Multi-Phase MPQ2908A with Thermal Balancing

12V Output DC/DC Converter for 48V Batteries


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1 Overview

1.1 Description

New automotive designs are adopting 48V power systems to reduce the weight and power loss in the vehicle’s cable harnesses. Moreover, when the system must withstand high loads, the required power increases, which means it is vital to use power converter topologies with higher deliverable power, such as an interleaved topology. When using this topology, it is usually required to optimize thermal distribution to equalize the MOSFETs’ degradation and avoid overheating parts of the board. An excellent layout can help with these thermal constraints, as well as promoting good current sharing between both controllers by equally distributing the load current between all converters. Passing the same current through both phases, as well as creating a symmetrical layout, helps the MOSFETs experience an equal temperature rise, which means they will degrade at a similar speed.

This reference design showcases a 48V to 12V interleaved converter that can supply up to 20A of output load. To improve current sharing between both controllers, a thermal balancing circuit is implemented, and a frequency spread spectrum (FSS) modulator is added to reduce EMC.

1.2 Features

  • Wide 4V to 60V Operating Input Range
  • Dual N-Channel MOSFET Driver Phases
  • 0.8V Reference Voltage with ±1.5% Accuracy for
    Over-Temperature Conditions
  • Low-Dropout Operation: Maximum Duty Cycle at 99.5%
  • 100kHz to 1000kHz Configurable Frequency
  • 180° Out-of-Phase SYNCO Pin
  • Configurable Soft Start (SS)
  • Power Good (PG) Output Voltage (VOUT) Monitoring
  • Selectable Cycle-by-Cycle Current Limit
  • Output Over-Voltage Protection (OVP)
  • Over-Current Protection (OCP)
  • External Reverse-Polarity Protection (RPP)
  • External Input OVP
  • Forced Continuous Conduction Mode (CCM)
  • External Frequency Spread Spectrum (FSS) Modulation
  • Enable Phase Thermal Balancing
  • Available in TSSOP20-EP and QFN-20 (3mmx4mm) Packages
  • Available in a Wettable Flank Package
  • Available in AEC-Q100 Grade 1

Figure 1: EVQ2908A_48V_L_02A

1.3 Applications

  • Automotive and Industrial Power Systems

2 Reference Design

2.1 Block Diagram

Figure 2 shows the reference design block diagram. The MPQ2908A is a buck converter with 48V nominal input, 12V/20A output capability, input EMI filter, reverse-polarity protection (RPP), over-voltage protection (OVP), two-phase interleaving, frequency spread spectrum (FSS) modulation, and phase thermal balancing.

Figure 2: Block Diagram

2.2 Related Solutions

This reference design is based on the following MPS solution(s):

Table 1: MPS Solutions

MPS Integrated Circuit Description
MPQ2908A 4V to 60V input, current mode, synchronous step-down controller, AEC-Q100 qualified

2.3 System Specifications

Table 2: System specifications

Parameter Specification
Input voltage (VIN) range 24VDC to 60VDC
Output voltage (VOUT) 12VDC
Maximum output current (IOUT) 20A (with 12V output)
Switching frequency (fSW) 225kHz
Board form factor 150mmx100mm
Peak efficiency 95.83% (13A load, 48V input)
12V output ripple 22mVPP

2.4 Schematic

Figure 3: Schematic (Page 1)

Figure 4: Schematic (Page 2)

Figure 5: Schematic (Page 3)

Figure 6: Schematic (Page 4)

