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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16
votes
1answer
14k views

Open Drain vs Open Collector

Is there a practical difference between Open Drain and Open Collector outputs, or are the terms used interchangably? If they are indeed different, what are the contexts where each is advantageous? My ...
9
votes
4answers
15k views

Open-drain microcontoller ports

I want to understand the concept of open-drain ports like port P0 of the 8051 microcontroller. Why do we need to connect pull up resistors to the port P0? I have basic knowledge of MOSFETs and other ...
6
votes
3answers
871 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 ...
5
votes
6answers
2k views

Why do I2C lines use open drain driver instead of tri-state drivers?

My understanding is that I2C lines use pull-up resistors to passively pull up the bus to logic high because the drivers used on the bus are active drivers, namely open collector/open-drain. Since open ...
5
votes
3answers
2k views

DS1307-breakout-board

I want to build an RTC clock for the Raspberry Pi. Adafruit has a guide to accomplish this with Dallas DS1307. On the schematic they put a 2.2K resistor between VCC and SCL and do the same for VCC and ...
4
votes
1answer
171 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 ...
3
votes
2answers
7k views

Electrical difference between Push pull and open drain?

I made a little boo boo in the code of my STM32F4: for 2 years outputs that I thought to be in Open Drain where actually in Push Pull. It got me thinking a bit more about that, and I have come to the ...
3
votes
4answers
217 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 ...
3
votes
1answer
6k views

Driving a LED with an open drain digital output

I need to drive an LED from an STM32F217ZG. So I was thinking about a classic circuit with a BJT. But then I saw that GPIO outputs of the microcontroller are configurable as open drain. Would this ...
3
votes
1answer
2k views

Confused between push-pull and open-drain

I am planning to use i2c based port expander (earlier I was using atmega328P's GPIO) for inputs and outputs. On a digikey search, I found MCP23008, MCP23009 and MCP23017 as possible replacements. Out ...
3
votes
1answer
520 views

Very odd open-drain output design

I ran across a open-drain design and am baffled by the resistor between the nFET source and ground. There are only two purposes that I see it could serve. 1) It's series source termination, matching ...
2
votes
2answers
601 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 ...
2
votes
1answer
497 views

TPS56221 Open Drain PGOOD

The datasheet says the PGOOD signal is open drain but I want to use a 3.3V microcontroller to read PGOOD with the internal pulldown resistor, when PGOOD is asserted - will the voltage at the pin be ...
2
votes
2answers
1k views

PIC18F2550 I2C Open Drain?

As far as I have read, the I2C pins are Open Drain or Open collector, but in the PIC18F2550 the datasheet doesnt say anything about those pins, and even says they are a digital output if you select ...
2
votes
3answers
2k views

Open Collector/Drain vs Push pull

Given the situation where an LED is being used for a status indicator or similar, not toggling quickly. Which is the best configuration for the IO pin, push pull or open drain? As I see it either ...
2
votes
2answers
374 views

Can I use an open-drain NXP 74LVC07A output as level translator for an 8V CMOS input?

I'm designing circuitry that uses an NXP 74HC4051 analog mux with a +8V supply. An MCU with 3.3V GPIOs needs to control the mux S0-S2 selection inputs. I am wondering whether an NXP 74LVC07A, powered ...
2
votes
1answer
1k views

How to measure open-drain vs. hi-z with multimeter

I have an output pin configured to be either open-drain or hi-z. How can I use my multimeter to tell which mode it is in?
2
votes
1answer
331 views

PWM drivers of Shift registers that are not open drain?

I am need of a 16 channel PWM Serial based LED driver, or serial in – parallel out shiftregister. I had been looking at TLC5940 and TLC59025 respectively. But for my current set up the ouptuts ...
2
votes
1answer
688 views

PIC24 Open-Drain Config for 5V PWM Operation

I'm running a PIC24HJ series processor with a supply voltage of 3.3V. I need my PWM signal to be 0-5V, not 0-3.3V. Can I simply connect the PWM line to a 5V supply with a pull-up resistor? Or do I ...
2
votes
2answers
368 views

Open collector with Atmega48

After looking at this, I think I already know the answer, but I just wanted some clarification. Open collector microcontroller output I have a part that is going to drive my mosfet at 15V. I have ...
1
vote
3answers
1k views

Open Drain Serial TX output on Arduino

I have been trying to implement an open drain Serial output using a Arduino Nano. In the following example I have used 2 Arduino Nanos (both operating at 5V Vcc), using one Arduino as the transmitter ...
1
vote
4answers
1k views

Input pins hardware interface uC

I am trying to figure out how to interface a A2235-H GPS module. The datasheet says that one pin(nRST) must be connected to open collector or open drain output of uC while an other one(ON_OFF) must ...
1
vote
4answers
2k views

Wired-or open drain with open collector outputs

I have a comparator with open collector output (LM311) and a gate with open drain output (SN74LVC1G06). I want join these two outputs to make a wired-or, with a pull-up resistor tied to +3.3V. In a ...
1
vote
2answers
325 views

Can Transmission gates be used to implement 3 State Logic?

