signal, the ISP can decide to safely stop operation before the DC/DC output voltage drops or it may need to execute back-up procedures to save important data before the power fails.

Benefits can be provided here by HYS (hysteresis) external adjustment and detect delay times.

• HYS(hysteresis)external adjustment
  In the example, the detection/release voltage = 7V / 9V, but generally voltage detectors have a release voltage fixed at a level of roughly +5% of the detection voltage, so it is not possible to designate detection / release voltages which have consideration for cold cranks in this way.Voltage detectors with HYS (hysteresis) external adjustment function makes it possible to set any desired detection voltage and release voltage using an external resistor, which is essential for applications with direct connections to batteries due to their severe fluctuations.
• Setting of detection delay time
  If the voltage drop is only for a very short duration it can be desirable not to stop the ISP, so to avoid false resets a Voltage Detector with the detect delay function is used.

RESET IC with watchdog function, for monitoring ISP power supply voltage and operation

One RESET IC with the watchdog function can monitor both the ISP power supply voltage and normal operation.

Voltage detectors with watchdog function

XD6130: Voltage detector with watchdog function, watchdog timeout time using one external capacitor, with manual reset function

XD6131: Voltage detector with watchdog function, watchdog timeout time using one external capacitor, with watchdog ON/OFF function

The voltage monitoring function signals when the secondary DC/DC output voltage has risen up sufficiently, begins operation of the ISP, and also signals when the voltage drops to prevent malfunction of the ISP.
After ISP start-up, if a pulse from the ISP reaches the WD pin at regular interval, the operation is judged to be normal. If that signal is not received, the ISP is judged to be out of control, and it is restarted by applying a RESET signal.

As we have seen, small, compact DC/DCs and Voltage Detectors can be used to a configure a simple power supply, optimised for safe, efficient operation.Conventionally, LDOs have been used to prevent noise, but due to an increase in the quiescent current of ISP and CMOS sensor, and issues of heat associated with their miniaturization, high-performance DC/DCs are becoming required.
Furthermore, by controlling with a voltage detector with special functions as described above, it is possible to realize more suitable control for the safe and accurate operation required for Automotive equipments.

• Compact units directly connected to 12V battery
• Compact units connected to 8V secondarly rail
• Automotive camera modules