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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How many loads can I have on an open drain output?

So I am using this AND gate which has an open drain output. I am trying to determine how many loads that I can place on this output. I see in the datasheet, that the Iol is over 1mA, but I am unsure ...
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Difference between open drain and push-pull modes

The figures show diagrams of line signals: the first in the open-drain + pull up mode, the second push-pull + pull-down. There are several questions: Why does a push pull output have a faster slope ...
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Is a pull-up on open drain required when output is not used?

On a LTC3886-1 I can read this: I see that all open-drain outputs are tied to VDD on the following application schematics: Is there a reason why pull-ups seem required when the output is not used?
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What is meant by "monotonic reset"?

Can someone tell me what does it mean by Monotonic Reset? I read this below paragraph from this document and got this doubt. A reset generator / voltage monitor is one option to provide a proper ...
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How many times larger should the gate resistors be than the drain resistor?

I was asked this question in class and could not come to a concise answer. This is question was asked in terms of MOSFET design. Are there any general rules or guidelines to follow?
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Can I connect a pull-up to a open drain output with current source ? Using LTC4124 charge controller

On the LTC4124 there is a CHRG pin connected to an LED. Datasheet says it is a open drain but indicates a current source between source and ground. Could I use a pull up resistor connected to VCC and ...
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MOSFET parasitic capacitance (Cds) behavior when the source is floating (open)?

I recently looked into an interesting circuit designed by some other guys 6 years ago. The I2C SCL/SDA looks weird. The SDA is an open drain output but somehow it was designed this way, connected to a ...
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2 answers
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Can I connect the pull-up resistors of I2C lines to 3.3 V on a 1.8 V device?

I need to use the following sensor in my project : AS7341 (ams). It is a spectrometer whose data are accessed through an I2C inteface. The datasheet can be found here. It is stated that its power ...
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3 answers
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Power Consumption for Open Drain Communication

When using an open drain communication scheme, like I2C, it seems that the majority of power consumption comes from the sinking of current through the pull up resistor when a logic 0 is transmitted. ...
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Expected behaviour of a non-inverting buffer IC

I am using an NL17SZ07 buffer w/ open drain. Is it to be expected that I need to pull the output high with a pull-up resistor to have the output behave as expected? I would have anticipated that the ...
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On what factors does the I2C pull up resistor values depend upon

I was reading this Article regarding the pull up resistor calculation. I understood that the value of the pull up resistors depend upon the currents, the supply voltage and the Logic Level voltages ...
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Can I leave an unused open-drain output disconnected?

I'm designing a circuit using the MAX22203 motor driver and it has a few open drain outputs to indicate current throttling. In my design I don't need to read these outputs, so my question is what ...
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Using a series diode to protect input with pull-up resistor

I have a switch input that I need to protect from miswiring to 12V battery power, reverse wiring to power, ESD and transients. I tried using a Zener diode circuit to handle the overvoltage: Steering ...
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How do open-drain I/O pins work on a PIC16 microcontroller?

I'm trying to understand how to operate an open-drain I/O port on an older PIC (PIC16F1718.) My goal is to use it for bit-banged bidirectional open-drain I2C communication. I know how to enable and ...
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How to wire two open-drain logic outputs to a three pin bi-color LED

I am very new to working with electronics; my main experience is in programming. I am working on a project and intend to use this MCP73833/4 Li-Ion Charger. It has two "Charge Status Output" ...
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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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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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1 answer
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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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7 answers
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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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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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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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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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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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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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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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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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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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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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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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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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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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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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2 votes
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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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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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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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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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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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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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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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1 answer
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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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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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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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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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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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1 vote
3 answers
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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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8 votes
3 answers
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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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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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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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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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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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