ST AN2565 APPLICATION NOTE

AN2565

Application note

PM6680A evaluation kit dual step-down controller with auxiliary voltages

Introduction

PM6680A evaluation kit order code: STEVAL-ISA053V2.

The PM6680A is a dual step-down controller with adjustable output voltages. The PM6680A evaluation kit is designed to test the performance of the PM6680A by employing a typical application circuit that allows testing of all the PM6680A device functions. The kit features two switching sections, with (typically) 3.3 V and 1.8 V outputs, from a 6 V to 36 V input voltage. The typical operating switching frequency of the two switching sections is 200 kHz / 300 kHz, respectively. Each switching section delivers more than 2.5 A of output current. Moreover, an internal linear regulator can provide 5 V @ 100 mA peak current.

Figure 1. PM6680A evaluation kit

April 2008

Rev 2

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www.st.com

Contents	AN2565

Contents

1	Main features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		. 4
2	Evaluation kit schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		5
3	Component list . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		6
4	Evaluation board layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		8
5	I/O interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		10
6	Recommended equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		11
7	Quick start . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		12
8	Jumper settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		13
9	Feedback output connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		15
10	Test setup and performance summary . . . . . . . . . . . . . . . . . . . . . . . . .		16
	10.1	Test setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	16
	10.2	Power-up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	16
	10.3	Soft-start and shutdown waveforms . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	17
	10.4	OUT1 and OUT2 output efficiency vs. load current . . . . . . . . . . . . . . . . .	19
	10.5	Power consumption analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	20
	10.6	Switching frequency vs. load current . . . . . . . . . . . . . . . . . . . . . . . . . . . .	23
	10.7	Linear regulator output voltages vs. output current . . . . . . . . . . . . . . . . .	24
	10.8	Load transient response . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	24
11	Representative waveforms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		26
12	Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		28

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AN2565	List of figures

List of figures

Figure 1. PM6680A evaluation kit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Figure 2. Evaluation kit schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 Figure 3. PM6680A eval board layout - top layer (PGND plane and component side) . . . . . . . . . . . . 8 Figure 4. PM6680A eval board layout - inner layer 1 (SGND layer and VIN plane) . . . . . . . . . . . . . . . 8 Figure 5. PM6680A eval board layout - inner layer 2 (SGND layer and signals). . . . . . . . . . . . . . . . . 9 Figure 6. PM6680A eval board layout - bottom layer (PM6680A and component side) . . . . . . . . . . . 9 Figure 7. Test setup connections. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 Figure 8. Power-up sequence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 Figure 9. Section 1 soft-start waveforms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 Figure 10. Section 2 soft-start waveforms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 Figure 11. Section 1 shutdown waveforms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 Figure 12. Section 2 shutdown waveforms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 Figure 13. OUT1 efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 Figure 14. OUT2 efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 Figure 15. Input current vs. input voltage. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 Figure 16. Input current vs. input voltage. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 Figure 17. Input current vs. input voltage. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 Figure 18. Device current consumption vs. input voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 Figure 19. Device current consumption vs. input voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 Figure 20. OUT1 switching frequency vs. load current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 Figure 21. OUT2 switching frequency vs. load current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 Figure 22. LDO5 output vs. load current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 Figure 23. OUT1 load transient response . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 Figure 24. OUT2 load transient response . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 Figure 25. SMPS pulse skip mode. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 Figure 26. SMPS no-audible skip mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 Figure 27. SMPS PWM mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

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Main features	AN2565

1Main features

●Constant on-time control allows very fast load transients

●6 V to 36 V input voltage range

●5 V auxiliary output voltage

●Adjustable switching outputs

●Lossless current sensing using low side MOSFET RDS(on)

●Negative current limit

●Soft-start internally fixed at 2.8 ms

●Soft-end for output discharge

●200 kHz / 300 kHz, 300 kHz / 400 kHz, 400 kHz / 500 kHz (OUT1 / OUT2 selectable switching frequency)

●Selectable pulse skip and no-audible skip modes at light loads

●Independent power good signals

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AN2565	Evaluation kit schematic

