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LT1129CQ-3.3 Datasheet(PDF) 9 Page - Linear Technology |
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LT1129CQ-3.3 Datasheet(HTML) 9 Page - Linear Technology |
9 / 16 page LT1129/LT1129-3.3/LT1129-5 9 112935ff Input Pin: Power is supplied to the device through the input pin. The input pin should be bypassed to ground if the device is more than 6 inches away from the main input filter capacitor. In general, the output impedance of a battery rises with frequency so it is advisable to include a bypass capacitor in battery-powered circuits. A bypass capacitor in the range of 1μF to 10μF is sufficient. The LT1129 is designed to withstand reverse voltages on the input pin with respect to both ground and the output pin. In the case of a reversed input, which can happen if a battery is plugged in backwards, the LT1129 will act as if there is a diode in series with its input. There will be no reverse current flow into the LT1129 and no reverse volt- age will appear at the load. The device will protect both itself and the load. Output Pin: The output pin supplies power to the load. An output capacitor is required to prevent oscillations. See the Applications Information section for recommended value of output capacitance and information on reverse output characteristics. Shutdown Pin ( SHDN): This pin is used to put the device into shutdown. In shutdown the output of the device is turned off. This pin is active low. The device will be shut down if the shutdown pin is actively pulled low. The shutdown pin current with the pin pulled to ground will be 6μA. The shutdown pin is internally clamped to 7V and – 0.6V (one VBE). This allows the shutdown pin to be driven directly by 5V logic or by open collector logic with a pull-up resistor. The pull-up resistor is only required to supply the leakage current of the open collector gate, normally several microamperes. Pull-up current must be limited to a maximum of 20mA. A curve of shutdown pin input current as a function of voltage appears in the Typical Performance Characteristics. If the shutdown pin is not used it can be left open circuit. The device will be active, output on, if the shutdown pin is not connected. Sense Pin: For fixed voltage versions of the LT1129 (LT1129-3.3, LT1129-5) the sense pin is the input to the error amplifier. Optimum regulation will be obtained at the point where the sense pin is connected to the output pin. For most applications the sense pin is connected directly to the output pin at the regulator. In critical applications small voltage drops caused by the resistance (RP) of PC traces between the regulator and the load, which would normally degrade regulation, may be eliminated by con- necting the sense pin to the output pin at the load as shown in Figure 1 (Kelvin Sense Connection). Note that the voltage drop across the external PC traces will add to the dropout voltage of the regulator. The sense pin bias current is 15μA at the nominal regulated output voltage. This pin is internally clamped to –0.6V (one VBE). Adjust Pin: For the LT1129 (adjustable version) the adjust pin is the input to the error amplifier. This pin is internally clamped to 6V and –0.6V (one VBE). This pin has a bias current of 150nA which flows into the pin. See Bias Cur- rent curve in the Typical Performance Characteristics. The adjust pin reference voltage is equal to 3.75V referenced to ground. PIN FUNCTIONS Figure 1. Kelvin Sense Connection The LT1129 is a micropower low dropout regulator with shutdown, capable of supplying 700mA of output current at a dropout voltage of 0.4V. The device operates with very low quiescent current (50μA). In shutdown the quiescent current drops to only 16μA. In addition to the low quies- cent current the LT1129 incorporates several protection APPLICATIONS INFORMATION features which make it ideal for use in battery-powered systems. The device is protected against reverse input voltages. In battery backup applications where the output can be held up by a backup battery when the input is pulled to ground, the LT1129 acts like it has a diode in series with its output and prevents reverse current flow. IN LT1129 GND SHDN 112935 F01 SENSE OUT RP 1μF LOAD 10μF RP + |
Similar Part No. - LT1129CQ-3.3 |
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Similar Description - LT1129CQ-3.3 |
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