ST AN2865 APPLICATION NOTE

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 STUSBCD01B description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

2 Application circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

3 Interface and control pins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

3.1 Status/method pin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

3.2 Detect pin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

3.3 Default method pin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

4 Current sink detection method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

5 Dedicated charger detection method . . . . . . . . . . . . . . . . . . . . . . . . . . 11

6 Software detection and hardware detection . . . . . . . . . . . . . . . . . . . . . 14

7 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

8 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

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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 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 components and its power consumption is extremely low.

against overvoltage. The device requires few external

BUS

BAT

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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

● 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

clamping circuit

BUS

VBAT

USB PHY

(Transceiver)

(Transceiver) DM DP VBUS

DM DP VBUS

100nF

I/O

CONTROLLER

CONTROLLERCONTROLLER

100nF

1V8V DETECT

SHUTDOWN

SHUTDOWN STATUS/METHOD

STATUS/METHOD /OE

/OE DEF. METHOD

DEF. METHOD

STUSBCD01

GND

VBAT

VBUS

A B

100nF

R3 = 470Ω

R1 = 470Ω

R2 = 470Ω

VBUS

D+

D-

GND

USB

Receptacle

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

voltage, VIO voltage and default

BAT

method input. See Tab l e 1 for a summary of all operating conditions.

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AN2865 Application circuit

Table 1. STUSBCD01B operating modes

BAT

BUS

Shutdown

Status/method

Default method

Operating mode

< 2.2 V - - - - - Power down

> 2.2 V

Not

present

Not

present

Not

present

> 2.2 V Present Present V

> 2.2 V Present

> 2.2 V Present Present GND V

> 2.2 V Present Present GND GND

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

Not

present

Present - - V

- - - Standby (no SW control)

BAT

Present - - GND

- - Standby (SW control)

(1)

Not

present

- - - Standby (SW control)

Active, HW detection,

current sink method

Active, HW detection,

dedicated method

Active, SW detection,

current sink method

Active, SW detection,

dedicated method

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

the V

pin voltage (node A) never exceeds 6 V when USB V

BUS

clamping feature. If a value of 470 Ω is used,

BUS

voltages up to 10 V

BUS

are applied (node B). Every device needing overvoltage protection must be connected to the V

pin of the STUSBCD01B as shown in Figure 1: STUSBCD01B

BUS

application circuit (node A). Bus-powered devices cannot take advantage of this

clamping feature because high currents drawn from the USB V

voltage would

BUS

cause a voltage drop over the R3 resistor. If this voltage drop is too high, the device's V

comparators would read a false V

BUS

level which might lead to malfunctioning.

BUS

It is therefore strongly recommended to connect bus-powered USB devices directly to the USB receptacle's V

line (node B).

BUS

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Interface and control pins AN2865

3 Interface and control pins

The STUSBCD01B is controlled and communicates with the controller using 5 I/Os. While shutdown and OE (Status/Method, default method and detect) have different characteristics.

3.1 Status/method pin

This pin is either input or output depending on the operating conditions. It is input before the start of the detection process (used to set the detection method) and is output at the end of the detection process (it outputs the result of the detection). The application designer should program the application controller so that it sets the level of this pin (V detection starts and maintains it during the falling edge of the shutdown signal (when the value is internally latched). The STUSBCD01B then outputs the detection result (at the end of detection) on this pin and therefore the application should read it after the maximum detection time has passed (see parameters T STUSBCD01B datasheet). The output structure is not a standard CMOS output but consists of a weak pull-up or a weak pull-down (~10 kΩ) connected to the pin depending on the detection result as shown in figure 2.

are standard VIO referred CMOS inputs, the remaining pins

or GND) before the

VBUS_DET_CS

and T

VBUS_DET_DC

on the

Figure 2. Status/method pin I/O

STATUS/

STATUS/ METHOD

METHOD

3.2 Detect pin

This pin is an open-drain output which can be used as a V detection result. It is always enabled in hardware detection mode, while in software detection mode it is enabled/disabled by the OE open-drain structure (see Figure 3) uses a PMOS transistor to pull the pin high (V the detection is successful, otherwise an internal pull-down resistor (~ 300 kΩ) keeps the output low.

