Datasheet

R
DROOP
+
2500 N
PH
V
DROOP
I
OUT
R
CS
V
REF
V
OUT
+
2500 N
PH
V
DROOP
V
CS1
) V
CS2
) V
CS3
) V
CS4
R2
R1 ) R2
OUTPUTVOLTAGE
vs
OUTPUTCURRENT
V
OUT
V
OUT
-OutputVoltage-V
I
OUT
-OutputCurrent- A
V
DROOP
I
OUT(max)
0
I
DROOP
13
12
11
9
GNDS
DIFFO
VOUT
REF
10
7
8
COMP
FB
DROOP
R3
C1
R1
+
+
+
700mV
R2
Error
Amplifier
Differential
Amplifier
I
DROOP
R
DROOP
TPS40090
TPS40091
www.ti.com SLUS578B –OCTOBER 2003– REVISED MAY 2006
SETTING THE OUTPUT VOLTAGE DROOP
In many applications, the output voltage of the converter is intentionally allowed to droop as load current
increases. This approach (sometimes referred to as active load line programming) allows for better use of the
regulation window and reduces the amount of the output capacitors required to handle the same load current
step. A resistor from the REF pin to the DROOP pin sets the desired value of the output voltage droop.
where: (9)
• V
DROOP
is the value of droop at maximum load current I
OUT
• N
PH
is number of phases
• R
CS
is the current-sense resistor value
• 2500 Ω is the inversed value of transconductance from the current sense pins to DROOP
• V
CSx
, are the average voltages on the current sense pins
Figure 4. Figure 5.
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