AN2865 datasheet(11/17 Pages) STMICROELECTRONICS

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AN2865

Dedicated charger detection method

Doc ID 15283 Rev 1

11/17

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 VBUS voltage is detected, the state machine starts the

following operations:

– Phase 1: a current source (IDCH_SRC = 15 - 30 µA) is connected to the DP line. If at

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

proceeds to phase 2;

– Phase 2: IDAT_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 IDP_SINK current sink to the DP line. This current sink is stronger than

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

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

the voltage drop over IDP_SINK or R1 is higher than expected and the voltage at the

STUSBCD01B's DP pin exceeds the VDAT_REF threshold, the state machine proceeds to

phase 2 which fails because the DM line is driven high by VDM_SRC connected inside the

HCP (the DM line is expected to be low during phase 2). This scenario is shown in figure 7.

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

Equation 7

VDM_SRC(min) - R2*(IDAT_SINK(max)) > VDAT_REF(max)

Figure 7.

STUSBCD01B dedicated charger detection method applied to a charging host port

DAT_REF

DAT_SINK

DCH_SRC

STUSBCD01

DAT_REF

DP_SINK

DM_SRC

Charging Host Port

1.8 V

(Connected

only during

phase 2)

THDPL

DAT_REF

DAT_SINK

DCH_SRC

STUSBCD01

DAT_REF

DP_SINK

DM_SRC

Charging Host Port

1.8 V

(Connected

only during

phase 2)

THDPL

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