Closed at detection end if

Closed at detection end if charger detected

charger detected

Closed at detection end if

Closed at detection end if charger not detected

charger not detected

GND

(active low) digital input. When enabled, the

referred signal for the

BAT

) when

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AN2865 Interface and control pins

Figure 3. Detect pin output

BAT

DETECT

GND

3.3 Default method pin

This pin is a V

referred digital input. It is used to choose the detection method in

BAT

hardware detection mode. Its level is ignored in software detection mode. It has to be driven high for the current sink method, low for the dedicated method.

Note: This pin must never be left floating to avoid increased power consumption.

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Current sink detection method AN2865

4 Current sink detection method

The STUSBCD01B's current sink detection method is suitable to detect both dedicated USB chargers (e.g. wall chargers) and charging host ports and distinguish them from standard USB host ports. See figure 4 for a simplified schematic description of these devices.

A dedicated charger typically shorts the USB DP/DM lines with a resistance not greater than 200 Ω, while standard USB host ports have pull-down resistors connected to DP and DM (14.25 - 24.80 kΩ).

A charging host port is normally not distinguishable from standard host ports but if it detects that an external device connected to its DP/DM lines is attempting to perform a detection, then it simulates a short between DP/DM, applying a voltage source to DM (V

DM_SRC

Figure 4. USB ports

= 0.5 - 0.7 V) and a current sink to DP (I

DP_SINK

= 50 - 150 µA).

Dedicated

Charging Port

After a stable V

DCHG_DAT

Max

Max 200Ω

200Ω

voltage has been detected, if the STUSBCD01B is enabled, the state

BUS

Standard Host

Port

Charging Host

machine starts the detection procedure which consists of the following steps:

– Phase 1: a current sink is connected to the DM pin (I

DAT_SINK

– Phase 2: 5 ms (min) after DM current sink is connected, a voltage source

DAT_SRC

= 0.615 - 0.7 V) is applied to the DP pin and maintained for at least 100

ms;

– When the detection finishes, both the current sink and the voltage source are

disconnected from the DP/DM pins. If the detection is successful, 40 ms (min.) after the end of the detection process, the detect and/or Status/Method outputs are pulled high.

Port

DAT_REF

DP_SINK

DM_SRC

= 50 - 100 µA);

The detection process can be interrupted if one of the following conditions is satisfied:

–V

voltage goes low;

BUS

– Shutdown input is pulled high (only in SW detection mode); – Voltage levels on the DP/DM pins are different than expected.

The detection is successful if the DM pin is low during phase 1 and it goes high for at least 20 ms during phase 2.

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AN2865 Current sink detection method

The DM check during phase 1 is needed to ensure that PS2 to USB adapters, pulling the DM line high, are not recognized as chargers. If a PS2 port is recognized as a charger, the high current drawn during the charging process could damage old PC motherboards which is why the detection is stopped if the DM line is high during this phase.

On the other hand, if DM is low during phase 1, phase 2 is entered. If a dedicated charging port is connected to the DP/DM lines, the voltage source connected to the DP line pulls the DM line over the V

DAT_REF

threshold because of the short-circuit between DP and DM inside the charging port. The same happens when a charging host port is connected. After detecting the V

DAT_SRC

source to the DM line which exceeds the V

voltage on the DP line, the charging host port connects a voltage

DAT_REF

threshold.

Both ports allow the detection to be successful.

On the other hand, if a standard host port is connected to the DP-DM lines, the DM voltage during phase 2 is always low because of the pull-down resistor connected to it. This causes the detection to fail.

Figure 5. STUSBCD01B current sink method applied to a dedicated charger

Phase 1

STUSBCD01

LOW

DAT_SRC

DAT_REF

LOW

I = 0

DCHG_DAT

Phase 2

STUSBCD01

HIGH

DAT_SRC

DAT_REF

HIGH

DCHG_DAT

I =

I = I

DAT_SINK

Dedicated

Charger

The maximum value of R V

DAT_SRC

DAT_REF

minus the voltage drop on the series R1+R2+ R

. The worst-case conditions are obtained using the minimum value of V

DCHG_DAT

recognized as a charger can be easily calculated:

and (R1+R2) and the maximum value for V

DAT_SINK

DAT_REF

and I

DCHG_DAT

DAT_SINK

Dedicated

Charger

must not go below

DAT_SRC

Equation 1

DAT_SRC(min)

- I

DAT_SINK(max)

(R1+R2+R

DCHG_DAT

) > V

DAT_REF(max)

Therefore,

Equation 2

DCHG_DAT

< [(V

DAT_SRC(min)

- V

DAT_REF(max)

)/I

DAT_SINK(max)

