DS4201 REFERENCE DESIGN:
USB BUS POWERED SPEAKER
USB POWER OVERVIEW
The USB specification defines two device power configurations: self powered and bus powered. Self powered devices
draw most of their power from an external source and may draw up to 100mA from the bus. Bus powered devices draw
all their power from USB. For bus powered devices, the USB specification defines two type of devices: high power and
low power. Low power functions are those that draw less than 100mA from the bus. High power functions are those that
draw more than 100mA but are limited to 500mA. With the MaxPower configuration descriptor, a USB device reports
whether it is a low or high powered function.
For USB hubs there are two classifications: bus-powered and self-powered. Bus-powered hubs get all power from USB.
Each down stream port from a bus-powered hub can provide NO MORE than 100mA. Self-powered hubs have a local
power supply. Each down stream port from a self-powered hub can provide up to 500mA.
In addition to operating current consumption, the USB specification imposes two additional power requirements on
devices: in-rush current draw at device attachment and suspend state current consumption. In-rush current is not
explicitly defined as an amperage value in the USB specification. Instead the worst case load a USB peripheral should
present to the bus upon attachment is specified as 10µF in parallel with 44Ω. The 44Ω resistive value equates to 100mA
at the minimum allowable bus voltage of 4.4V. The intent of the USB specification is to limit the amount of voltage droop
due to in-rush current to 330mV.
This is accomplished with the load of 44Ω paralleled with 10µF.
For
measurement/evaluation purposes, a good rule of thumb is to limit in-rush current to 500mA maximum. Finally, all
devices which draw power from the bus must be able enter the suspend state and reduce their current consumption from
the bus to less than 500 µA.
USB BUS POWERED SPEAKERS
With a nominal bus power voltage of 5V and 500mA of available current, it is possible to build a set of bus powered USB
speakers that have a total power budget of approximately 2.5W. The schematic that accompanies this document
provides a reference design that has been implemented and tested by Dallas Semiconductor.
One of the challenges to implement a bus powered speaker set is satisfying USB in-rush and suspend current
requirements. The DS4201 SUSO output signal combined with minimal external circuitry, can be used to implement a
power control circuit to satisfy both requirements; the power control circuit is highlighted on sheet one of the reference
schematic. The SUSO output signal is used to turn the power control circuit on/off. The power control circuit is turned off
when USB enters a suspend state or before the DS4201 is configured. When the DS4201 is configured and USB is in an
active state the power control circuit is turned on. Upon initial attachment to the bus, the power control circuit is off thus
disconnecting the amplifier and large filter capacitance from the bus, this prevents large in-rush currents from being
generated. When USB goes into a suspend state the power control circuit is again off and the DS4201 goes into a low
power mode enabling the 500 µA requirement to be satisfied.
This unique combination of a DS4201 specific control signal, SUSO , and simple/inexpensive external circuitry enables a
USB compliant bus powered speaker solution to be designed for high volume production.
USB SPECIFICATION CONSIDERATIONS
Devices that draw more than 100mA from the bus are high powered devices and must be reported as so with the
MaxPower configuration descriptor. Bus powered hubs can provide no more than 100mA to an attached device, therefore
high powered devices cannot be used with bus powered hubs. Dallas Semiconductor assumes no responsibility with bus
powered speaker designs and system configurations that violate these two specification requirements.
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EMI Filter or Ferrite Bead
U1
L1
8
4
IN
OUT
R1
2
1
4
C1
5
1.0
SHDN
GND
3
Amplifier power control circuit
C2
VBUS
DD+
GND
+
C6
1.0
LT1121N8
J1
1
C4
C5
1.0
0.1
C3
22
0.1
Q1
IRFD9014
2
(or equivalent)
3
4
C7
C8
1.0
0.1
S
R2
1.5K
SHELL
VCC
G
1M
5
R5
R4
1M
U2
24, 1%
D
Q2
2N7000
1
22
DS4201
USB SERIES-B
11
3
D
R3
G
24, 1%
Ferrite Bead
12
C10
C11
33pF
13
33pF
17
18
C13
15
0.1
16
C15
LOUT
ROUT
DSUSO
RMIC
VCM
LMIC
X2I
C18
C12
1.0
C14
X2
10
33pF
12.288 MHz
C16
33pF
C19
33pF
2
AGND
DGND
DGND
C20
0.1
X1
21
14
8
4
5
0.1
24
+
SPM
22
ROUT
25
9
X1O
DGND
0.1
LOUT
7
X2O
LAUX
VREFI
C9
1.0
20
19
6
RAUX
0.1
23
C21
D+
X1I
2
C17
VA
R6
EMI Filter or
VD
VB
L2
3
S
C22
12.0 MHz
33pF
Notes:
1. Unless noted, resistors are 5%, 0.25W.
2. Unless noted, capacitor values are in microfarads.
3. Regulator U1: LT1121-3.3, S-813, MIC-5207-3.3 or equivalent.
4. EMI filters/Ferrite beads are optional but will help with EMI noise
reduction. When using EMI filters, L1 and L2 are Murata
1
BLM21P221SG or equivalent.
1
5. Transistor Q1 is a medium power p-channel MOSFET that can
Title
handle more than 1A and has a Rds of less than 0.5 ohm.
DS4201 BUS POWER USB ELECTRONICS REFERENCE
6. LED D1 is a green "low current" device. Operating current
Size
must be less than or equal to 2mA. Possible sources include:
A
Document Number
Rev
-
-
Siemens LG 3369-EH, HP & Stanley HLMP7040 or HLMP4740.
Date:
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Friday, December 18, 1998
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Sheet
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of
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VCC
R12
4
2
+
4
C23
R7
100
1.5K
Power On/Off LED
D1
C24
100
R8
100
C25
0.47
+
U3
16
11
50K
C30
0.001
C29
BOOT1
8
7
6
SVR
BOOT2
FEED2
GND
3
J2
5
R
4
14
C28
3
3
1
C32
C33
100
470
2
AUDIO OUT
2
1
L
C34
0.47
13
12
9
5
C35
GND
4
+
GND
2
OUT2
GND
100
BRIDGE
IN2
GND
R10
VOLUME CONTROL
15
100
+
33pF
FEED1
C31
100
C27
470
OUT1
+
+
R9
IN1
+
10
TEA2025B
VS
4.7
+
C26
+
ROUT
3
2
100
LOUT
C36
4.7
+
R11
50K
C37
33pF
C38
0.001
1
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