iC-WJ, iC-WJZ

iC-WJ, iC-WJZ
LASER DIODE DRIVER
FEATURES
APPLICATIONS
♦ Laser diode driver for continuous and intermittent operation
(CW to 300kHz) up to 250mA
♦ Averaging control of laser power
♦ Simple adjustment of the laser power via external resistor
♦ Adjustable watchdog at the switching input to protect the
laser diode
♦ Smooth starting after power-on
♦ Driver shutdown in the case of overtemperature and
undervoltage
♦ Single 5V supply
♦ Simple circuitry
◊ iC-WJ for laser diodes with 50..500µA monitor current
◊ iC-WJZ for laser diodes with 0.15..1.5mA monitor current
♦ Driver with protective functions
for CW laser diodes
PACKAGES
iC-WJ, iC-WJZ
SO8
BLOCK DIAGRAM
DRIVER STAGE
3
VCC
5
+5V
REF
C1
1
100µF
REFERENCE
C3
THERMAL
2nF
ISET
SHUTDOWN
KLD
4
8
RSET
10kΩ
6
INPUT
VCC
IN
LD MD
R1
12Ω
POWER DOWN
REF
AMD
7
74HCxx
2
4
1:1 iC-WJ
1:3 iC-WJZ
WATCHDOG
iC-WJ/WJZ
CWD
CI
2
3
CWD
CI
100nF..470nF
GND
1
usable LD models
©1997
Rev A1
iC-Haus GmbH
Integrated Circuits
Am Kuemmerling 18, D-55294 Bodenheim
Tel +49-6135-9292-0
Fax +49-6135-9292-192
http://www.ichaus.com
iC-WJ, iC-WJZ
LASER DIODE DRIVER
Rev A1, Page 2/12
DESCRIPTION
The iC-WJ and iC-WJZ devices are driver ICs for laser diodes in continuous and intermittent operation up
to 300kHz. The laser diode is activated via switching input IN. A control to the mean value of the optical
laser power and integrated protective functions ensure nondestructive operation of the sensitive
semiconductor laser.
The IC contains protective diodes to prevent destruction due to ESD, a protective circuit to guard against
overtemperature and undervoltage and a starting circuit for the laser diode driver to protect the laser diode
when switching on the supply voltage.
An external resistor at ISET is employed to adapt the power control to the laser diode being used. The
capacitor at CI determines the recovery time constants and the starting time.
A watchdog circuit monitors the switching input IN. If IN remains low longer than preset by the capa-citor at
CWD, the capacitor of the power control is discharged at pin CI. This ensures that the current through the
laser diode during the next high pulse at input IN is not impermissibly high.
PACKAGES SO8 to JEDEC Standard
PIN CONFIGURATION SO8
(top view)
PIN-FUNKTIONEN
No. Name Function
1
2
3
4
5
6
7
8
GND
CWD
CI
ISET
VCC
IN
AMD
KLD
Ground
Capacitor for Watchdog
Capacitor for Power Control
Attachment for RSET
5V Supply Voltage
Input
Anode Monitor Diode
Cathode Laser Diode
iC-WJ, iC-WJZ
LASER DIODE DRIVER
Rev A1, Page 3/12
ABSOLUTE MAXIMUM RATINGS
Values beyond which damage may occur; device operation is not guaranteed.
Item
Symbol
Parameter
Conditions
Fig.
Unit
Min.
Max.
G001 VCC
Supply Voltage
0
6
V
G101 I(CI)
Current in CI
-4
4
mA
G102 V(KLD)
Voltage at KLD
IN= lo
0
6
V
G103 I(KLD)
Current in KLD
IN= hi
-4
600
mA
G104 I(AMD)
Current in AMD
-4
4
mA
G201 I(IN)
Current in IN
-10
2
mA
G301 I(ISET)
Current in ISET
-2
2
mA
G401 I(CWD)
Current in CWD
IN= lo
-2
2
mA
EG1 Vd()
ESD Susceptibility at
CWD, CI, ISET, IN, AMD, KLD
MIL-STD-883, HBM 100pF
discharged through 1.5kΩ
2
kV
TG1 Tj
Junction Temperature
-40
150
°C
TG2 Ts
Storage Temperature
-40
150
°C
-6
6
mA
iC-WJZ with a monitor current rating of 0.15..1.5mA
Max. ratings for iC-WJ are valid with the following replacements:
G104 I(AMD)
Current in AMD
THERMAL DATA
Operating Conditions: VCC= 5V ±10%
Item
Symbol
Parameter
T1
Ta
Operating Ambient Temperature
Range
(extended temperature range on
request)
T2
Rthja
Thermal Resistance
Chip to Ambient
Conditions
Fig.
