Well, I said it was going to be fiddly, and it is.
Not only do I have a very short time window to work with before the chip shuts itself down, but the pins are so tiny that my multimeter probes look like giant's fingers by comparison.
So far I have measured the battery at 4.12V and VIN (pin 10, power to the whole chip) at 4.11V.
Which is good as it tells me we definitely are getting the right amount of voltage through the system and that there is no UVLO in play.
Actualy, a ;ittle more can be gleaned from this - from the datasheet:
Quote:
8.3.8 Fault Handling And Recovery
The TPS65185x monitors input/output voltages and die temperature. The device will take action if operating conditions are outside normal limits when the following is encountered:
• Thermal Shutdown (TSD)
• Positive Boost Under Voltage (VB_UV)
• Inverting Buck-Boost Under Voltage (VN_UV)
• Input Undervoltage Lockout (UVLO)
it shuts down all power rails and enters STANDBY mode. Shut-down follows the order defined by DWNSEQx registers. The exception is VCOM fault witch leads to immediate shutdown of all rails. Once a fault is detected, the PWR_GOOD and nINT pins are pulled low and the corresponding interrupt bit is set in the interrupt register.
...
(blah)
...
Whenever the TPS65185x encounters undervoltage on VNEG (VNEG_UV), VPOS (VPOS_UV), VEE (VEE_UV)
or VDDH (VDDH_UV), rails are not shut down but the PWR_GOOD and nINT is pulled low with the
corresponding interrupt bit set. The device remains in ACTIVE mode and recovers automatically once the fault
has been removed.
|
So since we have one of the first four errors, the device goes into STANDBY (not ACTIVE), which means some of the input voltages may still be present. We know we don't have TSD and UVLO, so that only leaves VB_UV and VB_UV. The datasheet is not explicit as whether undervoltage condition applies to the input or output voltages for DCDC2 or DCDC1, I suspect it means the output. To confirm I need to try and measure the output from DCDC2 (pin 25, VN_SW) when the chip is powering up.