D372A Datasheet, PDF (6/12 Pages) List of Unclassifed Manufacturers – Electroluminescent Lamp Driver IC

II. Inductor Switching Frequency (CHF) Selection
Selecting the appropriate value of capacitor (CHF) for the high frequency oscillator will set the inductor switching
frequency of the D372 inverter. Figure 4 graphically represents the effect of the CHF capacitor value on the oscillator
frequency at V+ = 3.0V.
25
20
15
10
50
75
100
125
150
175
200
CHF (pF)
Figure 4: Typical Inductor Frequency vs. CHF Capacitor
The inductor switching frequency may also be controlled with an external clock signal. The inductor will charge
during the low portion of the clock signal and discharge into the EL lamp during the high portion of the clock signal.
III. Inductor (L) Selection
The inductor value and inductor switching frequency have the greatest impact on the output brightness and current
consumption of the driver. Figures 5 and 6 show typical brightness and current draw of a D372 circuit with several
different inductor and CHF values. The CLF value was modified in each case such that the output voltage was
approximately 200Vpp. The data was taken with average inductors. Please note that the DC resistance (DCR) and
current rating of inductors with the same inductance value may vary with manufacturer and inductor type. Thus,
inductors made by a different manufacturer may yield different outputs, but the trend of the different curves should be
similar.
9
50
8
68 pF Luminance
100 pF Luminance
45
7
68 pF Current
100 pF Current
40
6
35
5
30
4
25
3
2
20
1
15
0
10
0.0
1.0
2.0
3.0
4.0
5.0
6.0
CLF (nF)
9
50
8
68 pF Luminance
45
100 pF Luminance
7
68 pF Current
40
100 pF Current
6
35
5
30
4
25
3
2
20
1
15
0
10
0.0
1.0
2.0
3.0
4.0
5.0
6.0
CLF (nF)
Figure 5: Luminance and Current
vs. Inductor and CHF Value
Conditions: V+ = 3.0 V, 1.5 in² EL Lamp
7
Figure 6: Luminance and Current
vs. Inductor and CHF value
Conditions: V+ = 5.0 V, 4in² EL Lamp