Unit
Min.
-25
surface mounted on PCB, without
special cooling
All voltages are referenced to ground unless otherwise noted.
All currents into the device pins are positive; all currents out of the device pins are negative.
Typ.
Max.
90
°C
140
K/W
iC-WJ, iC-WJZ
LASER DIODE DRIVER
Rev A1, Page 4/12
ELECTRICAL CHARACTERISTICS
Operating Conditions: VCC= 5V ±10%, RSET= 2.7..27kΩ,iC-WJ: I(AMD)= 50..500µA,
iC-WJZ: I(AMD)= 0.15..1.5mA, Tj= -25..125°C, unless otherwise noted.
Item
Symbol
Parameter
Conditions
Tj
°C
Fig.
Unit
Min.
Typ.
Max.
Total Device
001 VCC
Permissible Supply Voltage
Range
4.5
5.5
V
15
mA
65
135
ns
002 Iav(VCC) Supply Current in VCC
(average value)
Iav(KLD)= 100mA,
f(IN)= 200kHz ±20%
003 tp(IN-KLD Delay Time Pulse Edge
V(IN) to I(KLD)
IN(hi←→lo),
V(50%):I(50%)
004 Vc()lo
Clamp Voltage lo at VCC, IN,
AMD, KLD, CI, CWD, ISET
I()= -2mA, other pins open
-1.5
-0.3
V
005 Vc()hi
Clamp Voltage hi at IN, AMD,
KLD, GND, CI, CWD, ISET
Vc()hi= V()-VCC;
I()= 2mA, other pins open
0.3
1.5
V
101 Vs(KLD)
Saturation Voltage at KLD
IN= hi, I(KLD)= 200mA
1.3
V
102 I0(KLD)
Leakage Current in KLD
IN= lo, V(KLD)= VCC
103 I(KLD)
Current in KLD
IN= hi, I(AMD)= 0
104 V(AMD)
iC-WJ: Voltage at AMD
I(AMD)= 500µA
105 tr
Current Rise Time in KLD
106 tf
Driver Stage
10
-25
27
70
125
225
250
250
250
250
0.5
µA
mA
mA
mA
mA
1.5
V
Imax(KLD)= 20..250mA,
Ip(): 10%→90%
100
ns
Current Fall Time in KLD
Imax(KLD)= 20..250mA,
Ip(): 90%→10%
100
ns
107 K/KL
Control Tolerance
K= I(AMD) × RSET
VCC steady
KL= constant for each lot
0.95
1
1.05
108 CR1()
iC-WJ: Current Ratio
I(AMD) / I(ISET)
I(CI)= 0, closed control
0.8
1
1.2
109 CR2()
iC-WJ: Current Ratio
I(AMD) / I(CI)
V(CI)= 1..3.5V, ISET open
0.9
1
1.1
Input IN
201 Vt()hi
Threshold hi
1.60
-25
27
70
125
202 Vt()lo
Threshold lo
1.58
-25
27
70
125
203 Vt()hys
Hysteresis
10
Pull-Down Resistor
V(IN)= -0.3..VCC+0.3V
205 V0()
Open-loop Voltage
I(IN)= 0
V
V
V
V
V
2.10
V
V
V
V
V
190
mV
mV
mV
mV
mV
16
kΩ
0.1
V
1.76
1.78
1.79
1.81
-25
27
70
125
204 Rin
2.20
1.84
1.87
1.88
1.91
80
90
90
100
4
iC-WJ, iC-WJZ
LASER DIODE DRIVER
Rev A1, Page 5/12
ELECTRICAL CHARACTERISTICS
Operating Conditions: VCC= 5V ±10%, RSET= 2.7..27kΩ,iC-WJ: I(AMD)= 50..500µA,
iC-WJZ: I(AMD)= 0.15..1.5mA, Tj= -25..125°C, unless otherwise noted.
