LTC3877 Design Query

Hi Team,

Awaiting for your feedback.

Another query, Is the Inductor value is same for all the output voltage and current requirement?

Are there any excel calculation for LTC3877?

Hello,

The LTC3877 can be used for a single output design with the 2nd phase unused. Just tie the CHL_SEL pin to GND to configure the LTC3877 for dual outputs and make these connections:
ITH2  open
TK/SS2 open
VFB2+/- open
TG2 open
SW2 open
BG2 open
BOOST2 open
SNSA2+, SNSD2+ and SNS2- tied to each other and to GND

The only difference between the LTC3877EUK and the LTC3877IUK are the operating temperature ranges. The E grade version is guaranteed over the 0C to 85C range while the I grade version is guaranteed over the -40C to 125C range. See Note 3 on page 5 of the data sheet for more details.

The LTC3877 can be used as a single phase design provided the hot spot temperature does not exceed 110C approximately.

Best regards,

Mike

Hi mike.shriver 

For my application requirement, Which one would you suggest? To use both Output or Single Output?

Our requirement is as below,

VIN- 12V,

Vout- 1.025V, Iout- 23~25A With VID.

Also let us know, Any excel calculation available for this part?

Hello KLN,

As a starting point, select an inductor which will provide an inductor ripple current which is 40% of the maximum DC phase current at the maximum Vout. Smaller or larger inductors can be used. However, the trade-off for larger inductor values is a larger footprint, larger DCR and higher conduction losses and a lower current sense ripple voltage. The trade-off for smaller inductors is higher output voltage ripple and possibly higher core losses.

We do not have an Excel design tool or an LTpowerCAD design tool for the LTC3877. However, the LTC3875 design tool can be used instead. The LTC3877 is an LTC3875 with VID control. When using the LTC3875 LTpowerCAD design tool select a feedback divider to match the programmed VOUT.

Best regards,

Mike

Hello,

For a 1.025V 23A-25A output, a single phase design will work provided the ambient temperature is not too high or the air cooling is sufficient. The standard demo board for the LTC3877 operates at 30A per phase which is higher 25A. Therefore, it is feasible. When the demo board is setup for dual outputs of 1.0 / 30A on phase 1 and 1.5V / 30A on phase 2, an input voltage of 12V and Fsw=400kHz, the hot spot temperature is about 60 degrees C above ambient with no airflow. This is measured on a 6.0" x 7.0' 6 layer PCB with 2 oz copper on the outer layers and 1 oz copper on the inner layers. As a guideline, the hot spot temperature should not exceed 110C approximately. The demo board could operate with a maximum ambient of 50C with no air cooling.

As mentioned above, we do not have an Excel design tool or an LTpowerCAD design tool for the LTC3877. However, the LTC3875 design tool can be used instead. The LTC3877 is an LTC3875 with VID control. When using the LTC3875 LTpowerCAD design tool select a feedback divider to match the programmed VOUT.

Best regards,

Mike