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 syst ems. This demonst ration board re presents a t ypical applica tion
circuit. The PM6681A demonstration board allows testing of all funct ion s of th e 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
1 Main 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 R
●
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.
DS(on)
4/32
AN2829 Applications
2 Applications
● 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
6/32
AM01408v1
AN2829 Component list
4 Component list
Table 1. Bill of materials
Qty Component Description Package Part number MFR Value
3C1:C3
1C4
2C5, C6
1C19
1C7
2C9, C10
1C11
1C8
1C12
2C13, C14
2C15, C16
Ceramic
capacitor
Ceramic
capacitor
Ceramic
capacitor
Ceramic
capacitor
POSCAP
capacitor
Ceramic
capacitor
POSCAP
capacitor
POSCAP
capacitor
POSCAP
capacitor
Ceramic
capacitor
Ceramic
capacitor
1812 UMK325BJ106KM-T Taiyo-Yuden 10 µF - 50 V
1812 NM 10 µF - 50
0805 100 nF - 50 V
0805 100 nF - 50 V
7343 NM Sanyo
0805 NM
7343 NM Sanyo
7343 6TPB330M Sanyo
7343 6TPB330M Sanyo
0603 5.6 nF - 50 V
0603 1 nF - 50 V
330 µF -
12 mR - 6 V
330 µF -
12 mR - 6 V
2C17, C18
1C20
1C21
1C22
1C23
1CIN
1 CREF
1C26
Ceramic
capacitor
Ceramic
capacitor
Tantalum
capacitor
Ceramic
capacitor
Ceramic
capacitor
Electrolytic
capacitor
Ceramic
capacitor
Tantalum
capacitor
0603 47 pF - 50 V
0805 1 µF - 10 V
3216 4.7 µF - 16 V
0805 220 nF - 10 V
0805 10 pF
D=10 mm NM
0805 100 nF - 50 V
6032 4.7 µF - 35 V
7/32
Component list AN2829
Table 1. Bill of materials (continued)
Qty Component Description Package Part number MFR Value
1C24, C25
1C27
1C28
1D1
2D2, D3
1IC1
1 L1 Inductor
1 L2 Inductor
4M1:M4
1 R3 Resistor 0805 22 kΩ - 1%
1 R4 Resistor 0805 36 kΩ - 1%
1 R5 Resistor 0805 3.3 kΩ - 1%
Tantalum
capacitor
Tantalum
capacitor
Tantalum
capacitor
Dual schottky
diode
Diode 1 A -
30 V
PM6681A
device
MOSFET
control FET
0805 10 µF - 6.3 V
0805 10 µF - 6.3 V
3216 4.7 µF - 16 V
SOT23 BAT54A STMicroelectronics
DO216AA STPS1L30M STMicroelectronics
QFN-32 PM6681A STMicroelectronics
13 mm x
13 mm
13 mm x
13 mm
SO-8 STS12NH3LL
MLC1538-152ML Coilcraft 1.5 µH - 12 A
MLC1515-252ML Coilcraf 2.5 µH - 8 A
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
R20, R21,
4
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%
Resistor 0805 0 Ω - 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,
RLD3V
Resistor 0805 NM
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
Loading...