Item
Symbol
Parameter
Conditions
Tj
Fig.
Unit
°C
Min.
-25
27
70
125
2.4
2.0
1.5
1.0
Typ.
Max.
Input IN (continued)
206 Vtwd()
Threshold for Watchdog
3.2
2.8
2.3
1.8
V
V
V
V
1.27
V
V
Reference und Thermal Shutdown
301 V(ISET)
Voltage at ISET
1.20
27
V(CI)= 1..3.5V, I(AMD)= 0
1.22
302 CR()
Current Ratio I(CI) / I(ISET)
0.9
1
1.1
303 RSET
Permissible Resistor at ISET
(Control Set-up Range)
2.7
50
kΩ
304 Toff
Thermal Shutdown Threshold
125
150
°C
305 Thys
Thermal Shutdown Hysteresis
10
40
°C
4.3
V
V
Power-Down and Watchdog
401 VCCon
Turn-on Threshold VCC
3.5
27
402 VCCoff
Undervoltage Threshold at VCC
403 VCChys
Hysteresis
VCChys= VCCon-VCCoff
404 Vs(CI)of
Saturation Voltage at CI in case
of Undervoltage
3.8
3.2
3.7
V
300
450
mV
mV
I(CI)= 300µA,
VCC < VCCoff
1.6
V
405 Vs(CI)wd Saturation Voltage at CI for
IN= lo
I(CI)= 300µA,
t(IN= lo) > tp (*)
1.5
V
406 Isc(CWD) Pull-Up Current at CWD
V(CWD)= 0, IN= lo
3
15
µA
407 tpmin
Min. Activation Time for
Watchdog
IN= lo, CWD open
10
45
µs
408 Kwd (*)
Constant for Calculating the
Watchdog Activation Time
IN= lo
0.57
µs/pF
1.5
V
27
400
0.19
0.38
iC-WJZ with a monitor current rating of 0.15..1.5mA
Characteristics for iC-WJ are valid with the following replacements:
104 V(AMD)
Voltage at AMD
I(AMD)= 1.5mA
0.5
108 CR1()
Current Ratio I(AMD) / I(ISET)
I(CI)= 0, closed control
2.4
3
3.6
109 CR2()
Current Ratio I(AMD) / I(CI)
V(CI)= 1..3.5V, ISET open
2.7
3
3.3
(*): tp = ( C(CWD) × Kwd ) + tpmin (see Applications Information)
iC-WJ, iC-WJZ
LASER DIODE DRIVER
Rev A1, Page 6/12
APPLICATIONS INFORMATION
Laser Power Adjustment
The iC-WJ and iC-WJZ devices can be adapted to CW laser diodes from 2 to 40mW. Models can be used in
which the cathode of the monitor diode is connected to the anode or the cathode of the laser diode.
The pin ISET is used for the adjustment to the sensitivity of the monitor diode and to set the desired optical
laser power. The setpoint for the averaging control of the monitor diode current is preset at this pin.
Fig. 1: Operation of a laser diode according to the example
To calculate the current required at ISET, the average optical laser power is to
determine:
Pav
Ppeak ×
twhi
with peak value Ppeak and pulse/period duration twhi/T
T
Fig. 2
Example iC-WJ: Laser diode with 5mW maximum optical output, monitor diode with 0.13mA/mW, pulse duty
factor set to 20% with Ppeak= 5mW:
The resultant average optical power is 1mW and the average monitor diode current is 0.13mA. The resistor
RSET is calculated as:
RSET
CR1 V (ISET)
Iav (AMD)
1 1.22V
≈ 9.4kΩ
0.13mA
with the Electrical Characteristics No. 301 for V(ISET)
and with No. 108 for current ratio CR1
Example iC-WJZ: Laser diode with 5mW maximum optical output, monitor diode with 0.75mA at 3mW, CW
operation (pulse duty factor 100%) with Pcw= 1mW:
For the monitor diode current of 0.25mA the resistor RSET is calculated as:
RSET
CR1 V (ISET)
Iav (AMD)
3 1.22V
≈ 14.6kΩ
0.25mA
with Electrical Characteristics No. 301 for V(ISET) and
with No. 108 (iC-WJZ) for current ratio CR1
iC-WJ, iC-WJZ
LASER DIODE DRIVER
Rev A1, Page 7/12
Averaging control
The control of the average optical laser power requires a capacitor at pin CI. This capacitor is used for averaging and must be
adjusted to the selected pulse repetition frequency and the
charging current preset with RSET. The ratios are linear in both
cases, i.e. the capacitor CI must be increased in size
proportionally as the pulse repetition frequency slows or the
current from ISET increases:
CI ≥
440 × I (ISET)
f × V (ISET)
Example:
440
f × RSET
Pulse repetition frequency 100kHz, RSET= 10kΩ:
CI= 440nF, chosen 470nF
Otherwise the charging of the capacitor CI during the pulse
pauses (with I(ISET)= 1.22 V/RSET) will create an excessive
mean value potential and may destroy the laser diode during the
next pulse. The capacitor CI is correctly dimensioned when the
current through the laser diode and the optical output signal do
not show any overshooting following the starting flank.
