CS5208-1GT3

CS5208-1 CS5208-1 8A LDO 3-Pin Adjustable Linear Regulator Description The CS5208-1 linear regulator provides 8A at adjustable voltages from 1.25V to 4.5V. This adjustable device requires two external resistors to set the output voltage and provide the minimum load current for proper regulation. This regulator is intended for use as a post regulator and microprocessor supply. The fast loop response and low dropout voltage make this regulator ideal for applications where low voltage operation and good transient response are important. The circuit is designed to operate with dropout voltages as low as 1.0V at 8A. The regulator is protected against overload conditions with overcurrent and thermal shutdown protection circuitry. The regulator is available in a TO-220 package. Features s 1.25V to 4.5V VOUT at 8A s Dropout Voltage < 1.0V @ 8A s 1.5% Trimmed Reference s Fast Transient Response s Thermal Shutdown s Current Limit s Short Circuit Protection Package Options Applications Diagram 3 Lead TO-220 5.0V VIN VOUT 3.3V @ 8A CS5208-1 Adj 124 100mF 0.1mF 200 Load 300mF 1 1. Adjust 2. VOUT 3. VIN Tab = VOUT Cherry Semiconductor Corporation 2000 South County Trail, East Greenwich, RI 02818 Tel: (401)885-3600 Fax: (401)885-5786 Email: info@cherry-semi.com Web Site: www.cherry-semi.com Rev. 6/11/97 1 A ¨ Company CS5208-1 Absolute Maximum Ratings Input Voltage ...............................................................................................................................................................................6V Operating Junction Temperature Range ..........................................................................................................0¡C ² TJ ² 150¡C Storage Temperature Range ...............................................................................................................................-65¡C to +150¡C Lead Temperature Soldering: Wave Solder (through hole styles only).........................................10 sec. max, 260¡C peak ESD Damage Threshold ...........................................................................................................................................................2kV Electrical Characteristics: 0¡C²TA ² 70¡C, 0¡C²TJ ² 150¡C, VAdj = 0V unless otherwise specified. PARAMETER TEST CONDITIONS MIN TYP MAX UNIT Reference Voltage Line Regulation Load Regulation Minimum Load Current (Note 1) Adjust Pin Current Current Limit Short Circuit Current Ripple Rejection (Note 2) Thermal Regulation (Note 2) Dropout Voltage (Minimum VIN -VOUT) (Note 3) VIN=2.75V to 5.5V, IOUT=10mA to 8A VIN=2.75V to 5.5V, IOUT=10mA VIN=2.75V,IOUT=10mA to 8A VIN=5V, ÆVOUT= +1.5% VIN=2.75V,IOUT=10mA VIN=2.75V,ÆVOUT= -1.5% VIN=2.75V,VOUT=0V VIN=3.25V Avg, VRipple=1VP-P@120Hz, IOUT=4A,CAdj=0.1µF; COUT = 22µF 30ms Pulse, TA=25¡C IOUT=100mA IOUT=1A IOUT=2.75A IOUT=4A IOUT=8A Freq=10Hz to 10kHz, TA=25¡C 1.234 (-1.5%) 1.253 .02 .04 5 70 9.0 8.5 80 1.271 (+1.5%) .20 .50 10 120 V % % mA µA A A dB 8.1 6.0 60 0.002 0.92 0.93 0.94 0.95 0.96 0.003 0.5 180 25 1.15 1.15 1.15 1.15 1.30 %/W V V V V V %VOUT % ¡C ¡C RMS Output Noise Temperature Stability Thermal Shutdown (Note 4) Thermal Shutdown Hysteresis (Note 4) Note 1: Note 2: Note 3: Note 4: 150 210 The minimum load current is the minimum current required to maintain regulation. Normally the current in the resistor divider used to set the output voltage is selected to meet the minimum load current requirement. This parameter is guaranteed by design and is not 100% production tested. Dropout voltage is defined as the minimum input/output voltage differential required to maintain 1.5% regulation. This parameter is guaranteed by design, but not parametrically tested in production. However, a 100% thermal shutdown functional test is performed on each part. Package Pin Description PACKAGE PIN # PIN SYMBOL FUNCTION 3L TO-220 1 Adjust This pin is connected to the low side of the internally trimmed 1.5% bandgap reference voltage and carries a bias current of about 70µA. A resistor divider from Adj to VOUT and from Adj to ground sets the output voltage. Also, transient response can be improved by adding a small bypass capacitor from this pin to ground. This pin is connected to the emitter of the power pass transistor and provides a regulated voltage capable of sourcing 8A of current. This is the supply voltage for the regulator . For the device to regulate, this voltage should be between 1.1V and 1.30V (depending on the output current) greater than the output voltage. 