Datasheet

R
DCM(hi)
R
DCM
1
15
12
VREF
CS
DCM
20 mA
R = 77 kW
C = 6.5 pF
R = 77 kW
C = 6.5 pF
+
DCM_COMP
2-Cycle
Counter
0 = DCM
1 = CCM
PWM
Other Blocks
Moving into
DCM Mode
0 10
Load Current - A
0.8
4
Duty Cycle - %
DUTY CYCLE
vs
LOAD CURRENT
0.4
0
0.6
0.2
1 2 3 5 6 7 8 9
V
S(min)
V
S(max)
Burst Mode
Area
Setting D
MIN
15.6%
UCC28950
SLUSA16B –MARCH 2010– REVISED OCTOBER 2011 www.ti.com
Dynamic SR ON/OFF Control (DCM Mode)
The voltage at the DCM pin provided by the resistor divider Rdcmhi between VREF pin and DCM, and Rdcm
from DCM pin to GND, sets the percentage of 2-V current limit threshold for the Current Sense pin, (CS). If the
CS pin voltage falls below the DCM pin threshold voltage, then the controller initiates the light load power saving
mode, and shuts down the synchronous rectifiers, OUTE and OUTF. If the CS pin voltage is higher than the
DCM pin threshold voltage, then the controller runs in CCM mode. Connecting the DCM pin to VREF makes the
controller run in DCM mode and shuts both Outputs OUTE and OUTF. Shorting the DCM pin to GND disables
the DCM feature and the controller runs in CCM mode under all conditions.
Figure 14. DCM Functional Block
Figure 15. Duty Cycle Change Over Load Current Change
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