ST AN2937 Application note

AN2937

Application note

Power system demonstration kit based on the PM6686 dual step-down controller with adjustable voltages and adjustable LDO

Introduction

The PM6686 is a dual step-down controller with adjustable output voltages, adjustable LDO and charge pump circuit for notebook power systems. The PM6686 demonstration kit for system supply represents a typical application circuit, and allows testing of all the functions of the PM6686 device. It provides two switching sections with 5 V (OUT1) and 3.3 V (OUT2) outputs from 8 V to 28 V input battery voltage. The operating switching frequency of the two sections is 400 kHz and 300 kHz, respectively. Each switching section delivers more than 5 A of output current. An internal linear regulator can provide 5 V at 100 mA peak current. The charge pump circuit provides an auxiliary 12 V output voltage.

Figure 1. PM6686 demonstration kit for system supply

August 2009

Doc ID 15418 Rev 1

1/41

www.st.com

Contents	AN2937

Contents

1	Main features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		. 5
2	Demonstration kit schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		. 6
3	Jumper settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		7
4	Component list . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		8
5	Demonstration kit layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		11
6	I/O interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		13
7	Recommended equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		14
8	Quick start . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		14
9	Jumper settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		15
	9.1	Switching sections - operating modes . . . . . . . . . . . . . . . . . . . . . . . . . . .	15
	9.2	Enable switching section 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	16
	9.3	Enable switching section 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	16
	9.4	Switching sections - frequency selection (TON) . . . . . . . . . . . . . . . . . . . .	17
	9.5	Linear regulator LDO enable (EN_LDO) . . . . . . . . . . . . . . . . . . . . . . . . .	17
	9.6	LDO regulation (LDOREFIN) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	18
	9.7	External bypass connections for the linear regulator (BYP) . . . . . . . . . . .	18
	9.8	OUT1 switching section regulation (FB1) . . . . . . . . . . . . . . . . . . . . . . . . .	19
	9.9	Current limit of OUT1 switching section (ILIM1) . . . . . . . . . . . . . . . . . . . .	19
	9.10	OUT2 switching section regulation (REFIN2) . . . . . . . . . . . . . . . . . . . . . .	20
	9.11	Current limit of OUT2 switching section (ILIM2) . . . . . . . . . . . . . . . . . . . .	20
	9.12	Connection of LDO output (5 V) to the PVCC pin (LDO5V_BYP) . . . . . .	21
	9.13	Regulation of the charge pump CP (CP SEL) . . . . . . . . . . . . . . . . . . . . .	21
	9.14	Output 1, virtual ESR connection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	21
	9.15	Output 2, virtual ESR connection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	22
	9.16	LGATE source for charge pump circuit . . . . . . . . . . . . . . . . . . . . . . . . . . .	22

2/41	Doc ID 15418 Rev 1

AN2937	Contents

9.17 MOSFET dual option, high-side connection section 1 . . . . . . . . . . . . . . . 22 9.18 MOSFET dual option, high-side connection section 2 . . . . . . . . . . . . . . . 23

10	Test setup and performance summary . . . . . . . . . . . . . . . . . . . . . . . . .		24
	10.1	Test setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	24
11	Representative waveforms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		25
	11.1	Operating modes - Skip, NA skip, PWM . . . . . . . . . . . . . . . . . . . . . . . . . .	25

11.1.1 Switching sections soft-start and soft-end . . . . . . . . . . . . . . . . . . . . . . . 26 11.1.2 Load transient . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 11.1.3 Fault management: overvoltage and undervoltage . . . . . . . . . . . . . . . . 31

11.2 Typical operating characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

33

11.2.1 OUT1 and OUT2 output efficiency vs. load current . . . . . . . . . . . . . . . . 33 11.2.2 OUT1 and OUT2 switching frequency vs. load current . . . . . . . . . . . . . 34 11.2.3 OUT1 and OUT2 output voltage vs. load current . . . . . . . . . . . . . . . . . . 35 11.2.4 Power consumption analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

