BQ24295 Datasheet, PDF (23/45 Pages) Texas Instruments – I2C Controlled 3A Single Cell USB Charger

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VDP_SRC
VLGC_HI
CHG_DET
D+
IDP_SRC
IDM_SINK
VDAC_REF
bq24295
SLUSBC1 – SEPTEMBER 2013
D-
RDM_DWN
Figure 23. USB D+/D- Detection
DCD (Data Contact Detection) uses a current source to detect when the D+/D– pins have made contact during
an attach event. The protocol for data contact detect is as follows:
• Detect VBUS present and REG08[2]=1 (power good)
• Turn on D+ I_{DP_SRC} and the D– pull-down resistor R_{DM_DWN} for 40ms
• If the USB connector is properly attached, the D+ line goes from HIGH to LOW, wait up to 0.5 sec.
• Turn off I_{DP_SRC} and disconnect R_{DM_DWN}
The primary detection is used to distinguish between USB host (Standard Down Stream Port, or SDP) and
different type of charging ports (Charging Down Stream Port, or CDP, and Dedicated Charging Port, or DCP).
The protocol for primary detection is as follows:
• Turn on V_{DP_SRC} on D+ and I_{DM_SINK} on D– for 40ms
• If PD is attached to a USB host (SDP), the D– is low. If PD is attached to a charging port (CDP or DCP), the
D– is high
• Turn off V_{DP_SRC} and I_{DM_SINK}
Table 2 shows the input current limit setting after D+/D– detection.
Table 2. bq24295 USB D+/D– Detection
D+/D– DETECTION
0.5 sec timer expired in DCD (D+/D-
floating)
USB Host
Charging Port
INPUT CURRENT LIMIT
Proceed to Non-standard adapter
detection
500 mA
3A
REG08[7:6]
00
01
10
When DCD 0.5 sec timer expires, the non-standard adapter detection is used to distinguish three different divider
bias conditions on D+/D- pins. When non-standard adapter is detected, the input current limit (REG0[2:0]) is set
based on the table shown below and REG08[7:6] is set to 10 (Adapter port). If non-standard adapter is not
detected, REG08[7:6] is set to 00 (Unknown) and the input current limit is set in REG0[2:0] to 500mA by default.
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