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TPS61160DRVTG4 Datasheet(PDF) 12 Page - Texas Instruments |
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TPS61160DRVTG4 Datasheet(HTML) 12 Page - Texas Instruments |
12 / 39 page ![]() FB LED SET V I R 12 TPS61160, TPS61161 SLVS791E – NOVEMBER 2007 – REVISED JULY 2016 www.ti.com Product Folder Links: TPS61160 TPS61161 Submit Documentation Feedback Copyright © 2007–2016, Texas Instruments Incorporated Feature Description (continued) 7.3.2 Open LED Protection Open LED protection circuitry prevents device damage as the result of white LED disconnection. The TPS61160 and TPS61161 monitor the voltage at the SW pin and FB pin during each switching cycle. The circuitry turns off the switch FET and shuts down the device when both of the following conditions persist for 8 switching clock cycles: 1. The SW voltage exceeds the VOVP threshold; and 2. The FB voltage is less than half of regulation voltage. As a result, the output voltage falls to the level of the input supply. The device remains in shutdown mode until it is enabled by toggling the CTRL pin logic. To allow the use of inexpensive low-voltage output capacitor, the TPS61160/1 has different open lamp protection thresholds. The threshold is set at 26 V for the TPS61160 and 38 V for the TPS61161. Select the appropriate device so that the product of the number of external LEDs and each LED's maximum forward voltage plus the 200 mV reference voltage does not exceed the minimum OVP threshold or (nLEDS × VLED(MAX)) + 200 mV ≤ VOVP(MIN). 7.3.3 Current Program The FB voltage is regulated by a low 0.2-V reference voltage. The LED current is programmed externally using a current-sense resistor in series with the LED string. The value of the RSET is calculated using Equation 1: where • ILED = output current of LEDs • VFB = regulated voltage of FB • RSET = current sense resistor (1) The output current tolerance depends on the FB accuracy and the current sensor resistor accuracy. 7.3.4 LED Brightness Dimming Mode Selection The CTRL pin is used for the control input for both dimming modes, PWM dimming and one-wire dimming. The dimming mode for the TPS61160 or TPS61161 is selected each time the device is enabled. The default dimming mode is PWM dimming. To enter the one-wire mode, the following digital pattern on the CTRL pin must be recognized by the device every time the device starts from the shutdown mode. 1. Pull CTRL pin high to enable the TPS61160 or TPS61161 and to start the one-wire detection window. 2. After the EasyScale detection delay (tes_delay, 100 μs) expires, drive CTRL low for more than the EasyScale detection time (tes_detect, 260 μs). 3. The CTRL pin has to be low for more than EasyScale detection time before the EasyScale detection window (tes_win, 1 msec) expires. EasyScale detection window starts from the first CTRL pin low to high transition. The device immediately enters the one-wire mode once the above three conditions are met. the EasyScale communication can start before the detection window expires. Once the dimming mode is programmed, it can not be changed without another start-up. This means the device needs to be shutdown by pulling the CTRL low for 2.5 ms and restarts. See Figure 12 for a graphical explanation. |
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