12

Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

39

Doc ID 15418 Rev 1

3/41

List of tables	AN2937

List of tables

Table 1. Component list . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Table 2. Demonstration board test points. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 Table 3. Jumper S1 SKIP (connect SKIP pin to S1). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 Table 4. Jumper S2 EN2 (connect the EN2 pin to S2) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 Table 5. Jumper S3 EN1 (connect EN1 pin to S3) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 Table 6. Jumper S4 TON (connect TON pin to S4) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 Table 7. Jumper S5 EN_LDO (connect EN_LDO pin to S5) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 Table 8. Jumper S6 LDOREFIN (connect LDOREFIN pin to S6) . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 Table 9. Jumper S7 BYP (connect LDO_SW pin to S7). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 Table 10. Jumper S8 FB1 (connect FB1 pin to S8) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 Table 11. Jumper S9 ILIM1 (connect ILIM1 pin to S9) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 Table 12. Jumper S10 REFIN2 (connect REFIN2 pin to S10) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 Table 13. Jumper S11 ILIM2 (connect ILIM2 pin to S11) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 Table 14. Jumper S12 LDO5V BYP (connect PVCC pin to S12) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 Table 15. Jumper S13 CP SEL (connect CP_FB pin to S13). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 Table 16. Jumper S14 VESR1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 Table 17. Jumper S15 VESR2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 Table 18. Jumper S16 CP_SOURCE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 Table 19. Jumper S17 DUAL_GATE_1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 Table 20. Jumper S18 DUAL_GATE_2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 Table 21. Document revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

4/41	Doc ID 15418 Rev 1

AN2937	List of figures

List of figures

Figure 1.	PM6686 demonstration kit for system supply . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	. 1
Figure 2.	PM6686 demonstration kit schematic diagram. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	. 7
Figure 3.	PM6686 demonstration board layout - top layer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	12
Figure 4.	PM6686 demonstration board layout - inner layer 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	12
Figure 5.	PM6686 demonstration board layout - inner layer 2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	13
Figure 6.	PM6686 demonstration board layout - bottom layer. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	13
Figure 7.	Test setup connections. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	25
Figure 8.	SMPS pulse skip mode, no load. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	26
Figure 9.	SMPS no-audible skip mode, no load. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	26
Figure 10.	SMPS PWM mode, no load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	27
Figure 11.	Section 1 soft-start waveforms; 5 A constant current load applied . . . . . . . . . . . . . . . . . . .	27
Figure 12.	Section 2 soft-start waveforms; 5 A constant current load applied . . . . . . . . . . . . . . . . . . .	28
Figure 13.	OUT1 soft-end, no load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	28
Figure 14.	OUT2 soft-end, no load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	29
Figure 15.	Tracking soft-start EN2 connected to VREF2, no loads applied. . . . . . . . . . . . . . . . . . . . .	29
Figure 16.	Tracking soft-end EN2 connected to VREF2, no loads applied . . . . . . . . . . . . . . . . . . . . .	30
Figure 17.	OUT1 = 5 V PWM load transient 2 A/µs 0-5 A . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	30
Figure 18.	OUT2 = 5 V skip load transient 2 A/µs 0-5 A . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	31
Figure 19.	OUT2 = 3.3 V PWM load transient 2 A/µs 0-5 A . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	31
Figure 20.	OUT2 = 3.3 V skip load transient 2 A/µs 0 - 5 A . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	31
Figure 21.	Undervoltage protection (UVP) management. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	32
Figure 22.	Overvoltage protection management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	33
Figure 23.	Overvoltage protection management: EN pulled low . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	33
Figure 24.	Efficiency vs. load current; OUT1=5 V, TON=VCC. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	34
Figure 25.	Efficiency vs. load current; OUT2=3.3 V, TON=VCC . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	34
Figure 26.	Switching frequency vs. load current; OUT1=5 V, TON=VCC . . . . . . . . . . . . . . . . . . . . . .	35
Figure 27.	Switching frequency vs. load current; OUT2=3.3 V, TON=VCC. . . . . . . . . . . . . . . . . . . . .	35
Figure 28.	Output voltage vs. load current; OUT1=5 V, TON=VCC . . . . . . . . . . . . . . . . . . . . . . . . . .	36
Figure 29.	Output voltage vs. load current; OUT2=3.3 V, TON=VCC . . . . . . . . . . . . . . . . . . . . . . . . .	36
Figure 30.	Input current vs input voltage, PWM mode. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	37
Figure 31.	Input current vs. input voltage, NA skip mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	37
Figure 32.	Input current vs. input voltage, skip mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	38
Figure 33.	Input current consumption vs. input voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	38
Figure 34.	Input current consumption vs. input voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	39

