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| www.fairchildsemi.com RC2951 Adjustable Micropower Voltage Regulator Features * * * * * * * * * * * * High accuracy output voltage Guaranteed 100 mA output current Extremely low quiescent current Extremely tight load and line regulation Requires only a 1.0F output capacitor for stability Internal Current and Thermal Limiting Error flag warns of output dropout Logic-controlled electronic shutdown Output programmable from 1.24 to 29V Fixed 3.3V version available -25C to +85C operating range 8 lead SOIC package Description The RC2951 is a voltage regulator specifically designed to maintain proper regulation with a very low dropout voltage (Typ. 40mV at light loads and 380 mV at 100mA). It has a low quiescent bias current of 75A and is capable of supplying output currents in excess of 100mA. It has internal current and thermal limiting protection. The output can be programmed from 1.24V to 29V with two external resistors. A fixed output voltage (3.3V) is also available. The error flag output can be used as power-on reset for warning of a low output voltage. The Shutdown input feature allows a logic level signal to turn on and off the regulator output. The RC2951 is ideally suited for battery powered computer, consumer, and industrial equipment where an extension of useful battery life is desirable. The RC2951 is available in an 8-pin SOIC package. Block Diagram Unregulated DC 7 + FeedBack 8 Input 1 Output 2 + - From CMOS or TTL 3 Shut Down + + 60 mV + 1.23V Reference - Error 4 Ground Error Detection Comparator To CMOS or TTL Error Amplifier 6 VTAP 5 330k + See Application Discussion Sense VOUT IL 100 mA PRELIMINARY INFORMATION describes products that are not in full production at the time of printing. Specifications are based on design goals REV. 1.0.1 4/8/02 and limited characterization. They may change without notice. Contact Raytheon for current information. RC2951 PRODUCT SPECIFICATION Pin Assignments 8 Lead SOIC Package Output Sense Shutdown Ground 1 2 3 4 8 7 6 5 Input Feedback VTAP Error Top View Absolute Maximum Ratings Power Dissipation Lead Temp. (Soldering, 5 seconds) Storage Temperature Range Operating Junction Temperature Range Input Supply/Voltage Feedback Input Voltage2,3 Shutdown Input Voltage2 Error Comparator Output Voltage2 1 Internally Limited 260C -65 to +150C -55 to +150C -0.3 to +30V -1.5 to +30V -0.3 to +30V -0.3 to +30V Notes: 1. Junction to ambient thermal resistance for the S.O. (M) package is 160C/W. 2 May exceed input supply voltage. 3. When used in dual-supply systems where the output terminal sees loads returned to a negative supply, the output voltage should be diode-clamped to ground. Electrical Characteristics The * denotes that the limits apply at temperature extremes. Parameter Output Voltage (RC2951M) Conditions1 TJ = 25C -25C TJ 85C Output Voltage (RC2951M) Output Voltage (RC2951M-3.3) 100A IL 100mA TJ TJMAX TJ = 25C -25C TJ 85C Output Voltage (RC2951M-3.3) Output Voltage Temperature Coefficient7 Line Regulation9, 10 Load Regulation9 (VONOM + 1)V Vin 20V 100 A IL 100 mA 100A IL 100mA TJ TJMAX * * * * * * * * * Typ. 5.0 5.0 5.0 3.3 3.3 3.3 20 0.03 0.08 Tested Limit2 5.025 4.975 5.06 4.94 5.075 4.925 3.317 3.284 3.340 3.260 3.346 3.254 120 0.1 0.5 0.2 0.4 Units V max V min V max V min V max V min V max V min V max V min V max V min ppm/C % max % max % max % max * * 2 REV. 1.0.1 4/8/02 PRODUCT SPECIFICATION RC2951 Electrical Characteristics (continued) The * denotes that the limits apply at temperature extremes. Parameter Dropout Voltage3 Conditions1 IL = 100 A IL = 100 mA Ground Current IL = 100 A IL = 100 mA Dropout Ground Current Current Limit Thermal Regulation8 Output Noise, 10 Hz to 100 KHz CL = 1 F (5V Only) CL = 200 F CL = 3.3 F (Bypass = 0.01 F Pins 7 to 1 (RC2951) * * Reference Voltage 5 Typ. * * * * * * 50 380 75 8 110 160 0.05 430 160 100 Tested Limit2 