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| Pulse skipping on Vneg of TPS65130 |
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| thmjpr:
TPS65130 Split-Rail Converter with Dual, Positive and Negative Outputs (300mA typ) Datasheet: http://www.ti.com/lit/ds/symlink/tps65130.pdf 5V in and getting +/- 8V out. Positive supply is working fine, 1.3MHz constant, with minimal ripple: Negative supply is stuck in pulse skipping mode producing a ton of ripple: The device has power save mode, enabled by pulling PSN (power save negative) or PSP to Vin. Disabled with Gnd. Soldering: - PSN and PSP pin continuity checked to Gnd, looks ok under microscope as well. - I only had the one chip (new from LCSC), so will update when I receive and test another chip. Going to try a TPS65131 as well (higher current version). Inductor: - 4.7uH recommended, 10uH is being used. Tried a 4.7uH and skipping was still present. Load: - No load or 20mA load didn't change anything. Anything I might have missed? Some other discussions: https://www.eevblog.com/forum/projects/tps65131-split-rail-power-board/ https://e2e.ti.com/support/power-management/f/196/t/717199?TPS65131-negative-output-voltage-abnormal |
| SiliconWizard:
Sorry if I've missed it, but I didn't see any capacitor at +Vo and -Vo. That's probably going to be a problem. |
| thmjpr:
--- Quote from: SiliconWizard on January 19, 2020, 01:08:39 am ---Sorry if I've missed it, but I didn't see any capacitor at +Vo and -Vo. That's probably going to be a problem. --- End quote --- My fault, its in another area of the circuit. 47uF on each +Vo and -Vo to Gnd. 25V 47uF X5R. Recommended value is 22uF. Making it larger might help but I suspect it will still skip. |
| T3sl4co1l:
Are you sure it's not compensated incorrectly? Pulse skipping is, well, skipping pulses, but that's a burst waveform. Some controllers still do that, but I don't know if that's typical for this one. Tim |
| thmjpr:
--- Quote from: T3sl4co1l on January 19, 2020, 06:06:32 am ---Are you sure it's not compensated incorrectly? Pulse skipping is, well, skipping pulses, but that's a burst waveform. Some controllers still do that, but I don't know if that's typical for this one. Tim --- End quote --- You are right the terminology is confusing, its more of burst/sleep mode. TI seems to like to call it that: --- Quote ---The converter operates with a fixed frequency PWM control topology and, if power-save mode is enabled, it uses a pulse-skipping mode at light-load currents. --- End quote --- I've tried with Cn, compensation cap removed, no major difference seen there. With Cf-, feedforward capacitor removed, duty cycle of the pulses increases to ~%50, ripple reduces significantly, and power consumption goes up a bit. So thats on the right path. But removing it is too risky. Note here about >33uF not recommended, but I'm getting same issue with lower values: https://e2e.ti.com/support/power-management/f/196/t/799796 Also there, at a point below ~80mA on the Vneg, discontinuous conduction occurs. When testing today I found dropping Vin from 5V to ~4.2V would kick it out of power-save mode and into normal PWM. It would also get into some wild states above 5.3V. Might need to play with that a bit more.. |
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