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USB
T
I
EXAS
NSTRUMENTS
ENTYPD1.PPT 10/5/97
MSP

Power Supply Products
Printer
Cable Box
Keyboard
Mouse
Phone/Answering
Machine
Modem
Hand Scanner
USB
Digital Audio
Game Controllers
USB
Universal Serial Bus
Jonathan M Bearfield
j-bearfield1@ti.com
972-480-3734 T
I
EXAS
NSTRUMENTS
ENTYPD1.PPT 10/5/97
MSP

Power Supply Products
Hub - Power Distribution Requirements
Bus-Powered Hubs:
Draws all power from USB connector
power pins
Self-Powered Hubs:
Internal function and downstream port
power does not come from USB.
Low Powered Function:
1 Unit Load = 100mA
High Powered Function:
5 Unit Loads = 500mA
USB Switch Application:
The Host and all Self-powered hubs must
implement over-current protection. They
must detect the overcurrent condition
and report it to the USB Host Controller.
The controller will then remove power to
that port.
LDO Regulator:
Each hub must run on 3.3V. The Vbus
supplies 5V nom and inputs may be as low
as 4.40V. A 500mV max dropout voltage
is recommended.
Embedded
Function
Upstream
Data Port
Downstream
Data Ports
Downstream
Vbus
Upstream
Vbus
On/Off
5 Unit Loads
1 Unit Load per port
On/Off
1 Unit Load
Hub Controller
(TUSB2040)
Switch
(TPS2010-15)
LDO Reg.
(TPS7201)
(TPS7133)
(TPS7333)
100mA/port
USB Bus-Powered Hub
Embedded
Function
Upstream
Data Port
Downstream
Data Ports
Downstream
Vbus
On/Off
5 Unit Load per port
On/Off
1 Unit Load
Downstream
Vbus
On/Off
5 Unit Load per port
Upstream
Vbus
Power
Supply
Hub Controller
(TUSB2070)
Regulator
Current Limit
(TPS2010-15)
LDO Reg.
(TPS7201)
(TPS7133)
(TPS7333)
Current Limit
(TPS2010-15)
(500mA/port)
(500mA/port)
USB Self-Powered Hub T
I
EXAS
NSTRUMENTS
ENTYPD1.PPT 10/5/97
MSP

Power Supply Products
Host or Self-
Powered Hub
4.75V (min)
Bus-Powered
Hub
4.40V
(min)
Bus-Powered
Function
5V+/- 3%
Power Supply
5V +/-5%
Switch &
Current Limit
PCB Traces
& Connector
Host Power Supply Requirements:
Output Regulation - +5%/-7%
Power Supply Regulation - 5%
PCB/ Connector Voltage Drop - 25mV
Expanded View
r
DS(on)
< 150mOhm
HUB Interconnect Requirements:
Maximum Voltage Drop = 350mV
(USB Spec)
Maximum Cable Length = 5.0m
(USB Spec)
Cable resistance (20 Awg.) = 0.036 Ohm/m

The requirements shown are taken directly from
sections 6 and 7 of the USB specification, and the
general PC power supply requirements. The limits
shown are all minimum requirements and/or maximum
allowable tolerances.
Working within general power supply limitations and
the USB specification a maximum r
DS(on)
for the
switch/current limit device used in the system is
150mOhm. On resistances higher than this, like those
found in polyfuses, would consume power in excess of
the specified USB voltage budget. Lower values for
r
DS(on)
would allow for increases in other system
tolerances over time and temperature.
Based on these requirements the maximum
allowable switch resistance is 150mOhm
for a 500mA USB port.
4.75V (min)
5V +/-5%
USB Voltage Requirements T
I
EXAS
NSTRUMENTS
ENTYPD1.PPT 10/5/97
MSP

