MIC3263 Datasheet, PDF (27/32 Pages) Micrel Semiconductor – Six-Channel WLED Driver for Backlighting Applications with Flicker-Free Dimming

Micrel, Inc.
The explanation of the method to find the best R
snubber is beyond the scope of this data sheet. Use
R_SNUBBER ≈ 2Ω ½ W and C_SNUBBER ≈ 470pF to 1000pF. If
a snubber is used, the power dissipation in the R_SNUBBER
is:
R_SNUBBER = C_SNUBBER × V_OUT2 × F_SW
P_SNUBBER = 470pF × 34V² × 1MHz = 0.54W
Table 2 illustrates the power losses in the Design
Example.
Description
Power Loss in the L
Power Loss in the Schottky Diode
MIC3263 Power Loss
Maximum Total Losses
Minimum Efficiency
Value
0.069W
0.09W
1.46W
1.62W
80%
Table 2. Major Power Losses
MIC3263
OVP
The output voltage that the OVP will trigger is set
according to Equation 19. Using the values for this
example gives a max output voltage of:
Equation 19:
V_OVP= 2.4× (R2+R2)/R1=40V
RSLP
To find RSLP use Equation 1 (which is repeated here):
Use the minimum V_IN and the maximum V_OUT.
RSLP
=
V_OUT(MAX) - L × F_sw
8.64 × 10-6 × V_IN(MIN)
In this example:
34 - 22μH × 1Mhz
RSLP = _{8.64 × 10-6 × 8} = 174kΩ
January 2010
27
M9999-012110