]- (R1+R2)

(max)

Considering 1% tolerance for R1 and R2 (470 Ω nominal) and min/max values taken from the USB battery charging specification and the STUSBCD01B datasheet, we obtain:

Equation 3

DCHG_DAT

< [(0.615-0.34)/(100*10-6)]-(470*2*1.01) = 1800.6 Ω

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Current sink detection method AN2865

This shows that even by adding R1 and R2 series resistors there is still enough margin over the dedicated charger’s detection (R

In the case of charging host ports, V

DCHG_DAT(max)

DM_SRC

= 200 Ω according to USB specs).

is applied directly to R2 as shown in figure 6. The maximum value for R2 which allows a charging host port to be recognized as the charger after it applies V

DM_SRC

and I

DP_SINK

to DM and DP can be calculated as follows:

Equation 4

DM_SRC(min)

- R2*(I

DAT_SRC(max)

) > V

DAT_REF(max)

Equation 5

R2 < (V

DM_SRC(min)

- V

DAT_REF(max)

)/I

DAT_SINK(max)

That is:

Equation 6

R2 < (0.5-0.34)/(100*10-6) = 1600 Ω

A value of 470 Ω (1%) is therefore well within limits.

Figure 6. STUSBCD01B current sink method applied to a charging host port

STUSBCD01

DAT_SINK

DAT_SRC

DAT_REF

Charging Host Port

DP_SINK

DAT_REF

DM_SRC

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AN2865 Dedicated charger detection method

5 Dedicated charger detection method

The STUSBCD01B's current sink detection method is not able to distinguish between a charging host port and a dedicated charger. If the result of the current sink method detection is positive, the user may want to perform a new detection to understand what kind of charger is connected. The dedicated charger detection method is successful only if a dedicated charger is connected to the DP/DM lines. If the STUSBCD01B is enabled and configured to use this method, after a stable V following operations:

– Phase 1: a current source (I

the end of this phase (100 ms min), both DP and DM lines are high, the detection proceeds to phase 2;

– Phase 2: I

DAT_SINK

current sink (same as in current sink method, 50 - 100 µA) is

connected to the DM line for at least 40 ms.

If at the end of phase 2 both DP and DM are low, the detection is successful and detect and/or Status/Method outputs are pulled high.

If a standard host port is connected, the dedicated charger detection method stops at phase 1 because the pull-down resistor on the host side pulls the DM line low.

The case of a charging host port (CHP) is a little bit more complex. During phase 1, the CHP connects the I I

DCH_SRC

and therefore pulls the DP line low, causing the detection to fail (the voltage drop

DP_SINK

current sink to the DP line. This current sink is stronger than

over the R1 resistor is negligible because of the low current flowing in it). If for some reason the voltage drop over I

DP_SINK

STUSBCD01B's DP pin exceeds the V phase 2 which fails because the DM line is driven high by V HCP (the DM line is expected to be low during phase 2). This scenario is shown in figure 7.

voltage is detected, the state machine starts the

BUS

DCH_SRC

= 15 - 30 µA) is connected to the DP line. If at

or R1 is higher than expected and the voltage at the

DAT_REF

threshold, the state machine proceeds to

DM_SRC

connected inside the

Figure 7. STUSBCD01B dedicated charger detection method applied to a charging host port

1.8 V

STUSBCD01

DCH_SRC

THDPL

DAT_SINK

(Connected

(Connected only during

only during phase 2)

phase 2)

1.8 V

DAT_REF

Charging Host Port

DP_SINK

DAT_REF

DM_SRC

The maximum value for the R2 resistor can be easily calculated:

Equation 7

DM_SRC(min)

- R2*(I

DAT_SINK(max)

) > V

DAT_REF( max)

Doc ID 15283 Rev 1 11/17

Dedicated charger detection method AN2865

Equation 8

R2 < (V

DM_SRC(min)

- V

DAT_REF(max)

)/(I

DAT_SINK(max)

)

Equation 9

= (0.5 - 0.34)/(100*10-6) = 1600 Ω

(max)

This result is consistent with the value in Equation 6 on page 10.

In the case of a dedicated charger, the maximum DP/DM short resistance which is detected as a charger can be calculated as follows. During phase 1, the value is not significant as I

DAT_SINK

is off, therefore the resistor series (R1 + R

DCHG_DAT

+ R2) is connected to a high

voltage on the DP side and is floating on the DM side. The voltage is high on both sides.

