Datasheet

REF
SUM
(V 2.5 V)
V
me
0.5 R s
æ ö
-
=
ç ÷
´ m
è ø
5 200
R
sum
- Resistor - kW
0.50
100
Slope - V/ms
SLOPE
vs
RESISTOR
0.45
0.10
0
0.30
0.20
0.05
0.25
20 40 80 120 140 18060 160
0.15
0.40
0.35
UCC28950
www.ti.com SLUSA16B –MARCH 2010–REVISED OCTOBER 2011
If the resistor from RSUM pin is connected to VREF pin, then the controller operates in voltage mode control, still
having the slope compensation added to CS signal used for cycle-by-cycle current limit. In such a case the slope
is defined by the following Equation 13.
(13)
In Equation 12 and Equation 13, the VREF is in volts, RSUM is in kΩ, and me is in V/µs. These are empirical
equations without unit agreement. As an example, substituting VREF = 5 V and RSUM = 40 kΩ, yields the result
0.125 V/µs. The related plot of me as function of RSUM is shown in Figure 13. Because VREF = 5 V, the plots
generated from Equation 12 and Equation 13 coincide.
Figure 13. Slope of the Added Ramp Over Resistor RSUM
NOTE
The recommended resistor range for R
SUM
is 10 kΩ to 1 MΩ.
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