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NZQFN28 Datasheet(PDF) 10 Page - Roithner LaserTechnik GmbH |
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NZQFN28 Datasheet(HTML) 10 Page - Roithner LaserTechnik GmbH |
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10 / 20 page  iC-NZ FAIL-SAFE LASER DIODE DRIVER Rev B2, Page 10/20 1. Enabling the system Before iC-NZ is put into operation for the first time the external circuitry should be checked for the following (see block diagram): • Resistor RSMD should be of low impedance. It may not, however, be lower than 250 Ω, otherwise the in- ternal iC check will generate an error message. • The resistors at pins RMDL, RMDM and RMDH should be of high impedance (low output). • Inputs LENL, LENM and LENH should be switched to low (the driver stages switched off). So that iC-NZ can be switched on pin EN must be set to high and pin ENCAL to low. A current in the milliampere range (Electrical Characteristics No. 501) now flows into pin NERR. This indicates that the de- vice is now in its start-up phase. The voltage at pin RSI is set to 0.5 V and capacitor CLDA charged at pin LDA. Once voltage V(LDA) has reached its final value the control unit and safety monitor diode are checked, if the latter is in use (see also Operation without a second monitor diode). Following this check the cur- rent into pin NERR is lowered (Electrical Characteris- tics No. 502). The residual current still remaining (ca. 500 µA) indicates that the control unit is not yet in oper- ation (N-type: V(MDL) < 0.5 V, P-type: VDD – V(MDL) < 0.5 V). The entire process is described in Figure 6. V(EN) V(SMD) VCHK V(MDL) VREF V(LDA) V(NERR) Figure 6: Signal pattern when the system is enabled Demo board Before the demo board is put into operation trimmers PSMDL, PML, PMM and PMH should be set to the left and trimmer PSMDH to its centre setting. Possible sources of error • V(NERR) remains at low: – Check the current in NERR. Is the impedance of the pull-up resistor too high? • Too high a current is flowing through pin NERR: An error has occurred during the device self-test. Check the following: – Is ENCAL lo? – Is RSMD of too low an impedance? RSMD may not be lower than 250 Ω. – Is pin SMD open or has it directly short- circuited with VCC? – Is there a direct connection between pin LDK and ground? – Is there a low-impedance connection between pin LDA and ground? – Have all CIx capacitors (x: L, M, H) been prop- erly soldered and placed close to the iC? – Is VCC properly back upped? 2. Calibrating the low and middle channels So that the optical power can be regulated pin REGEN must be set to high. The level at pin ENCAL is of no consequence when setting the low and middle chan- nels. Setting the low output level Pin LENL is first switched from low to high. The in- tegration capacitor at CIL is then charged. Until the control unit has settled a small amount of current flows in pin NERR. Following this the voltage at pin MDL is 0.5 V for an N-type diode and VDD – 0.5 V for a P-type diode. The required optical power can now be set at resistor RML. Demo board By way of example, three output levels of 1 mW, 3 mW and 5 mW are to be set. With an optical power of 1 mW laser diode HL6339G has a typical monitor current (IM) of 15 µA. The following value is then obtained for the resistor at pin MDL (RMLn = PML + RML): RMLn = V (MDL) IM = 0.5 V 15 µA = 33.34 k Ω Setting the middle channel Pin LENL must remain at high and LENM be switched from low to high. Following the settling of the control unit at CIM (N-type: V(MDL) < 0.5 V; P-type: VDD – V(MDL) < 0.5 V) the required optical power can be set at resistor RMM. |
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