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Using Charge Pump as a DC-DC converter for Portable Device

Former Member
With the development of low power technology, the power consumption of portable devices such as blue-tooth earphone and MP3 player has dropped down to the level less than 100 mA, it is possible that charge pump is used as a DC-DC converter for portable devices. Compared with common Buck DC-DC converter, charge pump features smaller profile (without inductor), simpler peripheral circuit, lower cost, etc. Although the conversion efficiency is little lower (generally up to 87%), it is still acceptable.
For example, the LETC3240 from LTC can offer 150mA output current with efficiency up to 87%, especially suitable for the portable devices with awfully small size.

 

Let’s discuss this topic freely!

 

 

 

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  • can you tell me  how this circuit work when input voltage from 2.7V~4.5V but constant output 3.3V, as we know ,Charge Pump can increase output .but when input is 3.3V~4.5V,how to work?

  • in reply to Former Member

    This DC-DC converter IC is regarded a LDO+Charge Pump,when input is greater than output by
    about 100mV it operates as a low dropout regulator(LDO),when output is greater than input it

    automatically switches into charge pump mode to boost input to the regulated output voltage.

  • in reply to Jason
    Hi Jason I have not used these ICs but does it mean that if it is acting as a linear regulator in buck mode then the efficiency must vary according to the battery voltage (higher inefficiency when input voltage is higher)? When the battery is at its maximum (4.5v) and the load is pulling 150mA then input power is 0.655watts. With the output power being (3.3*0.15) 0.495watts this gives an efficiency of (0.495/0.655) <76% (worse case scenario of course). Is this correct? Regards Malcolm
  • in reply to Malcolm

    hello Malcolm:

    You're right, you can see the curve when the input voltage is lower than output, the device worked on charge pump modeimage and the efficiency is decrease as the input voltage increase. When the input voltage reach to V_out+100mV, the device changed to work on LDO mode, ang the efficiency is jump to higher and decrease as input voltage increase.

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  • in reply to Malcolm

    hello Malcolm:

    You're right, you can see the curve when the input voltage is lower than output, the device worked on charge pump modeimage and the efficiency is decrease as the input voltage increase. When the input voltage reach to V_out+100mV, the device changed to work on LDO mode, ang the efficiency is jump to higher and decrease as input voltage increase.

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