Questions tagged [open-drain]

Questions about Open-Drain devices and protocols. Open-Drain connections have two states, Open/Floating, or Drain to ground. Typically require Pullup resistors.

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72 views

Confused about pull-up resistor

I'm a software guy trying to implement a 1-wire interface. I have modified a USB-to-UART device as indicated here, but I don't understand the "pull up" resistor concept. Googling "open-...
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0answers
30 views

How to drive an open drain/collector?

I'm connecting a Digi XBee radio to a Kinetis microcontroller and would like to know how to control reset. The XBee datasheet describes the reset pin 5 as both input and open drain output: ...
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1answer
78 views

Why have resistors on a signal line

I'm new to electronics so forgive me if this is an obvious question. I'm making a small circuit to read out a digimatic caliper. There are many designs only and I'm wondering why some components are ...
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7answers
2k views

Why are open-drain outputs needed?

I have almost no knowledge in electronics and electricity. I've encountered the concept of open-drain output recently and I think I got the idea. What I have understood is that it is a transistor ...
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1answer
96 views

What to do with unused open drain pins

I have a light sensor IC. I have 2 questions: The I2C Lines is connected between the microcontroller (3.3V domain) and the light sensor IC. The microcontroller is placed on a PCB and the light sensor ...
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1answer
80 views

STM32L1 GPIO pin configuration - Power supply current increase due to pin with open-drain setup

Setup I have an STM32L151 mcu(application processor) and on its PB5 pin I have a peripheral (SARA-N3) connected. The requirements for the peripheral are that the pin is configured as an open drain ...
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6answers
2k views

Why do we need NMOS transistors for NAND gate?

I have a hard time understanding how gates are built from CMOS transistors. For example, I don't understand why do we need the NMOS transistors if the PMOS transistors will already produce the desired ...
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2answers
171 views

When using an open-drain output to drive an NPN transistor, can the base resistor be replaced by a pull-up?

Assuming the value of R1 is the correct value for the base resistor for the given motor L1, is it okay to omit the additional base resistor, used in push-pull applications, for an open-collector ...
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3answers
112 views

Trying to understand push-pull output mode and open-drain output mode in a MCU's GPIO pin

I have a MCU (STM32H7xx) whose GPIOs, when configured as output, can be configured either as open-drain or push-pull. Before seeing this, I though that open-drain meant hihg-Z, however I don't see how ...
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1answer
58 views

Understanding ECU Lowside Output Circuit

Hello StackExchange, I'm trying to understand this low side output circuit so that I can interface it with a load. I will have to add another MOSFET/Relay/Driver of some description on the lowside ...
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1answer
103 views

TLC5940 resets itself when driving certain DC motors

So I had the following setup: I was just driving a small DC motor with this circuit by either sinking current on pin 0 or 1 on the TLC with a motor voltage of 5 volts and everything was fine. The ...
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1answer
43 views

Serial Communication with HV5623

I'm just trying to understand the communication protocol with the HV5623. Here is the Function table: I want to be able to hold the HV output while I shift in the new states into the shift register, ...
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1answer
41 views

what will happen when providing two pull up resistors in same line

If two pull ups given in a situation one pull is 4.7 K-ohm and other pull up is 10 k-ohm was given to open-drain pin then what will happen? Imagine the open-drain was connecting to an IO pin of an ...
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1answer
43 views

Understanding Master/Slave trigger configuration through open-drain GPIO

I am working with two industrial cameras that I want to trigger synchroniously through hardware triggering. For this the STROBE_OUT pin (which is an open drain pin) from one camera (Master camera) ...
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1answer
72 views

Can several Ethernet PHYs cause damage to one another if they transmit on MDIO bus simultaneously?

I have 4 ethernet devices (1 PHY - AR8035; and 3 Dual PHYs - DP83849IFVS) on my custom PCB board. ICs are controlled by SoC AM335x via MDIO bus. Previous revisions of the board worked fine. New ...
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3answers
76 views

Connection of two open drain outputs to control common LEDs by PIC32MZ

I want to use this Single Cell Li-Ion Battery Charger (MCP73833). The pins STAT1 STAT2 and /PG are an open collector outputs and it will be connected to low power LEDs as shown in the schematic. If I ...
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1answer
40 views

Question about open drain

In which region does a NMOS work when its drain is open circuit? Let's say the input is high voltage lavel, how can I determine whether it is saturation of triode region when drain is open?
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1answer
843 views

Why do they keep series resistor with each open drain output during Wired OR logic?

