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CS8361 датащи(PDF) 4 Page - Cherry Semiconductor Corporation |
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CS8361 датащи(HTML) 4 Page - Cherry Semiconductor Corporation |
4 / 6 page 4 Circuit Description Application Notes The function switches the output transistor for VTRK on and off. When the lead voltage exceeds 1.4V(typ), VTRK turns off. This input has several hundred millivolts of hysteresis to prevent spurious output activity during power-up or power-down. The is an open collector NPN transistor, con- trolled by a low voltage detection circuit sensing the VSTBY (5V) output voltage. This circuit guarantees the output stays below 1V (0.1V typ) when VSTBY is as low as 1V to ensure reliable operation of microprocessor-based systems. This output uses the same type of output device as VSTBY, but is rated for 250mA. The output is configured as a tracking regulator of the standby output. By using the standby output as a voltage reference, giving the user an external programming lead (Adj lead), output voltages from 5V to 20V are easily realized. The programming is done with a simple resistor divider (Figure 2), and follow- ing the formula: VTRK = VSTBY ´ (1 + R1/R2) + IAdj ´ R1 If another 5V output is needed, simply connect the Adj lead to the VTRK output lead. VTRK Output Voltage RESET RESET RESET Function ENABLE ENABLE ENABLE Function Output capacitors for the CS8361 are required for stability. Without them, the regulator outputs will oscillate. Actual size and type may vary depending upon the application load and temperature range. Capacitor effective series resistance (ESR) is also a factor in the IC stability. Worst- case is determined at the minimum ambient temperature and maximum load expected. Output capacitors can be increased in size to any desired value above the minimum. One possible purpose of this would be to maintain the output voltages during brief conditions of negative input transients that might be char- acteristic of a particular system. Capacitors must also be rated at all ambient temperatures expected in the system. To maintain regulator stability down to -40ûC, capacitors rated at that temperature must be used. More information on capacitor selection for Smart Regulatorsª is available in the Smart Regulator applica- tion note, ÒCompensation for Linear Regulators.Ó The maximum power dissipation for a dual output regula- tor (Figure 1) is: PD(max) = {VIN(max)ÐVOUT1(min)}IOUT1(max)+ {VIN(max)ÐVOUT2(min)}IOUT2(max)+VIN(max)IQ (1) Where VIN(max) is the maximum input voltage, VOUT1(min) is the minimum output voltage from VOUT1, VOUT2(min) is the minimum output voltage from VOUT2, IOUT1(max) is the maximum output current, for the application IOUT2(max) is the maximum output current, for the application IQ is the quiescent current the regulator consumes at IOUT(max). Once the value of PD(max) is known, the maximum per- missible value of RQJA can be calculated: RQJA = (2) The value of RQJA can then be compared with those in the package section of the data sheet. Those packages with RQJA's less than the calculated value in equation 2 will keep the die temperature below 150¡C. In some cases, none of the packages will be sufficient to dissipate the heat generated by the IC, and an external heat sink will be required. Figure 1: Dual output regulator with key performance parameters labeled. VIN VOUT2 IIN IQ Control Features } IOUT2 VOUT1 IOUT1 Smart Regulator 150¡C - TA PD Calculating Power Dissipation in a Dual Output Linear Regulator External Capacitors |
Аналогичный номер детали - CS8361 |
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Аналогичное описание - CS8361 |
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