80 150 500 700 120 140 14 15 250 300 200 220 0.2 Units mV max mV max mV max mV max A max A max mA max mA max A max A max mA max mA max %/W max V rms V rms V rms Vin = (VONOM - 0.5)V IL = 100 A Vout = 0 Reference Voltage 1.235 1.25 1.26 1.22 1.2 1.27 1.19 V max V max V min V min V max V min nA max nA max ppm/C nA/C * * * 20 20 0.1 Feedback Pin Bias Current Reference Voltage Temperature Coefficient7 Feedback Pin Bias Current Temperature Coefficient Error Comparator Output Leakage Current Output Low Voltage Upper Threshold Voltage4 Lower Threshold Voltage4 Hysteresis4 VOH = 30V Vin = (VONOM - 0.5)V IOL = 400 A 40 60 * * * * 0.01 150 60 75 15 1 2 250 400 40 25 95 140 A max A max mV max mV max mV min mV min mV max mV max mV REV. 1.0.1 4/8/02 3 RC2951 PRODUCT SPECIFICATION Electrical Characteristics (continued) The * denotes that the limits apply at temperature extremes. Parameter Shutdown Input Input Logic Voltage Low (Regulator ON) High (Regulator OFF) Shutdown Pin Input Current Vshutdown = 2.4V Vshutdown = 30V Regulator Output Current in Shutdown6 * * * * * 1.3 0.6 2.0 30 450 3 50 100 600 750 10 20 V V max V min A max A max A max A max A max A max Conditions1 Typ. Tested Limit2 Units Notes: 1. Unless otherwise specified all limits guaranteed for TJ = 25C, Vin = (VONOM + 1)V, IL = 100A and CL = 1 F for 5V versions, and 2.2 F for 3V and 3.3V versions. Additional conditions for the 8-pin versions are Feedback tied to VTAP, Output tied to Output Sense and Vshutdown < 0.8V. 2. Guaranteed and 100% production tested. 3. Dropout Voltage is defined as the input to output differential at which the output voltage drops 100 mV below its nominal value measured at 1V differential. At very low values of programmed output voltage, the minimum input supply voltage of 2V (2.3V over temperature) must be taken into account. 4. Comparator thresholds are expressed in terms of a voltage differential at the Feedback terminal below the nominal reference voltage measured at Vin = (VONOM + 1)V. To express these thresholds in terms of output voltage change, multiply by the error amplifier gain = Vout/Vref = (R1 + R2)/R2. For example, at a programmed output voltage of 5V, the Error output is guaranteed to go low when the output drops by 95 mV x 5V/1.235V = 384 mV. Thresholds remain constant as a percent of Vout as Vout is varied, with the dropout warning occurring at typically 5% below nominal, 7.5% guaranteed. 5. Vref < Vout (Vin - 1V), 2.3V Vin 30V, 100A IL 100 mA, TJ TJMAX. 6. Vshutdown 2V, Vin 30V, Vout = 0, Feedback pin tied to VTAP. 7. Output or reference voltage temperature coefficient is defined as the worst case voltage change divided by the total temperature range. 8. Thermal regulation is defined as the change in output voltage at a time T after a change in power dissipation is applied, excluding load or line regulation effects. Specifications are for a 50 mA load pulse at VIN = 30V (1.25W pulse) for T = 10 ms. 9. Regulation is measured at constant junction temperature, using pulse testing with a low duty cycle. Changes in output voltage due to heating effects are covered under the specification for thermal regulation. 10. Line regulation for the RC2951 is tested at 150C for IL = 1 mA. For IL = 100 A and TJ = 125C, line regulation is guaranteed by design to 0.2%. See Typical Performance Characteristics for line regulation versus temperature and load current. 