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iC-VJSO16N Datasheet(PDF) 7 Page - IC-Haus GmbH |
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iC-VJSO16N Datasheet(HTML) 7 Page - IC-Haus GmbH |
7 / 10 page iC-VJ, iC-VJZ LASER DIODE CONTROLLER Rev A1, Page 7/10 Oscillator The internal oscillator operates in the range approx. 10 kHz to 4 MHz. This enables laser pulse repetition frequencies from 1 to 200 kHz. Fig. 2 shows the pulse repetition frequency as a function of the oscillator cir- cuit. Example R1 = 620 Ω, C1 = 82 pF: f ≈ 200 kHz 200 100 f [kHz] R1 [k Ω] 1 2 3 4 5 6 7 8 C1= 82pF C1= 1nF C1= 220pF Figure 2: Pulse repetition frequency Averaging Control The control of the average optical laser power requires the external capacitor C2 at pin CI. This capacitor is used for averaging and must be adjusted to the se- lected pulse repetition frequency and the charging cur- rent preset with RSET. The ratios are linear in both cases, i.e. C2 must be increased in size proportionally as the pulse repetition frequency slows or resistance RSET decreases. C2 ≥ 440 ∗ I(ISET ) f ∗ V (ISET ) = 440 f ∗ RSET Example Frequency 10 kHz, RSET = 10 kΩ: C2 ≈ 4.7 µF Otherwise the charging of C2 during the pulse pauses (with I(ISET) = 1.22 V / RSET) will result in excessive mean value potential at pin CI and the laser diode may be destroyed with the next pulse. C2 is correctly di- mensioned when the current through the laser diode and the optical output signal do not show any over- shooting on the rising edge. In steady-state condition, signals will then appear at the IC pins as shown in Fig. 3. In this case the laser pulse exhibits a minimal overshoot on the rising edge, but this can be tolerated. The increase in the current in KLD and the laser pulse follow directly after the signal at the divider output PRF. The outputs PRF and NPRF are used for receiver synchronisation. LASER Output PRF [1V/div] I(KDL) [50mA/div] KDL [1V/div] Timebase = 1:s/div [2mW/div] Figure 3: Settled control with 200 kHz pulse repeti- tion frequency Turn-on and Turn-off Behavior Capacitor C2 also determines the starting time from switching on the supply voltage VCC to steady-state laser pulse operation. The values of C2 which are necessary higher for low pulse repetition frequencies increase this starting time to several milliseconds (Fig. 4). The following applies for estimating the starting time: Ton ≈ 2.5 V ∗ C2 I(ISET ) = 2.5 V ∗ C2 ∗ RSET 1.22 V Example C2 = 4.7 µF, RSET = 10 kΩ: Ton ≈ 96 ms Timebase = 20 ms/div LASER Output [2mW/div] VCC [2V/div] PRF [2V/div] C [1V/div] Figure 4: Turn-on behavior f = 10 kHz, RSET = 10 kΩ, C2 = 4.7 µF LASER Output LASER Output [1mW/div] C [200mV/div] Figure 5: Setteling of the averaging control For high pulse repetition frequencies (200 kHz) and low C2 values (220 nF) and for RSET = 10 kΩ the aver- aging control achieves its operating point after 3.5 ms. Fig. 5 shows the turn-on, Fig. 6 the turn-off behavior, here in case of undervoltage. |
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