MPQ3910A Reference Design - High Voltage Boost for APD in LiDAR applications

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1. Overview

1.1 Description

The autonomous vehicle has been a hot topic for a while, but now it is staring to become a reality. To enable high degrees of autonomy, vehicles are using combined methods of surroundings detection, like cameras, RADAR and LiDAR.

LiDAR is a ranging device that works similar to a RADAR; but uses light waves instead of RF waves. A laser diode emits light pulses, and an advanced photodiode (APD) senses the reflection to determine the time of flight and thus the distance to the reflecting object.

A design challenge that presents when working with LiDAR systems is providing a high voltage power supply to bias the APD sensor, as these kinds of photodiodes can need up to 300V depending on their size. The power supply must be cost effective and pass the EMC regulations in the automotive industry.

This reference design uses the MPQ3910A to control a boost converter working in DCM. This allows the use of cheap small sized components and to overcome the limitations due to very high duty cycle. The boosted voltage is effectively doubled through a charge pump to achieve >350V output capability while still using lower voltage rating semiconductors, which are smaller, cheaper and have better performance than their high voltage counterparts.

1.2 Features

  • AEC-Q100 Qualified
  • CISPR-25 Class 5 Compliant
  • Wide 5V to 35V operating input range
  • Single N-Channel MOSFET gate driver with 12V 1A capability
  • Programmable frequency range: 30kHz - 400kHz
  • External sync clock range: 80kHz - 400kHz
  • Programmable soft start (SS)
  • Over-current protection (OCP)
  • Output over-voltage protection (OVP)
  • Short-circuit protection (SCP)
  • Internal LDO with external power supply option
  • Pulse-skipping operation at light load
  • Available in MSOP-10 Package


figure 1 eval board

Figure 1: Evaluation Board

1.3 Applications

Automotive LiDAR APD power supply

2 Reference Design

2.1 Simplified Schematic

Boost converter with 12V nominal input, 300V 15mA output capability, EMI filter and polarity protection.

block diagram

Figure 2: Block Diagram

2.2 Related Solutions

This reference design is based on the following MPS solutions:

MPS Integrated Circuit Description
MPQ3910A 5V-35V Input, Peak Current Mode, Asynchronous Boost Controller. AEC-Q100 Qualified


2.3 System Specifications

Parameter Specification
Input voltage range 3VDC to 35VDC
Output voltage 300VDC
Maximum output current 15mA
Switching frequency 375kHz
Board form factor 89mmx63mmx5mm
Peak Effciiency 83%
300V output ripple 200mVp-p

3 Design

3.1 Schematics

3

Figure 3: Schematics

3.2 BOM

Designator Qty Value Package Manufacturer Part Number
C1, C3, C16 3 0.1µF 250V 0805 TDK CGA4J3X7T2E104K125AE
C2, C4 2 0.47µF 250V 1812 Murata GCJ43DR72E474KXJ1L
C5 1 15nF 50V 0603 Murata GCM188R72A153KA37D
C6, C8, C9 3 4.7µF 50V 0805 TDK CGA4J3X5R1H475M125AB
C7 1 47µF 50V 6x6 Panasonic EEE-FT1H470AP
C10 1 0.47µF 450V 1812 TDK C4532X7T2W474M230KE
C11 1 1µF 50V 0805 Murata GCM21BR71H105KA03L
C12 1 4.7µF 25V 0805 TDK CGA4J1X7R1E475K125AC
C13 1 0.47µF 16V 0603 Murata GCM188R71C474KA55D
C15 1 6.8nF 16V 0603 Murata GCM188R72A682KA37D
D1, D2, D3 3 BAS21 SOD-323 Rohm BAS21VMFHTE-17
D4 1 NRVTS245ESFT3G SOD-123 ON Semiconductor NRVTS245ESFT3G
D5 1 SMBJ30CA-E3/52 SMB Comchip ATV06B240JB-HF
D6 1 PMEG6010CEJ SOD-323 Nexperia PMEG6010CEJ,115
L1 1 12µH 1.75A 6235 Coilcraft LPS6235-123MRB
L2 1 4.7µH 0.6A 0805 Murata LQM21PZ4R7NGRD
L3, L4 2 1µH 1.3A 0805 Murata LQM21PZ1R0NGRD
Q1 1 SQJ454EP SO-8FL Vishay SQJ454EP-T1_GE3
R1, R3, R13 3 0Ω 5% 0603 Vishay Dale CRCW06030000Z0EB
R2, R7, R8, R9, R10 5 100kΩ 1% 0603 Vishay CRCW0603100KFKEA
R4 1 6.2kΩ 1% 0603 Panasonic ERJ-3EKF6201V
R5 1 50mΩ 1% 1206 Panasonic ERJ-8CWFR050V
R6 1 7.5kΩ 5% 0603 Vishay CRCW06037K50FKEA
R11 1 82kΩ 1% 0603 Vishay CRCW060382K0FKEA
R12 1 2kΩ 1% 0603 Vishay CRCW06032K00FKEA
U1 1 MPQ3910 MSOP-10 MPS MPQ3910GK-AEC1