In my application i need to use a common line shared between two peripherals, i have to indicate to the devices whenever the bus is free or not, hence i can't have push-pull output where the output is ...
1
vote
2answers
1k views

STM32F3 Discovery 5V output

I want to use a STM32F3 GPIO (3.6V) to drive another device using 5V input. Which is the correct way to do so? I know that is possible to use the open drain mode on the GPIO, but I'm not sure if I ...
1
vote
1answer
913 views

Using Open drain to get +5V

I have a legacy board in my product that has 1 temperature input with 2 rtd temperature probes. Until the new boards are ready the manufacturer has used a relay already mounted on the board to switch ...
1
vote
3answers
840 views

How does this voltage detector IC work in a circuit? What does open drain vs. CMOS output mean?

I'm evaluating the Rohm BD48/BD49 series voltage detector. I'm having trouble understanding the data sheet. I want to generate a high signal when the input voltage is above a desired threshold (3.0 ...
1
vote
2answers
1k views

Why does the I2C interface use the open-collector/open-drain?

The open-collector adds inconveniences like requiring an external pull-up resistor and slows down the throughput. Why did the I2C designers choose to use open-collector/open-drain?
1
vote
3answers
507 views

Diode Drop vs Open Drain Output Tolerance

I have an LED Driver IC that states a 5.5V tolerant Open Drain Output. It's Absolute Maximum section indicates 6.5V with a note saying "The input negative-voltage and output voltage ratings may be ...
1
vote
2answers
242 views

open-drain reliability problems

I've built a run of simple boards like the one shown below to control LEDs in automobiles. The boards have twenty of the NX3008 mosfets in an open-drain configuration as shown, which are controlled by ...
1
vote
2answers
222 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 ...
1
vote
1answer
194 views

When an open-drain output asserts low, where does the line capacitance discharge?

I was looking at the auto-retry functionality of the TI part TPS2553 (datasheet http://www.ti.com/lit/ds/symlink/tps2553.pdf) and came across something I didn't understand and thought it a good ...
1
vote
1answer
3k views

Connecting Open-Drain inputs or outputs together with one resistor

I had a couple of quick questions. I am designing a board using 10 IO expanders which I'll use as inputs. Each has an !INT pin which is open drain and pulled high to 5v through a resistor. Can I ...
1
vote
2answers
500 views

Resistance values for open drain

I am trying to establish SPI connection between C8051F931 and SD card. One of the sample programs I have found contains the following comments. ...
1
vote
1answer
56 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 ...
1
vote
3answers
166 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 ...
0
votes
1answer
94 views

MOSFET Vgs doesn't go to zero when controlling it with open drain output

I have this simple circuit to drive on and off a 12v rail from a microcontroller. R707 = 10KOhm, R708 = 10KOhm, and Q701 is a P channel mosfet (IRLML6402TRPBF) I'm driving this with a ...
0
votes
2answers
728 views

Optoisolator With LED in series not working

I'm using an FODM8061 Optoisoltor with and open collector Logic Output. I'm referencOptoisolator Logic Output Question Here's my current circuit: LED 1(on the left) connects to an open-collector ...
0
votes
4answers
1k views

Oops! N-channel Mosfet on sinking output

I have designed a simple circuit to drive LEDs using a MAX6964 I2C LED driver/GPO chip. Unfortunately, I somehow missed missed that the outputs are open-drain current-sinking outputs. This is not ...
0
votes
3answers
2k views

How does open drain io act as bidirectional

Could someone explain how open drain io acts as bidirectional. Whether it is actually bidirectional or it can act only as input or output at a time.
0
votes
2answers
534 views

Open drain in I2C

In I2C, why SCK and SDA should be open drain? What will happen if they are not open drain. I am trying to implement I2C communication using bit banging. Should I enable Open drain circuitry of GPIO ...
0
votes
1answer
101 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 ...
0
votes
3answers
134 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 ...
0
votes
2answers
477 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 ...
0
votes
3answers
114 views

Is my reasoning about an ATMega328p connected to equipment requiring an open-drain pin correct?

I am part of a research group that is developing a concept for a PCB for an external piece of equipment. This piece of equipment can be controlled with a microcontroller. It communicates to my ...
0
votes
2answers
161 views

Open Drain Output to Microcontroller?

I want to check my Li-ion Charger( Microchip MCP73833 ) status with nRF52832. So i will connect Stat 1,2 and PG to nRF But MCP73833 have an open-drain output If i connect pins to nRF without Pull-...
0
votes
2answers
686 views

Designing a open drain LED driver

Will this open drain LED driver circuit work ? The open drain IO is governed by the following equation 0.5 <= V_LED_OUT <= 3.6 V (abs_max) V_LED_OUT is the voltage from open drain IO pin to ...
0
votes
2answers
97 views

What is the output type of the sn74lvc1g04?

It doesn't seem to clearly say totem-pole, open-collector, open-drain, etc. I wanted to place a pull-up at the output to guarantee a default state, but I feel like this is a bad decision. datasheet
0
votes
2answers
1k views

Voltage level in an open drain bus (I2C)

I have a setup as seen in this image: The question is what will the voltage at the line on the left size (marked with [Volt ??] ) be when the open-drain logic is active? The goal is to have a logic ...
0
votes
3answers
86 views

Problems understanding I2C pullup calculation

I have been trying to read about I2C pullups such that I can select an appropriate pullup resistor for an EEPROM (24LC02B-I/P) which I want to use as serial ROM to drive some 7-segment displays. ...