Power Supply Products
Host Calculations:
Output Regulation - 5%
Power Supply Regulation - 3%
PCB/ Connector Voltage Drop - 25mV
Solve for r
DS(on)
:
Example:
V
reg
= 5% of 5V = 250mV, I
o(HP)
= 500mA
V
PSreg
= 3% of 5V = 150mV, V
out(min)
= 4.75V
V
PCB
= 25mV
r
DS(on)
< 250mV - 150mV - 25mV
500mA
< 150mOhm
HUB Interconnect Calculations:
Max. Voltage Drop = 350mV (USB Spec)
Max. Cable Length = 5.0m (USB Spec)
Cable resistance = 0.036 Ohm/m
(20 AWG)
V
HUB
> V
switch
+ 4* V
Connector
+ 2* V
Cable
@ I
max
= 500mA
Example:
V
Switch
= I
max
* (R
PCB
+ r
DS(on)
) = 100mV
(by definition)
V
Connector
= I
max
* R
Connector
= 15mV
V
Cable
= I
max
* R
Cable
, R
Cable
= 5m* .036 Ohm/m
r
DS(on)
< 100mV
500mA < 200mOhm
PC Board & Switch
Resistance Combined
( )
V
reg
- V
PSreg
- V
PCB
I
O
V
reg
< V
PSreg
+ V
PCB
+ (I
O
* r
DS(on)
)
r
DS(on)
<
Solve for r
DS(on)
:
r
DS(on)
<
V
Switch
I
max
System Calculations T
I
EXAS
NSTRUMENTS
ENTYPD1.PPT 10/5/97
MSP

Power Supply Products
¾ Must consider cumulative voltages drops in cables,
connectors, pc board traces, current limit devices, etc.
¾ V
BUS(min)
determined by V
DROP
and V
DROOP
ª<b>V
DROP
caused by IR drop in cables, connectors (Steady State)
ª<b>V
DROOP
caused by inrush current during hot plug (Transient)
¾ V
BUS(min)
set by V
CC(in)
voltage regulator at EOL device
ª<b>Assumes a 500mV dropout for a 3.3V ± 5% regulator
ª<b>V
BUS(min)
= 4.1V measured at device connector
¾ Must consider different topologies
ª<b>Host to high-power device or bus-powered hub
ª<b>Host through bus-powered hub to low-power device
Voltage Drop/Droop Requirements T
I
EXAS
NSTRUMENTS
ENTYPD1.PPT 10/5/97
MSP

Power Supply Products
V
DROP
: Host to Self-powered Hub
Host or
Self
Powered
Hub
4.75V
4.50V
4.45V
500 mA/port
100 mV
Per
Design
250 mV
50 mV
HP device
500 mA/port
Power
Supply
Device
Controller
¾ Power Supply 5.00v +/- 5%
¾ Host can drop 100mV
ª<b>traces, ferrite beads, connector, current limit device
¾ Detachable cable may drop 250mV max @ 500mA
¾ Bus-powered device may drop up to 50mV
ª<b>traces, connectors, etc T
I
EXAS
NSTRUMENTS
ENTYPD1.PPT 10/5/97
MSP

Power Supply Products
Voltage Drop - Host thru Hub to BP-device
Host
Integral
Cable
4.10V
Not Specified
Bus
Powered
Hub
4.40V
100 mV
Power
Supply
100 mA/port
Device
Controller
LP device
350 mV
100 mA/port
300 mV
500 mA
(max)
4.75V
¾ Bus-powered hub with integral cable can drop 350mV max.
ª<b>connector, traces, power distribution switch, ferrite beads, etc
¾ Bus-powered Hub can use and/or distribute up to 500mA
¾ To meet worst case system power distribution requirements
the Bus-powered Hub may need an integral cable.
Defined
by designer T
I
EXAS
NSTRUMENTS
ENTYPD1.PPT 10/5/97
MSP

Power Supply Products
Voltage Droop and Inrush Current
USB DESIGN REQUIREMENTS:
¾ 330mV max. V
DROOP
when hot-plugging
¾ USB devices must draw less than 100mA from the
V-bus during hot-plug
¾ Maximum hot-plug load at downstream cable end is
10
µ
F in parallel with 44 ¾ Downstream ports must be bypassed with no less than
a 120
µ
F tantalum capacitor
¾ Bus-powered Hubs must provide surge limiting
ª<b>soft start when enabling downstream ports
Bus
Powered
Hub
4.40V/330mV
4.75V/330mV
SP Hub /
Host
Bus
Powered
Device
V
O
/V
DROOP
4.10V/100mV
(not specified) T
I
EXAS
NSTRUMENTS
ENTYPD1.PPT 10/5/97
MSP

