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Hi,
I'm designing Battery management system (BMS) for 24V electric bike. I want to use LDO for MCU sleep mode and buck converter for MCU active mode to reduce the BMS standby current. Kindly propose a design strategy to proceed further.
Design requirements:
Vin : 20 to 30
vout : 3.3
buck current : 0.2 to 0.3A
LDO current : 0.1A
Thanks,
Vignesh
Hello Vignesh,
As John Tucker mentions, The TPS5401 is a reasonable device to begin your search with.
The efficiency of a switcher can be very good over a wide load range, depending on the modes of operation.
There is very little change from 0.3A to 0.1A ~90% in this 12Vin 5Vout, TPS5401 datasheet example.
TPS5401 has High Efficiency at Light Loads With a PulseSkipping Eco-mode™ Control Scheme
LDO current : 0.1A
LDO efficiency is always Vout/Vin, 3.3Vout/30Vin = 11%
For an LDO to be effective, the load current needs to be much much less, falling off the left edge of the efficiency graph shown.
If indeed your currents are 0.3A to 0.1A then a high efficiency switcher with light load optimization will be your best solution.
Here is a Webench design for TPS5401 ‑ 20V-30V to 3.30V @ 0.3A
https://webench.ti.com/appinfo/webench/scripts/SDP.cgi?ID=63B7EE26E6CD8AE4
The efficiency is very good at low load currents. Better than an LDO could achieve.
Next, here is a Webench design for LMR23610 ‑ 20V-30V to 3.30V @ 0.3A
https://webench.ti.com/appinfo/webench/scripts/SDP.cgi?ID=EB345E3483874BB4
The efficiency is excellent at very low load currents.
This device has improved light load efficiency, better than the TPS5401.
(note the Log-Scale on the lower graph)
There are also reference designs for E-Bike type of applications.
These will provide a good baseline for your design to follow.
Hello EdWalker,
Thanks for the reply.
LMR23610 will be over rated for our design.it have 1A capability and price also high. we are looking into cost effective solution from TI.
We planned to use TPS54061 and its our requirements. please give your opinion on this device.
Actually we are designing 24V and 36V BMS with bq76930. it will be great if we are able to use one buck converter for both design.
Thanks,
Vignesh