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Hersteller: American Standard Dateigröße: 101.71 kb Dateiname: sic-rc4194n.pdf Unterrichtssprache:

Brownout Protection The RC4194 is one of the most easily applied and trouble- free monolithic ICs available. When used within the data sheet ratings (package power dissipation, maximum output current, minimum and maximum input voltages) it provides the most cost-effective source of regulated ±15V for powering linear ICs. 0.001µF +VS 4194 Comp+ R0 RSET Comp- R0 RSET 0.01µF 0.01µF 0.001µF 4.7µF * +VS –VS +VOUT –VOUT Note: All Capacitors are Ceramic Disc Except * = Solid Tantalum +VOUT –VS –VOUT Figure 9. RC4194 Recommended Compensation Sometimes occasions arise in which the RC4194 ratings must be exceeded. One example is the “brownout.” During a brownout, line voltages may be reduced to as low as 75 VRMS, causing the input voltage to the RC4194 to drop below the minimum dropout voltage. When this happens, the negative output voltage can go to positive. The maximum amount of current available is approximately 5 mA. In general this is not enough current to damage most ICs which the RC4194 might be supplying, but it is a potentially destructive condition. Fortunately, it is easy to protect against. As shown in the typical application circuit in Figure 11, a diode, D, can be connected to the negative output. 4194 0.001µF Comp++VS -VS R0 RSET Comp- R 0 RSET 0.01µF 0.01µF 0.001 F 4.7µF * -VOUT +VOUT+VOUT -VOUT 65-4202 +VS -VS To -VOUT Note: All Capacitors are Ceramic Disc Except * = Solid Tantalum Figure 10. RC4194 Regulator Showing All Protective Diodes RC4194 PRODUCT SPECIFICATION RC4194 PRODUCT SPECIFICATION tive output voltage at about +0.55V. A Schottky barrier or germanium device would clamp the voltage at about +0.3V. Another cure which will keep the negative output negative at all times is the 1 mW resistor connected between the +15V output and the Comp-terminal. This resistor will then supply drive to the negative output transistor, causing it to saturate to -1V during the brownout. Heatsinking Voltage Regulators are power devices which are used in a wide range of applications. When operating these devices near their extremes of load current, ambient temperature and input-output differential, consideration of package dissipation becomes important to avoid thermal shutdown at 175°C. The RC4194 has this feature to prevent damage to the device. It typically starts affecting load regulation approximately 2°C below 175°C. To avoid shutdown, some form of heatsinking should be used or one of the above operating conditions would need to be derated.* The following is the basic equation for junction temperature: TJ=TA+ – PDqJA Equation 1 where TJ = junction temperature (°C) TA = ambient air temperature (°C) PD = power dissipated by device (W) qJ-A = thermal resistance from junction to ambient air (°C/W) The power dissipated by the voltage regulator can be detailed as follows: = % – )Z + . PD VIN VOUT IO VIN IQ Equation 2 where VIN = input voltage VOUT = regulated output voltage IO = load current IQ = quiescent current drain ——————————————— Let’s look at an application where a user is trying to determine whether the RC4194 in a high temperature environment will need a heatsink. Given: TJ at thermal shutdown = 150°C TA = 125°C qJ-A = 41.6°C/W, K (TO-66) pkg. VIN = 40V VOUT = 30V IQ = 1 mA + 75 mA/VOUT x 30V = 3.25 mA* TJ –TA = ----------------- qJA – PD TJ –TA PD = -----------------qJA – = % – )Z + . VIN VOUT IO VIN IQ Solve for IO, TJ –TA Z IQ VIN IO = -------------------------------------------------– ---------------------------------- % – )% – ) qJA– VIN VOUT VIN VOUT –3 150°C – 125°C 40 Z 3.25 Z 10 IO = -----------------------------------------– --------------------------------------- 41.6°C/W Z 10V 10 = 60 mA – 13 mA ~ 47 mA If this supply current does not provide at least a 10% margin under worst case load conditions, heatsinking should be employed. If reliability is of prime importance, the multiple regulator approach should be considered. In Equation 1, qJ-A can be broken into the following compo nents: qJ-A = qJ-C + qC-S + qS-A where qJ-C = junction-to-case thermal resistance qC-S = case-to-heatsink thermal resistance qS-A = heatsink-to-ambient thermal resistance *The current drain will increase by 50mA/VOUT on positive side and 100mA/VOUT on negative side PRODUCT SPECIFICATION RC4194 PRODUCT SPECIFICATION RC4194 Given: IO = 200 mA, TJ –TA = -------------------------------------------------------------------------- qJA – % – )Z + . VIN VOUT IO VIN IQ 50°C – 125°C = --------------------------------------------------------------------------------- –3 10V Z 200mA + 40 Z 3.25 Z 10 = 11.75°C/W Given qJ-C = 7.15°C/W for the 4194 in the K package, qC-S + qS-A = 11.75°C/W – 7.15°C/W = 4.6°C/W When using heatsink compound with a metal-to-metal interface, a typical qC-S = 0.5°C/W for the K package. The remaining qS-A of approximately 4°C/W is a large enough thermal resistance to be easily provided by a number of heatsinks currently available. Table 1 is a brief selection guide to heatsink manufacturers. Table 1. Commer...

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