Datasheet LT3010, LT3010-5 (Analog Devices) - 9

LT3010/LT3010-5
APPLICATIONS INFORMATION
The LT3010 is a 50mA high voltage low dropout regulator The adjustable device is tested and specified with the with micropower quiescent current and shutdown. The ADJ pin tied to the OUT pin and a 5µA DC load (unless device is capable of supplying 50mA at a dropout voltage otherwise specified) for an output voltage of 1.275V. Speci- of 300mV. The low operating quiescent current (30µA) fications for output voltages greater than 1.275V will be drops to 1µA in shutdown. In addition to the low quies- proportional to the ratio of the desired output voltage to cent current, the LT3010 incorporates several protection 1.275V; (VOUT/1.275V). For example, load regulation for an features which make it ideal for use in battery-powered output current change of 1mA to 50mA is –10mV typical systems. The device is protected against both reverse at VOUT = 1.275V. At VOUT = 12V, load regulation is: input and reverse output voltages. In battery backup ap- (12V/1.275V) • (–10mV) = –94mV plications where the output can be held up by a backup battery when the input is pulled to ground, the LT3010 acts
Output Capacitance and Transient Response
like it has a diode in series with its output and prevents reverse current flow. The LT3010 is designed to be stable with a wide range of output capacitors. The ESR of the output capacitor
Adjustable Operation
affects stability, most notably with small capacitors. A minimum output capacitor of 1µF with an ESR of 3Ω or The adjustable version of the LT3010 has an output voltage less is recommended to prevent oscillations. The LT3010 range of 1.275V to 60V. The output voltage is set by the is a micropower device and output transient response ratio of two external resistors as shown in Figure 2. The will be a function of output capacitance. Larger values device servos the output to maintain the voltage at the of output capacitance decrease the peak deviations and adjust pin at 1.275V referenced to ground. The current provide improved transient response for larger load current in R1 is then equal to 1.275V/R1 and the current in R2 is changes. Bypass capacitors, used to decouple individual the current in R1 plus the ADJ pin bias current. The ADJ components powered by the LT3010, will increase the pin bias current, 50nA at 25°C, flows through R2 into the effective output capacitor value. ADJ pin. The output voltage can be calculated using the formula in Figure 2. The value of R1 should be less than Extra consideration must be given to the use of ceramic 250k to minimize errors in the output voltage caused by capacitors. Ceramic capacitors are manufactured with a the ADJ pin bias current. Note that in shutdown the output variety of dielectrics, each with different behavior across is turned off and the divider current will be zero. temperature and applied voltage. The most common dielectrics used are specified with EIA temperature char- A small capacitor (C1) placed in parallel with the top resistor acteristic codes of Z5U, Y5V, X5R and X7R. The Z5U and (R2) of the output divider is necessary for stability and tran- Y5V dielectrics are good for providing high capacitances sient performance of the adjustable LT3010. The impedance in a small package, but they tend to have strong voltage of C1 at 10kHz should be less than the value of R1. and temperature coefficients as shown in Figures 3 and 4. When used with a 5V regulator, a 16V 10µF Y5V capacitor IN OUT VOUT can exhibit an effective value as low as 1µF to 2µF for the LT3010 R2 C1 + VIN DC bias voltage applied and over the operating tempera- ADJ GND R1 ture range. The X5R and X7R dielectrics result in more 30105 F02 stable characteristics and are more suitable for use as the output capacitor. The X7R type has better stability across R2 VOUT = 1.275V 1 + + (I ( )R1 ADJ)(R2) temperature, while the X5R is less expensive and is avail- VADJ = 1.275V I able in higher values. Care still must be exercised when ADJ = 50nA AT 25°C OUTPUT RANGE = 1.275V TO 60V using X5R and X7R capacitors; the X5R and X7R codes
Figure 2. Adjustable Operation
only specify operating temperature range and maximum 30105fe 9 Document Outline Features Applications Description Typical Application Absolute Maximum Ratings Pin Configuration Order Information Electrical Characteristics Typical Performance Characteristics Pin Functions Applications Information Typical Applications Package Description Revision History Typical Application Related Parts