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Moteur de recherche de fiches techniques de composants électroniques |
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Moteur de recherche de fiches techniques de composants électroniques |
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ISL97672B Fiches technique(PDF) 11 Page - Renesas Technology Corp |
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ISL97672B Fiches technique(HTML) 11 Page - Renesas Technology Corp |
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11 / 17 page  ISL97672B FN7995 Rev.3.00 Page 11 of 17 Sep 7, 2017 If R1 and R2 are chosen such that the OVP level is set at 40V, then VOUT is allowed to operate between 24V and 40V. If the VOUT requirement is changed to an application of six LEDs of 21V, then the OVP level must be reduced. Users should follow the VOUT = (60% ~100%) OVP level requirement; otherwise, the headroom control will be disturbed such that the channel voltage can be much higher than expected. This can sometimes prevent the driver from operating properly. The resistances should be large, to minimize power loss. For example, a 1MΩ RUPPER and a 30kΩ RLOWER sets OVP to 41.9V. Large OVP resistors also allow COUT to discharge slowly during the PWM Off time. Parallel capacitors should also be placed across the OVP resistors such that RUPPER/RLOWER = CLOWER/CUPPER. Using a CUPPER value of 30pF is recommended. These capacitors reduce the AC impedance of the OVP node, which is important when using high-value resistors. For example, if RUPPER/RLOWER = 33/1, then CUPPER/CLOWER = 1/33 with CUPPER = 100pF and CLOWER =3.3nF. UNDERVOLTAGE LOCK-OUT If the input voltage falls below the UVLO level, the device stops switching and is reset. Operation restarts only when VIN returns to the normal operating range. INPUT OVERCURRENT PROTECTION During a normal switching operation, the current through the internal boost power FET is monitored. If the current exceeds the current limit, the internal switch is turned off. Monitoring occurs on a cycle-by-cycle basis in a self-protecting way. Additionally, the ISL97672B monitors the voltage at the LX and OVP pins. At start-up, the LX pins inject a fixed current into the output capacitor. The device does not start unless the voltage at LX exceeds 1.2V. The OVP pin is also monitored such that if it rises above and subsequently falls below 20% of the target OVP level, the input protection FET is also switched off. OVER-TEMPERATURE PROTECTION (OTP) The ISL97672B includes two over-temperature thresholds. The lower threshold is set to +130°C. When this threshold is reached, any channel that is outputting current at a level significantly below the regulation target is treated as an “open circuit” and is disabled after a time-out period. This time-out period is 800µs when it is above the lower threshold. The lower threshold isolates and disables bad channels before they cause enough power dissipation (as a result of other channels having large voltages across them) to hit the upper temperature threshold. The upper threshold is set to +150°C. Each time this threshold is reached, the boost stops switching, and the output current sources switch off. Once the device has cooled to approximately +100°C, the device restarts, with the DC LED current level reduced to 75% of the initial setting. If dissipation persists, subsequent hitting of the limit causes identical behavior, with the current reduced in steps to 50% and finally 25%. Unless disabled via the EN pin, the device stays in an active state throughout. For complete details of fault protection conditions, see Figure 21 and Table 1. FIGURE 21. SIMPLIFIED FAULT PROTECTIONS Q5 VSC CH5 VSET PWM/OC0/SC0 REF FET DRIVER LX IMAX ILIMIT DRIVER FAULT OVP VIN T2 OTP SHDN Q0 CH0 VOUT VSET PWM/OC5/SC5 TEMP SENSOR LOGIC LX T1 OTP THRM O/P SHORT FAULT DETECT LOGIC PWM GENERATOR FAULT FLAG /FLAG |
Numéro de pièce similaire - ISL97672B |
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Description similaire - ISL97672B |
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