BQ25886: I want to test whether USB CDP can be used

ZheTao Xie

Part Number: BQ25886

HI Ricardo！

If I want to test whether USB CDP can be used,How do I change my EVM connection？

The portable device outputs a nominal 0.6-V output on the D– line and reads the voltage input on the D+ line. The portable device concludes the equipment is connected to a CDP if the data line being read remains less than the nominal data detect voltage of 0.3 V. The portable device concludes it is connected to a DCP if the data line being read is greater than the nominal data detect voltage of 0.3 V.
How can I get this 0.6V voltage？I try to put D- in PULL-UP, D + in PGND,but it doesn't work .It still works in SDP mode.

Another question，When calculating the output capacitor, what is the ripple voltage △VSYS of the power supply? The calculation formula given in the data sheet contains CSYS. Isn't this the value I asked for.At the same time, I also want to know the calculation method of PMID capacitor(C9)and SW capacitor(C14).

Best regards from China,

Zhetao Xie

over 5 years ago

0 Ricardo over 5 years ago

TI__Genius 10385 points

Zhetao,

CDP can be tricky to get working properly as some CDP ports expect an enumeration from the charger that is usually provided by the host controller on the end equipment. Without this enumeration, the CDP will operate as an SDP (500mA, max). To simulate this enumeration, you can pull D- high to 0.8V almost immediately. Hold it high until you see /PG flicker and let D- float again. This should take no more than ~1 sec. Below I have attached a scope shot showing the D+/D- handshake and a multimeter showing the IVBUS.

Normally customers design based on typical application schematic values and equation 9 provides an approximation of the output ripple they can expect. If you would like to calculate a CSYS value, rearrange the equation and set VSYS ripple value.

Thanks,

Ricardo