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CFAH1202A-YYB-JP Display Sleep

Heffo

New member
Hi guys,

I was wondering what the best way to put a CFAH1202A-YYB-JP to sleep was. My device will be powered constantly, but deep-sleeping when not in use. Ideally I would like to draw no power when sleeping, but simulating sleep would be fine. I am mainly concerned about the LCD elements themselves.

I do have a digital pot driving the VO pin on the LCD, so I can crank the LCD's voltage to GND during sleep if it will make a difference to lifetime.
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Since the supply current is so low (1.2 mA typ), I would supply logic 5 V to the display through an I/O pin (assuming you have 5 volts at your I/O), so you can shut it off. Otherwise, I don't know of a way to reduce power consumption. You'd then have to re-init at each power-up, but that's not a big deal.

Assumes you simultanously remove backlight power. And, yes, setting Vo to 0 will avoid violating the Vlcd spec during shutdown.
 

Heffo

New member
Supplying the power from the controller sounds like an idea, but I have run out of port pins. I do have a shutdown line for my CAN driver, but it's shutdown mode is at +5v, not GND. I do have a TI Little-Logic, single inverter gate package I could use to give me the GND signal for shutdown from the CAN shutdown line and run the LCD's logic supply off that, but the gate is only good for 8mA, and I would be a little worried about inrush currents from the LCD spiking the chip.

Now that I think about it, a PNP transistor might be a better option. no need for the inverter, I can still use the CAN shutdown line and I get about 100mA of headroom to play with. I already am using a BC807 on the backlight so another for the LCD Logic would be ok.

Sound like I am on the right track?
 
Yes, a transistor to switch the power to the LCD would do fine. I assume you're PWM'ing the backlight, else you could use the same transistor. Myself, I'd choose a logic level pFET (IRLML6402), just to avoid having to use a resistor to limit base current for a bipolar transistor.
 

Heffo

New member
It's all a case of what components I have available or I can get without a Credit-Card. I can run down town and pick up 10 surface-mount BC807s for about $1.50, and I have some 10k resistors in 0805 package so going the BJT is easy, getting a logic-level FET is a bit harder.
 

CF Tech

Administrator
Be sure to put all the lines of the LCD to 0v at shutdown. It will "phantom power" through the ESD protection diodes if any I/O line is high.

Just FYI, if you are out of port pins:

1) are you already in 4-bit mode?

2) you can tie R/W to ground.

3) you can re-use all the pins except E for reading switches (you need to include a series resistor) or other tri-stateable devices.
 

Heffo

New member
As it stands, I am using 8-bit mode. I wanted to keep as much CPU time as possible free for other tasks like monitoring the CAN bus, calculating speed, driving 32 LEDs via SPI, maybe even listening to the NEMA stream from a GPS board I got.

That way, I just bang the byte I want into the port and clock the LCD, instead of doing all the shifting and masking to get the same result.

Thanks for the tips about setting all pins to 0v in power-off mode, It would have been a headache trying to diagnose the phantom power :D
 
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