ST AN2829 Application note

AN2829

Application note

Dual step-down controller with auxilary voltages for notebook system power

Introduction

The PM6681A is a dual step-down controller with adjustable output voltages that can be used in notebook power systems. This demonstration board represents a typical application circuit. The PM6681A demonstration board allows testing of all functions of the device and provides two switching sections, with (typ.) 1.5 V (OUT1) and 1.05 V (OUT2) outputs from 5.5 V to 28 V input battery voltage. The typical operating switching frequency of the two sections is 200 kHz/300 kHz, respectively. Each switching section delivers more than 5 A of output current. An internal linear regulator provides a fixed 5 V output voltage. Another internal linear regulator provides an adjustable output voltage (default 3.3 V). Both linear regulators can deliver up to 100 mA peak current.

Figure 1. PM6681A demonstration board

AM01407v1

February 2009

Rev 1

1/32

www.st.com

Contents	AN2829

Contents

1	Main features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		. 4
2	Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		5
3	Demonstration board schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		6
4	Component list . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		7
5	Demonstration board layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		10
6	I/O interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		12
7	Recommended equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		13
8	Quick start . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		14
9	Jumper settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		15
10	Feedback output connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		17
11	Test setup and performance summary . . . . . . . . . . . . . . . . . . . . . . . . .		18
	11.1	Test setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	18
	11.2	Power-up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	18
	11.3	Soft-start and shutdown waveforms . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	19
	11.4	1.5 V and 1.05 output efficiency vs. load current . . . . . . . . . . . . . . . . . . .	21
	11.5	Power consumption analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	22
	11.6	Switching frequency vs. load current . . . . . . . . . . . . . . . . . . . . . . . . . . . .	25
	11.7	Linear regulator output voltages vs. output current . . . . . . . . . . . . . . . . .	26
	11.8	Load transient response . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	27
12	Representative waveforms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		29
13	Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		31

2/32

AN2829	List of figures

List of figures

Figure 1. PM6681A demonstration board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Figure 2. Demonstration board schematic diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Figure 3. PM6681A demonstration board layout - top layer (PGND plane and component side) . . . 10 Figure 4. PM6681A demonstration board layout - inner layer 1 (SGND layer and VIN plane) . . . . . 10 Figure 5. PM6681A demonstration board layout - inner layer 2 (SGND layer and signals). . . . . . . . 11 Figure 6. PM6681A demonstration board layout - bottom layer (PM6681A and component side) . . 11 Figure 7. Setup connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 Figure 8. REF, LDO5 and LDO power-up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 Figure 9. Section 1 soft-start waveforms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 Figure 10. Section 2 soft-start waveforms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 Figure 11. Section 1 shutdown waveforms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 Figure 12. Section 2 shutdown waveforms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 Figure 13. 1.5 V SMPS efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 Figure 14. 1.05 V SMPS efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 Figure 15. Input current vs. input voltage. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 Figure 16. Input current vs. input voltage. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 Figure 17. Input current vs. input voltage. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 Figure 18. Device current consumption vs. input voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 Figure 19. Device current consumption vs. input voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 Figure 20. 1.5 V output switching frequency vs. load current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 Figure 21. 1.05 V output switching frequency vs. load current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 Figure 22. LDO5 output vs. load current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 Figure 23. ADJ_LDO load regulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 Figure 24. SMPS 1.5 V load transient response . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 Figure 25. SMPS 1.05 V load transient response . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 Figure 26. SMPS pulse skip mode. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 Figure 27. SMPS no-audible skip mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 Figure 28. SMPS PWM mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

3/32

Main features	AN2829

1Main features

●5.5 V to 36 V input voltage range

●Adjustable output voltages

●0.9-3.3 V adjustable LDO delivers 100 mA peak current

●5 V LDO delivers 100 mA peak current

●1.237 V ±1% reference voltage available

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

●Negative current limit

●Soft-start internally fixed at 2 ms

●Soft output discharge

●Latched UVP

●Non-latched OVP

●Selectable pulse skipping at light loads

●Selectable minimum frequency (33 kHz) in pulse skip mode

●4 mW maximum quiescent power

●Independent Power Good signals

●Output voltage ripple compensation.

