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LM22670: LM22670MRE-ADJ/NOPB

Takashi Matsumura
Intellectual 705 points
Part Number: LM22670
 
Hi TI TEAM,
I would like to know the effiency of this LM22670MRE-ADJ/NOPB regulator in the low current region.
On the datasheet, the effiency curve is shown on Fig. 20, but it does not show the efficiency in the 
low current region.
 
The customer showed the input / output condition as the following.
       Input voltage : 36Vdc
       Input current : 0.08A
       Output voltage : 5.0Vdc
       Output current : 0.225A
 
In the above condition, the efficiency is about 39%. 
On the datasheet, the effiency is not shown in the low current region. 
 
Could you ask the MFG to show the effiency in the low current region for reference?
 
1. If you think this effiency is too low as a good IC, could you advice the customer how to raise 
the effienciency?
2. If you think this effiency is normal, could you show what makes the effiency of this IC low  as 
a standard switching regulator?
 
Thank you for your support.
Best Regards
Takashi
Digi-Key Japan connect
  • 0
    TI__Mastermind 28020 points

    Hi Takashi,

    Unfortunately, the low efficiency at light load looks as expected.

    Switching power supplies have switching losses associated with driving the FETs. Every time that the power supply switches, it consumes a fixed amount of power. At heavier load, this amount of power is small compared to the output power. However, at light load the switching losses are a large compared to the output power, resulting in lower efficiency. You may be able to increase the efficiency somewhat by reducing the switching frequency, but maybe not as much as needed.

    The LM22670 operates in PWM mode which has a fixed switching frequency over all load conditions. In order to improve the efficiency at light load you should consider using a device that operates in PFM at light load. At light load, the switching frequency gets reduced in order to reduce the switching losses. This greatly improves the light load efficiency.

    You may want to look at a device like LMR33630. The efficiency remains high at light load due to the PFM mode.

    Regards, Jason

  • 0 in reply to J Arrigo
    Intellectual 705 points

    Thank you so much Arrigo-san!