SLUU161 – April, 2003

6

TPS40051-Based Design Converts 12-V Bus to 1.8 V at 15 A (SLUP195)

4

Component Selection

4.1

TPS40051 Device Selection

The TPS4005x family of parts offers a range of output current configurations including source only (TPS40050),

source/sink capability is selected. This serves to maintain continuous inductor ripple current all the way to zero

load to improve the small signal loop response by preventing the inductor current from transitioning to the

discontinuous current mode.

The TPS4005x family is packaged in TI’s PWP PowerPAD thermally enhanced package which should be

soldered to the PCB using standard solder flow techniques. The PowerPAD

 technology uses a thermally

conductive epoxy to attach the integrated circuit die to the leadframe die pad, which is exposed on the bottom

of the completed package. The PWP PowerPAD package has a

temperature rise relatively low even with the power dissipation inherent in the onboard MOSFET drivers. This

power loss is proportional to switching frequency, drive voltage, and the gate charge needed to enhance the

N-channel MOSFETs. Effective heat removal allows the use of ultra-small packaging while maintaining high

component reliability.

package.

4.2

Frequency of Operation

The clock oscillator frequency for the TPS40051 is programmed with a single resistor from RT (pin 2) to signal

ground. The following equation (1) from the datasheet allows selection of RT in k

Ω for a given switching

frequency in kHz.

R

1

f

SW

17.82

* 23 (kW)

For 300-kHz operation, R2 is selected to be 165 k

Ω.

using equation (2).

R

58.14

R

(k

W)

(1)

(2)