Datasheet

( )
OUT
C IN OUT OC
SW IN
V
1
V V V I DCR
2 R1 C1 f V
= ´ - ´ + ´
´ ´ ´
R1 +
L1
DCR C1
R1
L1
DCR
C1
To CSRTx
To CSx
V
OUT
V
IN
+ V
C −
M_CH1M_CH2
S2_CH1
S1_CH2S2_CH2
S3_CH1
S4_CH1
S3_CH2
S4_CH2
Phase
S1_CH1
S5_CH2
NOT USED
S5_CH1
NOT USED
M
R
S1
R
S2
S3
S4
ILIM 2=hi
PHSEL connection
TPS40140
www.ti.com SLUS660H –SEPTEMBER 2005–REVISED JUNE 2013
Figure 5-22. Ten-Phase System with Slaves Not Attached
Clocking between the attached slave channels is as shown.
5.29 DESIGN EXAMPLES INFORMATION
5.29.1 INDUCTOR DCR CURRENT SENSE
The preferred method for sampling the output current for the TPS40140 is known as the inductor DCR
method. This is a lossless approach, as opposed to using a discrete current sense resistor which occupies
board area and impacts efficiency as well. The inductor DCR implementation is shown in Figure 5-23.
Figure 5-23. Inductor DCR Current Sense Approach
The inductor L1 consists of inductance, L, and resistance, DCR. The time constant of the inductor: L /
DCR should equal the R1×C1 time constant. Then choosing a value for C1 (0.1 μF is a good choice)
solving for R1 is shown in Equation 17.
(17)
The voltage into the current sense amplifier of the controller , V
C
, is calculated in Equation 18.
(18)
As the DC load increases the majority of the voltage, V
C
, is determined by (I
OC
×DCR), where I
OC
is the
per phase DC output current. It is important that at the overcurrent set point that the peak voltage of V
C
does not exceed 60 mV, the maximum differential input voltage. If the voltage V
C
exceeds 60 mV, a
resistor, R2,can be added in parallel with C1 as shown in Figure 5-24. Adding R2 reduces the equivalent
inductor DCR by the ratio shown in Equation 20
Copyright © 2005–2013, Texas Instruments Incorporated APPLICATION INFORMATION 41
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