Doc ID 15418 Rev 1

5/41

Main features	AN2937

1Main features

●5.5 V to 28 V input voltage range

●Dual fixed 1.05 V/3.3 V and 1.5 V/5.0 V outputs or adjustable 0.7 V to 5.5 V (SMPS1) and 0 V to 2.5 V (SMPS2), ±1.5% accuracy over valley regulation

●Low-side MOSFET RDS(on) current sensing and programmable current limit

●Constant on-time control

●Selectable switching frequency

●Soft-start (internally fixed at 2.8 ms) and soft-stop

●Selectable pulse skipping at light loads

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

●Independent Power Good and EN signals

●Latched OVP and UVP

●Charge pump feedback

●Fixed 3.3 V/5.0 V, or adjustable output 0.7 V to 4.5 V, ±1.5% (LDO): 200 mA

●3.3 V reference voltage ± 2.0%: 5 mA

●2.0 V reference voltage ±1.0%: 50 µA

6/41	Doc ID 15418 Rev 1

2

AN2937

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Jumper settings	AN2937

3Jumper settings

●S7 (BYP jumper) shorted to OUT1

●S8 (FB1 jumper) 1 shorted to GND

●S9, S11 (ILIM1, ILIM2 jumper) shorted to resistors

●S12 (LDO to PVCC jumper) shorted

●S10 (REFIN2 jumper) shorted to VCC

●S6 (LDOREFIN jumper) shorted to GND

●S13 (CP_SEL jumper) floating

●S14 (VESR OUT1) open

●S15 (VESR OUT2) shorted to OUT2

●S16 (CP connection) open

●S17-S18 (HS MOS connections) shorted

8/41	Doc ID 15418 Rev 1

AN2937	Component list

4 Component list

Table 1.	Component list
Reference		Description	Value
	C1	Ceramic capacitor 0603 6.3 V	100 nF
	C2	Ceramic capacitor 0603 6.3 V	1 µF
	C3	Ceramic capacitor 0603 6.3 V	NM
	C4	Ceramic capacitor 0805 25 V	1 µF
	C5	Ceramic capacitor 0805 6.3 V	4.7 µF
	C6	Ceramic capacitor 0603 6.3 V	100 nF
	C7	Ceramic capacitor 0603 6.3 V	1 µF
	C8	Ceramic capacitor 0805 16 V	100 nF
	C9	Ceramic capacitor 0805 16 V	100 nF
	C10	Ceramic capacitor 0805 16 V	100 nF
	C11	Ceramic capacitor 0805 16 V	100 nF
	C12	Ceramic capacitor 0603 6.3 V	100 nF
	C13	Ceramic capacitor 10 µF 1210 35 V	UMKK325BJ106KM
			Taiyo Yuden
	C14	Ceramic capacitor 10 µF 1210 35 V	UMKK325BJ106KM
			Taiyo Yuden
	C15	Ceramic capacitor 10 µF 1210 35 V	UMKK325BJ106KM
			Taiyo Yuden
	C16	Ceramic capacitor 10 µF 1210 35 V	UMKK325BJ106KM
			Taiyo Yuden
	C17	Ceramic capacitor 0603 6.3 V	100 nF
	C18	POSCAP capacitor 6TPF220ML
	C19	POSCAP capacitor 12 mΩ	220 µF
	C20	Ceramic capacitor 0805 50 V 1 nF	NM
	C21	Ceramic capacitor 0603 6.3 V	100 nF
	C22	POSCAP capacitor 6TPF220ML
	C23	POSCAP capacitor 220 µF 12 mΩ	NM
	C24	Ceramic capacitor 0805 50 V 1 nF	NM
	C25	Ceramic capacitor 0603 6.3 V 100 nF	100 nF
	C26	Ceramic capacitor 10 µF 1210 35 V	NM
	C27	Ceramic capacitor 0603 6.3 V 1 nF	NM
	C28	Ceramic capacitor 0603 6.3 V 1 nF	NM
	C29	Ceramic capacitor 10 µF 1210 35 V	NM