In a design schematic I have seen series resistors being used in WIRED OR logic. All 4 input signals are open-drain signals and hence being represented as switches. Can anyone explain why we need R1-...
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1answer
68 views

How to drive pin to open drain/collector?

I'm looking at a datasheet for a bit of hardware I am adding to a design. However, one of the pins on the chip is listed as: ON/OFF - 1.8V must be driven to open drain/collector It does not specify ...
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1answer
107 views

What about MCP23S17 GPIO pins output ports being also used to be read by input pins?

We are connecting Raspberry Pi3B with some MCP23S17 expanders: MCP23S17. I have read that they could emulate an open-drain outputs, playing with high Z state of the pin when configured as input. ...
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1answer
187 views

Open collector and open drain logical gates

Can somebody explain what open collector and open drain mean? I'm a CS student, and I'm really a newbie in terms of electronics and I only managed to find some "expert level" explanations, which I ...
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3answers
501 views

GPIO Open Drain LED driving

I was trying to understand GPIO open drain configuration. As far as I understood, to avoid floating output, one should use internal or external pull-up resistors. This is OK. However, I saw multiple ...
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1answer
89 views

Open collector / drain question

I'm trying to to find the best way to force an inverting amplifier to postive saturation with a gate input, but otherwise leave the function of the op-amp intact. I've come up with a few ways to do ...
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2answers
216 views

Pin compatible shift register with open drain outputs

I'm looking for a pair of otherwise interchangeable 8 bit output shift registers where one has open drain (or open collector) outputs, and the other has "normal logic outputs" (ie a pull up transistor ...
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1answer
107 views

MCU PIN Open Drain Protection

I am trying to control a PC fan using a micro-controller(STM32F0) According Intel's PWM fan spec, the fan will pull up the PWM signal to up to 5.25V. ...
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1answer
37 views

Open and short test for 2 ground pin

If a device has two ground pins. Using the normal open and short test will not tell if one ground pin is open and the other is good. How to detect this kind of situation? Thanks.
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1answer
99 views

Usage of 74LVC1T45 in open-drain case

I want to do one 'universal' or 'multiprotocol'-capable IO block and currently thinking of using 74LVC1T45 level translator to do the communication between two different voltage leveled systems. I ...
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1answer
73 views

Bidirectional level translator using N channel MOSFET

I'm using a n channel MOSFETa bidirectional level translator. The case when the body diode conducts the source end will be literally 0V or forward voltage of body diode, so the difference in voltage ...
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2answers
726 views

I2C Communication Open drain benefits vs Push pull

I am reading this TI I2C App Note for understanding the I2C operation and need to understand how Multi master I2C will operate. I was not able to understand this para in the app note, "Since no ...
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3answers
218 views

logic gate's open drain output pulled to voltage higher than supply voltage

I am using 74AHC1G09, it has an open drain output. It says the maximum Vo is 7V, but also says "The input and output voltage ratings may be exceeded if the input and output current ratings are ...
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3answers
1k views

How can I float a pin that otherwise should be low?

I want to enable/disable a TI TPS54302 buck regulator with a microcontroller. The enable (EN) pin should float to enable the device, or be tied low to disable it. I currently have the EN pin ...
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1answer
206 views

Driving 5V mosfet with 5V tolerant pins on 3.3V dsPIC33F

I need to drive a MOSFET (IRFZ44N) with a microcontroller (dsPIC33FJ64MC202). The problem is, the PIC runs at 3.3V and the FET's Vgs(th) lies between 2V and 4V, so there will be times my PIC won't ...
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1answer
673 views

How to invert an open drain output?

