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AAT3221IGV-2.3-T1 Datasheet(PDF) 11 Page - Advanced Analogic Technologies |
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AAT3221IGV-2.3-T1 Datasheet(HTML) 11 Page - Advanced Analogic Technologies |
11 / 16 page AAT3221/2 150mA NanoPower™ LDO Linear Regulator PowerLinearTM PRODUCT DATASHEET 3221.2007.11.1.12 11 www .analogictech.com maximum conditions are calculated at the maximum operating temperature where TA = 85°C, under normal ambient conditions TA = 25°C. Given TA = 85°C, the maximum package power dissipation is 267mW. At TA = 25°C, the maximum package power dissipation is 667mW. The maximum continuous output current for the AAT3221/2 is a function of the package power dissipa- tion and the input-to-output voltage drop across the LDO regulator. Refer to the following simple equation: IOUT(MAX) = PD(MAX) (VIN - VOUT) For example, if VIN = 5V, VOUT = 2.5V and TA = 25°C, IOUT(MAX) < 267mA. The output short-circuit protection threshold is set between 150mA and 300mA. If the out- put load current were to exceed 267mA or if the ambient temperature were to increase, the internal die tempera- ture would increase. If the condition remained constant and the short-circuit protection did not activate, there would be a potential damage hazard to the LDO regula- tor since the thermal protection circuit would only acti- vate after a short-circuit event occured on the LDO regulator output. To determine the maximum input voltage for a given load current, refer to the following equation. This calcu- lation accounts for the total power dissipation of the LDO regulator, including that caused by ground current. PD(MAX) = (VIN - VOUT)IOUT + (VIN · IGND) This formula can be solved for VIN to determine the maximum input voltage. VIN(MAX) = (PD(MAX) + [VOUT · IOUT]) (IOUT + IGND) The following is an example for an AAT3221/2 set for a 2.5 volt output: VOUT = 2.5 volts IOUT = 150mA IGND = 1.1μA VIN(MAX) = VIN(MAX) = 6.95V (667mW + [2.5V · 150mA]) (150mA + 1.1µA) From the discussion above, PD(MAX) was determined to equal 667mW at TA = 25°C. Thus, the AAT3221/2 can sustain a constant 2.5V output at a 150mA load current as long as VIN is ≤6.95V at an ambient temperature of 25°C. 5.5V is the maximum input operating voltage for the AAT3221/2, thus at 25°C the device would not have any thermal concerns or operational VIN(MAX) limits. This situation can be different at 85°C. The following is an example for an AAT3221/2 set for a 2.5 volt output at 85°C: VOUT = 2.5 volts IOUT = 150mA IGND = 1.1μA VIN(MAX) = VIN(MAX) = 4.28V (267mW + [2.5V · 150mA]) (150mA + 1.1µA) From the discussion above, PD(MAX) was determined to equal 267mW at TA = 85°C. Higher input-to-output voltage differentials can be obtained with the AAT3221/2, while maintaining device functions in the thermal safe operating area. To accom- plish this, the device thermal resistance must be reduced by increasing the heat sink area or by operating the LDO regulator in a duty-cycled mode. For example, an application requires VIN = 5.0V while VOUT = 2.5V at a 150mA load and TA = 85°C. VIN is greater than 4.28V, which is the maximum safe continu- ous input level for VOUT = 2.5V at 150mA for TA = 85°C. To maintain this high input voltage and output current level, the LDO regulator must be operated in a duty- cycled mode. Refer to the following calculation for duty- cycle operation: IGND = 1.1μA IOUT = 150mA VIN = 5.0 volts VOUT = 2.5 volts %DC = 100 PD(MAX) ([VIN - VOUT]IOUT + [VIN · IGND]) %DC = 100 %DC = 71.2% 267mW ([5.0V - 2.5V]150mA + [5.0V · 1.1µA]) PD(MAX) is assumed to be 267mW. |
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