Doc ID 15418 Rev 1

9/41

Component list				AN2937
	Table 1.	Component list (continued)
	Reference		Description	Value
		D1	Schottky diode STPS1L30M
		D2	Schottky diode STPS1L30M
		D3	Schottky diode BAT54SFILM
		D4	Schottky diode BAT54SFILM
		D5	Schottky diode BAT54AFILM	NM
		L1	Coilcraft MSS1048-332
		L2	Coilcraft MSS1048-332
		M1	Power NMOS SO-8 STS17NH3LL	NM
		M2	Power NMOS SO-8 STS17NH3LL	NM
		M3	Power NMOS SO-8 STS15N4LLF3	NM
		M4	Power NMOS SO-8 STS15N4LLF4	NM
		Q1	Power SO-8 DUAL STS9DNH3LL
		Q2	Power SO-8 DUAL STS9DNH3LL
		R1	Resistor 0603	220 kΩ
		R2	Resistor 0603 0.5%	51 kΩ
		R3	Resistor 0603 0.5%	11 kΩ
		R4	Resistor 0603 0.5%	NM
		R5	Resistor 0603 0.5%	NM
		R6	Resistor 0603	300 kΩ
		R7	Resistor 0805	NM
		R8	Resistor 0805	2.2 Ω
		R9	Resistor 0805	NM
		R10	Resistor 0603	200 kΩ
		R11	Resistor 0603	39 kΩ
		R12	Resistor 0805	NM
		R13	Resistor 0805	2.2 Ω
		R14	Resistor 0805	NM
		R15	Resistor 0603	220 kΩ
		R16	Resistor 0603	300 kΩ
		R17	Resistor 0805 3 Ω	NM
		R18	Resistor 0805 3 Ω	NM
		R19	Resistor 0603	150 kΩ
		R20	Resistor 0603	390 kΩ
		R21	Resistor 0805	0 Ω
		R22	Resistor 0805	0 Ω

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Doc ID 15418 Rev 1

AN2937				Component list
	Table 1.	Component list (continued)
	Reference		Description	Value
		R23	Resistor 0805	0 Ω
		R24	Resistor 0805	0 Ω
		R25	Resistor 0603	NM
		R26	Resistor 0603	NM
		R27	Resistor 0603	NM
		R28	Resistor 0603	NM

Doc ID 15418 Rev 1

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Demonstration kit layout	AN2937

5 Demonstration kit layout

Figure 3. PM6686 demonstration board layout - top layer

Figure 4. PM6686 demonstration board layout - inner layer 1

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Doc ID 15418 Rev 1

AN2937	Demonstration kit layout

Figure 5. PM6686 demonstration board layout - inner layer 2

Figure 6. PM6686 demonstration board layout - bottom layer

Doc ID 15418 Rev 1

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