LAN8720 power consumption - Page 1
Forum section: electronics / projects

author: Mad ID
author_rank: Regular Contributor
timestamp: May 18, 2013, 06:55:13 am
content: Hello,I'm having trouble with the LAN8720 Ethernet PHY and wonder is anyone used it?Datasheet states that power consumption should be around 45mA with 100Mbit traffic.These are my results (ampermeter in series with LAN820 power pins, tested on custom board)After reset, no cable connected - 42mAPower Down - 2.5mA100Mbit operation - 80mA.It's almost 2x the specified and I noticed that the IC is a little hot.Is this maybe a mistake in the datasheet and 80mA is normal (RJ45 LEDs not included)?The communication is working properly. I'm working on a commercial product and must be absolutely sure that my design is OK. If the current consumption isa result of some error the IC could die in the field.Thank you.

author: Mad ID
author_rank: Regular Contributor
timestamp: May 18, 2013, 09:46:33 am
content: OK I have found that magnetics is consuming additional 40mA (+ LEDs) even when no traffic and that normal.Case closed

author: bmcdonnell-ionx
author_rank: Newbie
timestamp: February 20, 2018, 11:46:08 pm
content: Quote from: Mad ID on May 18, 2013, 06:55:13 amI know this is a super-old thread, but if you see this, could you possibly share tips or even the code of how you powered down the 8720? I'm having an issue where when I power it down, I lose the ability to halt the microcontroller, i.e. it breaks debugging.Details here:https://community.nxp.com/message/988269https://os.mbed.com/forum/bugs-suggestions/topic/29243/(same content)Thanks.

author: bmcdonnell-ionx
author_rank: Newbie
timestamp: February 21, 2018, 08:30:48 pm
content: Quote from: blueskull on February 20, 2018, 11:56:05 pmWhat do you mean by "MCU bootstrapping pins"? (I know MCU means the micro...)I don't think I can use the PHY bootstrapping pins. They are connected to MCU GPIOs. Section 3.7.2 of theLAN8720 datasheetsays, "When a soft reset occurs...the configuration of the 10/100 digital block is controlled by the register bit values and the MODE[2:0] configuration straps have no ."The HDK_MBED_RESET net goes to both PHY NRST and the MCU reset, so I can't make the MCU reboot the PHY to read its bootstrap pins. (If only!)

author: Cerebus
author_rank: Super Contributor
timestamp: February 21, 2018, 11:21:08 pm
content: Quote from: bmcdonnell-ionx on February 21, 2018, 08:30:48 pmHe means pins that the MCU uses at reset time to determine some part of its configuration and are then released for other uses such as IO pins. Typically they have a pullup or pulldown resistor to set the configuration intention but not such a strong pull up/down that they can't be deliberately driven to other states for their normal runtime usage.

author: bmcdonnell-ionx
author_rank: Newbie
timestamp: February 26, 2018, 11:33:51 pm
content: Quote from: bmcdonnell-ionx on February 21, 2018, 08:30:48 pmQuote from: Cerebus on February 21, 2018, 11:21:08 pmThe only pull-ups or pull-downs on any of the PHY pins which are connected to the micro GPIOs are shown in the schematic excerpt I attached to my previous comment. One of them is a pulldown on one of the 3 PHY bootstrap pins.