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ISL97691 Datasheet(PDF) 16 Page - Renesas Technology Corp |
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ISL97691 Datasheet(HTML) 16 Page - Renesas Technology Corp |
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16 / 19 page  ISL97691 FN7840 Rev.2.00 Page 16 of 19 Sep 8, 2017 Fault Protection and Monitoring The ISL97691 features extensive protection functions to handle failure conditions automatically. Refer to Figure 15 and Table 3 for details of the fault protections. The LED failure mode is either open or short circuit. An open circuit failure of an LED only results in the loss of one channel of LEDs without affecting other channels. Similarly, a short circuit condition on a channel that results in that channel being turned off does not affect other channels. Due to the lag in boost response to any load change at its output, certain transient events (such as LED current steps or significant step changes in LED duty cycle) can transiently look like LED fault modes. The ISL97691 uses feedback from the LEDs to determine when it is in a stable operating region and prevents apparent faults during these transient events from allowing any of the LED stacks to fault out. See Table 3 for more details. Short Circuit Protection (SCP) The short circuit detection circuit monitors the voltage on each channel and disables faulty channels which are above the short circuit protection threshold, nominally 8V (the action taken is described in Table 3). Open Circuit Protection (OCP) When one of the LEDs becomes open circuit, it can behave as either an infinite resistance or a gradually increasing finite resistance. The ISL97691 monitors the current in each channel such that any string which reaches the intended output current is considered “good”. Should the current subsequently fall below the target, the channel will be considered an “open circuit”. Furthermore, should the boost output of the ISL97691 reach the VOVP limit, all channels which are not “good” will immediately be considered as “open circuit”. Detection of an “open circuit” channel will result in a time-out before disabling of the affected channel. Undervoltage Lockout If the input voltage falls below the VUVLO level of ~2.15V, the ISL97691 will stop switching and be reset. Operation will restart only if the VIN is back in the normal operating range. Over-Temperature Protection (OTP) The ISL97691 has an over-temperature protection threshold set to +150°C. If this threshold is reached, the boost stops switching and the channel output current sinks are switched off. The ISL97691 can be restarted by toggling VIN to below the VUVLO level of ~2.15V, then back up to the normal input voltage level. FIGURE 24. EXAMPLE OF PCB LAYOUT |
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