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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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Output mode configuration on GPIOs: When to use push/pull vs open drain?

Hello guys I'm relatively new to Embedded engineering. I wanted to know if there's any specific rule that experienced embedded engineers use when selecting when to use one of these output ...
tadm123's user avatar
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1 answer
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What's the real absolute maximum output voltage of the 74LVC07?

Datasheets for the 74LVC07, such as this one from TI, and this one from Nexperia, state that the absolute maximum output voltage for the open-drain outputs (in high state) is +6.5V. There is a table ...
Simon Fitch's user avatar
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How to connect buffer with open drain to opto isolator circuit?

I'm trying to connect SN74LVC07A open drain output to Si87xx opto isolator circuit. I have tried to connect 10k and 100k pullup and that did not seem to work. This is due to the current being limited. ...
shotsimon's user avatar
2 votes
1 answer
49 views

Efficient method to isolate open drain output from mcu

I'm using the LTC4418 power path controller My power sources include a solar panel which can produce voltages close to 30V. I want to send the VALID status outputs to my MCU but it is on a different ...
davegravy's user avatar
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2 answers
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What types of outputs apart from Open Drain/Open Collector exist?

I am trying to grasp the idea of an Open Circuit/Open Drain, but I haven't been able to find, which other types of outputs exist ("Closed Circuits", so to speak). It would be helpful, if you ...
Andrew's Quest's user avatar
3 votes
2 answers
311 views

How can I make a non-inverting open-collector (or open drain) with a single transistor?

I had a PCB made for a homebrew SBC but while waiting for the boards I discovered a bug. I have a 74HC138 output (I believe this is just normal push-pull) that I need to hook up to a CPU pin but I ...
Procrastin8's user avatar
4 votes
2 answers
476 views

Why don't we use decoupling capacitors for open-drain outputs?

If an IC with open-drain outputs (and hence pull-up resistors) is used, we of course put decoupling capacitors on the IC supply, but why don't we also add decoupling capacitors between the power pin ...
John Arg's user avatar
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Naming of the output with an unprotected open drain or open collector on the silkscreen

An issue has arisen regarding the pin labeling on the silkscreen. These pins are user-defined, so I want to clearly indicate that the output is transistor open-drain. As you may understand, it's a ...
Sig Elso's user avatar
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2 answers
217 views

ECP5: Determining max current an FPGA pin can sink from datasheet

I have a circuit where I want to drive the CS# input on a SPI flash chip from an output pad on an FPGA. The flash IC's datasheet recommends putting an external ...
jemalloc's user avatar
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1 answer
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Open drain input that switches additional circuitry on

I want to create a active cooling for power supply when charging a battery with BQ24610 IC. BQ24610 has open drain pin "STAT1" that switches on when battery is being charged. * I'd like to ...
Oxmaster's user avatar
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Can an open-drain pin be used to control an N-channel mosfet?

I'm implementing an on/off pushbutton circuit using the LTC2950 to control 5V and 6V regulators via their enable pins. However, I also want to be able to control the 12V supply since it's used to ...
E.HP.S's user avatar
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2 answers
151 views

Can a voltage divider be used to safely lower pull-up voltage?

I'm working with an LTC2950 pushbutton on/off chip that's meant to toggle the enable pins of voltage regulators based presses from a momentary pushbutton. The LTC's enable pin is open drain and is ...
E.HP.S's user avatar
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0 answers
38 views

Thermal analysis of a step down regulator

LTM8053 datasheet I tried to plot the thermal graphic (watt-celcius) for this buck converter in MATLAB. The main goal is to find losses which turn into heat. Reasons for heat most of time switching ...
BlueWolf's user avatar
1 vote
1 answer
91 views

How to multiplex open drain sensors

I have 64 digital hall effect sensors with open drain outputs (A3144), and would like to read their outputs with an MCU. Is there a simple way to multiplex these sensors to limit the number of IOs ...
reivax-boucoi's user avatar
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54 views

Type of output of this AND Gate

I am unable to find whether the output of this IC is a push-pull output or an open drain output. I didn't notice either words in the datasheet. Hence, can someone help me to tell which output type is ...
Freshman's user avatar
1 vote
8 answers
436 views

Why should an open drain/collector comparator go low when pull up is not connected if it is essentially a floating node?

