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| ILD4071 Datasheet, PDF (20/25 Pages) Infineon Technologies AG – LED Driver for High Power LEDs | |||
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ILD4071
Application Information
8.2
Switching Frequency Determination
The switching concept of the ILD4071 is based on peak current regulation with constant OFF time (tOFF). Thus the
switching frequency fSW is dependent on Input voltage (VREC) variations.
With the external RFREQ, CFREQ, RCOMP RCLAMP and ZCLAMP network, it is possible to adjust and stabilize the
switching frequency of the regulator and achieve a.
1) no compensation, fSW increases accordingly to the VREC increase
2) switching frequency stabilized in a defined VREC range via compensation resistor RCOMP
3) switching frequency stabilized over the whole VREC range via RCOMP and additional clamping circuit ZCLAMP and
RCLAMP (=1kΩ)
1
1
VREC
FREQ 6
GND
7
RFREQ
CFREQ
2
1
VREC
FREQ 6
RCOMP
GND
7
RFREQ
CFREQ
3
RCLAMP
1
VREC
FREQ 6
RCOMP
GND
7
RFREQ
CFREQ
ZCLAMP
700000
fSW â Without Compensation
600000
500000
400000
300000
200000
100000
0
5
10
15
20
25
VREC [V]
700000
fSW â Compensation via RCOMP
600000
500000
400000
300000
200000
100000
0
5
10
15
20
25
VREC [V]
fSW â Compensation via RCOMP + VREC Clamp
700000
600000
500000
400000
300000
200000
100000
0
5
10
15
20
25
VREC [V]
Figure 10 Setting tOFF Time of Regulator with External RFREQ, CFREQ Network, stabilize fSW via RCOMP,
RCLAMP and ZCLAMP
Setup 2 applies for the table displayed in Figure 11: VREC=12V, VLED=7.2V, LSW=220µH, RSET=14kΩ.
Rcomp
255.8kΩ
115.8kΩ
69.7kΩ
46.8kΩ
72.8kΩ
52.7kΩ
Rfreq
17.1kΩ
7.7kΩ
4.6kΩ
3.1kΩ
4.9kΩ
3.5kΩ
Cfreq
220pF
220pF
220pF
220pF
100pF
100pF
Figure 11 RFREQ, CFREQ versus fSW Table
Datasheet
20
fsw
50kHz
100kHz
150kHz
200kHz
250kHz
300kHz
toff
6.47μs
3.19μs
2.12μs
1.59μs
1.27μs
1.06μs
Rev. 1.0, 2011-11-16
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