SLAZ606V August   2014  – May 2021 MSP430F67641

 

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6.5 AUXPMM2

AUXPMM Module

Category

Functional

Function

Latch-up in AUXPMM

Description

Latch-up current can appear at the AUXPMM module supply pins in the following two scenarios:

Scenario 1: When the AUXPMM is configured for hardware- or software-controlled switching and the module switches from DVCC to AUXVCC2, latch-up current can appear at AUXVCC2 at the switching point defined by SVSMHCTL.SVSMHRRL (or AUXCTL2.AUX0LVLx). The probability for this event to occur depends on:
a) Operating temperature (higher temperatures increase probability)
b) External AUXVCC2 voltage level (higher voltages increase probability)
c) SVSMHRRL level (lower levels increase probability) defining the switching level in hardware-controlled mode
d) AUX0LVLx level (lower levels increase probability) defining the switching level in software-controlled mode (applicable to DVCC only)

Scenario 2: When a battery is connected to DVCC, AUXVCC1 or AUXVCC2 as the first voltage supply, due to the low internal resistance of the battery a very fast rise time is seen by the AUXPMM and latch-up current can appear at the connected supply if:
a) Rise times are in the range of 140 kV/s (faster rise times increase probability)
b) Device operates at temperatures of 75 deg C and above (higher temperatures increase probability)

The latch-up current disappears after complete power cycles of all supply sources.

Workaround

For scenario 1:
- Increase SVSMRRL to a level above maximum external voltage expected on AUXVCC2. SVSMRRL = 6 or 7 (requires VCORE level of 3) is applicable for AUXVCC2 of up to maximum voltage, 3.58V, while a lower SVSMRRL setting can be selected if a lower voltage (e.g. 3.3V) is expected on AUXVCC2.

Or

- Connect all 3 supplies via 3 external diodes to DVCC and realize the switching externally without using the internal AUXPMM switches. See application report "Implementation of a Three-Phase Electronic Watt-Hour Meter Using the MSP430F471xx" for details.

Or

- Use AUXVCC1 instead of AUXVCC2 for backup supply

For scenario 2:
Limit the supply voltage ramp up time through a series resistor (e.g. 10 Ohm) in the critical supply path. Side effects such as voltage dips due to high current consumption of the device need to be considered.