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LT3495B Datasheet(PDF) 10 Page - Linear Technology |
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LT3495B Datasheet(HTML) 10 Page - Linear Technology |
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10 / 16 page  LT3495/LT3495B/ LT3495-1/LT3495B-1 10 3495b1b1fa APPLICATIONS INFORMATION Figure 2. Feedback Connection Using the CAP Pin or the VOUT Pin SW CAP VCC SHDN CTRL VOUT FB GND R1 LT3495 C1 C3 VOUT SW CAP VCC SHDN CTRL VOUT FB GND R1 3495 F02 LT3495 C1 SW CAP VCC SHDN CTRL VOUT FB GND 3495 F03 LT3495 C1 ILOAD Figure 1. CTRL to FB Transfer Curve Figure 3. Improved Efficiency Connection Setting Output Voltage and the Auxiliary Reference Input The LT3495 series is equipped with both an internal 1.235V reference and an auxiliary reference input. This allows the user to select between using the built-in refer- ence and supplying an external reference voltage. The voltage at the CTRL pin can be adjusted while the chip is operating to alter the output voltage for purposes such as display dimming or contrast adjustment. To use the internal 1.235V reference, the CTRL pin must be held higher than 1.5V. When the CTRL pin is held between 0V and 1.235V, the parts will regulate the output such that the FB pin voltage is nearly equal to the CTRL pin voltage. At CTRL voltages close to 1.235V, a soft transition occurs between the CTRL pin and the internal reference. Figure 1 shows this behavior. To set the maximum output voltage, select the values of R1 according to the following equation: R1= 76 • VOUT 1.235 – 1 ⎛ ⎝⎜ ⎞ ⎠⎟ kΩ When CTRL is used to override the internal reference, the output voltage can be lowered from the maximum value down to nearly the input voltage level. If the volt- age source driving the CTRL pin is located at a distance to the LT3495, a small 0.1µF capacitor may be needed to bypass the pin locally. Choosing a Feedback Node The single feedback resistor may be connected to the VOUT pin or to the CAP pin (see Figure 2). Regulating the VOUT pin eliminates the output offset resulting from the voltage drop across the output disconnect PMOS. Regu- lating the CAP pin does not compensate for the voltage drop across the output disconnect, resulting in an output voltage VOUT that is slightly lower than the voltage set by the resistor divider. Under most conditions, it is advised that the feedback resistor be tied to the VOUT pin. Connecting the Load to the CAP Node The efficiency of the converter can be improved by con- necting the load to the CAP pin instead of the VOUT pin. The power loss in the PMOS disconnect circuit is then made negligible. By connecting the feedback resistor to the VOUT pin, no quiescent current will be consumed in the feedback resistor string during shutdown since the PMOS transistor will be open (see Figure 3). The disadvantage of this method is that the CAP node cannot go to ground during shutdown, but will be limited to around a diode drop below VCC. Loads connected to the part should only sink current. Never force external power supplies onto the CAP or VOUT pins. CTRL VOLTAGE (V) 0 1.5 1.2 0.6 0.9 0.3 0 0.9 3495 F01 1.5 0.6 0.3 1.2 |
Similar Part No. - LT3495B_15 |
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Similar Description - LT3495B_15 |
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