2 2 3 VOUT VIN CS5208-1 Block Diagram VIN BIAS and TSD VREF EA + - + IA - VOUT Adj Typical Performance Characteristics 0.100 0.075 0.050 IO=10mA VIN=2.75V 0.250 0.225 Output Voltage Deviation (%) 0.200 0.175 0.150 0.125 0.100 0.075 0.050 0.025 0.000 0.00 1.00 2.00 3.00 4.00 TCase=125°C Output Voltage Deviation (%) 0.025 -0.000 -0.025 -0.050 -0.075 -0.100 -0.125 -0.150 0 10 20 30 40 50 60 70 80 90 100 110 120 130 TCase =25°C TCase=0°C 5.00 6.00 7.00 8.00 TJ (°C) Output Current (A) Reference Voltage vs. Temperature Load Regulation vs. Output Current 90.00 IO=10mA 85.00 Adjust Pin Current (mA) 72.6 72.4 72.2 72.0 71.8 71.6 71.4 71.2 71.0 70.8 70.6 70.4 70.2 70.0 0 10 20 30 40 50 60 70 80 90 100 110 120 130 0.0 0.8 1.6 2.4 3.2 4.0 IOUT (A) 4.8 5.6 6.4 7.2 8.0 Adjust Pin Current (mA) 80.00 75.00 70.00 65.00 60.00 TCase (°C) Adjust Pin Current vs Temperature Adjust Pin Current vs. IOUT 3 CS5208-1 Typical Performance Characteristics: continued 1.25 20.0 18.0 1.00 16.0 Output Current (A) 0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 Dropout Voltage (V) 14.0 12.0 10.0 8.0 6.0 4.0 2.0 0.75 0.50 0.25 0.00 0.0 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 Output Current (A) VIN-VOUT (V) Dropout Voltage vs. Output Current Short Circuit Current vs. VIN - VOUT 1.00 0.98 Minimum Load Current (mA) 0.96 90.0 80.0 70.0 0.94 Ripple Rejection (dB) 0.92 0.90 0.88 0.86 0.84 0.82 0.80 1.00 2.00 3.00 VIN – VOUT (V) TCASE = 0°C TCASE = 23°C TCASE = 125°C 60.0 50.0 40.0 30.0 20.0 10.0 VIN - VOUT = 2V VRipple = 1VPP IOUT = 4A CAdj = 0.1mF COUT = 22mF 4.00 5.00 10 1 10 2 10 3 10 4 10 5 10 6 Frequency (Hz) Minimum Load Current vs. VIN - VOUT Ripple Rejection vs. Frequency Application Notes Theory of Operation output voltage is set according to the formula: VOUT = VREF ´ R1 + R2 + R2 ´ IAdj R1 The CS5208-1 linear regulator has a composite PNP-NPN output stage that requires an output capacitor for stability. A detailed procedure for selecting this capacitor is included in the Stability Considerations section. Adjustable Operation Design Guidelines This LDO adjustable regulator has an output voltage range of 1.25V to 4.5V. An external resistor divider sets the output voltage as shown in Figure 1. The regulatorÕs voltage sensing error amplifier maintains a fixed 1.25V reference between the output pin and the adjust pin. A resistor divider network R1 and R2 causes a fixed current to flow to ground. This current creates a voltage across R2 that adds to the 1.25V across R1 and sets the overall output voltage. The adjust pin current (typically 50µA) also flows through R2 and adds a small error that should be taken into account if precise adjustment of Vout is necessary. The 4 The term IAdj ´ R2 represents the error added by the adjust pin current. R1 is chosen so that the minimum load current is a least 10mA. R1 and R2 should be of the same composition for best tracking over temperature. The divider resistors should be placed as close to the IC as possible and connected to the output with a separate metal trace. CS5208-1 Application Notes: continued EXTERNAL SUPPLY VIN VOUT CS5208-1 Adj VIN R1 R2 VOUT VAdj Figure 1. While not required, a bypass capacitor connected between the adjust pin and ground will improve transient response and ripple rejection. A 0.1µF tantalum capacitor is recommended for Òfirst cutÓ design. Value and type may be varied to optimize performance vs price. Other Adjustable Operation Considerations Figure 2. Stability Considerations The output compensation capacitor helps determine three main characteristics of a linear regulator: start-up delay, load transient response, and loop stability. The capacitor value and type is based on cost, availability, size and temperature constraints. A tantalum or aluminum electrolytic capacitor is best, since a film or ceramic capacitor with almost zero ESR can cause instability. The aluminum electrolytic