Texas Instruments TPS40090EVM-002 manual Component Selection, Frequency of Operation

				SLUU195 − June 2004
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				1.5V/100A

Figure 3. TPS40090EVM−002 Schematic Part 3 − Power Stage

4 Component Selection

4.1Frequency of Operation

The clock oscillator frequency for the TPS40090 is programmed with a single resistor from RT

(pin 16) to signal ground. Equation (1) from the datasheet allows selection of the RT resistor in kΩ for a given switching frequency in kHz.

RT + R12	+ KPH ￿39.2 10	3	*1.024	* 7￿ (kW)	(1)
			fPH

where

•KPH is the coefficient that depends on the number of active phases

•fPH is the single phase frequency, in kHz

•for 2-phase and 3-phase configurations KPH=1.333

•for 4-phase KPH=1.0 is a single phase frequency, kHz.

The RT resistor value is returned by the last expression in kΩ. For 420 kHz, RT is calculated as 65.8 kΩ and a resistor with a 64.9-kΩ standard value is used.

TPS40090 Multi-Phase Buck Converter and TPS2834 Drivers Steps-Down from 12-V to 1.5-V at 100 A 7