Vybrid MVF62NN151CMK40 SNVS_LP current consumption

[jasonlewis]

Is there any way of minimising the current consumption of the SNVS_LP module when only using the real time clock?

We would like to use a super capacitor to maintain the real time clock when the vybrid processor is powered down, but at the moment, the low power SNVS consumes about 14uA in this state.   I think most of the SNVS_LP features are set at their default values, so are there any features that can be turned off to considerably reduce the 14uA current consumption? Ideally we would like to get it below 1uA which is more in line with a dedicated real time clock chip.

Thanks

[naoumgitnik]

Dear Jason,

Frankly, 1uA is quite difficult to reach (Vybrid is not an electronic watch IC) but units of uA quite possible.

Plus, power consumption strongly depends on temperature, but you provided no such details about your application nor if you need the precise 32.768kHz crystal-based clock or the internal low-precision 32kHz (128 divided by 4) would suffice.

Below are some data (in a raw form) from our documentation + advices on how to reach your goal, so, please, do the required math:

• Only the relevant power rails shall be connected to Vybrid, i.e. disconnect/disbale EVERYTHING your application does not need.
• Lowest consumption LPStop1 (no memory retained) with FIRC (Fast internal RC oscillator (24 MHz)) disabled.
• VBAT minimum value - 2.4V.

• Datasheet "Table 70. Slow internal RC oscillator electrical characteristics":

          IRCL = 3.1uA typ. (TA= 25 °C)

• Datasheet "Table 15. Power consumption operating behaviors":

          IDD_VBAT (Battery backup mode) 5uA typ., 45uA max. (All supplies OFF, SRTC, 32kXOSC ON, tampers and monitors ON. 128k IRC optionally ON.)

• Review Reference Manual "Table 14-2. Power gating and clock gating overview" for power domains information.

• Datasheet "Table 68. OSC32K Main Characteristics":

          Current consumption 4μA typ.

          Note:

          The 4 μA is the consumption of the oscillator alone (OSC32k).

          Total supply consumption will depend on what the digital portion of the RTC consumes.

          The ring oscillator consumes 1μA when ring oscillator is inactive, 20 μA when the ring oscillator is running. Another 1.5 μA is drawn from vdd_rtc in the power_detect block. So, the total current is 6.5 μA on vdd_rtc when the ring oscillator is not running.

• Reference Manual: FXOSC/FIRC clocks are configured by the CCM module - FIRC (Fast internal RC oscillator (24 MHz)) - CCM Control Register (CCM_CCR) [FIRC_EN] - 0 Disable on-chip RC oscillator.
• Reference Manual: SXOSC/SIRC clocks are configured by the SCSC module - CCM Control Register (CCM_CCR) - SIRC- 128kHz controller; SIRC Control Register (SCSC_SIRC_CTR) [SIRC_EN] - 0 Disable SIRC.

(Typ numbers represent the average value taken from a matrix lot of parts across normal process variation at ambient temperature.)

(Max numbers represent the single worst case value taken from a matrix lot of parts across normal process variation at maximum temperature.)

Sincerely, Naoum Gitnik.

[jasonlewis]

Hi Naoum,

Many thanks for a quick and comprehensive reply.  It looks like we may have to replace the capacitor with a battery if we need to maintain the RTC for long periods when the processor is powered down.

Best regards,

Jason

[naoumgitnik · Accepted solution]

Yes, Jason, a battery, rechargeable or regular, might be a good option.

/Naoum G.