Search results

  1. R

    Voltage threshold issue

    Hi all, We are trying to use a FT230x CBUS3 to control the BOOT status of a STM32F215. The boot pin of the STM32 is tied to 0V via a 10K pull down. The internal pull up of the FT device is used to toggle the boot pin. I have attached a diagram. We are seeing a voltage of 0.5V which does not...
  2. R

    Usb 2.0 component selection

    , I am using USB 2.0 full speed for a design. Power to the electronics is 5V from the USB, into a FTDI device ( which has an internal 3V3) regulator to power my electronics. I have a couple of questions, FTDi recommend a LC filter, they have also added an extra 10nF at the input and 4.7uF to...
  3. R

    Reset issue

    Hi all, I am using a ft232r usb UART device. I use cbus0 to control the reset line of a supervisory ic @3v3. The supervisory ic also connects to the reset line of a PIC microcontroller. The supervisory device is active low with a push pull output. It is a device from ON semi CAT809JTBI-GT3. I...
  4. R

    USBC

    Hi all, I am using a USB C connector in a design. This is a receptacle that fits into a PCB. There are 2 x D- and D+ lines. These are connected together as per the guidelines. This is a through-hole connector. I have attached a picture of the layout of the said connections. One set of tracking...
  5. R

    Automotive reverse polarity

    Hi all, I am using 12V from a car battery to power electronics. The current consumption of my circuit is 1A max, however it will run closer to around 850mA. I need to add reverse polarity protection to my circuit. I have opted for a simple Schottky diode solution, as I am limited for PCB space...
  6. R

    DCDC converter output power

    Hi all, I have an application described below. 12V from car battery going to Buck DCDC converter (LM53600) to generate 5V. 5V from DCDC output feeds into LDO which generates 3V3 (MCP1826) This 3V3 powers the Micro, Bluetooth and WiFi devices. To simulate current of 0.5A, I put a 5R load...
  7. R

    DC DC buck to LDO

    Hi all, I have an automotive application (powered from 12V car battery). I am looking to drop 12V to 5V using a DC DC buck regulator (one of my circuits require a 5V supply, then use this 5V to power a LDO at 3.3V fixed). The current will be 600mA max. Looking at low quiescent current. I am...
  8. R

    MOSFET

    Hi all, I have the circuit connected below, I am using the following AQY222R2T MOS Relay. Basically I am using the MOS relay to switch an output of 10V @ 400mA. The device is AQY222R2TY I have worked out the input resistor as R = Vin - VF ---------- IF From the datasheet this works out as...
  9. R

    Tracking and layout help

    Hi all, I need some advice please on a layout of PCB. I have a power track which is for a 12V 3A supply line. I need to add a led + resistor to this line as an indicator. My question is, do I need to make the track width for the led + resistor the same as the width of the supply line? Or can I...
  10. R

    USB differential signals

    Hi all, I am laying out a board that has a USB connector. It will be used for USB 2.0. From the connector the signals route out to a TVs clamp then to a FTDI chip. However the D+ and D- signals cross over when they go to the FDTI chip to get to the appropriate pins. How can I overcome this? Are...
  11. R

    USB filtering confusion

    Hi, I have attached a part of the datasheet for a FTDi device. The evaluation schematic board has a filter and 10nF connected between VBUS1 and 0V. I can't see the point of the filter as VBUS1 is connected directly to the FTDI chip (pin 12)? The FTDI hardware recommendations state there is a...
  12. R

    USB connector shield

    Hi all, I wonder if someone could please clear this up for me. I have a portable tablet device which has a USB type A connector. Which I am going to connect a separate set of electronics, to get power and GND via a micro USB connector. Do I need to connect the shield of the micro USB to OV or...
  13. R

    USB upstream downstream

    Hi, I wonder if someone could please clear this up for me. I have a set of electronics that will be powered from 5V USB. I need some USB ESD/EMI protection. I have seen quite a few solutions but some are upstream and others downstream. I have looked at various sites but am still confused. Which...
  14. R

    Car battery voltage spikes

    Hi all, I was after a bit of advice. I want to measure voltage spikes from a car battery using my scope. I am building a car voltage monitor (to show state of battery), I am a bit worried that I might damage my scope. Are there any precautions that I should take? Do I need some kind of divider...
  15. R

    Testing TVS diode

    Hi all, I have selected a SA20A to try out and test for my own understanding. I am thinking of the following: 1. Measure VBR by placing resistor in series say 10K at 10V so we get 1mA. Would this give me the break down voltage. 2. The reverse voltage, should not affect any operation of a...
  16. R

    Relay help (opto mos)

    Hi all, I have attached a schematic of an issue. I have a relay AQY212S, which is fed from a car supply of 12V. This is then switched by a relay. The relay is breaking down, I think it is due to voltage. The relay is rated at max load voltage of 60V. I am thinking of using a diode suppression...
  17. R

    Spi connections

    Hi all, I am connecting a 4 wire spi to 4 wire spi. Master is a micro, slave is a temp sensor. Do I connect as follows SCLK to SCK SS to CS MOSI to MOSI MISO to MISO The micro is the master. Thanks in advance
  18. R

    Why a pull down resistor for transistor base

    Hi I have attached a image I saw on the web. The transistor is used to drive a relay module by inverting the logic, which ensures that the relay PNP is switched off too. Why is the 10K required pull down from base of transistor? How is this value calculated? If the input of the transistor...
  19. R

    Padstack footprint

    Hi I am doing a footprint for a smd 0603 resistor. Can someone clear what padstack (pad, paste mask and solder mask) and footprint dimensions i need. I believe the footprint is from the land pattern. Its my first design so please bear with me. Thanks
  20. R

    LC parallel tank circuit

    Hi all, I have seen a common emitter transistor circuit with a LC parallel tank circuit connected between the base and OV. I want to ask why this would be the case and how to test it. If I found the resonance point by sweeping frequencies on the LC circuit (i think it is around 140KHz), should...
Top