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Si7904DN Datasheet(PDF) 7 Page - Analog Devices |
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Si7904DN Datasheet(HTML) 7 Page - Analog Devices |
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7 / 22 page  REV. ADN8830 –7– APPLICATION NOTES Principle of Operation The ADN8830 is a controller for a TEC and is used to set and stabilize the temperature of the TEC. A voltage applied to the input of the ADN8830 corresponds to a target temperature setpoint. The appropriate current is then applied to the TEC to pump heat either to or away from the object whose tem- perature is being regulated. The temperature of the object is measured by a thermistor and is fed back to the ADN8830 to correct the loop and settle the TEC to the appropriate final temperature. For best stability, the thermistor should be mounted in close proximity to the object. In most laser diode modules, the TEC and thermistor are already mounted in the unit and are used to regulate the temperature of the laser diode. A complete TEC controller solution requires: • A precision input amplifier stage to accurately measure the difference between the target and object temperatures. • A compensation amplifier to optimize the stability and temperature settling time. • A high output current stage. Because of the high output currents involved, a TEC controller should operate with high efficiency to minimize the heat generated from power dissipation. In addition, an effective controller should operate down to 3.3 V and have an indication of when the target temperature has been reached. The ADN8830 accomplishes all of these requirements with a minimum of external components. Figure 1 shows a reference design for a typical application. Temperature is monitored by connecting the measurement thermistor to a precision amplifier, called the error amplifier, with a simple resistor divider. This voltage is compared against the temperature set input voltage, creating an error voltage that is proportional to their difference. To maintain accurate wave- length and power from the laser diode, this difference voltage must be as accurate as possible. For this reason, self-correction auto-zero amplifiers are used in the input stage of the ADN8830, providing a maximum offset voltage of 250 μV over time and temperature. This results in final temperature accuracy within ±0.01°C in typical applications, eliminating the ADN8830 as an error source in the temperature control loop. A logic output is provided at TEMPLOCK to indicate when the target temperature has been reached. The output of the error amplifier is then fed into a compensa- tion amplifier. An external network consisting of a few resistors and capacitors is connected around the compensation amplifier. This network can be adjusted by the user to optimize the step THERMFAULT THERMIN RTH 10k @25 C R2 7.68k 0.1% VREF C8 10 F 3.3V VREF TEMPLOCK TEMPSET R3 10k 0.1% R4 7.68k 0.1% VTEC 9 10 11 12 13 14 15 16 C9 10 F R6 100k R5 205k C11 1 F R7 1M 24 23 22 21 20 19 18 17 3.3V ADN8830 C5 10nF 3.3V TEC+ C7 10 F Q3 FDW2520C-A Q4 FDW2520C-B C4 22 F CDE ESRD 3.3V Q2 FDW2520C-A TEC– C3 10 F L1 4.7 H COILCRAFT DO3316-472 Q1 FDW2520C-B 32 31 30 29 28 27 26 25 C1 0.1 F R1 150k SYNCOUT TEMPOUT 3.3V C6 2.2nF C10 330pF 3.3V C12 3.3nF C2 22 F CDE ESRD 1 2 3 4 5 6 7 8 Figure 1. Typical Application Schematic D |
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