D365A Datasheet, PDF (6/12 Pages) List of Unclassifed Manufacturers – Electroluminescent Lamp Driver IC

I. Lamp Frequency Capacitor (CHF) Selection
Selecting the appropriate value of CHF capacitor will specify the inductor switching frequency (HF) and the lamp
frequency (LF) of the D365 EL driver. A divider circuit in the internal oscillator circuitry of the D365A divides the
inductor switching frequency by 72 to get the lamp frequency (LF = HF/72). Lamp frequencies of 200 – 500 Hz are
typically used for longer EL lamp life. Figure 1 graphically represents the effect of CHF capacitor value on the lamp
frequency oscillator at V+=3.3V. In this example at V+=3.3V, LF = 2000 nF-Hz/CHF.
1400
1200
1000
800
600
400
200
0
0
5
10
15
20
25
CHF (nF)
Figure 1: Typical Lamp Frequency vs. CLF Capacitor
Alternatively, a high frequency clock input may be connected to the CHF pin of the D365A to specify the output driver
frequency. The internal oscillator circuitry in the D365A divides the input clock frequency by 72 to get the output
frequency. Thus, for example, to get a 250Hz lamp frequency from a D365A, the input clock signal must be 18kHz.
The selection of the capacitor value can also affect the brightness of the EL lamp because of its control of LF and HF.
Although input voltage and lamp size can change EL lamp frequency as well, LF mainly depends on the CHF value
selected or the frequency of the input clock signal to CHF. Figure 2 shows typical brightness of a D365 circuit with
respect to lamp frequency on different EL lamp sizes. In this example, the supply voltage and inductor values were
kept constant while only varying frequency.
9
8
7
6
5
4
3
2
1
100
2in²
4in²
6in²
300
500
700
Lamp Frequency (Hz)
Figure 2: Luminance vs. Lamp Frequency
(V+ = 3.3V, Durel 3 Green EL Lamp)
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