I am trying to use a output signal to reset a counter, but the signal I have is "low when counting" and I need "low during reset". I want to "invert" an open drain output to a new signal so that when ...
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0answers
149 views

UART in open drain causes mosfet switching voltage spikes [duplicate]

I'm using an ATMEGA3208 and I have configured the UART peripheral to open drain mode. I'm using an external pullup 1KΩ. I'm experiencing switching voltage spikes that goes negative. They are about 0....
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4answers
589 views

multiple Open Drain UART over long distance [duplicate]

I have 9 microcontrollers ATMEGA3208 and I have connected the RX and TX lines of 8 of them in parallel. My configuration is in master-slave. The master microcontroller send data to one of the 8 RX ...
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0answers
296 views

Can I connect two MCUs directly to one micro SD card without additional components?

I am new to this community so I am sorry if I'm asking in a wrong place or something out of topic. I think I have considered everything. :) So, now the basic info: I am working on a project which ...
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1answer
653 views

Converting Open-Drain to Active-High (low voltage, low power)

In my design, I need an RTC (PCF85263A) to enable a boost converter (TPS61021A) after the RTC alarm triggers an interrupt. The interrupt pin on the RTC (INTA) is open-drain, but the enable pin on the ...
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2answers
665 views

Open Drain pin not going to GND

I'm using an MCP73833 (link to the datasheet) as the charging chip in one of my projects. We use its STAT1 pin (which is an open drain that goes to GND when a battery is being charged and floats if ...
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1answer
93 views

Pullup resistor operation between the ESP32 and a Bus MCU

I have an ESP32 as my main controller and a Bus. The bus operates where Pins 55 & 56 needs to be HIGH in order for the bus to be OFF. My ESP will drive the bus by enabling it by pulling those ...
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2answers
161 views

Microcontroller Wired-OR connection

I would like to connect several microcontrollers as shown in the circuit diagram below. The software makes sure that the PA1 pin always has the low or floating state. It's a kind of open drain ...
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1answer
268 views

Does direct GPIO communication between 2 microcontrollers requires pull up/down

If I want to use GPIO pins of two microcontrolles as a mean of simple communication (e.g. reporting an event by sending 1 or 0), Do I need to enable internal pull up or pull down resistors on any of ...
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1answer
401 views

Multiple Open Drain Outputs to one MCU-pin

i want to use two DRV8844 (http://www.ti.com/lit/ds/symlink/drv8844.pdf) Motor Drivers. It has an Open-Drain output, that indicates an error, when it is LOW (nFault). What happens, when i connect ...
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3answers
380 views

Are activated open-collector and open-drain circuits wasting energy?

Consider the following reference circuit for a 6N137 optocoupler. My understanding is that this circuit uses a pull-up resistor on the output node so when the optocoupler led is activated, the ...
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3answers
222 views

Microcontroller overheating when sensor is plugged in [closed]

I am building a board based around an STM32L051C6 microcontroller, which will measure a hall effect sensor (AH3362Q) and count the time in between the edges the sensor sees. The sensor is powered from ...
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1answer
298 views

GPIO connected as open-drain to opto-isolator's cathode

When connecting GPIO output pins (RPi, uC, ...) to an opto-isolator, the classical way I know is the following (at least I understand that it can roughly be depicted like that): simulate this circuit ...
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1answer
67 views

si7021 with 5V MCU [duplicate]

i need to connect Si7021 wich is an 3.3v I2C humidity sensor with Arduino, this sensor has open drain SCL and SDA drivers. is it possible to connect this sensor directly to Arduino 5V?.
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1answer
192 views

Identify this open collector serial protcol

I'm trying to analyze the serial link between two devices, respectively a motor controller board and a Li-Po battery manager, which battery powers both devices. The application is a battery-powered ...
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2answers
642 views

Driving a power-good LED with two open drain outputs

So I have two same DC/DC step down converters and I'd like to have a green LED driven with the converters' open drain PGOOD signals. The signal is active-high and the LED should be on, when the power ...
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1answer
946 views

STM32F303 Microcontroller open drain GPIO, Can it reach / be pulled up to 5 Volts?

I hope you are all doing well... :). I'm working on a project with pulse width modulation however I need my logical high output to be 5V. However, as my Vdd is 3.3V, the output high level is ...
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2answers
682 views

connecting Open drain and Push pull outputs to drive the same pin

I am designing a circuit in which has a voltage supervisor (MCP121-33)with active low output nRST connected to RESET input of the microcontroller which is straightforward. Also, there is a another ...