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LM4051_EM3-12 Datasheet(PDF) 11 Page - Maxim Integrated Products |
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LM4051_EM3-12 Datasheet(HTML) 11 Page - Maxim Integrated Products |
11 / 14 page 50ppm/°C Precision Micropower Shunt Voltage References with Multiple Reverse Breakdown Voltages ______________________________________________________________________________________ 11 Detailed Description The LM4050/LM4051 shunt references use the bandgap principle to produce a stable, accurate volt- age. The device behaves similarly to an ideal zener diode; a fixed voltage is maintained across its output terminals when biased with 60µA to 15mA of reverse current. The LM4050/LM4051 clamps to a voltage of one diode drop below ground when biased with for- ward currents up 10mA. Figure 3 shows a typical operating circuit. The LM4050/LM4051 are ideal for providing stable refer- ences from a high-voltage power supply. Applications Information The LM4050/LM4051s’ internal pass transistors are used to maintain a constant output voltage (VSHUNT) by sinking the necessary amount of current across a source resistor. The source resistance (RS) is determined from the load current (ILOAD) range, supply voltage (VS) variations, VSHUNT, and desired quiescent current. Choose the value of RS when VS is at a minimum and ILOAD is at a maximum. Maintain a minimum ISHUNT of 60µA at all times. The RS value should be large enough to keep ISHUNT less than 15mA for proper regulation when VS is maximum and ILOAD is at a minimum. To prevent damage to the device, ISHUNT should never exceed 20mA. Therefore, the value of RS is bounded by the following equation: [VS(MIN) - VR ] / [60µA + ILOAD(MAX)] > RS > [VS(MAX) - VR ] / [20mA + ILOAD(MIN)] Choosing a larger resistance minimizes the total power dis- sipation in the circuit by reducing the shunt current (PD(TOTAL) = VS ISHUNT). Provide a safety margin to incorporate the worst-case tolerance of the resistor used. Ensure that the resistor’s power rating is adequate, using the following general power equation: PDR = ISHUNT (VS(MAX) - VSHUNT) Output Capacitance The LM4050/LM4051 do not require external capacitors for frequency stability and are stable for any output capacitance. Temperature Performance The LM4050/LM4051 typically exhibit output voltage temperature coefficients within ±15ppm/°C. The polari- ty of the temperature coefficients may be different from one device to another; some may have positive coeffi- cients, and others may have negative coefficients. High Temperature Operation The maximum junction temperature of the LM4050/ LM4051 is +150°C. The maximum operating temperature for the LM4050/LM4051_E_ is +125°C. At a maximum load current of 15mA and a maximum output voltage of 5V, the parts dissipate 75mW of power. The power dissi- pation limits of the 3-pin SC70 call for a derating value of 2.17mW/°C above +70°C and thus for 75mW of power dissipation, the parts self-heat to 35.56°C above ambient temperature. If the ambient temperature is +125°C, the parts operate at 159.56°C, thereby exceeding the maxi- mum junction temperature value of +150°C. For high- temperature operation, care must be taken to ensure the combination of ambient temperature, output power dissi- pation, and package thermal resistance does not con- spire to raise the device temperature beyond that listed in the Absolute Maximum Ratings. Either reduce the out- put load current or the ambient temperature to keep the part within the limits. Figure 3. Typical Operating Circuit LM4050 ILOAD ISHUNT RS VS VR ISHUNT + ILOAD Pin Description PIN NAME FUNCTION 1 + Positive Terminal of the Shunt Reference 2 − Negative Terminal of the Shunt Reference 3 N.C. No connection. Leave this pin unconnected or connected to pin 2. |
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