TPS40140_15 Datasheet, PDF (43/71 Pages) Texas Instruments – TPS40140 Dual or 2-Phase, Stackable Controller

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TPS40140
SLUS660I – SEPTEMBER 2005 – REVISED JANUARY 2015
P_SRtot + P_SRcond ) P_DIODE + 1.47 W
(35)
9.2.1.2.5 Step 5: Peripheral Component Design
9.2.1.2.5.1 Switching Frequency Setting (RT Pin 5)
( ) R = 1.33 ´ 39.2 ´103 ´ ƒ -1.058 - 7 ,
PH
(36)
In the design, a 62-kΩ resistor is selected. The actual switching frequency is 510 kHz.
9.2.1.2.5.2 Output Voltage Setting (FB1 Pin 36)
Substitute R1 with 10 kΩ and then calculate R_BIAS.
R1
R = 0.7 ×
= 8.75 kΩ
BIAS
V - 0.7
OUT
(37)
9.2.1.2.5.3 Current Sensing Network Design (CS1 Pin 31 and CSRT1 Pin 32)
For small pulse width, to avoid the sub-harmonics brought by the loop delay, a resistor divider is usually used to
attenuate the current feedback information as described in the Inductor DCR Current Sense section.
Choosing C1 a value for 0.1-μF, and let R1 and R2 be equal, calculating R1 and R2 with Equation 38 and
Equation 39. In this design, R1 and R2 are 10 kΩ.
L
R1//R2 = _{DCR ´ C1} = 5.8 kΩ
(38)
R1 = R2 = 11.6 kΩ
(39)
A simplified equation to determine if the design produces sub-harmonics is shown in Equation 40.
L _> V_IN × Ac
DCR_(eqv) 2 × V_ramp × f_sw
(40)
DCR_(eqv)
=
R2
R1+ R2
×
DCR
=
DCR
2
(41)
In this design, a 1-μF capacitor is placed at the CSRT1 pin for the purpose of eliminating noise. It can be
removed without degrading performance.
9.2.1.2.5.4 Overcurrent Protection (ILIM1 Pin 34)
The resistor selection equations in the CALCULATING OVERCURRENT PROTECTION LEVEL section are
simplified to calculate the over current setting resistors. Set the DC over current rating at 30 A.
DCRe qv ´ Ac ´ IPK + ^VRAMP + ^VRAMP ´ VSH
R1 =
2 ´ NPH VIN
(1- ^VRAMP ) ´ ILIM
= 22.5kW
VIN
(42)
DCRe qv ´ Ac ´ IPK + ^VRAMP + ^VRAMP ´ VSH
R2 =
2 ´ NPH VIN
VRAMP _{´ ILIM}
= 510kW
VIN
where
• A_C is the gain transfer to comparator (typ 12.5)
• V_RAMP is the ramp amplitude (typ 0.5 V)
• V_SH is the V_SHARE reference voltage (typ 1.8 V)
• I_LIM is the current limit output current (typ 20 µA)
• N_PH is 6 if V_PHSEL = 1.6 V ±0.2 V, otherwise N_PH = 8
(43)
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