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LX8816 Datasheet(PDF) 6 Page - Microsemi Corporation |
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LX8816 Datasheet(HTML) 6 Page - Microsemi Corporation |
6 / 9 page Microsemi Integrated Products 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 6 Copyright 2000 Rev. 1.2a, 2002-11-01 LX8816 Dual Channel 1A Low Dropout Regulator PRODUCTION DATA SHEET I N T E GR A T ED PRO DUC T S APPLICATION INFORMATION Description The LX8816 is part of a family of Dual LDO (Low Drop-Out) linear regulators in Microsemi’s S-PAK power package, which offer maximum power dissipation in a low profile surface mount technology. The family includes combination fixed and adjustable versions. Each channel can supply up to one amp independently with a regulator design optimized for system efficiency by consuming minimal ground current and directing quiescent current to the load. Input Capacitor To improve load transient response and noise rejection a input bypass capacitor is of at least 2.2uF is required. Generally we recommend a 20uF ceramic or tantalum or 22uF electrolytic capacitor. Output Capacitor The regulator requires output capacitors connected between V1, V2 and GND to stabilize the internal control loop. Many types of capacitors are available, with different capacitance values tolerances, temperature coefficients and equivalent series resistance. We recommend a minimum of 4.7uF. To ensure good transient response from the power supply system under rapidly changing current load conditions, designers generally use additional output capacitors connected in parallel. Such an arrangement serves to minimize the effects of the parasitic resistance (ESR) and inductance (ESL) that are present in all capacitors. The regulator has been tested stable with capacitor ESR’s in the range of 0.05 to 2 ohms. We have found it best to use the same type of capacitor for both input and output bypass. Adjustable Output Voltage The LX8816 develops a 1.25V reference voltage between the adjust terminal and GND (See Figure 2). By placing a resistor, R2, between these two terminals, a constant current is caused to flow through R1 and down through R2 to set the overall output voltage. Because IADJ is very small and constant when compared with the current through R2, it represents a small error and can usually be ignored. LX8816-04 R1 R2 V IN ADJ V 1 FIGURE 2 - BASIC ADJUSTABLE REGULATOR V REF 1 2 1 1 1 R I R R V V ADJ REF + + = I ADJ 1µA V 2 Minimum Load Requirement The LX8816 has a minimum load is requirement for proper output regulation. This minimum current is specified at 0mA for the fixed output and 2ma for the adjustable output regulators. Temperature Protection The thermal protection shuts the LX8816 down when the junction temperature exceeds 1400C. Each output has independent thermal shutdown capability. Exposure to absolute maximum rated conditions for extended periods may affect device reliability, see Thermal Considerations below. Current Limit Protection The LX8816 includes over current protection, when the output load current exceeds typically 1.4A the circuit forces the regulator decrease in output. Thermal Considerations Thermal shutdown protects the integrated circuit from thermal overload caused from a rise in junction temperature during power dissipation. This means of protection is intended for fault protection only and not as a means of current or power limiting during normal application usage. Proper thermal evaluation should be done to ensure that the junction temperature dose not exceed it’s maximum rating. Operating at the maximum TJ of 150°C can impact reliability . Due to variation in individual device electrical characteristics and thermal resistance , the built in thermal overload protection may be activated at power levels slightly above or below the rated dissipation. Also peak output power should be considered for each individual output. Power dissipation for regulator can be calculated using the following equation: PD = (VIN(MAX)-V1) * I1 + (VIN(MAX)-V2 ) * I2 (Note: power dissipation resulting from quiescent (ground) current is negligible) For the S-PAK package, thermal resistance, θTAB-AMB is 25-450C/W depending on mounting technique when mounted on a FR4 copper clad PCB. Junction temperature of the integrated circuit can be calculated using: TJUNCTION = TJUNCTION-TAB RISE _+ TTAB-AMB RISE + TAMB TTAB = PD MAX * θJT ; TTAB-AMB = (PD REG1 + PD REG2) * θPCB An example: Given conditions: TA = 50°C, VIN= 5.0V, V1= 2.5V, I1= 210mA, V2= 3.3V I2= 1A. Calculated values: TJ-TAB REG1 = (5V-2.5V) * (210mA) * 4.5°C/W = (0.525) * 4.5°C/W = 2.4°C TJ-TAB REG2 = (5V-3.3V) * (1.0A) * 4.5°C/W = (1.7) * 4.5°C/W = 7.7°C TTAB-AMB RISE = ( 0.525W + 1.7W ) * 30°C/W = 66.8°C TJUNCTION = 10.1°C + 66.8°C + 50°C = 126.9°C It is important to note that although each output of the regulator will produce up to 1A in current, the individual or total power dissipation may limit the useful total current draw. The junction temperature should be calculated for each individual output as well as the combined outputs to insure the maximum junction temperature in not exceeded. |
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