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LTM4686BIVPBF 数据表(PDF) 36 Page - Analog Devices |
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LTM4686BIVPBF 数据表(HTML) 36 Page - Analog Devices |
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36 / 130 page  LTM4686B 36 Rev. 0 For more information www.analog.com OPERATION Peak Output Overcurrent Fault Response Due to the current mode control algorithm, peak inductor current is always limited on a cycle by cycle basis. The value of the peak current limit is specified in the Electrical Characteristics table. The current limit circuit operates by limiting the COMPna maximum voltage. DCR sensing is used so the COMPna maximum voltage has a temperature dependency directly proportional to the TC of the DCR of the inductor. The LTM4686B automatically monitors the power stage temperature sensors and modifies the maximum allowed COMPna to compensate for this term. The overcurrent fault processing circuitry can execute the following behaviors: n Current Limit Indefinitely n Shut Down Immediately—Latch Off n Shut Down Immediately—Retry Indefinitely using the Time Interval Specified in MFR_RETRY_DELAYn The overcurrent responses can be deglitched in incre- ments of (0 to 7) • 16ms. See Table 26. RESPONSES TO TIMING FAULTS TON_MAX_FAULT_LIMITn is the time allowed for VOUT to rise and settle at start-up. The TON_MAX_FAULT_LIMITn condition is predicated upon detection of the VOUT_UV_ FAULT_LIMITn as the output is undergoing a SOFT_START sequence. The TON_MAX_FAULT_LIMITn time is started after TON_DELAYn has been reached and a SOFT_START sequence is started. The resolution of the TON_MAX_ FAULT_LIMITn is 10µs. If the VOUT_UV_FAULT_LIMITn is not reached within the TON_MAX_FAULT_LIMITn time, the response of this fault is determined by the value of the TON_MAX_FAULT_RESPONSEn command value. This response may be one of the following: n Ignore n Shut Down (Stop Switching) Immediately—Latch Off n Shut Down Immediately—Retry Indefinitely using the Time Interval Specified in MFR_RETRY_DELAYn This fault response is not deglitched. A value of 0 in TON_MAX_FAULT_LIMITn means the fault is ignored. The TON_MAX_FAULT_LIMITn should be set longer than the TON_RISEn time. It is recommended TON_MAX_ FAULT_LIMITn always be set to a non-zero value, oth- erwise the output may never come up and no flag will be set to the user. See Table 28. RESPONSES TO SVIN OV FAULTS SVIN overvoltage is measured with the ADC; therefore, the response is naturally deglitched by up to the 90ms typical response time of the ADC. The fault responses are: n Ignore n Shut Down Immediately—Latch Off n Shut Down Immediately—Retry Indefinitely using the Time Interval Specified in MFR_RETRY_DELAYn See Table 28. RESPONSES TO OT/UT FAULTS Internal Overtemperature Fault/Warn Response An internal temperature sensor protects against EEPROM damage. Above 85°C, no writes to EEPROM are recom- mended. Above 130°C, the internal over temperature warn threshold is exceeded and the part disables EEPROM writes and does not re-enable until the temperature has dropped to 125°C. When the die temperature exceed 160°C the internal over temperature fault response is enabled and the PWM is disabled until the die temperature drops below 150°C. Temperature is measured by the ADC. Internal temperature faults cannot be ignored. Internal temperature limits cannot be adjusted by the user. See Table 27. External Overtemperature and Undertemperature Fault Response Two temperature sensors within the LTM4686B are used to sense power stage temperature. The OT_FAULT_ RESPONSEn and UT_FAULT_RESPONSEn commands |
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