BQ77216: COUT/DOUT output capability and recommended resistor between VDD and VBAT

Hello Ethan,

Ethan Liu said:

1. What is the output voltage of COUT and DOUT of the BQ7721611 chip? What is the load capacity? (open-drain output)

If configured to be active-high 6-V. The voltage will be roughly 6-V to ~7-V.

For open-drain configuration, the output will be whatever the pull-up voltage is. The device would pull-down in this case, the datasheet provides the load capability for this to be ~3-mA:

Ethan Liu said:

2. In addition, from the block diagram of the datasheet, COUT and DOUT are directly connected to VDDD, so I am a little worried about the output voltage of them. Can you help provide the instructions of internal voltage conversion on this? Do you have detailed internal block diagram?

It would only connect directly to Vdd if the device is configured to pull-up to Vdd. This is an allowed configuration. From releases devices, it will only pull up to ~7-V or be open-drain.

Ethan Liu said:

3. In the schematic diagram of the BQ7721611EVM board, it was found that the power supply of VDD is connected to the highest node of the battery through a 100R 0603 resistor. Is the power consumption of this resistor appropriate? Because I need to use COUT and DOUT to drive 2 optocouplers, and the driving current of a single optocoupler needs to be 5mA. In this case, how should the size and package of the resistor between VDD and the highest node of the battery be selected?

If you use an open-drain configuration, current would be coming from the highest cell itself. So no current would flow directly from the IC itself. If it is pulling-low the current would be coming into the COUT/DOUT pins, not from Vdd.

Considering what you are talking about, I imagine that they would require a device spin. Could you provide some more detail on this project?

Best Regards,

Luis Hernandez Salomon

Hi Luis,

This is a 60V lawn mower project. Due to the requirements of the end customer, the AFE uses GMD1003 and BQ77216 is used as protection.

By observing the below figure, if the DOUT and COUT can only achieve open-drain output? and the open-drain output must achieve by external mos? And the pull-up resistor is connected to VDD in the below figure, how to transfer VDD to 6V-7V high level output?

Besides, I guess that the external mos is to enhance the driver capability of DOUT and COUT, because 3mA is too small. Do you think so? If you also think so, if the the function of DOUT and COUT is to output PWM signal?

In the EVM, the pull-up resistor of DOUT and COUT are connected to DO and CO, if the voltage of DO and CO is given through external power suppy?

Best regards!

Ethan

Hello Ethan,

Ethan Liu said:

By observing the below figure, if the DOUT and COUT can only achieve open-drain output? and the open-drain output must achieve by external mos? And the pull-up resistor is connected to VDD in the below figure, how to transfer VDD to 6V-7V high level output?

No that's not quite correct. DOUT and COUT in the Figure 9-1 would be in an active-high configuration, more typically 6-V active-high. 

Open drain means that the device will keep the pins in high-Z mode. So it will not output any voltage. So it is not possible to turn-on the external N-Channel MOSFETs with an open-drain configuration (Unless there's an external pull-up voltage.

Normally this device is meant to drive a chemical FUSE. So the N-Channel FET pulls down the third terminal of the chemical FUSE to blow it. The N-Channel FET would turn-on when COUT/DOUT go high to ~6-V. 

Ethan Liu said:

In the EVM, the pull-up resistor of DOUT and COUT are connected to DO and CO, if the voltage of DO and CO is given through external power suppy?

There are no pull-ups on the EVM. DO and CO is just the same as DOUT and COUT. Meant to monitor the voltage of the outputs.

Best Regards,

Luis Hernandez Salomon