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

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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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