3.3 PCB Layout

4

Figure 4:PCB Layer 1

5

Figure 4:PCB Layer 2

6

Figure 4:PCB Layer 3

7

Figure 4:PCB Layer 4

Test Results

4.1 Efficiency and Regulation

8

Figure 8: Efficiency vs. Load Current

9

Figure 9: Line RegulationFigure

9

Figure 10: Load Regulation

4.2 Time Domain Waveforms

VIN = 12V, VOUT = 300V, L = 12µH, FSW = 375kHz, TA = 25ºC

11-12

Figure 11: Steady state - Figure 12: Steady State

13-14

Figure 13: Start-up through VIN - Figure 14: Start-up through VIN

15-16

Figure 15: Shutdown through VIN - Figure 16: Shutdown through VIN

17-18

Figure 17: Start-up through EN - Figure 18: Start-up through EN

19-20

Figure 19: Shutdown through EN - Figure 20: Shutdown through EN

21-22

Figure 21: Single load step - Figure 22: Single load step

23-24

Figure 23: Repetitive load step 5kHz - Figure 24: Repetitive load step 10kHz

25-26

Figure 25: Repetitive load step 20kHz - Figure 26: Repetitive load step 50kHz

4.3 Thermal Measurements

VIN = 12V, VOUT = 300V, L = 12µH, FSW = 375kHz, TA = 25ºC, 2h run time

27

Figure 27: Thermal image

4.4 EMC Measurements

This circuit has a very aggressive square signal in its switch node, with a high dV/dt due to the ~150V voltage swing. The high dV/dt creates strong electric fields which can make noise couple to other circuits and cable harnesses present in the system. To mitigate this, the APD power supply should be placed inside a metallic housing, or near a metallic plate in the car that could act as a shield for the electric fields.

An alternative in case this is not possible, is to place a small metallic shield on the noisy area of the PCB; it should cover the inductor, MOSFET, rectifier and output capacitors. This is the approach that has been taken to test this PCB as a standalone device for this document. The pictures below show the shield that has been used:

Figure 28: PCB with a local shield made of copper.

Figure 28: PCB with a local shield made of coper

Figure 29: Area covered by the shield

Figure 29: Area covered by the shield

The following graphs show the test results from CISPR25 Conducted Emissions and Radiated Emissions tests performed in an ALSE with this board.

VIN = 12V, VOUT = 300V, IOUT = 10mA L = 12µH, FSW = 375kHz, TA = 25ºC, with shield

30

Figure 30: CISPR25 Class 5 Conducted Emissions

31

Figure 31: CISPR25 Class 5 Radiated Emissions

5 Start-Up

    1. Connect the positive and negative terminals of the load to the VOUT and GND pins, respectively. Make sure that the load is suited for voltages of 300V or higher. Be aware that electronic loads represent a negative impedance to the regulator and if set to a too high current will trigger over-current-protection or short-current protection.
    2. Preset the power supply output between 3V and 30V, and then turn off the power supply.
    3. Connect the positive and negative terminals of the power supply output to the VIN and GND pins, respectively. If the input voltage is higher than 13V make sure R13 is removed.
    4. If the input voltage is lower than 5V, remove R1 and connect an auxiliary power supply to VBIAS up to 13V.
    5. Turn the power supply on. The board will automatically start up. The default VOUT is 300V.
    6. The external resistor divider R7-R11 and R12 are used to set the output voltage. For VOUT = 300 V the sum of R7 -R11 must be 482 kΩ and R12 must be 2 kΩ.
    7. $$R_{12}= {R_{11}\over{\frac {V_{out}}{1.237} -1}}$$
    8. In order to increase the output current capabilities, higher power rated parts can be reworked on the board. Make sure that TJ does not exceed 175 ºC on the external discrete semiconductors.

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