PDF CS8128YN8 Data sheet ( Hoja de datos )

Número de pieza	CS8128YN8
Descripción	5V Linear Controller/Driver
Fabricantes	Cherry Semiconductor Corporation
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No Preview Available ! CS8128 5V Linear Controller/Driver Description Features The CS8128 contains all the necessary control circuitry to implement a 5V lin- ear regulator. An external pass device is used to produce superior performance compared to conventional monolithic regulators. The CS8128 with a TIP42 PNP transistor typically provides a 100mV dropout voltage at 500mA, increasing to 350mV at 3A. Quiescent current at 500mA is only 5mA. Monolithic regulators cannot approach these figures because their power tran- sistors do not provide the high beta and excellent saturation characteristics at high currents. The CS8128 is compatible with a wide variety of external transis- tors, allowing flexibility for thermal, space, and cost management. The CS8128 includes thermal shutdown and externally programmable current limit and over-voltage shutdown, mak- ing it suitable for use in automotive and switching regulator post regulator appli- cations. An optional external RC filter added to the CS8128 supply lead pro- vides EMC hardening in addition to the on-chip EMC hardening. The SENSE lead allows remote sensing of the output voltage for improved regulation. An active microprocessor RESET func- tion is included on-chip with externally programmable delay time. During power-up, or after detection of any error in the regulated output, the RESET lead will remain in the low state for the dura- tion of the delay. Types of errors include short circuit, low input voltage, over- voltage shutdown, thermal shutdown, or others that cause the output to become unregulated. This function is independent of the input voltage and will function correctly with an output voltage as low as 1V. Hysteresis is included in both the reset and delay comparators for noise immunity and to prevent oscillations. A latching dis- charge circuit is used to discharge the delay capacitor, even when triggered by a relatively short fault condition. This circuit improves upon the commonly used SCR structure by providing improved noise immunity and full capacitor discharge (0.2V typ). Block Diagram Pwr Gnd Ref Gnd VIN Delay IC Power Gnd IC Reference Gnd PRE- REGULATOR Regulated Supply for Circuit Bias 10µA Delay Current Latching Discharge QS R - + Vdis Over Voltage Shutdown Thermal Shutdown Bandgap Reference 1.25V Error Amp - + - Reset Comparator Delay - Comparator + SHUTDOWN VOUT Sense RESET s Externally Set Delay for Reset s 60V Load Dump Protection s Internal Thermal Overload Protection s 3% Output Accuracy s Active RESET s Noise Immunity s On Chip EMC Hardening Protection Incorporated s Externally Set Current Limit s Externally Set Overvoltage Shutdown Package Options 8L SO & 8L PDIP VIN 1 Sense 2 Delay 3 RESET 4 8 VOUT 7 Pwr Gnd 6 SHUTDOWN 5 Ref Gnd Rev. 2/5/99 Cherry Semiconductor Corporation 2000 South County Trail, East Greenwich, RI 02818 Tel: (401)885-3600 Fax: (401)885-5786 Email: [email protected] Web Site: www.cherry-semi.com 1 A ® Company 1 page VIN VOUT (5V) CO 10µF Test Circuit TIP42B RIN 220Ω CIN 0.022µF RBIAS 560Ω ROUT 220Ω CDelay 0.022µF RRST 4.7 kΩ VIN VOUT Sense Delay Pwr Gnd CS8128 SHUTDOWN RESET Ref Gnd Gnd RESET Application Information Overvoltage Shutdown The CS8128 includes an over voltage shutdown circuit which is activated by connecting the SHUTDOWN lead to the input. Shutdown typically occurs at 36V. Grounding the SHUTDOWN lead disables this function. With the overvoltage shutdown disabled, the CS8128 will continue to regulate during an overvoltage condition. Thermal Shutdown The CS8128 includes a thermal shutdown circuit that dis- ables the output when junction temperature exceeds approximately 180˚C. This is a self-protection feature designed to protect the CS8128. The thermal shutdown cir- cuit does not monitor the temperature of the pass transis- tor, which will probably be much hotter. To optimize ther- mal shutdown, board design should minimize the differ- ence in temperature of the CS8128 and the pass device. “leaking”. It also speeds the turn-off of the pass device during an overvoltage transient. For proper operation over temperature, the recommended value is 560Ω, although it may be increased or decreased for a particular application. ROUT Resistor - This resistor controls the drive current available to the pass transistor. It also determines regula- tor start-up current and short circuit current limit. For bipolar pass transistors, it can be selected by use of the fol- lowing formulae: ROUT = VIN(min) – 1V IOUT(max) x ßQ1* *βQ1 = Pass transistor minimum β @ maximum output current. Typical start-up current and current limit can be calculat- ed as follows: ISTART ≈ 4V ROUT + 5mA External Component Selection External Pass Device - Select a pass device that will deliv- er the desired output current, withstand the maximum expected input voltage, and dissipate the resulting power. The CS8128 is compatible with a wide variety of Bipolar and FET pass transistors. Output Capacitor - An output capacitor is required for sta- bility in most applications. Though a 10µF capacitor should be sufficient, regulator stability is dependent on the characteristics of the pass transistor. Capacitor effective series resistance (ESR) also factors in system stability. Some bench work may be required to determine the capacitor characteristics required for use in a particular application. BIAS Resistor - This resistor provides bias current for the CS8128 output stage, and prevents the pass device from ILimit ≈ VIN – 1V ROUT x ßQ1 @ Current Limit For example, if the minimum input voltage is 6V, maxi- mum output current is 1Amp, and minimum transistor β @ 1Amp is 60, then ROUT can be calculated as follows: ROUT ≈ 6V – 1V 1Amp x 60 = 300Ω IStart ≈ 4V + 5mA = 18.3mA 300Ω With VIN = 14V, and a pass transistor β of 40 @ current limit: ILimit ≈ 14V – 1V 300Ω x 40 = 1.7Amps 5 5 Page

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