As we know the open drain/collector output stage of a comparator looks something like this: This is essentially a high impendance floating node. If we fail to connect pull up, the output does not go ...
needbrainscratched's user avatar
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2 answers
409 views

Calculation of pull-up resistor for open-drain output - multiple loads

Link to voltage supervisor Link to AND gate I would like to drive an open-drain output to multiple (5) loads, all of the same type. I calculated the pull-up resistor range needed and wanted to double ...
Matty's user avatar
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1 vote
1 answer
221 views

Open-drain Input mode

I have a GPIO expander (namely the MAX7317+ from Maxim Intergrated). The I/O is open-drain. I want to configure these I/O as Input mode. Can I just connect them directly to my switch like this so that ...
Michael's user avatar
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0 answers
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Common-output WS2812 LED strip alternative control

I try to build an RPi controlled LED strip, however, while the Linux is booting, I still want a minimal effect on the LED strip. So my idea is that once the device gets voltage, a cheap ...
samsmith94's user avatar
0 votes
1 answer
177 views

Can I/O pins on a PLD (e.g. ATF16V8B) be configured to act as an open-drain output that is usable in a wired-OR circuit?

I designed a peripheral card for an 8-bit home computer which uses an ATF16V8B for address decoding and glue logic. I want this card to be able to generate interrupt requests by driving the system's /...
Craig Iannello's user avatar
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1 answer
285 views

How to use an open drain signal to power a relay/MOSFET package?

I have a controller with a particular signal output (open drain, which I believe provides a ground when activated?) with an internal circuit breaker limiting to 175 mA that I want to use to drive a ...
Optical Carrier's user avatar
0 votes
1 answer
138 views

Open drain output with parasitic indicator LED

I'm designing a "minimal parts / as simple as possible" open drain NOR gate (also known as 2 N-MOSFETs and a wire), but I'd like it to have an output state LED. I was thinking of having ...
nonchip's user avatar
  • 207
2 votes
1 answer
547 views

Converting Open-Drain to Active-Low

My question is very similar to Converting Open-Drain to Active-High, however instead of an active high, I want an active low. I am trying to interface TI BQ51050B (QI receiver + LiPo Charger) and TI ...
jb0's user avatar
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2 votes
1 answer
622 views

Calculating hysteresis with an open drain comparator

I have a circuit as follows which will compare an input voltage to a 2.5 V (actually 2.3 V) reference. In one of the documents, it mentions that the feedback resistor must be 100 × Rpullup. If my ...
Matty's user avatar
  • 217
2 votes
1 answer
219 views

Using an open drain buffer as a logic level step down converter

I'm trying to convert a 3V3 UART to 1V8 UART with an open drain buffer, but the output of the buffer is always high. See the schematic below for the circuit. On the input to the buffer, there is a 0V -...
skipper_the_penguin's user avatar
0 votes
1 answer
69 views

Can the 74LVC06A input be connected to an open-drain output?

The picture above is the SN74LS06 schematic from Texas Instruments. It appears that the input of the SN74LS06 can be connected to an open-drain output. I purchased the 74LVC06APW from Nexperia. But I ...
Jelly Tea's user avatar
4 votes
2 answers
890 views

Connecting Led to push-pull instead of open-drain

I am using the PCA10056 Nordic dev board which integrate a nRF52840. The following LEDs are wired to some of the MCU GPIOs. Currently, my MCU firmware configures those GPIOs as Push-pull output. But I ...
The_Average_Engineer's user avatar
1 vote
1 answer
652 views

Open-drain output using N-channel MOSFET in addition to pull-up resistor

I'm trying to understand a design in an evaluation board and I need some assistance. In the above schematic, the PG output pin is open-drain so it requires a pull-...
steve's user avatar
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2 answers
137 views

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 ...
Matty's user avatar
  • 217
8 votes
1 answer
9k views

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 ...
1i10's user avatar
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0 votes
1 answer
305 views

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?
nowox's user avatar
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1 answer
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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 ...
user avatar
0 votes
0 answers
70 views

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?
Ryan Magee's user avatar
0 votes
1 answer
48 views

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 ...
sometimes_clueless's user avatar
0 votes
0 answers
243 views

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 ...
Zac Chien's user avatar
1 vote
2 answers
751 views

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 ...
JackOfHearts's user avatar
3 votes
3 answers
277 views

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. ...
Jake Hertz's user avatar
0 votes
4 answers
436 views

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 ...
J Collins's user avatar
  • 585
2 votes
1 answer
255 views

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 ...
user avatar
0 votes
4 answers
1k views

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 ...
csiz's user avatar
  • 174
0 votes
1 answer
1k views

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 ...
Luminaire's user avatar
  • 355
0 votes
2 answers
1k views

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 ...
Luminaire's user avatar
  • 355
2 votes
1 answer
102 views

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" ...
Dan's user avatar
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0 votes
2 answers
381 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-...
user127813's user avatar
0 votes
0 answers
128 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: ...
simonhaines's user avatar
2 votes
1 answer
131 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 ...
John Smith's user avatar
11 votes
7 answers
8k 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 ...
anmomu92's user avatar
  • 161
1 vote
1 answer
1k 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 ...
user avatar
1 vote
1 answer
226 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 ...
akarapatis's user avatar
9 votes
6 answers
3k 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 ...
Nulik's user avatar
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