In steady-state condition and for a pulse duty factor of 50%
(pulse/pause 1:1), signals as shown in Fig. 3 are present at the
IC pins.
Fig. 4 shows the corresponding signals for a pulse duty factor of
20%. The influence of the pulse duty factor on the peak value of
the monitor current proportional to the laser current is
apparent. The average kept constant by the control (RSET
unchanged) means a peak value increased by the factor 2.5. The
pulse duty factor for which RSET was dimensioned should there
fore be kept constant if at all possible.
Fig. 3: Steady-state averaging control,
f(IN)= 100kHz (1:1), CI= 470nF,
RSET= 10kΩ
Fig. 4: Steady-state averaging,
f(IN)= 100kHz (1:4), CI= 470nF,
RSET= 10kΩ
Turn-on and turn-off behavior
Capacitor CI also determines the starting time from switsching on
the supply voltage VCC to steady-state laser pulse operation or
after a discharge of CI by the watchdog. The following applies for
estimating the starting time (Fig. 5):
Ton ≈
2.5V × CI
I (ISET)
Example:
2.5V × CI × RSET
1.22V
Fig. 5: Turn-on behavior,
f(IN)= 100kHz (1:1),
CI= 470nF, RSET= 10kΩ
CI= 470nF, RSET= 10kΩ:
Ton ≈ 9.6ms
Figure 6 shows a detailed view of the start of laser operation;
Figure 7 shows the shut-down behavior. The decline in the voltage at CI and the absence of the laser pulses are signs that the
undervoltage detector is active.
Fig. 6: Turn-on behavior, detailed view
f(IN)= 100kHz (1:1),
CI= 470nF, RSET= 10kΩ
iC-WJ, iC-WJZ
LASER DIODE DRIVER
Rev A1, Page 8/12
Watchdog
In order for the watchdog to function correctly, the input IN must
be activated with a CMOS output (e.g. with an HCMOS gate: see
Fig. 1).
The watchdog ensures that the capacitor CI is discharged during
protracted pulse pulses at IN. During the pulse pauses the
potential at CI increases by ∆V (Fig. 3):
∆V
I (ISET) × twlo
CI
The discharge of capacitor CI by the watchdog protects the laser
diode from being destroyed by an excessive turn-on current
during the next pulse.
The capacitor CWD should be dimensioned such that the
response time tp of the watchdog is slightly longer than the pulse
pause twlo of the input signal. As a result, the watchdog is just
short of being activated.
For response times tp longer than tpmin applies:
CWD
tp
tpmin
Kwd
Fig. 7: Turn-off behavior,
f(IN)= 100kHz (1:1),
CI= 470nF, RSET= 10kΩ
with tpmin and Kwd from Electrical
Characteristics No. 407, 408
Figure 8 shows the signal curves during normal operation,
without the watchdog being activated. The potential at CWD rises
during pulse pauses but does not reach the watchdog activation
threshold.
Fig. 8: Watchdog, CWD open,
f(IN)= 100kHz (1:1),
CI= 470nF, RSET= 10kΩ
Figure 9 shows the watchdog behavior when the input frequency
is reduced from 100kHz to 10kHz. The pulse pauses are longer
than the watchdog’s response time. The watchdog begins to
discharge the capacitor CI current limited. The remaining charge
time during the pulse pauses before further watchdog
intervention is not sufficient to maintain the initial potential at CI.
