AN2865
Application note
STUSBCD01B configuration and operation
Introduction
With the ever-increasing number of mobile devices adopting the USB bus as the standard
communication port and source for recharging, a standardization of the characteristics of
the charging devices and methods to detect them is required to optimize the performance of
the charging process and reduce the risks of damaging standard USB ports.
The new USB battery charging specification provides rules and guidelines to follow when
designing new USB architectures capable of battery charging and when defining new
charging host ports. The specification also extends the range of current which can be drawn
from a USB port.
In order to be able to distinguish between this new class of USB ports, standard USB host
ports and dedicated chargers, the new specification also defines detection methods which
must be used to determine the right amount of current the portable device can draw from the
USB bus. This also guarantees backward compatibility with standard USB ports.
The STUSBCD01B is a USB charging detection IC developed on the base of the USB
battery charging specification which can be easily added in new platforms to provide them
with charging detection capability.
September 2009
Doc ID 15283 Rev 1
1/17
www.st.com
Contents
AN2865
Contents
1
2
3
STUSBCD01B description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Application circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Interface and control pins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
3.1
3.2
3.3
Status/method pin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Detect pin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Default method pin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
4
5
6
7
8
Current sink detection method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Dedicated charger detection method . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Software detection and hardware detection . . . . . . . . . . . . . . . . . . . . . 14
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
2/17
Doc ID 15283 Rev 1
AN2865
STUSBCD01B description
1
STUSBCD01B description
The STUSBCD01B is the ideal solution for all mobile products using the USB bus for battery
charging. It can be used in all USB architectures (low-, full- or high-speed) where the
transceiver or the battery charger does not have smart charger detection. The
STUSBCD01B implements two different detection methods to distinguish between
dedicated chargers, charging host ports and standard host ports.
The device can be fully controlled through digital inputs (software detection mode) and is
also able to perform the charger detection automatically when the battery voltage is too low
to allow the application controller to be operative (hardware detection mode). A V
BAT
-
referred open-drain output (detect) is available for direct control over the USB charging
controller.
The STUSBCD01B also provides a clamping circuit which can be used to protect each USB
IC connected to the USB V
BUS
against overvoltage. The device requires few external
components and its power consumption is extremely low.
Doc ID 15283 Rev 1
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Application circuit
AN2865
2
Application circuit
The STUSBCD01B requires only five external components:
●
●
●
two capacitors to bypass the power supplies to ground
one resistor for the V
BUS
clamping circuit
two series resistors on the DP/DM data lines
Figure 1 shows the typical application circuit for the STUSBCD01B.
Figure 1.
STUSBCD01B application circuit
USB CHARGING
CONTROLLER
VBAT
USB PHY
(Transceiver)
DM DP VBUS
V
IO
C1
C2
V
I/O
100nF
1V8V
V
IO
DETECT
100nF
CONTROLLER
VBAT
USB
Receptacle
VBUS
D+
D-
GND
SHUTDOWN
STATUS/METHOD
/OE
DEF. METHOD
VBUS
DP
A
R3 = 470Ω
R1 = 470Ω
B
STUSBCD01
GND
DM
R2 = 470Ω
The STUSBCD01B can operate in two different modes: hardware detection mode, which
does not require external control, and software detection mode. The user can choose
between two different detection methods: dedicated method and current sink method. More
details on each operating mode are provided in the following paragraphs. The operating
mode is defined by the status of the digital I/Os, V
BAT
voltage, V
IO
voltage and default
method input. See
Table 1
for a summary of all operating conditions.
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AN2865
Application circuit
Table 1.
V
BAT
< 2.2 V
> 2.2 V
> 2.2 V
> 2.2 V
> 2.2 V
> 2.2 V
> 2.2 V
> 2.2 V
STUSBCD01B operating modes
V
IO
-
Not
present
Not
present
Not
present
Present
Present
Present
Present
V
BUS
-
Not
present
Present
Present
Present
Not
present
Present
Present
Shutdown
-
-
-
-
V
IO
-
GND
GND
Status/method
pin
-
-
-
-
-
-
V
IO(1)
GND
(1)
Default method
pin
-
-
V
BAT
GND
-
-
-
-
Operating mode
Power down
Standby (no SW control)
Active, HW detection,
current sink method
Active, HW detection,
dedicated method
Standby (SW control)
Standby (SW control)
Active, SW detection,
current sink method
Active, SW detection,
dedicated method
1. The level of the Status/Method pin is read and latched on the falling edge of the shutdown input signal. When detection is
finished, this pin becomes output.
SW = Software: HW = Hardware; “-” = Don't Care
The external resistors are very important to guarantee proper operation:
– The R1 and R2 series resistors are needed to mask the DP/DM pins’ parasitic
capacitance which is seen on the bus during high-speed USB communication.
Removing these resistors might lead to degradation of USB high-speed signal quality
and eye pattern failure. A value of 470
Ω
is suggested in order to have optimal
performance;
– The R3 resistor is required for the V
BUS
clamping feature. If a value of 470
Ω
is used,
the V
BUS
pin voltage (node A) never exceeds 6 V when USB V
BUS
voltages up to 10 V
are applied (node B). Every device needing overvoltage protection must be
connected to the V
BUS
pin of the STUSBCD01B as shown in
Figure 1: STUSBCD01B
application circuit
(node A). Bus-powered devices cannot take advantage of this
clamping feature because high currents drawn from the USB V
BUS
voltage would
cause a voltage drop over the R3 resistor. If this voltage drop is too high, the device's
V
BUS
comparators would read a false V
BUS
level which might lead to malfunctioning.
It is therefore strongly recommended to connect bus-powered USB devices directly to
the USB receptacle's V
BUS
line (node B).
Doc ID 15283 Rev 1
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