STM32f429 and USB_OTG_FS connections

Haresh Prajapati · ‎2017-12-01

Posted on December 01, 2017 at 09:40

Hello STM members,

Currently i am working on STM32f429 (144-LQFN) controller.

For this project we have requiremnt USB_OTG_FS interface.

I have query regarding USB OTG connections.

1. Our system is working on 3.3v Now we want to connect USB micro-B connector to our controller.

2. If we connect USB device to our controller is there any problem because USB working on 5V.

3. Is there any level sifter is needed ?

##stm32f429 ##stm32f ##usb-otg-fs

Ben K · ‎2017-12-01

Posted on December 01, 2017 at 10:12

The controller in USB host role shall provide 5V power over the bus to supply the connected devices. The USB data lines use the 0 .. 3.3V voltage range (e.g. FS device has pull-up on DP to 3.3V). Therefore you need a 5V power supply in your design, but the controller should be powered by a 3.3V supply so it has the appropriate supply voltage to drive the USB data lines.

Haresh Prajapati · ‎2017-12-01

Posted on December 01, 2017 at 13:46

Hello Ben K,

Thanks for your reply it help full for us.

Here i share our system block diagram. so you can help us in proper way.

USB working which we need

1. Provide power to charging IC ,fuel guage for charging Battery

2. STM32f429 has OTG support so we want to take data from storage.

Question

So, what is the easiest way to make this functionality in proper manner ?

Ben K · ‎2017-12-01

Posted on December 01, 2017 at 15:43

Let me get this straight: the device is battery-powered, and uses the USB port in device role when connected to a host/charger to charge the battery. The same USB port is used during battery-operated mode to attach a mass-storage device. Is this correct?

The other thing that's missing is how the system itself is powered, e.g. by a 3.3V LDO from the battery.

What you might want to do is get a boost converter that produces the 5V USB supply from the battery voltage. Another thing to take care of is the power switching, i.e. the 5V is only supplied on the USB port when the controller is switched to host mode. You can do this by controlling the enable pin of the boost converter by the MCU. For further OTG design hints refer to the freely available schematics of any OTG supporting discovery board (e.g.

STM32F429I-DISC1)

on the ST website.

Haresh Prajapati · ‎2017-12-02

Posted on December 02, 2017 at 09:50

Dear Ben Thanks for your reply,

Regarding USB operation:- Yes you are right, We want to use USB as battery charge as well as m

ass storage device.

Yes i miss LDO and thanks for notifying me i am adding LDO 3.3v and here i attached updated Block diagram.

Regarding your inputs, my inputs are below which i understand.

1. We can add boost converter which is convert into 5V from battery or LDO.

2. We use boost converter which has EN(enable) pin so we can control boost converter when USB mass storage is detect on USB_OTG_ID pin.

Am i right ?

When i seem schematic of

STM32F429I-DISC1 then i realized that 5V is given by STMPS2141STR power switch and control of this switch has MCU.

But i has one query regarding USB_VBUS_FS connection. When EN signal is on 5V applied to the VBUS of USB and this VBUS connect with PB13 pin so this 5v might be applied to PB13, So am i right? or i am done something wrong.

Here i am attached USB section of STM32F429I-DISC1 board.

Ben K · ‎2017-12-03

Posted on December 03, 2017 at 23:15

1. It's much harder to justify connecting the boost converter to the LDO output than to the battery.

2. Yes

The VBUS pin of the MCU is one of the 5V compatible pins - it can only drive VDD as output, but connecting it to 5V as input won't damage it, and senses the input level correctly.