2 Evaluation kit schematic

Figure 2. Evaluation kit schematic

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Component list	AN2565

3 Component list

Table 1.		Component list
Qty	Reference		Description	Value	Package	Part number
3	C1, C2, C3		Ceramic capacitor	10 µF, 50 V	1210	Tayio Yuden - UMK325BJ106KM
1		C4	Ceramic capacitor	10 µF, 50 V	1210
2		C5, C6	Ceramic capacitor	100 nF, 50 V	0805
1		C19	Ceramic capacitor	100 nF, 50 V	0805
1		C7	Tantalum capacitor	N.M.	7343	N.M.
2		C9, C10	Ceramic capacitor	N.M.	0805	N.M.
1		C11	Tantalum capacitor	N.M.	7343	N.M.
1		C8	Tantalum capacitor	220 µF,	7343	Sanyo POSCAP - 6TPE220M
				25 mΩ, 6.3 V
1		C12	Tantalum capacitor	150 µF,	7343	Sanyo POSCAP - 4TPE150MI
				18 mΩ, 4 V
2	C13, C14		Ceramic capacitor	10 nF, 50 V	0603
2	C15, C16		Ceramic capacitor	1.5 nF, 50 V	0603
2	C17, C18		Ceramic capacitor	47 pF, 50 V	0603
1		C20	Ceramic capacitor	1 µF, 10 V	0805
1		C21	Tantalum capacitor	4.7 µF, 16 V	3216
1		C22	Ceramic capacitor	220 nF, 10 V	0805
1		C23	Ceramic capacitor	10 pF, 50 V	0805
1		CIN	Tantalum capacitor	N.M.	D = 10 mm
1		CREF	Ceramic capacitor	100 nF, 50 V	0805
1		C26	Ceramic capacitor	4.7 µF, 50 V	1210	Taiyo-Yuden - UMK325F475ZH
1	C24, C25		Ceramic capacitor	10 µF, 6.3 V	0805
1		C27	Tantalum capacitor	N.M.	0805
1		C28	Tantalum capacitor	N.M.	3216
1		D1	Dual Schottky		SOT23	ST - BAS70
			diode
2		D2, D3	Power Schottky		SMA	STPS1L30M
			rectifier
1		IC1	PM6680A		VFQFPN-32 5x5	ST - PM6680A
1		L1	Power inductor	4.7 µH, 4 A	10 mm x 10 mm	Wurth - TPC 7440650047
1		L2	Power inductor	8.2 µH, 3 A	10 mm x 10 mm	Wurth - TPC 7440650082
4		M1, M2	>40 V N-channel		SO-8	ST - STS5NF60L
			MOSFET

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AN2565						Component list
Table 1.		Component list (continued)
Qty	Reference		Description	Value	Package	Part number
4		M3, M4	> 40 V N-channel		SO-8	ST - STS7NF60L
			MOSFET
1		R3	Resistor 1%	20 kΩ	0805
1		R4	Resistor 1%	47 kΩ	0805
1		R5	Resistor 1%	2.2 kΩ	0805
1		R6	Resistor 1%	1.1 kΩ	0805
2		R7, R8	Resistor 1%	390 Ω	0805
1		R9	Resistor 1%	47 Ω	0805
2	R10, R11		Resistor 1%	10 Ω	0805
4		R12:R15	Resistor 1%	100 kΩ	0805
1		R16	Resistor 1%	43 kΩ	0805
1		R17	Resistor 1%	510 kΩ	0805
2	R18, R19		Resistor 1%	N.M.	0805
4	R20, R21,		Resistor 1%	0Ω	0805
	R22, R23
1		R24	Resistor 1%	1.1 kΩ	0805
1		R25	Resistor 1%	820 Ω	0805
1		R26	Resistor 1%	3.9 Ω	1206
1		R27	Resistor 1%	10 kΩ	0805
1		R29	Resistor 1%	10 kΩ	0805
1		R28	Resistor 1%	27 kΩ	0805
1		R30	Resistor 1%	10 kΩ	0805
1		R31	Resistor 1%	N.M:	0603
1		R32	Resistor 1%	N.M.	0603
1		R33	Resistor 1%	N.M.	0805
1		RLD5V,	Resistor	N.M.	0805
		RLD3V

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Evaluation board layout	AN2565

4 Evaluation board layout

Figure 3. PM6680A eval board layout - top layer (PGND plane and component side)

Figure 4. PM6680A eval board layout - inner layer 1 (SGND layer and VIN plane)

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AN2565		Evaluation board layout
	Figure 5.	PM6680A eval board layout - inner layer 2 (SGND layer and signals)

Figure 6. PM6680A eval board layout - bottom layer (PM6680A and component side)

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