IC-NZ Datasheet, PDF (10/20 Pages) IC-Haus GmbH – FAIL-SAFE LASER DIODE DRIVER

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(LDA)
V(SMD)
VCHK
VREF
V(MDL)
V(NERR)
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):
V (MDL) 0.5 V
RMLn = _IM = _{15 µA} = 33.34 k Ω
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.
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.