The potential is thus gradually reduced until it reaches the
saturation voltage Vs(CI)wd (Electrical Characteristics No. 405).
The watchdog therefore protects the laser diode from destruction
when the input signal change in such a manner that the capacitor
CI is not longer adequate for averaging.
Furthermore, the intervention of the watchdog permits long pulse
pauses and activation of the laser diode with pulse packets.
Fig. 9: Watchdog, CWD open,
f(IN)= 100kHz → 10kHz (1:1),
CI= 470nF, RSET= 10kΩ
iC-WJ, iC-WJZ
LASER DIODE DRIVER
Rev A1, Page 9/12
CW OPERATION
In case of CW operation, the input IN can be connected to the power supply VCC. The pin CWD may be
unloaded, because the capacitor for the watchdog is not necessary. The capacitor CI for the averaging control
can be reduced to 100nF.
Fig. 10: CW operation via cable
Operation of laser diode via cable
It is recommended to connect a capacitor from 1nF up to 10nF across the laser diode in order to protect the
laser diode against destruction due to ESD or build-up transients. This capacitor should be placed close to the
laser diode and not at the entry of the LD supply line.
An approx. 12Ω series resistor at pin KLD reduces the IC power consumption and damps possible resonances
of the load circuit caused by the inductive LD supply line. This resistor is useful for many applications, also for
those which do not operate via cable.
When the LD supply line is printed on the PCB, the forward path VCC should be arranged in parallel with, i.e.
be close to the return path to KLD, even when the line is only a few centimeters in length.
Analog modulation during CW operation
The modulation cut-off frequency is determined by the capacitor CI as well as by the operating point set with
the resistor RSET. With CI= 100nF and RSET= R2= 10kΩ the cut-off frequency is approx. 40kHz, with CI=
22nF and the same resitor value of about 230kHz.
Fig. 11: Analog modulation during CW operation
iC-WJ, iC-WJZ
LASER DIODE DRIVER
Rev A1, Page 10/12
The laser power can also be modulated by adapting a current source, e.g. by using an operational amplifier with
a current output (OTA). To limit the current at pin ISET while turning on the power supply for the OTA circuitry,
however, the OTA output should be linked to the base point of RSET (instead of to GND). The maximum
current possible at ISET must be taken into consideration when dimensioning the capacitor CI.
CW operation with a laser diode current of up to 2A
Using the circuitry in Figure 12 the current capability can be increased. Laser diodes with a common cathode
cannot be used here. The laser diode operating voltage must not be lower than 1.5V.
Fig. 12: Circuitry for higher laser diode currents
PC BOARD LAYOUT
The ground connections of the external components CI, CWD and RSET have to be directly connected at the
IC with the GND terminal.
iC-WJ, iC-WJZ
LASER DIODE DRIVER
Rev A1, Page 11/12
DEMO BOARD
The iC-WJ/WJZ/WJB devices are equipped with a Demo Board for test purposes. The following figures show
the wiring as well as the top and bottom layout of the test PCB.
Fig. 13: Schematic diagram of the Demo Board
Fig. 14: Demo Board (components side)
Fig. 15: Demo Board (solder dip side)
iC-WJ, iC-WJZ
LASER DIODE DRIVER
Rev A1, Page 12/12
ORDERING INFORMATION
Type
Package
Order designation
iC-WJ
WJ Demo Board
SO8
iC-WJ-SO8
WJ Demo Board
iC-WJZ
WJZ Demo Board
SO8
iC-WJZ-SO8
WJZ Demo Board
For information about prices, terms of delivery, options for other case types, etc., please contact:
iC-Haus GmbH
Am Kuemmerling 18
D-55294 Bodenheim
GERMANY
Tel +49-6135-9292-0
Fax +49-6135-9292-192
http://www.ichaus.com
This specification is for a newly developed product. iC-Haus therefore reserves the right to modify data without further notice. Please contact
us to ascertain the current data. The data specified is intended solely for the purpose of product description and is not to be deemed
guaranteed in a legal sense. Any claims for damage against us - regardless of the legal basis - are excluded unless we are guilty of
premeditation or gross negligence.
We do not assume any guarantee that the specified circuits or procedures are free of copyrights of third parties.
Copying - even as an excerpt - is only permitted with the approval of the publisher and precise reference to source.