HT7533 can be used for STM32F105RBT6 power supply?

[ax369]

Many engineers I know use HT7533 as power supply for STM32F105RBT6 in automotive boards. I looked up the specs, and found that HT7533 is only rated for 100mA. Is it too low for STM32F105RBT6? Is TI's TPS7B91 or TPS7B92 better in this case? Thank you.

[Peter BENSCH]

First of all, a note: the STM32F105RBT6 are not approved for automotive applications, so they may only be used there for additional devices.

As for your question: the STM32F105RBT6 itself requires a maximum current of slightly less than 100mA. However, there are several things to consider:

• An STM32F105RBT6 is usually surrounded by other components whose current requirements must also be taken into account. For example, LEDs could be driven on the GPIOs, which would exhaust the maximum permissible currents IVDD or IVSS of 150mA.
• The HT7533 is an LDO that converts the entire voltage difference between input and output into heat. You have not specified your input parameters, but in the automotive sector, 12V operation is assumed to be up to 38V, which the connected devices must be able to process. If you then allow 100mA to flow, the 3.3V regulator (every LDO, not just the HT7533) burns (38V-3.3V)*0.1A = 3.47W, for which it and its cooling must be designed. However, the HT7533 can only withstand a maximum of 30V, and it can only dissipate a maximum of 0.7W in the TO-92, even less in the smaller packages. The TPS7B91 can also only handle a maximum of 1.375W power dissipation at 25°C, so it would also be overloaded in this scenario.

I have only picked out a few things to consider. For better help, you would need to provide a few relevant details about your application, e.g.

• minimum and maximum input voltage
• devices connected to the STM32F105RBT6, possibly with their current requirements

Regards
/Peter