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MAX16822BEVKIT Folha de dados(PDF) 3 Page - Maxim Integrated Products |
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MAX16822BEVKIT Folha de dados(HTML) 3 Page - Maxim Integrated Products |
3 / 6 page MAX16822B Evaluation Kit _______________________________________________________________________________________ 3 Enable and HBLED Dimming Control The MAX16822B EV kit features a jumper to enable and disable the MAX16822B IC (U1). Installing jumper JU1 disables the MAX16822B IC. Additionally, HBLED dim- ming is achieved on the MAX16822B EV kit by applying a digital PWM signal at the DIM PCB input pad. Remove the shunt at jumper JU1 to enable HBLED dim- ming using a digital PWM signal at the DIM and PGND PCB pads. Apply a digital PWM signal with a 0.6V logic-low (or less) and a 2.8V logic-high (or more) level and frequencies from 200Hz to 20kHz. To adjust the HBLED brightness, vary the signal duty cycle from 0 to 100%. See Table 1 for jumper JU1 setting of the HBLED dimming operation. Thermal Foldback and Temperature Simulation The MAX16822B EV kit features a thermal foldback and temperature simulation circuit available at the TEMP_I PCB pad and jumper JU2. Jumper JU2 sets the mode of operation, temperature simulation, or thermal fold- back. Potentiometer R2 and resistor R3 form the adjustable temperature simulation circuit. Test points TP1 and TP2 (PGND) provide access to the signal for adjusting the voltage. To evaluate the MAX16822B IC thermal foldback fea- ture, remove jumper JU2 and connect an NTC thermis- tor to the TEMP_I and PGND PCB pads. Refer to the Thermal Foldback section in the MAX16822A/ MAX16822B IC data sheet for information on using the thermal foldback feature. See Table 2 for configuring jumper JU2 for the desired mode of operation. Setting External HBLED Current Resistor R1 sets the MAX16822B EV kit average HBLED current up to 333mA. However, the HBLED average current can be set up to 350mA after replacing resistor R1. Use the following equation to calculate R1 when reconfiguring the HBLED current: where ILED is the desired HBLED average current. Refer to the Selecting RSENSE to Set LED Current sec- tion in the MAX16822A/MAX16822B IC data sheet for information on setting the HBLED current. R V ILED 1 02 = . Table 1. Enable and HBLED Dimming (Jumper JU1) SHUNT POSITION DIM PIN EV KIT ENABLE OR DIMMING OPERATION Not installed Connected to VIN through resistor R4 Enabled or analog dimming* (see Table 2) Not installed Connected to PWM signal Enabled, PWM signal applied at DIM PCB pad Installed Connected to PGND Disabled * Analog dimming is achieved by placing a resistor (RDIM) across the TEMP_I and PGND PCB pads. Remove the shunt across jumpers JU1 and JU2 and use the following equation to calculate the current for the TEMP_I PCB pad resistor, which is necessary to reduce the HBLED driving current. Refer to the Analog Dimming section in the MAX16822A/MAX16822B IC data sheet for information on the analog dimming feature. ILEDDIM = ILED [1 - 0.75 x (2 - (RDIM x 26.5µA))] where RDIM is the TEMP_I pad resistor, ILEDDIM is the required current for the desired HBLED current, and ILED is configured for 322mA. Alternatively, installing jumper JU2 and adjusting potentiometer R2 can simulate analog dimming. Or, for DC control analog dimming, install jumper JU2 and apply a DC voltage in the 0.7V to 2V range at the TP1 (positive) and TP2 (PGND) test points. Table 2. Temperature Simulation and Thermal Foldback (Jumper JU2) SHUNT POSITION TEMP_I PIN EV KIT OPERATION Installed Connected to R2 and R3 Temperature simulation Not installed Connected to external NTC thermistor Thermal foldback |
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