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LT1965IQPBF Datasheet(PDF) 8 Page - Linear Technology |
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LT1965IQPBF Datasheet(HTML) 8 Page - Linear Technology |
8 / 16 page LT1965 8 1965f APPLICATIONS INFORMATION The LT1965 is a 1.1A low dropout regulator with shut- down. The device is capable of supplying 1.1A at a typical dropout voltage of 290mV. The low operating quiescent current (500μA) drops to less than 1μA in shutdown. In addition to its low quiescent current, the LT1965 regulator incorporates several protection features that make it ideal for use in battery-powered systems. The device protects itself against both reverse input and reverse output volt- ages. In battery backup applications, if a backup battery holds up the output when the input is pulled to ground, the LT1965 performs like it has a diode in series with its output, preventing reverse current flow. Also, in dual sup- ply applications where the regulator load is returned to a negative supply, the output can be pulled below ground by as much as 20V. The LT1965 still starts and operates normally in this situation. Adjustable Operation The LT1965 has an output voltage range of 1.20V to 20V. Figure 1 illustrates that the ratio of two external resistors sets the output voltage. The device servos the output to maintain the ADJ pin voltage at 1.20V referenced to ground. R1’s current equals 1.20V/R1. R2’s current equals R1’s current plus the ADJ pin bias current. The ADJ pin bias current, 1.3μA at 25°C, flows through R2 into the ADJ pin. Use the formula in Figure 1 to calculate output voltage. Linear Technology recommends that R1’s value be less than 12.1k to minimize output voltage errors due to the ADJ pin bias current. In shutdown, the output turns off and the divider current is zero. For curves depicting ADJ Pin Voltage vs Temperature and ADJ Pin Bias Current vs Temperature, see the Typical Performance Characteristics section. The adjustable device is tested and specified with the ADJ pin tied to the OUT pin for an output voltage of 1.20V. Specifications for output voltages greater than 1.20V are proportional to the ratio of the desired output voltage to 1.20V: VOUT/1.20V. For example, load regulation for an output current change of 1mA to 1.1A is typically –4.25mV at VOUT = 1.20V. At VOUT = 5V, load regulation is: 5 120 425 1771 V V mV mV . •– . – . = Output Capacitance The LT1965’s design is stable with a wide range of out- put capacitors. The ESR of the output capacitor affects stability, most notably with small capacitors. A minimum output capacitor of 10μF with an ESR of 3Ω or less is recommended to prevent oscillations. The LT1965 is a low quiescent current device and output load transient response is a function of output capacitance. Larger values of output capacitance decrease the peak deviations and provide improved transient response for larger current changes. Ceramic capacitors require extra consideration. Manufac- turers make ceramic capacitors with a variety of dielectrics, each with different behavior across temperature and applied voltage. The most common dielectrics used are specified with EIA temperature characteristic codes of Z5U, Y5V, X5R and X7R. The Z5U and Y5V dielectrics provide high C-V products in a small package at low cost, but exhibit strong voltage and temperature coefficients as shown in Figures 2 and 3. When used with a 5V regulator, a 16V 10μF Y5V capacitor can exhibit an effective value as low as 1μF to 2μF for the DC bias applied and over the operat- ing temperature range. The X5R and X7R dielectrics yield much more stable characteristics and are more suitable for use as the output capacitor. The X7R type works over a wider temperature range and has better temperature stability whereas X5R is less expensive and is available in higher values. Care still must be exercised when using X5R and X7R capacitors; the X5R and X7R codes only specify operating temperature range and maximum capacitance change over temperature. Capacitance change due to DC bias with X5R and X7R capacitors is better than Y5V and Z5U capacitors, but can still be significant enough to drop Figure 1. Adjustable Operation IN 1965 F01 R2 OUT VIN VOUT ADJ GND LT1965 R1 + VV R R IR VV I OUT ADJ ADJ AD =+ ⎛ ⎝⎜ ⎞ ⎠⎟ + = 120 1 2 1 2 120 .• . JJ µA AT C OUTPUT RANGE V TO V = = 13 25 120 195 .º .. |
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