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Micrel, Inc.
Pin Descriptions
FSW
Sets the boost switching frequency. Connec t a resi stor
from FSW to GND to set the switching frequency between
400kHz and 1.8MHz. Use the fo llowing equation s to sele ct
R FSW :
R FSW (k ? ) ≈ 500 ? 0.3 × f SW (kHz)
RSL P
The boost section is a peak current mode ty p o logy and
needs slope compensation to eliminate s ub -harmonic
oscillation (see “Slope Compensation”).
OVPS
Thi s is a virtual ground of the resistor divider feedback
network in the boost stage. At turn on, a swit ch connects
this node-to-ground. When the part is disabled the switch
will open and disconnects the feedback resistor network
MIC3263
Use the following equations to determine the value for
R DFS :
R DFS (k ? ) = ? 20 × f DIM (kHz) + 432 (HF Mode)
R DFS (k ? ) = ? 335 × f DIM (kHz) + 433 (LF Mode)
Example:
For a dimming frequency of 10kHz, use the HF Mode:
R DFS (k ? ) = ? 20 × 10 + 432 = 232k ? in HF Mode
For 1kHz, u se LF Mode:
R DFS (k ? ) = ? 335 × 1 + 433 = 98k ? in LF Mode
Use the closest standard value.
from ground. This eliminates current draw from V IN by the
boost resistor divider network.
OVP
This is the over-voltage protection monitor. Also t his is the
feedback signal t hat connects to the error amp input.
MODE
450
400
350
300
250
200
150
RDFS(in k ? ) = -20*Dimming Frequency (in kHz) + 432
This selects the internal PWM dimming frequ ency range.
When mode is low the PWM dimming frequen cy range is
100Hz to 2kHz. When mode is high the PWM D frequency
range is 1.5kHz to 20kHz. Mode is high s elects High
Frequency (HF) mode; Mode is low s elects Low
100
50
0
0
2.5
5
7.5 10 12.5 15
Dimming Frequency (kHz)
17.5
20
22.5
Frequency (LF) mode.
DFS
DFS stands for Dimming Frequency Select. T he dimming
frequenc y of the LEDs is different than the input dimmin g
frequency at the DRC input. The MIC3263 uses a n in ternal
dimming frequency. This internal dimming frequency is
programmable by an external resistor to ground R DFS .
For direct dimming control, connect DFS to V DD and use
the MODE pin for the input dimming pulse. This method by
passes the internal dimming control and allows for
dimming control by the external PWM pulse.
Figure 5. R DFS vs. Dimming Frequency in HF Mode
RDFS(k ? ) = -335*Dim m ing Frequency (in kHz) + 433
500
400
300
200
100
0
When using internal dimming the range is determined by
0
0.2
0.4
0.6
0.8
1
1.2
1.4
the MODE pin and the actual frequency is determined by
R DFS . Connect a resistor to ground to select a dimming
frequency.
Dim m ing Frequency (kHz)
Figure 6. R DFS vs. Dimming Frequency in LF Mode
January 2010
15
M9999-012110
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