capacitor is the least expensive solution. However, when the circuit operates at low temperatures, both the value and ESR of the capacitor will vary considerably. The capacitor manufacturerÕs data sheet provides this information. A 300µF tantalum capacitor will work for most applications, but with high current regulators such as the CS5208-1 the transient response and stability improve with higher values of capacitance. The majority of applications for this regulator involve large changes in load current so the output capacitor must supply the instantaneous load current. The ESR of the output capacitor causes an immediate drop in output voltage given by: ÆV = ÆI ´ ESR. For microprocessor applications it is customary to use an output capacitor network consisting of several tantalum and ceramic capacitors in parallel. This reduces the overall ESR and reduces the instantaneous output voltage drop under transient load conditions. The output capacitor network should be as close to the load as possible for the best results. Protection Diodes When large external capacitors are used with a linear regulator it is sometimes necessary to add protection diodes. If the input voltage of the regulator gets shorted, the output capacitor will discharge into the output of the regulator. The discharge current depends on the value of the capacitor, the output voltage, and the rate at which VIN drops. In the CS5208-1 regulator, the discharge path is through a large junction and protection diodes are not usually needed. If the regulator is used with large values of output capacitance and the input voltage is instantaneously short5 The CS5208-1 linear regulator has an absolute maximum specification of 6V for the voltage difference between VIN and VOUT. However, the IC may be used to regulate voltages in excess of 6V. The main considerations in such a design are power-up and short circuit capability. In most applications, ramp-up of the power supply to VIN is fairly slow, typically on the order of several tens of milliseconds, while the regulator responds in less than one microsecond. In this case, the linear regulator begins charging the output capacitor as soon as the VIN to VOUT differential is large enough that the pass transistor conducts current. VOUT is essentially at ground, and VIN is on the order of several hundred millivolts, so the pass transistor is in dropout. As VIN increases, the pass transistor will remain in dropout, and current is passed to the load until VOUT is in regulation. Further increase in VIN brings the pass transistor out of dropout. The result is that the output voltage follows the power supply ramp-up, staying in dropout until the regulation point is reached. In this manner, any output voltage may be regulated. There is no theoretical limit to the regulated voltage as long as the VIN to VOUT differential of 6V is not exceeded. However, the maximum ratings of the IC will be exceeded in a short circuit condition. Short circuit conditions will result in the immediate operation of the pass transistor outside of its safe operating area. Over-voltage stresses will then cause destruction of the pass transistor before overcurrent or thermal shutdown circuitry can become active. Additional circuitry may be required to clamp VIN to VOUT differential to less than 6V if failsafe operation is required. One possible clamp circuit is illustrated below; however, the design of clamp circuitry must be done on an application by application basis. Care must be taken to ensure the clamp actually protects the design. Components used in the clamp design must be able to withstand the short circuit conditions indefinitely while protecting the IC. CS5208-1 Application Notes: continued ed to ground, damage can occur. In this case, a diode connected as shown in Figure 3 is recommended. A rule of thumb useful in determining if a protection diode is required is to solve for current I= C´V , where T Calculating Power Dissipation and Heat Sink Requirements High power regulators such as the CS5208-1 usually operate at high junction temperatures. Therefore, it is important to calculate the power dissipation and junction temperatures accurately to ensure that an adequate heat