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
2
3
4
5
6
7
8
9
10
11
Main features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Demonstration board schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Component list . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Demonstration board layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
I/O interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Recommended equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Quick start . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Jumper settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Feedback output connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Test setup and performance summary . . . . . . . . . . . . . . . . . . . . . . . . . 18
11.1
11.2
11.3
11.4
11.5
11.6
11.7
11.8
Test setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Power-up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Soft-start and shutdown waveforms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
1.5 V and 1.05 output efficiency vs. load current . . . . . . . . . . . . . . . . . . . 21
Power consumption analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Switching frequency vs. load current . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
Linear regulator output voltages vs. output current . . . . . . . . . . . . . . . . . 26
Load transient response . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
12
13
Representative waveforms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
2/32
AN2829
List of figures
List of figures
Figure 1.
Figure 2.
Figure 3.
Figure 4.
Figure 5.
Figure 6.
Figure 7.
Figure 8.
Figure 9.
Figure 10.
Figure 11.
Figure 12.
Figure 13.
Figure 14.
Figure 15.
Figure 16.
Figure 17.
Figure 18.
Figure 19.
Figure 20.
Figure 21.
Figure 22.
Figure 23.
Figure 24.
Figure 25.
Figure 26.
Figure 27.
Figure 28.
PM6681A demonstration board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Demonstration board schematic diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
PM6681A demonstration board layout - top layer (PGND plane and component side) . . . 10
PM6681A demonstration board layout - inner layer 1 (SGND layer and VIN plane) . . . . . 10
PM6681A demonstration board layout - inner layer 2 (SGND layer and signals). . . . . . . . 11
PM6681A demonstration board layout - bottom layer (PM6681A and component side) . . 11
Setup connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
REF, LDO5 and LDO power-up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Section 1 soft-start waveforms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Section 2 soft-start waveforms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Section 1 shutdown waveforms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Section 2 shutdown waveforms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
1.5 V SMPS efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
1.05 V SMPS efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Input current vs. input voltage. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Input current vs. input voltage. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Input current vs. input voltage. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
Device current consumption vs. input voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
Device current consumption vs. input voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
1.5 V output switching frequency vs. load current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
1.05 V output switching frequency vs. load current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
LDO5 output vs. load current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
ADJ_LDO load regulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
SMPS 1.5 V load transient response . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
SMPS 1.05 V load transient response . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
SMPS pulse skip mode. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
SMPS no-audible skip mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
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
DS(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
2
Applications
●
●
●
Notebook, tablet and slate computers
Mobile system power supplies
3-4 cell Li+ battery-powered devices
5/32
MicroPython开源版块
京公网安备 11010802033920号
Copyright © 2005-2026 EEWORLD.com.cn, Inc. All rights reserved
电子工程世界
