Tactile Mom Switch to enable IC - Page 1
Forum section: electronics / beginners

author: Lrv209
author_rank: Contributor
timestamp: January 24, 2022, 04:26:30 am
content: Hello,I have just joined the EEV forum although I have watched, enjoyed and learned a lot from Dave's videos over the past year. I am untrained in electronics but have had an interest in them for many years and have worked with Micro Controllers and Raspberry Pi as well as developing some simple items for use around the house such as IR switches for my Pantry light and for my rear TV screen lighting and completeing some minor electronic repairs. Simple stuff but very enjoyable as has been the very steep learning curve I have been on since starting on a project for my daughter.The project is a small portable table lamp designed to give low level lighting to a dinner table setting or any similar application. the lamp is housed in a ceramic base I slip mold for my daughter then she underglazes with her unique designs, patterns and colours. I have developed a small rechargeable power supply that is contained inside the ceramic base. The power is a LIPO 3.7v battery powering a Cree LED. FV for the LEd is 2.8v and I am running at 700mA to get the required lumens. By using other design info and TI's Webench I have developed a buck converter with output of 2.8v and utilising a TLV62569 IC. I had this design built as a PCB by JLCPCB and it worked as hoped for and as expected. I am using a LIPO USB charger to recharge the lipo battery via a charge base I have developed, I have realised however that as the lamp could be switched on when it is being charged I am in danger of causing a problem with overcharging the LIPo as I dont have load sharing with the standard LIPo charger I am using. So I am now hoping to develop a circuit that will include the buck converter and a load sharing charger. Additionally to complicate matters more (if reading this you may think I am mad or a glutton for punishment) I am very tight for space and would like to use a small tactile switch to Enable the TLV62569 via its logic pin. The IC is enabled when the pin is high and disabled when pin low so I have in my design simply shorted the pin to GND. This then becomes the ON/OFF switch for the lamp.Because I have used a 100kOhm resistor the current I am shorting is around 0.001mA so that works OK.So my question and hope some one can advise.In my basic circuit following (without the lipo charger included as I am still working on that) is it possible to use a micro MOM switch that can switch the EN pin. I know of a circuit that will essentially convert the Mom to an on/Off using a Flip/flop and schmidt triggers or a vesrion of the TI SN74HC with inbuilt triggers but that seems like a lot of electronics for such a simple task so I am wondering if my current approach to switching the EN pin of the IC is not better done in a new way using the Mom switch. I sort of doubt it but thought an ask might be worth it. OR a better way to convert the MOM switch to an Off/On switch.I have had extensive help in this process from the people at TI especially, in regard to the switch, from Emrys Maier who also recommended this forum.Long post and I apologise but I find it hard to explain what I am doing in shorter posts so hope OK for this forum.Regards

author: ledtester
author_rank: Super Contributor
timestamp: January 24, 2022, 04:59:35 am
content: Some ideas:- a capacitive touch pad detector IC such as the TTP223. Can be configured to operate in toggle mode.Explanatory video:TTP223 Capacitive Touch Switches - Simple Electronicshttps://youtu.be/XBHgJi6smls- a "smart push-button on/off controller chip" like what ST offers here:https://www.st.com/en/reset-and-supervisor-ics/on-off-controllers.htmlOut of the box can implement press to turn on/long press to turn off. Other vendors have similar products, e.g.:https://www.maximintegrated.com/en/products/power/supervisors-voltage-monitors-sequencers/pushbutton-debouncers-devices.html- a small microcontroller whose sole job is to monitor the button; it shouldn't be difficult to make it draw just a few microamps (or less)- for discrete solutions, google "latching power switch" or "soft power switch". There are several threads on this forum including:- eevblog video 262:https://youtu.be/Foc9R0dC2iI- some commentary on that video:https://www.eevblog.com/forum/blog/eevblog-262-world_s-simplest-soft-latching-power-switch-circuit/msg258359/#msg258359- a reference to this patented circuit:https://www.patentsencyclopedia.com/imgfull/20090237065_01- this circuit:https://daycounter.com/Circuits/Latching-Momentary-Switch/Latching-Momentary-Switch.phtmlMost seem to be designed as high-side switches rather than switching something to ground as you describe, but they could be easily modified or worked into your application.

author: Ian.M
author_rank: Super Contributor
timestamp: January 24, 2022, 05:15:48 am
content: Yes, you could use any of Ledtesters suggestions, (though PSA: Friends don't let friends design in single source Maxim parts!) but IMHO, for the simplest reliable way to use a momentary switch as an on/off switch, see the two inverter toggle latch circuit presented by eblc1388 here:https://www.eevblog.com/forum/beginners/help-on-how-to-choose-an-ic-for-a-project/It *really* cant get much simpler than a tiny little logic chip with an under 2mm square footprint, two resistors and a capacitor.Use a 74LVC2G04 dual inverter powered direct from the battery. You'll also be able to eliminate your 100K pullup on Enable, reducing the quiescent current consumption to only a few uA.You could also deal with your charging issue by having the charging circuit hold the lamp in it off state while its connected to the charger. There's various ways of doing that, but as you haven't shown us the charging circuit or how it connects, we cant really make a good recommendation. One approach that could work if you use a USB charger (or other max. 5.25V supply) would be to use a 74LVC2G02 dual NOR in the toggle latch instead of the dual inverter. On one gate tie the inputs together so its just an inverter. On the other, take one input from USB Vbus (with a RC network for ESD protection), with a pulldown resistor on Vbus to guarantee that input goes low properly with the charger disconnected. With that input low, the NOR gate acts as an inverter with respect to its other input, and the toggle latch operates normally. When Vbus is present, the input is high forcing the NOR gate output and thus your Enable pin low.

author: ledtester
author_rank: Super Contributor
timestamp: January 24, 2022, 06:06:54 am
content: Quote from: Ian.M on January 24, 2022, 05:15:48 amThat's a very nice idea!On another thread the potential problem of having the inverters come up in an unknown state is discussed and solved:https://www.eevblog.com/forum/beginners/going-slightly-mad-simple-tristate-buffer-not-properly-driving-output/msg3148998/#msg3148998Final schematic (fromthis post by Ian.M):