LD8100, LD8200, LD8300

PRECISION LASER DIODE DRIVERS

Description

The LD8100, LD8200 and LD8300 laser diode drivers contain all of the Laser Diode Driver features normally found in Full Featured Bench Top Controllers (see our LC8x71 series).

Theses are intended for the OEM or end user as a Low Cost Building Block for complete laser diode control systems. Interlocks, keylocks, emission indicators and output shunts are all provided by the LD8100, LD8200 and LD8300. Output current and voltage limits, output shunts and power supply monitoring are provided to protect the laser and eliminate unintended emissions.

Absolute Maximum Ratings

Supply Voltages-    V+,LD        +18V

                              V-         -18V

Current output                        10 A

Case temp.- operating         0 to+50 °C

Case temp.- storage           -40 to+70 °C

                                                             ! Warning !

These devices can generate large amounts of heat. Device failure will occur without proper cooling.

Lasers driven by these devices can cause serious eye and skin damage. Always follow the laser manufacturer's warnings.

Specifications- Measured at V+= 15V, V-= -15V, LD supply = 5V, T= 25°C

Parameter                                           Units            LD8100           LD8200           LD8300

Current mode operation

Output range- high range                                0 - 200 mA      0 - 2 A            0 - 10 A

                      low range                                0 - 50 mA      0 - 0.5 A           0 - 5 A

Output current accuracy- high range    mA            ±1                ±10                  ±50

                                       low range mA            ±1                ±10                  ±50

Temperature coefficient- see note 1    ppm/°C     <100             <100                <100

Short term stability, 10 min.- note 1    ppm          <10               <50                  <50

Long term stability, 24 hrs-note 1       ppm          <50               <200                <200

Wideband noise, 0 - 5 MHz               uA RMS       <2                <25                 <100

Compliance voltage range                   V          0 - VLD           0 - VLD            0 - VLD

Voltage limit                                     V          0 - 10             0 - 10              0 - 10

Current limit- high range                               0 - 200 mA        0 - 2 A             0 - 10A

                     low range                              0 - 50 mA        0 - 0.5 A           0 - 5 A

Current limit accuracy                       mA          ±1                 ±10                   ±50

Power mode operation

Photodiode input current                   mA         0 - 20             0 - 20               0 - 20

Photodiode current accuracy             uA          ± 20                ± 20                  ± 20

Photodiode current limit function        mA          0 - 20             0 - 20               0 - 20

Photodiode current limit fn. accuracy  uA          ± 20                ± 20                  ± 20

Temperature coefficient- see note 1  ppm/°C     <100               <100                 <100

Short term stability, 10 min.- note 1  ppm          100                  100                   100

Long term stability, 24 hrs- note 1    ppm          1000                1000                  1000

Note 1: Related to change of output as a fraction of half scale after 1 hour warm-up.

Power or current mode operation    Units             Minimum            Nominal         Maximum

Digital inputs- High (pins 1,3,4)             V                  V+/2                                   V+

                      Low (pins 1,3,4)           V                      0                                    1

Supply voltage- V+ (pin 15)                 V                   +12               +15              +18

                         V- (pin 17)              V                    -12               -15              -18

Supply voltage- LD (pin 14, 14A)          V                    4                                 see text

Digital output- current (pin 5)              mA                                                         10

10V reference output- (pin 22)            mA                                                          5

Pin functions

(Physical pin locations are shown on page with Mechanical Specifications.)

1. Interlock-      Ground to turn on module. When high or open will disable the output.

2. Ground-        Power and control ground.

3. Keylock-        Ground to turn on module. When high or open will disable the output.

4. On/off-          Ground to turn on module. When high or open will disable the output.

5. Laser on-       Pulled low when the output stage is energized. High or floating when                            the output stage is off.

6. PD anode-      Photodiode anode connection for power mode operation.

7. PD cathode-   Photodiode cathode connection for power mode operation.

8. No connection

9. No connection

10. No connection   

11. No connection

11A. LD cathode-  Laser diode cathode connection. Tied to ground in the module.                                    (not present on LD8100 or LD8200)

12.  LD cathode-    Laser diode cathode connection. Tied to ground in the module.

12A. LD Anode-     Laser diode anode connection. (not present on LD8100 or LD8200)

13.  LD Anode-       Laser diode anode connection.

14.  LD supply-       Power supply(+) for the power output stage of the module

14A. LD supply-     Power supply (+) for the power output stage of the module.                                          (not present on LD8100 or LD8200)

15.  V+-                 Power supply (+12 to +18V)

15A. Ground          (not present on LD8100 or LD8200)

16.  Ground

16A. Ground          (not present on LD8100 or LD8200)

17.  V-                    (-) Power supply (-12 to -18V)

18.  Range-           Connect to ILD sense pin for high power range in current mode.                                      Leave disconnected for low current range in current mode.                                           Leave disconnected in power mode.

19.  ILD Sense-       Laser diode current sense signal. Connect to feedback pin in                                        current mode.

20. Feedback-       Input to analog control loop. Must be connected to ILD sense or PD                               sense.

