400 Hot Springs Road, Carson City NV 89706 (775) 883-0820 Fax (775) 883-0827 www.hytek.com 41
HY6350
Laser Diode Driver, 5 Amp
Constant Current/Power Laser Diode Driver
The HY6350 Laser Diode Driver
is designed for
applications requiring high constant current drive for the
operation of laser diodes such as pump sources for
EDFA's and diode pumped semiconductors. The
HY6350 provides selectable drive current from zero to 5
ampere (with forced air cooling). The HY6350 includes
outputs for monitoring and control of over-current and la-
ser diode over-temperature conditions. The HY6350
comes in a 22 pin dual in-line ceramic package. An alu-
minum heat spreader is included as a part of the pack-
age for heat sinking the device.
Features:
F
Adjustable current to 5 amps
F
Enable pin for switching
F
Overtemp and over-current alarms
F
Common anode or isolated laser diodes
F
Thru-hole or surface-mount packaging
TEC Controllers
Laser Diode Drivers
Micro-heaters
Figure 2
42 400 Hot Springs Road, Carson City NV 89706 (775) 883-0820 Fax (775) 883-0827 www.hytek.com
HY6350
Laser Diode Driver, 5 Amp
Input Specifications
Power Supply Input (V
EE
): Pins 9,10, 11, 16
9 to 15V @ 5 amp max. (with forced air cooling)
Drive Enable (EN): Pin 7
V
EE
(off, disable), Ground or Open (on, enable)
Modulation (MOD): Pin 21
10 to 5000mA for input voltage V
EE
to (V
EE
+ 3V)
Ground (GND): Pins 18, 19, 20
Power supply ground
Feedback-Optical (FB): Pin 22
FB<MOD increases I
OUT
, FB>MOD decreases I
OUT
V
EE
< FB < V
EE
+ 5V
Over-Temperature Alarm Input (OTI+): Pin 1
with V
EE
< OTI+ < V
EE
+ 5V
Over-Temperature Alarm Input (OTI-): Pin 5
with V
EE
< OTI+ < V
EE
+ 5V
Over-Current Alarm Input (OCI-): Pin 6
Use to set overcurrent reference
Temperature Alarm Hysteresis: Pin 4
Use to increase temperature hysteresis
Temperature Alarm Hysteresis: Pin 3
Use to increase temperature hysteresis
Output specifications
Laser Diode Current Drive (I
OUT
): Pins 12, 13, 14
0 to 5 amp (with forced air cooling)
Reference Output (V
REF
): Pin 8
= V
EE
+5V at < 100mA
Over-Temperature Alarm Output (OTA): Pin 2
V
EE
(Alarm condition; normally grounded)
Over-Current Alarm Output (OCA): Pin 17
V
EE
(Alarm condition; normally grounded)
Environmental conditions
Operating Temperature
20C to +100C (case)
Storage Temperature
65C to +150C (case)
Signal descriptions
V
EE
Input power supply (9 to 15 VDC).
GND
Ground return for V
EE
(input power supply)
MOD
The modulation voltage programs the laser diode drive current, I
OUT
. When the input is at V
EE
the modulation cur-
rent is zero. Maximum modulation current occurs when the voltage at MOD is +3.0 V with respect to the V
EE
in-
put. The current is set by the voltage at the modulation input.
V
REF
The Reference voltage is a precision voltage reference with an output voltage of V
EE
+ 5V
DC
. The Reference volt-
age supplies a voltage for the adjustment of the current. It can also be used to power a resistive bridge input to
the over-temperature alarm, and to provide an adjustable reference voltage to the current alarm input.
EN
The Enable pin is used to enable/disable the output. When the Enable pin is connected to ground, or left open,
the output is enabled, allowing current to flow to the laser diode. When this pin is connected to V
EE
the laser
current is disabled.
I
OUT
The Output provides drive current to the laser diode (cathode/negative; connect anode to ground).
FB
This high input impedance, voltage feedback, input is used with a photodetector to control Output Current.
OTI+
Positive over-temperature alarm input.
OTI
Negative over-temperature alarm input.
OCA
Over-current alarm output. Alarm: V
EE
; No alarm: Ground
OCI
Over-current input. OCI controls the set point for the over-current alarm detector. V
EE
<V
OCI
< V
EE
+5V
OTA
Over-temperature alarm output. Alarm: V
EE
; No alarm: Ground
R
H
Resistor connected between pins 3 and 4 to vary the temperature detector hysteresis from 1 to 10%.
400 Hot Springs Road, Carson City NV 89706 (775) 883-0820 Fax (775) 883-0827 www.hytek.com 43
HY6350
Laser Diode Driver
Automatic Power Control (APC)
The HY6350 can be used in Constant Current Mode or in Constant Power Mode. In Constant Current Mode, a program-
ming voltage applied at pin 21, the Current Control input, sets a constant current output level to the laser diode which
does not vary with changes in load (with constant Vcc supply voltage). In Constant Power Mode, the feedback current
from a laser's backfacet photodetector (normally reverse biased as shown below) is used to adjust HY6350 output cur-
rent to help oppose reduction in laser diode light output caused by aging.
Feedback from the laser's reverse biased backfacet photodetector is directly connected into pin 22, Optical Feedback
Input (FB). As current feedback can vary widely among different models of laser diodes, from micro to milliamps, the
voltage presented at pin 22 usually must be adjusted with a parallel external resistor to ground.
Increasing the voltage at pin 22 will decrease the current drive to the laser diode. So, as the laser ages and light output
falls, feedback current and the voltage at pin 3 will also fall thereby increasing current drive to the laser diode to main-
tain a more constant light output.
As feedback will limit the maximum current output available to the laser diode, it should be adjusted down so that there
is only sufficient range to counteract laser aging effects. To accomplish this follow this procedure:
- Connect the HY6350 as depicted in Figure 1 except do not connect pin 22, optical feedback.
- Increase Current Control Input (CC), pin 21, from 0 volts until desired light output from the laser diode is achieved.
- Connect optical feedback from the reverse biased back facet photodetector of the laser to pin 22 Feedback (FB) input.
- Using 10k
potentiometer from Pin 22 to ground (Figure 1) attenuate the feedback voltage at Pin 22 until laser diode
light output is reduced by the amount predicted by the laser manufacturer over its expected life. e.g. if expected aging
light reduction is given as 15%, reduce feedback voltage until laser diode light output is reduced by 15% to 20%.
- Increase Current Control Input (CC), pin 21, from V
EE
until desired light output is restored.
The reduced feedback from the laser diode's backfacet photodetector as the laser ages will cause the HY6350 to in-
crease current drive to counteract this effect. To maintain light output precisely, some gain must be added to the opti-
cal feedback. The required gain, positive or negative, is highly dependent on the particular laser diode in use.
INPUT VOLTAGE VS OUTPUT CURRENT
V
EE
= - 10 VDC
0
1
2
3
4
5
6
-10.0
-9.9
-9.7
-9.6
-9.4
-9.3
INPUT VOLTAGE PIN 21
LOAD CURRENT (AMPS)
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