What's the current requirement for this display? - Page 1
Forum section: electronics / beginners

author: Freshman
author_rank: Regular Contributor
timestamp: October 21, 2024, 09:38:46 am
content: I was going through the datasheet (http://www.pdaatl.com/doc/tm5000.pdf)I see that to power this module, we require to provide +5V to this display?I couldn't find the current requirement for the +5V rail that powers this display? Can someone confirm?

author: tooki
author_rank: Super Contributor
timestamp: October 21, 2024, 09:55:29 am
content: That is a terrible datasheet.It doesn’t say what the total current is. It’s clearly using regulators and DC-DC converters to convert the 5V input to both 3.3V and something higher (perhaps 18V) for the backlight, which complicates just adding up the currents.But if you add up total power, it’s something like 2W max, so that should give you a ballpark. It can’t be that much since the FFC cable isn’t exactly capable of huge currents.

author: bborisov567
author_rank: Regular Contributor
timestamp: October 21, 2024, 09:57:22 am
content: According to page 19 there are 40 mA for backlight which seems to be the only component powered from the 5V rail. For the 3.3 V the max specified current is 25 mA.

author: jpanhalt
author_rank: Super Contributor
timestamp: October 21, 2024, 10:02:01 am
content: Page 19, Section 4.6.2 gives backlight current as 40 ma. Section 4.6.3 gives screen consumption (IDD) of 25 mA.

author: Freshman
author_rank: Regular Contributor
timestamp: October 21, 2024, 10:08:01 am
content: Since this is the FFC cable that is mentioned in the datasheet -https://www.digikey.com/en/products/detail/w%C3%BCrth-elektronik/687650100002/4573420,I went through the datasheet, and noted that it's capable of 0.5A. Hence, I believe that 0.5A should be the supply current for it's +5V, right? Would it be safe to assume that?

author: jpanhalt
author_rank: Super Contributor
timestamp: October 21, 2024, 12:06:34 pm
content: That's apparently the current capacity of the cable. (The link gave a 404 error.) Generally, you will want to supply the backlight (BL) separately from the display, since you may want to turn the BL off to save battery consumption.A 100mA total source should be sufficient. The programmer I use (Microchip ICD 3) has limited current capacity, so I usually supply the target (MCU board being programmed) separately.

author: tooki
author_rank: Super Contributor
timestamp: October 21, 2024, 01:24:53 pm
content: But the cable to the host doesn’t have a separate power rail for the backlight, and there are no other power connectors.And remember, folks: the 40mA maximum for the backlightis at a maximum 19.8V!!That’s why I said to look at total POWER (watts) and not total CURRENT.

author: jpanhalt
author_rank: Super Contributor
timestamp: October 21, 2024, 05:04:41 pm
content: Page from datasheet attached. That arrangement is quite common. The BL+/LED+, or - if you are so inclined, can easily be switched and/or PWM'd.

author: tooki
author_rank: Super Contributor
timestamp: October 21, 2024, 05:19:21 pm
content: Quote from: jpanhalt on October 21, 2024, 05:04:41 pmNot relevant, because that is the connector from board to display, not from host to board. The host interface on page 5 clearly does not have backlight pins.