Month: June 2015

Creation and Simulation of an OPA569 Laser Driver Circuit

The “OPA569 Laser Driver” circuit provides voltage- controlled constant- current biasing of a grounded- anode laser diode by using a negative supply voltage and a positive control voltage. As shown, the OPA569 op amp provides an output current of 500mA per volt input. Output is current- limited to 2A by R2. Frequency compensation is provided by C3 R3. This circuit takes advantage of the unique topology of the OPA569; it does not require a shunt resistor to measure its output current. This amplifier provides an output monitor current from pin 19 that is 1/475 th of its output current. This current is used as negative feedback to the amplifier’s inverting input (pin 5). A constant- current output is derived by this feedback.

Since no shunt resistor is required to measure output current, there is no reduction in output voltage compliance due to shunt resistor voltage drop and this circuit can swing its output voltage very close to its supply rail. This increases efficiency and reduces heat sinking requirements. In fact, supply voltage can be reduced to 3.3V for most laser diodes. The OPA569 features both a Current Limit (pin 4) and a Thermal Overtemp (pin 7) flag. These flags can be used to protect the amplifier and the Enable (pin 8) can be used to digitally control its status. (Circuit is created by Neil P. Albaugh, TI – Tucson)

OPA569 Laser Driver Circuit:

Creation and Simulation of an OPA569 Laser Driver Circuit

The great feature of the TINA circuit simulator that you can analyze this circuit immediately with TINACloud the online version of TINA.

Click here to invoke TINACloud  and analyze the circuit yourself, or  watch our tutorial video!

You can send this link to any TINACloud customers and they can immediatelly load it by a single click and then run using TINACloud.

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TINA Design Suite is fully compatible with TINACloud and you can create, edit or run the same circuits in both systems. You can also easily exchange circuits between TINA Design Suite and TINACloud.

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Time to Voltage Converter circuit

Applications such as rangefinders and ballistic chronographs require a high resolution measurement of time. This can be a time period of a few hundred nanoseconds to a few milliseconds. This is an analog circuit that can convert a time period to a voltage with high linearity and high resolution. In principle, a current source is used to charge a capacitor for the time interval and then the voltage across that capacitor is measured. A REF200 precision current source is used to furnish 200uA to a fast SPDT analog switch, represented by SW1 & SW2. This switch steers the current into ground or into a 100pF capacitor C2.

U1 is simply a high- precision buffer amplifier for the voltage on C2.

SW3 is a reset that zeros the voltage on C2. Initially, SW3 is open and SW2 steers the 200uA to ground until a START command is received; SW2 then opens and SW1 closes, steering the current into C2. The capacitor charges until a STOP command is received;  SW1 then opens and SW2 closes. The voltage on C2 is proportional to the time between START and STOP; scale time range is determined by the value of C2 so this capacitor should be high quality. A polystyrene or NPO (COG) ceramic is recommended for C2. A small DMOS SD211 can be used for SW3.  (Circuit is created by  Neil P. Albaugh, TI-Tucson)

Time to Voltage Converter circuit:

Online Simulation of a Time to Voltage Converter circuit:

The great feature of the TINA circuit simulator that you can analyze this circuit immediately with TINACloud the online version of TINA. Of course you can also run this circuit in the off-line version of TINA.

Click here to invoke TINACloud  and analyze the circuit yourself or watch our tutorial video!

You can send this link to any TINACloud customers and they can immediatelly load it by a single click and then run using TINACloud.

Michael Koltai
www.tina.com