Power Supply Products
Polyfuses vs MOSFET Switches
Polyfuse MOSFET
Report Overcurrent Condition
NO
YES
Fast Response Time
NO (150ms)
YES (45
µ
s)
Limit Output Current < 5A
YES
YES
Meets V
DROP
Requirements (80mV)
2.5A Device
YES
Enabled/Disabled by Controller
NO
YES
R1
R2
5V
GND
D+
D-
P
O
R
T
1
Polyfuse
MOSFET
Switch
Over Current Response
POWER
SUPPLY
5V
GND
OC1
DP1
DM1
USB
CONTROLLER
Port EN1
ON/OFF
Current Limit
OC
Complete Polyfuse Solution
with Enable and Over Current Response
Polyfuses do
NOT meet all of
the requirements
of the USB
specification
or application
Intelligent
MOSFET switches
do meet all of the
requirements of the
USB specification
and application T
I
EXAS
NSTRUMENTS
ENTYPD1.PPT 10/5/97
MSP

Power Supply Products
Non-Ganged Hub Power Dist.
Non-Ganged Configuration:
Power Dist. Switch
QTY 4
Ferrite Beads
None
Cap, 150
µ
F (USB req.) QTY 4
Cap, 1000
µ
F (option)
QTY 1
Cap, .1
µ
F
QTY 4
PROS:
Lower Current Devices
No Ferrite Beads Required
Good Voltage Droop Response
Faults only shut down the Port affected
(most user friendly)
CONS:
Highest Cost solution
GND
IN
IN
EN
TPS2014
OUT
OUT
OUT
OC
.1uF
GND
IN
IN
EN
TPS2014
OUT
OUT
OUT
OC
D+
D-
5V
GND
150uF
D+
D-
5V
GND
150uF
D+
D-
5V
GND
150uF
GND
IN
IN
EN
TPS2014
OUT
OUT
OUT
OC
.1uF
.1uF
5V
1000uF
opt.
D+
D-
5V
GND
150uF
GND
IN
IN
EN
TPS2014
OUT
OUT
OUT
OC
.1uF
NOTE: Low drop-out Voltage Regulators may be required for
powering Hub Controller from the USB V-bus T
I
EXAS
NSTRUMENTS
ENTYPD1.PPT 10/5/97
MSP

Power Supply Products
Ganged Configuration:
Power Dist. Switch
QTY 2
Ferrite Beads
QTY 8
Cap, 150
µ
F(USB req.) QTY 4
Cap, 1000
µ
F (option)
QTY 1
Cap, .1
µ
F
QTY 1
PROS:
Most Cost Effective
Lowest IC Count
CONS:
Fault on one port shuts down switch, and all ports go down
Ferrite Beads required (adds impedance between outputs, lowers V-droop)
Higher current devices required (2 X 500mA = 1A min, with 5A UL max)
GND
IN
IN
EN
TPS2015
OUT
OUT
OUT
OC
.1uF
Ganged Hub Power Distribution
D+
D-
5V
GND
Ferrite
Beads
150uF
D+
D-
5V
GND
Ferrite
Beads
150uF
D+
D-
5V
GND
Ferrite
Beads
150uF
D+
D-
5V
GND
Ferrite
Beads
150uF
GND
IN
IN
EN
TPS2015
OUT
OUT
OUT
OC
.1uF
5V
1000uF
opt.
NOTE: Low drop-out Voltage Regulators will be required for
powering Hub Controller from the USB V-bus T
I
EXAS
NSTRUMENTS
ENTYPD1.PPT 10/5/97
MSP

Power Supply Products
USB - The TI Advantage
TI has a Complete USB Hub Solution:
¾ TUSB2040/70 H