During phase one, the DM voltage is equal to the voltage drop over I

DAT_SINK

. This current sink is designed to have a maximum voltage drop, while in operation, of 150 mV. This value is lower than V

DAT_REF

so it is not critical. In order for the detection to be successful, the DP

line must also be low during phase 2:

Equation 10

IDAT_SINK(max)

+ I

DAT_SINK(max)

*[R

DCHG_DAT

+ (R1 + R2)(max)] < V

THDPL(min)

Equation 11

DCHG_DAT

< [(V

THDPL(min)

- V

IDAT_SINK(max)

)/I

DAT_SINK(max)

] - (R1 + R2)

(max)

Considering 1% tolerance for R1 and R2 (470 Ω nominal) we obtain:

Equation 12

DCHG_DAT(max)

= [0.6 - 0.15)/ (100*10-6)] - (470*2*1.01) = 3550.6 Ω

This result is higher than the one found in Equation 3 on page 9 for the current sink method. The actual result is even higher than this because in the above calculation we have considered a maximum value for the current flowing in the resistors higher than the real one. In fact, having two different current sources on the same branch causes the current to be set to the value of the weak current source (max 30 µA).

This shows that both methods are quite robust and there is sufficient margin in the choice of the R1 and R2 resistor values.

12/17 Doc ID 15283 Rev 1

AN2865 Dedicated charger detection method

Figure 8. STUSBCD01B dedicated charger detection method applied to a dedicated charger

1.8V

STUSBCD01

DCH_SRC

THDPL

(Connected only

(Connected only during phase 2)

during phase 2)

1.8V

DAT_SINK

DAT_REF

DCHG_DAT

Dedicated

Charger

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Software detection and hardware detection AN2865

6 Software detection and hardware detection

If the battery voltage is not high enough to wake up the application controller but is higher than 2.2 V, the STUSBCD01B can perform an automatic detection to allow the user to start charging the battery and make its voltage reach a value which will wake up the ASIC. This automatic detection is called hardware detection while the ASIC controlled detection is referred to as software detection.

When the ASIC wakes up, the result of the hardware detection is available until the STUSBCD01B is reset.

The hardware detection mode is automatically entered when the V In this mode of operation all V using the default method pin as described in Table 1 on page 5.

As in the software detection mode, the start of the detection process is triggered by the V

voltage going high. If the detection fails but the V

BUS

detection is performed once per second in an infinite loop as shown in the simplified flowchart in figure 9. This periodic detection is stopped only if:

– the detection result is positive; –the V –the V

Figure 9. HW/SW detection flowchart

BUS

HIGH

Timer expired

Or V

voltage drops under the V

BUS

voltage goes high.

goes

Yes

high?

voltage is not available.

referred inputs are ignored and the detection method is set

voltage is still present, a new

BUS

threshold;

detection

Is V

High?

Is V

High?

detection

TH_VBUS

Yes

End

(*)

Start

1s timer

Yes

Is DET

High?

End

(*)

Yes

(*)

DET = Detect. High if charger detected

14/17 Doc ID 15283 Rev 1

AN2865 References

7 References

– STUSBCD01B datasheet

– USB battery charging draft specification rel.1.1.

Doc ID 15283 Rev 1 15/17

Revision history AN2865

8 Revision history

Table 2. Document revision history

Date Revision Changes

21-Sep-2009 1 Initial release.

16/17 Doc ID 15283 Rev 1

AN2865

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Doc ID 15283 Rev 1 17/17

ST AN2865 APPLICATION NOTE

Specifications and Main Features

Frequently Asked Questions

User Manual

1 STUSBCD01B description

2 Application circuit

Figure 1. STUSBCD01B application circuit

Table 1. STUSBCD01B operating modes

3 Interface and control pins

3.1 Status/method pin

Figure 2. Status/method pin I/O

3.2 Detect pin

Figure 3. Detect pin output

3.3 Default method pin

4 Current sink detection method

Figure 4. USB ports

Figure 5. STUSBCD01B current sink method applied to a dedicated charger

Figure 6. STUSBCD01B current sink method applied to a charging host port

5 Dedicated charger detection method

Figure 7. STUSBCD01B dedicated charger detection method applied to a charging host port

Figure 8. STUSBCD01B dedicated charger detection method applied to a dedicated charger

6 Software detection and hardware detection

Figure 9. HW/SW detection flowchart

7 References

8 Revision history

Table 2. Document revision history