LTC3025 APPLICATIONS INFORMATION The LTC3025 will cycle in and out of thermal shutdown VOUT Start-Up and Supply Sequencing without latch-up or damage until the overstress condition During power-up, the output shutdown circuitry is not is removed. Long term overstress (TJ > 125°C) should be active below V avoided as it can degrade the performance or shorten the IN of about 0.65V DC (typical). As a result, the output voltage can drift up during power-up due to life of the part. leakage current (<1 mA typical) from VIN to VOUT . At 0.9V input, the shutdown circuitry is active and the output is Soft-Start Operation actively held off. This usually causes no circuit problems The LTC3025 includes a soft-start feature to prevent and is similar to 3-terminal regulators such as the LT3080, excessive current fl ow during start-up. When the LDO is LT1086 and LT317 which have no ground pin and can have enabled, the soft-start circuitry gradually increases the LDO the output rise under some conditions. A slowly rising reference voltage from 0V to 0.4V over a period of about VIN with the part enabled may result in non-monotonic 600μs. There is a short 700μs delay from the time the ramping of VOUT due to LDO circuitry becoming active at part is enabled until the LDO output starts to rise. Figure 5 VIN of about 0.65V (typical) as well. shows the start-up and shutdown output waveform. With fast rising inputs (>1V/ms) or with suffi cient resis- tive load on V ON OUT , output voltage rise during power-up is SHDN reduced or eliminated. Such conditions also reduce or OFF eliminate non-monotonic initial power-up with the part 1.2V enabled. If VBIAS is sequenced up before VIN, the leakage current from VIN to VOUT may increase until the shutdown circuitry is active at a VIN of about 0.65V typical. Thus, VOUT 200mV/DIV to minimize VOUT rise during start-up, sequence up VIN before VBIAS. At VIN = 0.9V, the output is actively held off in shutdown or it is actively held on when enabled under 0V all conditions. TA = 25°C 500μs/DIV 3025 F05 VIN = 1.5V VBIAS = 3.6V COUT = 1μF RLOAD = 4Ω Figure 5. Output Start-Up and Shutdown 3025fd 9
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