Multi-Phase MPQ2908A with Thermal Balancing

12V Output DC/DC Converter for 48V Batteries

REFERENCE DESIGN

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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 (V_IN) range	24V_DC to 60V_DC
Output voltage (V_OUT)	12V_DC
Maximum output current (I_OUT)	20A (with 12V output)
Switching frequency (f_SW)	225kHz
Board form factor	150mmx100mm
Peak efficiency	95.83% (13A load, 48V input)
12V output ripple	22mV_PP

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, V_BREAK = 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, I_D = 123A, V_DSBREAK = 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, I_D = 60A, V_DSBREAK = 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