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# BQ24800: How to enter hybrid power boost mode in my application

Part Number: BQ24800

Hi team,

The issue is we cannot enter hybrid power boost mode when we use docking to provide power to system.

The docking power is 60W(20V/3A) and input sense resistor is 5m ohms.

I know the condition to enter hybrid power boost is below:

1. Writes 1 to REG0x37[2]

2. Input current register REG0x37 must be set higher than 1536 mA

3. Input current is higher than 104/107% of input current limit

If we want to enter hybrid power boost mode, we need to set REG0x37 to 0x0600 and input current have to exceed 3194mA.

But it will cause the docking over current due to it's maximum power 60W.

My questions are below:

1. Why is it necessary to design a threshold of 1536mA to enter the hybrid power boost mode? Is there any special reason?

2. Do we have other way to decrease this value for entering Hybrid power boost mode early (customer cannot change input current sense resistor)?

3. If there is no way to change hybrid boost mode threshold 1536mA, do we have other methods to let this system to enter hybrid boost mode?

Best regards,

Hardy

• Hi team,

Any update?

Best regards,

Hardy

• Hi Hardy,

As you mentioned, the InputCurrent() register must be set to a value of 0x0600 or higher in order to enter hybrid boost mode. This corresponds to an input current of 768 mA with Rac = 20 mΩ, 1536 mA with Rac = 10 mΩ, or 3072 mA with Rac = 5 mΩ. I don't think there is a way around this requirement. Please note that the InputCurrent() register is 0x3F, not 0x37 (as you wrote in your original post).

An input current threshold of 1536 mA to enter hybrid boost mode is not a problem in typical notebook applications. It is assumed that the adapter can handle lower currents on its own, without needing the battery to provide supplement current.

I suggest that the customer should use the default value of Rac = 10 mΩ instead of 5 mΩ. This will lower the actual input current threshold to enter hybrid boost mode to ~1.6 A, which is well within the docking power's 3A current capability.

Best regards,

Angelo