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I want to design an Ultra low Power device with MSP430FR6047, which can work over 10 years. For the supply power of MSP430FR6047 in the datasheet it is mentioned that the voltage on the supply pin should be between 1.8V to 3.6 V:

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I want to use a long-life saft battery, which its voltage is 3.6 V:

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In the Absolute Maximum Ratings section of the datasheet we can see that the max voltage that we should not apply is 4.1 v, then it seems we can connect the battery directly ?!: enter image description here

Do you think I can directly connect the battery to MSP430? or I need to use a regulator for example TPS78001DDCR? I want to consider the voltage degradation of the battery over time, for example in 5 years, its voltage would not be 3.6 v but if I use a regulator (TPS78001DDCR), I would get the same voltage (3.6 v) from TPS even if the battery volatge has changed. On the other hand I would Loose a bit of power in the TPS regulator (IQ: 500 nA). Which one do you think is more reliable approach from the consumption perspective and robustness of the system?

What would be the minimum voltage of the battery after 9 years? does this voltage cross the minium voltage required for the MSP430 (1.8V)?

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    \$\begingroup\$ I have a few unused ones of the exact Saft battery type you linked. Their open-circuit voltage is a bit over 3.7V for my ones. \$\endgroup\$ Commented May 9 at 13:18

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Connecting the battery directly should be OK from a voltage perspective. Just take into account note(4) from the table you included in your post about According to SAFT Datasheet for LS 14250 the Open circuit voltage is 3.67V (at +20°C) and nominal voltage is 3.6V at 0.1mA (+20°C). Voltage ratings of SAFT LS14250

Regarding the low cut off voltage, the discharge profile is rather sharp, and before you get to the 1.8V point at which the MSP dies, the battery is already dead. chart of Typical discharge profiles of SAFT LS14250

Edit: I guess whether this is a robust design you need to evaluate based on your specifications.

I would as a rule of thumb try to stay away from the ends of the recommended operating conditions, but since a battery is unlikely to present an overvoltage failure mode, the realistic voltage seen by your circuit would likely be between Open Circuit and Nominal.

Are you making this as a one or few off, or are you planning on producing thousands? If you're only making a few, maybe you don't need as much design headroom as if you're making thousands - then all kinds of strange failure modes will start showing up. Another thing to consider is that the nominal numbers for the battery is for just one ambient temperature. Depending on the criticallity you should test your design assumptions.

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  • \$\begingroup\$ @ MrGerber I think you meant this by note 4 in the datssheet : Modules may have a different supply voltage range specification. See the specification of the respective module in this datasheet. Does this mean that for example in one sample the maimum voltage could be for example, 3.55 and in another could be 3.63? How we can see the disrtibution model of this in a large number of samples? if we can handle this issue, it seems connecting the battery directly is a good approach then? \$\endgroup\$
    – Andromeda
    Commented May 9 at 14:57
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    \$\begingroup\$ @Andromeda I don't know the MSP430FR6047 at all but from reading the datasheet briefly it seems they're not referring to the distribution model from chip to chip but to different modules in the IC. See for example table 8.13.9.1 - Recommended operating conditions for LCD_C - with different voltage ratings for Minimum recommended voltage. \$\endgroup\$
    – MrGerber
    Commented May 9 at 15:02
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As an alternative solution, you could consider a different battery chemistry, for example Li-MnO2. This is the chemistry that's used in the popular (and cheap) CR-type button cells, such as the CR2032. Those cells have similarly low self-discharge rates to Li-SOCl2 and are therefore suitable for long-term operation too, while at the same time having a slightly lower open-circuit voltage of 3.2V or less. The discharge cut-off voltage is 2V, so this fits comfortably within your MCU's operating range.

You can get these cells in any capacity you like, from the tiny CR2032 (with around 200 mAh), to the somewhat larger CR2477 (1000 mAh), all the way up to large cylindrical cells like the Saft LM17500 (3.3 Ah).

Using a CR2477 might be quite advantageous because it's readily and cheaply available - most large supermarkets carry it.

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  • \$\begingroup\$ @ Jonathan S. thank you for the nice and useful suggestion, based on my calculation, at least I need 7,7Ah. Is there any thing close to this capacity? \$\endgroup\$
    – Andromeda
    Commented May 9 at 14:45
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    \$\begingroup\$ @Andromeda The Saft M19 or M20, for example. \$\endgroup\$ Commented May 9 at 14:51

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