21.  PD sense-       Photodiode current sense signal. Connect to feedback pin in power                                mode.

22.  10V Ref.-         10 Volt 5 ma precision reference output. Used to generate setpoint                              and limits voltages.

23. Voltage limit-    Prevents the laser diode voltage from exceeding the voltage applied                             to this pin.

24.  Set point limit-  Prevents the setpoint from exceeding the value applied to this pin.

25.  Setpoint-         Sets the laser diode current in current mode operation. Sets the                                     laser diode power in power mode operation.

Theory of operation

The controller consists of four functional blocks: the digital control logic, the power supply monitor, the analog control circuits, and the power output stage.

The digital control logic takes the digital signals keylock, interlock and on/off (pins 1,3,4) and the enable signal from the power supply monitor to generate a laser on signal. This signal is used to enable the power driver stage and to remove the output protection shunt. The keylock, interlock, and on/off inputs are interchangeable and all three must have a digital low to turn on the module. There is a laser on (pin 5) output which can be used to drive a 10 mA LED as an emission indicator. When the laser on signal is generated, the output shunt is removed and the power stage enters a slow start sequence bringing the laser up to operating power in 20 ms without spikes or transients. The laser is turned off in less than 10 sec when a power supply fault is detected or the keylock, interlock or on/off inputs go high.

The power supply monitor generates an enable signal when the analog control supplies (V+ and V-) are over 9 volts and the LD supply is over 3 volts. These voltages were chosen as the minimum voltages at which the module can maintain stability and laser diode protection. Normal operation requires V+ and V- to be greater than +12 and -12 respectively. When V+ drops below 11 volts, the internal 10 volt reference will be unable to maintain a 10 volt output causing the setpoint and limits to decrease. Thus if operation is required at less than 12 volts, a custom module may be required. Please contact the factory.

The analog control circuits monitor the laser and adjusts the drive to the output power stage accordingly. They also compare output voltages and setpoints to voltage and setpoint limits to protect the laser from being overdriven. To keep the noise level as low as possible and avoid oscillations, the bandwidth is limited to 10 Hertz.

 In current mode, the analog control circuit compares the actual laser current, as measured in the power output stage, to the setpoint (pin 25) and provides drive to the output stage to maintain the current. The controller also compares the setpoint and output voltage to the setpoint limit and voltage limit (pins 24,23). When the setpoint or voltage approaches a limit, the drive is prevented from increasing further.

In power mode, the analog control circuit compares the current being returned from the photodiode to the setpoint and adjusts the drive to the output stage accordingly. In this mode the setpoint and setpoint limit refer to photodiode current,not to laser current. The module will increase the laser current until the desired photocurrent setpoint or setpoint limit is reached.With no photodiode feedback, the module can produce currents exceeding the rated output of the module and can result in damage to the laser and module. The voltage limit should be used to protect the diode or an external laser current limiting circuit can be implemented.

The power output stage is the high power section of the module and uses the lower voltage LDSupply (pins 14,14A), to permit operation of the stage with minimum dissipation. The drive signal is provided by the analog control section. The laser diode enable signal from the control logic section turns on the entire stage. The stage includes a low impedance resistor for monitoring the output current. This signal can be viewed externally at ILD sense (pin 19) and is fed back to the analog control section for current control. The power output stage includes a protection circuit to prevent damage to the laser diode when the module is turned off. It places a low impedance shunt across the laser diode to prevent static discharges through the diode. When the laser is turned on, the shunt is removed and the output driver stage provides active protection.

Warning!

The module provides several different forms of protection to the diode including static protection during storage and operation as well as setpoint and voltage limit protection during operation. There are situations which the controller cannot protect against. Power supply transients can be transmitted through the module and damage the laser thus clean power supplies are of critical importance. Wiring errors and loss of photodiode feedback can cause catastrophic failure of both the controller and laser. Improper handling of laser diodes can cause static and mechanical damage resulting in premature failure. Photodiode anodes and cathodes may be reversed by the manufacturer causing loss of feedback in power mode. (All diodes should be checked for polarity before operation.) Because of the range of problems that can damage a laser diode,it is imperative that all circuits be tested with expendable loads before operating any laser diode.

Operation

 V+, V- and LD supply (pins 15,17,14,14A) must be connected to the appropriate power supplies. A good quality triple output analog supply with regulation is recommended. Switching type power supplies generate high frequency noise which may degrade the noise performance of the modules. It is important that the power supplies be floating (not grounded) since laser diode packages have grounds at different pins. The module case is electrically isolated from the module grounds (pins 2, 15A, 16A, 16,). The LD cathode (pin 11A,12) is tied internally to ground. The LD supply voltage must be chosen with power dissipation in the module kept in mind. Since the controller is an analog circuit, the voltage difference between the LD supply (pin 14A,14) and the laser diode forward voltage is dissipated in the module. The dissipation is:

Power = Voltage difference x Current

The power dissipation should be kept below 3 watts for a module without a heat sink. LD8100 modules can safely use V+ (up to 18 volts) as the LD supply voltage without a heat sink. The LD8200 and LD8300 should use 1 to 2 volts over the laser diode forward voltage for LD supply and heat sinking is required. The case temperature must be kept below 50 C.