2.5 BOM

Table 3: Bill of Materials

Qty Ref Value Description Package Manufacturer Manufacturer PN
3 C1, C33, C51 1µF, 100V 10%, X7S, MLCC 0805 Murata GCM21BC72A105KE36L
1 C2 22nF, 100V 5%, X7R, MLCC 1206 Kemet C1206C223J1RACTU
3 C3, C17, C18 2.2µF, 100V 10%, X7S, MLCC 1206 Murata GCM31CC72A225KE02L
6 C4, C5, C14, C25, C34, C52 100nF, 100V 10%, X7R, MLCC 0603 Murata GCJ188R72A104KA01D
4 C10, C11, C21, C22 10µF, 100V 10%, X7S, MLCC 2210 TDK CGA9N3X7S2A106K230KE
2 C15, C16 47µF, 80V Aluminium electrolytic capacitor 10mm x 10mm Panasonic EEE-FN1K470UV
2 C19, C20 4.7µF, 100V 10%, X7S, MLCC 1210 Murata GCM32DC72A475KE02L
1 C26 1µF, 16V 10%, X7R, MLCC 0603 Murata GCM188R71C105KA64J
1 C27 6.8nF, 16V 10%, X7R, MLCC 0603 Vishay Vitramon VJ0603Y682KXJCW1BC
2 C28, C29 100nF, 25V 10%, X7R, MLCC 0603 Kemet C0603C104K3RAC7013
1 C31 47µF, 6.3V 20%, X5R, MLCC 0603 Taiyo Yuden JMK107BBJ476MA-RE
2 C35, C53 220nF, 16V 10%, X7R, MLCC 0603 Kemet C0603X224K4RACTU
4 C36, C38, C54, C56 4.7µF, 16V 10%, X5R, MLCC 0603 TDK C1608X5R1C475K080AC
4 C37, C44, C45, C46 22µF 25V 10%, X5R, MLCC 1210 Kemet C1210C226K3PACTU
2 C42, C58 10nF, 16V 5%, X7R, MLCC 0603 Kemet C0603C103J4RACTU
1 C43 4.7nF, 16V 10%, X7R, MLCC 0603 Kemet C0603C472K4RACTU
2 C47, C48 100µF, 25V Aluminium electrolytic capacitors 10mm x 10mm Panasonic EEE-FN1E101UV
6 D1, D3, D4, D5, D7, D9 200V, 0.25A General-purpose diode, VBREAK = 200V SOD-323 Nexperia BAS321,115
1 D2 10V, 5mA Zener diode SOD-523 On Semiconductor SZMM5Z10VT5G
1 D6 65V, 50nA Zener diode SOT-23 On Semiconductor SZBZX84C62LT1G
2 D8, D10 150V, 1A Schottky rectifier diode SOD-123FL Rohm RB168MM150TFTR
4 J1, J2, J3, J4 M3, 50A M3 through-hole terminal 7mm x 7mm Wurth 74650073R
2 L2, L3 2.2µH, 8A Fixed inductor 7030 Eaton Bussmann HCMA0703-2R2-R
2 L6, L7 6.8µH, 11.6A Fixed inductor 13mm x 12.5mm TDK SPM12565VT-6R8M-D
2 Q1, Q2 80V N-channel MOSFET, ID = 123A, VDSBREAK = 80V SOIC-8 On Semiconductor NVMFS6H818NT1G
1 Q3 NPN NPN BJT SOT-23-3 Nexperia BC846215
4 Q4, Q5, Q6, Q7 80V N-channel MOSFET, ID = 60A, VDSBREAK = 80V SO-8L Vishay Siliconix SQJA82EP-T1_GE3
8 R1, R6, R12, R13, R15, R16, R21, R26 1kΩ, 5% Thick film resistor 0603 Yageo RC0603JR-131KL
1 R2 1mΩ, 2% Current-sense resistor 1530 Ohmite FC4L76R001GER
1 R3 5.1kΩ, 1% Thick film resistor 0603 Yageo RC0603FR-075K1L
4 R4, R39, R43, R61 100kΩ, 5% Thick film resistor 0603 Vishay CRCW0603100KFKEBC
2 R5, R7 20kΩ, 1% Thick film resistor 0603 Yageo RC0603FR-1320KL
1 R19 1MΩ, 1% Thick film resistor 0603 Yageo RC0603FR-071ML
2 R20, R35 10kΩ, 1% Thick film resistor 0603 Rohm ESR03EZPF1002
1 R28 11kΩ, 5% Thick film resistor 0603 Panasonic ERJ-3GEYJ113V
2 R29, R30 10kΩ, 0.5% NTC thermistor 0603 TDK NTCG163JX103DTDS
1 R31 510kΩ, 1% Thick film resistor 0603 Yageo AC0603FR-07510KL
19 R32, R36, R38, R40, R44, R46, R48, R49, R50, R52, R56, R58, R62, R63, R65, R67, R68, R74, R77 0Ω Thick film resistor 0603 Vishay Dale CRCW06030000Z0EAHP
1 R34 33kΩ, 1% Thick film resistor 0603 Yageo RC0603FR-0733KL
1 R41 5.6kΩ, 5% Thick film resistor 0603 Vishay Dale CRCW06035K60JNEB
2 R42, R60 4mΩ, 1% Current-sense resistor 2512 Susumu KRL6432E-C-R004-F-T1
2 R47, R66 88.7kΩ, 1% Thick film resistor 0603 Panasonic ERJ-3EKF8872V
1 R51 10Ω, 5% Thick film resistor 0603 Yageo RC0603JR-0710RL
1 R53 169kΩ, 1% Thick film resistor 0603 Panasonic ERJ-3EKF1693V
1 R54 12kΩ, 1% Thick film resistor 0603 Panasonic ERJ-1GNF1202C
1 R57 8.66kΩ, 1% Thick film resistor 0603 Panasonic ERJ-3EKF8661V
1 U2 2V to 50V 555 timer SOIC-8 TI TLC555QDRQ1
1 U3 150kHz, 130dB Rail-to-rail operational amplifier TSOT-23 Analog Devices LTC2054IS5#TRMPBF
2 U4, U5 MPQ2908A Buck switching power converter QFN-20 (3mm x 4mm) MPS MPQ2908AGLE-AEC1

2.6 PCB Layout

Figure 7: Top Layer

Figure 8: Mid-Layer 1

Figure 9: Mid-Layer 2

Figure 10: Mid-Layer 3

Figure 11: Mid-Layer 4

Figure 12: Bottom Layer