4/32

AN2829	Applications

2Applications

●Notebook, tablet and slate computers

●Mobile system power supplies

●3-4 cell Li+ battery-powered devices

5/32

Demonstration board schematic	AN2829

3 Demonstration board schematic

Figure 2. Demonstration board schematic diagram

AM01408v1

6/32

AN2829	Component list

4 Component list

Table 1.		Bill of materials
Qty	Component		Description	Package	Part number	MFR	Value
3		C1:C3	Ceramic	1812	UMK325BJ106KM-T	Taiyo-Yuden	10 µF - 50 V
			capacitor
1		C4	Ceramic	1812	NM		10 µF - 50
			capacitor
2		C5, C6	Ceramic	0805			100 nF - 50 V
			capacitor
1		C19	Ceramic	0805			100 nF - 50 V
			capacitor
1		C7	POSCAP	7343	NM	Sanyo
			capacitor
2		C9, C10	Ceramic	0805	NM
			capacitor
1		C11	POSCAP	7343	NM	Sanyo
			capacitor
1		C8	POSCAP	7343	6TPB330M	Sanyo	330 µF -
			capacitor				12 mR - 6 V
1		C12	POSCAP	7343	6TPB330M	Sanyo	330 µF -
			capacitor				12 mR - 6 V
2		C13, C14	Ceramic	0603			5.6 nF - 50 V
			capacitor
2		C15, C16	Ceramic	0603			1 nF - 50 V
			capacitor
2		C17, C18	Ceramic	0603			47 pF - 50 V
			capacitor
1		C20	Ceramic	0805			1 µF - 10 V
			capacitor
1		C21	Tantalum	3216			4.7 µF - 16 V
			capacitor
1		C22	Ceramic	0805			220 nF - 10 V
			capacitor
1		C23	Ceramic	0805			10 pF
			capacitor
1		CIN	Electrolytic	D=10 mm	NM
			capacitor
1		CREF	Ceramic	0805			100 nF - 50 V
			capacitor
1		C26	Tantalum	6032			4.7 µF - 35 V
			capacitor

7/32

Component list							AN2829
Table 1.		Bill of materials (continued)
Qty	Component		Description	Package	Part number	MFR	Value
1		C24, C25	Tantalum	0805			10 µF - 6.3 V
			capacitor
1		C27	Tantalum	0805			10 µF - 6.3 V
			capacitor
1		C28	Tantalum	3216			4.7 µF - 16 V
			capacitor
1		D1	Dual schottky	SOT23	BAT54A	STMicroelectronics
			diode
2		D2, D3	Diode 1 A -	DO216AA	STPS1L30M	STMicroelectronics
			30 V
1		IC1	PM6681A	QFN-32	PM6681A	STMicroelectronics
			device
1		L1	Inductor	13 mm x	MLC1538-152ML	Coilcraft	1.5 µH - 12 A
				13 mm
1		L2	Inductor	13 mm x	MLC1515-252ML	Coilcraf	2.5 µH - 8 A
				13 mm
4		M1:M4	MOSFET	SO-8	STS12NH3LL
			control FET
1		R3	Resistor	0805			22 kΩ - 1%
1		R4	Resistor	0805			36 kΩ - 1%
1		R5	Resistor	0805			3.3 kΩ - 1%
1		R6	Resistor	0805			3 kΩ - 1%
2		R7, R8	Resistor	0805			680 Ω - 1%
1		R9	Resistor	0805			47 Ω - 1%
2		R10, R11	Resistor	0805			10 Ω - 1%
4		R12:R15	Resistor	0805			100 kΩ - 1%
1		R16	Resistor	0805			150 kΩ - 1%
1		R17	Resistor	0805			560 kΩ - 1%
2		R18, R19	Resistor	0805	NM
4		R20, R21,	Resistor	0805			0 Ω - 1%
		R22, R23
1		R24	Resistor	0805			1.1 kΩ - 1%
1		R25	Resistor	0805			820 Ω - 1%
1		R26	Resistor	1206			3.9 Ω - 1%
1		R27	Resistor	0805			10 kΩ - 1%
1		R29	Resistor	0805			11 kΩ - 1%
1		R28	Resistor	0805			6.8 kΩ - 1%
1		R30	Resistor	0805			1.8 kΩ - 1%

8/32

AN2829							Component list
Table 1.		Bill of materials (continued)
Qty	Component		Description	Package	Part number	MFR		Value
1		R31	Resistor	0603				5.6 kΩ - 1%
1		R32	Resistor	0603				15 kΩ - 1%
1		RLD5V,	Resistor	0805	NM
		RLD3V

9/32

Demonstration board layout	AN2829

5 Demonstration board layout

Figure 3. PM6681A demonstration board layout - top layer (PGND plane and component side)

AM01409v1

Figure 4. PM6681A demonstration board layout - inner layer 1 (SGND layer and VIN plane)

AM01410v1

10/32