 The module turns on when the keylock, interlock and on/off pins are between 0 V and 0.5 V. All three pins function in exactly the same way and are interchangeable. The laser on (pin 5) provides an active pull down when the power output stage is energized. This can be used to power a 10 mA LED as an emission indicator when connected between V+ and the laser on (pin 5) or to provide a digital input to a logic circuit. The laser on signal is also very important in troubleshooting the device. The most common reasons for the modules not to operate is the failure of the user to provide the correct power supply voltages or failure to ground the keylock, interlock and on/off pins. The laser on pin will be high if these things have not been done. (Note: The laser on pin will not be high if the V+ supply is absent , however, the LED used in fig 1 & 2 as an emission indicator will be off.)

The voltage limit (pin 23) operates the same way in all modes and for all versions of the modules. It limits the maximum voltage that can be generated across the laser diode (pins 11A, 12, 12A, 13) to the voltage placed on the voltage limit (pin 23).

Current Mode Operation

Refer to Fig. 1 for current mode operation. There are several jumpers that must be connected for proper operation. The ILD sense (pin 19) and feedback (pin 20) must be tied together. The operating current range must be selected. The low current range is selected by leaving the range (pin 18) unconnected. The high current range is selected by connecting range (pin 18) to ILD sense (pin 19). Voltages must be provided to the voltage limit, setpoint limit and setpoint(pins 23,24,25). A very stable 10 volt reference (pin 22) capable of supplying 5 ma is provided for generating these signals when using potentiometers or resistive dividers. (see Fig. 1) Best performance is obtained using 20 Kohm high quality 10 turn potentiometers or a 20 Kohm resistive divider. Alternatively, analog voltages from D/A converters or other sources can be used for the setpoint.The setpoint limit and voltage limit should always be generated with potentiometers or resistors as shownin Fig. 1. This provides the best laser protection in the event of a failure in other user supplied circuits. The output current to the laser is related to the voltage at setpoint as follows on next page:

Low Range

LD8100- 50 mA range

I(laser)= V(setpoint) x 5 mA/Volt

LD8200- 500 mA range

I(laser)= V(setpoint) x 50 mA/Volt

LD8300- 5 A range

I(laser)= V(setpoint) x 0.5 A/Volt

High Range

LD8100- 200 mA range

I(laser)= V(setpoint) x 20 mA/Volt

LD8200- 2 A range

I(laser)= V(setpoint) x 0.2 A/Volt

LD8300- 10 A range

I(laser)= V(setpoint) x 1 A/Volt

Power mode operation

Refer to Fig. 2 for power mode operation. There are several jumpers that must be connected for proper operation. The PD sense (pin 21) and feedback (pin 20) must be tied together. The range (pin 18) is left unconnected. In power mode, there is no low power range and full current is available from the module. A photodiode must be connected between PD anode and PD cathode (pins 6,7). One side of the photodiode must be connected to either the LD anode (pin 12A,13) or the LD cathode (pin 11A,12). Without a photodiode connected, the module can produce currents exceeding the rated output of the module and can result in damage to the laser and module.

Voltages must be provided to the voltage limit, setpoint limit and setpoint(pins 23,24,25). A very stable 10 volt reference (pin 22) capable of supplying 5 ma is provided for generating these signals when using potentiometers or resistive dividers. (see Fig. 2) Best performance is obtained using 20 Kohm high quality 10 turn potentiometers or resistive dividers. Alternatively, analog voltages from D/A converters or other sources can be used for the setpoint.The setpoint limit and voltage limit should always be generated with potentiometers or resistors as shown in fig. 2.This provides the best laser protection in the event of a failure in other user supplied circuits.

 In power mode, the analog control circuit compares the current being returned from the photodiode to the setpoint and adjusts the drive to the output stage accordingly. In this mode the setpoint and setpoint limit refer to photodiode current,not to laser current. The module will increase the laser current until the desired photocurrent setpoint or setpoint limit is reached.The module can produce currents exceeding the rated output of the module and can result in damage to the laser andmodule. The voltage limit should be used to protect the diode or an external laser current limiting circuit can be implemented. The photodiode current that the module will have the laser generate, can be related to the voltage at the setpoint (pin 25) by the equation:

LD8100, LD8200, LD8300

I(photodiode) = V(setpoint) x 2mA/Volt

 The setpoint limit (pin 24), in power mode operation, prevents the photodiode current from exceeding the limit value. It has the same transfer function as the setpoint and can be found from the equation given above.

Warranty

Vere, Inc. will, at our option, repair or replace any product found to be defective in materials or workmanship for 90 days from date of delivery. This warranty does not include damage due to improper use or thermal damage from inadequate heatsinking. No other warranty is expressed or implied.

Limitation of Liability

It is the customer's responsibility to determine the suitability of this product for their application. Vere, Inc. shall not be liable for loss or damage, whether direct or indirect, incidental or consequential, arising from the use of this product.