sink is used. Since the package tab is connected to Vout on the CS5208-1, electrical isolation may be required for some applications. Also, as with all high power packages, thermal compound in necessary to ensure proper heat flow. For added safety, this high current LDO includes an internal thermal shutdown circuit The thermal characteristics of an IC depend on the following four factors. Junction temperature, ambient temperature, die power dissipation, and the thermal resistance from the die junction to ambient air. The maximum junction temperature can be determined by: TJ(max) = TA(max) + PD(max) ´ RQJA The maximum ambient temperature and the power dissipation are determined by the design while the maximum junction temperature and the thermal resistance depend on the manufacturer and the package type. The maximum power dissipation for a regulator is: PD(max) = (VIN(max) -VOUT(min))IOUT(max) + VIN(max) ´ IIN(max) A heat sink effectively increases the surface area of the package to improve the flow of heat away from the IC and into the surrounding air. Each material in the heat flow path between the IC and the outside environment has a thermal resistance which is measured in degrees per watt. Like series electrical resistances, these thermal resistances are summed to determine the total thermal resistance between the die junction and the surrounding air, RQJA. This total thermal resistance is comprised of three components. These resistive terms are measured from junction to case (RQJC), case to heat sink (RQCS), and heat sink to ambient air (RQSA ). The equation is: RQJA = RQJC + RQCS + RQSA RQJC is rated @ 1.4¡C/W for the CS5208-1. For a high current regulator such as the CS5208-1 the majority of heat is generated in the power transistor section. The value for RQSA depends on the heat sink type, while the RQCS depends on factors such as package type, heat sink interface (is an insulator and thermal grease used?), and the contact area between the heat sink and the package. Once these calculations are complete, the maximum permissible value of RQJA can be calculated and the proper heat sink selected. For further discussion on heat sink selection, see our Cherry application note ÒThermal Management for Linear Regulators.Ó I is the current flow out of the load capacitance when VIN is shorted, C is the value of the load capacitance, V is the output voltage, and T is the time duration required for VIN to transition from high to being shorted. If the calculated current is greater than or equal to the typical short circuit current value provided in the specifications, serious thought should be given to including a protection diode. VIN VOUT CS5208-1 Adj Figure 3. Current Limit The internal current limit circuit limits the output current under excessive load conditions and protects the regulator. Short Circuit Protection The device includes foldback short circuit current limit that clamps the output current at approximately two amperes less than its current limit value. Thermal Shutdown The thermal shutdown circuitry is guaranteed by design to become activated above a die junction temperature of 150¡C and to shut down the regulator output. This circuitry includes a thermal hysteresis circuit with 25¡C of typical hysteresis, thereby allowing the regulator to recover from a thermal fault automatically. 6 CS5208-1 Package Specification PACKAGE DIMENSIONS IN mm (INCHES) PACKAGE THERMAL DATA Thermal Data RQJC RQJA typ typ 3L TO-220 1.4 50 ûC/W ûC/W 3 Lead TO-220 (T) Straight 10.54 (.415) 9.78 (.385) 2.87 (.113) 2.62 (.103) 3.96 (.156) 3.71 (.146) 4.83 (.190) 4.06 (.160) 1.40 (.055) 1.14 (.045) 6.55 (.258) 5.94 (.234) 14.99 (.590) 14.22 (.560) 1.52 (.060) 1.14 (.045) 14.22 (.560) 13.72 (.540) 1.40 (.055) 1.14 (.045) 6.17 (.243) REF 1.02 (.040) 0.63 (.025) 2.79 (.110) 2.29 (.090) 5.33 (.210) 4.83 (.190) 0.56 (.022) 0.38 (.014) 2.92 (.115) 2.29 (.090) Ordering Information Part Number CS5208-1GT3 Rev. 6/11/97 Description 3L TO-220 Straight 7 Cherry Semiconductor Corporation reserves the right to make changes to the specifications without notice. Please contact Cherry Semiconductor Corporation for the latest available information. © 1999 Cherry Semiconductor Corporation