Datasheet LT3013B (Analog Devices) - 8

LT3013B
APPLICATIONS INFORMATION
The LT3013B is a 250mA high voltage low dropout regulator output voltages greater than 1.24V will be proportional to with micropower quiescent current. The device is capable the ratio of the desired output voltage to 1.24V; (VOUT/ of supplying 250mA at a dropout voltage of 400mV. Op- 1.24V). For example, load regulation for an output current erating quiescent current is only 65μA. In addition to the change of 1mA to 250mA is –7mV typical at VOUT = 1.24V. low quiescent current, the LT3013B incorporates several At VOUT = 12V, load regulation is: protection features which make it ideal for use in bat- (12V/1.24V) • (–7mV) = –68mV tery-powered systems. The device is protected against both reverse input and reverse output voltages. In battery
Output Capacitance and Transient Response
backup applications where the output can be held up by a backup battery when the input is pulled to ground, the The LT3013B is designed to be stable with a wide range of LT3013B acts like it has a diode in series with its output output capacitors. The ESR of the output capacitor affects and prevents reverse current fl ow. stability, most notably with small capacitors. A minimum output capacitor of 3.3μF with an ESR of 3Ω or less is
Adjustable Operation
recommended to prevent oscillations. The LT3013B is a micropower device and output transient response will be The LT3013B has an output voltage range of 1.24V to 60V. a function of output capacitance. Larger values of output The output voltage is set by the ratio of two external resis- capacitance decrease the peak deviations and provide tors as shown in Figure 1. The device servos the output to improved transient response for larger load current maintain the voltage at the adjust pin at 1.24V referenced changes. Bypass capacitors, used to decouple individual to ground. The current in R1 is then equal to 1.24V/R1 and components powered by the LT3013B, will increase the the current in R2 is the current in R1 plus the ADJ pin bias effective output capacitor value. current. The ADJ pin bias current, 30nA at 25°C, fl ows through R2 into the ADJ pin. The output voltage can be Extra consideration must be given to the use of ceramic calculated using the formula in Figure 1. The value of R1 capacitors. Ceramic capacitors are manufactured with a should be less than 250k to minimize errors in the output variety of dielectrics, each with different behavior across voltage caused by the ADJ pin bias current. temperature and applied voltage. The most common dielectrics used are specifi ed with EIA temperature char- The adjustable device is tested and specifi ed with the ADJ acteristic codes of Z5U, Y5V, X5R and X7R. The Z5U and pin tied to the OUT pin and a 5μA DC load (unless otherwise Y5V dielectrics are good for providing high capacitances specifi ed) for an output voltage of 1.24V. Specifi cations for in a small package, but they tend to have strong voltage IN OUT VOUT LT3013B R2 + VIN ADJ GND R1 3013 F01 R2 VOUT = 1.24V 1 + + (IADJ)(R2) VADJ = 1.24V IADJ = 30nA AT 25°C OUTPUT RANGE = 1.24V TO 60V
Figure 1. Adjustable Operation
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