VLS_OUT going bad

[ankur_kala]

Hi,

I have a customer board in which the VLS_OUT has gone low permanently (shows less than 2V), The customer was testing a motor control application and reported application failing at current levels of around 4 Amps. The hardware is designed to sustain well above 20Amps. What can be probable cause for this scenario. Charge pump section is not populated on board and Corresponding VCP and CP pins are Not connected anywhere.

Regards,

Ankur

[RadekS]

Hi Ankur,

Unfortunately I am not sure what could be reason for that behavior, however I would like to recommend check:

1. Internal LDO for generating VLS_OUT is enabled by setting GFDE bit in GDUE register (with disabled GDU Write Protect).
2. Since VLS_OUT is generated by linear voltage regulator, we have to take into account input voltage at VSUP pin. If we do not use Boost feature (enabled by the GBOE register bit; the boost circuit requires external Shottky diodes, a coil and capacitors), VSUP have to be at least 7V.
3. When we do not use charge pump, we have to take into account that bootstrap capacitor CBS could be charged only when the low side driver is active. So, too small CBS or too short time for charging CBS (too high/too low duty ratio) could cause insufficiency in opening high side drivers. Additionally, the bootstrap capacitors must be precharged before turning on the high-side drivers for the first time.

I hope it helps you.

Have a great day,
RadekS

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[afarouk]

I have the same problem, although the GFDE is enabled, after flashing the code on S12ZVMC256 the VLS_OUT give 11V, with a very low to the BLDC motor, HD, VSUP, and VM=18.5V fixed
Other circuit conditions:
(charge pump circuit exist but is not active and not connected back to VSUP) 
(Boost circuit does not exist VSUPis fixed like HD 18.5V)
(Full load continuous running on 3000rpm and transient start of 1A and steady-state current of 600mA ) worked ok tested for more than 5 hours successfully.

The applied test code incrementing speed for a BLDC motor with full load make runs with n: speed from 100rpm  to 3400rpm and running for  22 seconds then stop running for 8 seconds, then next run with incrementing  100rpm n+=100 after some runnings and stops it after stops for around 8 seconds then start to run it doesn't go and the VLS_OUT go low some times <5V some time <2V, and the NXPchip draw extra current around 40mA, when debugging with CW11.0 the code pending GLVLSF and the GFDE is 1. So, I had to change with a new chip. that repeated three times.

When separated the VLS_out from VLS0,1,2 and supply external 11V to the VLS0,1,&VLS2, the code stop and I have to restart  some times it stops after speed arrives 1800, 1600, 2800, or 2700 rpm, it didn't complete the test to the end 3400rpm speed;

Below are graphs for the position of the motor to time showing the increasing speed test.

What makes VLS LDO blow out? how to protect it? by FW or HW?