4 REV. 1.0.1 4/8/02 PRODUCT SPECIFICATION RC2951 Applications Discussion The RC2951 regulator is designed with internal current limiting and thermal shutdown. It is not internally compensated and requires a 1.0F (or greater) capacitor between the output terminal and ground for stability. At lower output voltages, more capacitance is required (2.2F or more is recommended for 3V and 3.3V versions) for stability. Most types of aluminum, tantalum or multilayer ceramic capacitors will perform adequately. Solid tantalums or appropriate multilayer ceramic capacitors are suggested for operation below 25C. At lower values of output current, less capacitance is needed to maintain stability at output. The capacitor at the output can be reduced to 0.33F for currents less that 10mA, or 0.1F for currents below 1.0mA. Using the adjustable versions at voltages below 5V runs the error amplifier at lower gains so that more output capacitance is needed. For the worst-case situation of a 100 mA load at 1.23V output (Output shorted to Feedback) a 3.3 F (or greater) capacitor should be used. When setting the output voltage of the RC2951 versions with external resistors, a minimum load of 1 A is recommended. A 1 F tantalum or aluminum electrolytic capacitor should be placed from the RC2951 input to ground if there is more than 10 inches of wire between the input and the AC filter capacitor or if a battery is used as the input. Stray capacitance to the RC2951 Feedback terminal can cause instability. This may especially be a problem when using high value external resistors to set the output voltage. Adding a 100 pF capacitor between Output and Feedback and increasing the output capacitor to at least 3.3 F will fix this problem. Figure 1 is a timing diagram showing the ERROR signal and the regulated output voltage as the RC2951 input is ramped up and down. For 5V versions, the ERROR signal becomes valid (low) at about 1.3V input. It goes high at about 5V input (the input voltage at which VOUT = 4.75.) Since the RC2951's dropout voltage is load-dependent (see curve in typical performance characteristics), the input voltage trip point (about 5V) will vary with the load current. The output voltage trip point (approx. 4.75V) does not vary with load. 4.75V Output Voltage Error* Input Voltage 1.3V 5V 2950-10 Figure 1. ERROR Output Timing The error comparator has an open-collector output which requires an external pullup resistor. This resistor may be returned to the output or some other supply voltage depending on system requirements. In determining a value for this resistor, note that while the output is rated to sink 400 A, this sink current adds to battery drain in a low battery condition. Suggested values range from 100k to 1M. The resistor is not required if this output is unused. Programming the Output Voltage (RC2951) The RC2951 may be pin-strapped for the nominal fixed output voltage using its internal voltage divider by tying the output and sense pins together, and also tying the feedback and VTAP pins together. Alternatively, it may be programmed for any output voltage between its 1.235V reference and its 30V maximum rating. As seen in Figure 2 an external pair of resistors is required. Error Detection Comparator Output The comparator switches to a logic low whenever the RC2951 output falls out of regulation by more than approximately 5%. This value is the comparator's built-in offset of about 60 mV divided by the 1.235 internal reference voltage. This trip level remains "5% below normal" regardless of the value of the output voltage. For example, the error flag trip level is typically 4.75V for a 5V output or 11.4V for a 12V output. The out of regulation condition may be due either to low input voltage, current limiting, or thermal limiting. REV. 1.0.1 4/8/02 5 RC2951 PRODUCT SPECIFICATION . +VIN 100K Error Output 5 8 +VIN VOUT 1 ERROR VOUT 1.2 30V RC2951 **Shutdown 3 SD Input GND 4 R1 FB 7 1.23V R2 2950-11 + .01 F + 3.3F R1 V OUT = V REF 1 + ----- R 2 VREF ** Drive with TTL-high to shut down. Ground or leave open if shutdown feature is not to be used. Figure 2. Adjustable Regulator The complete equation for the output voltage is V OUT R1 = V REF * 1 + ----- + I FB R 1 R 2 Reducing Output Noise In reference applications it may be advantageous to reduce the AC noise present at the output. One method is to reduce the regulator bandwidth by increasing the size of the output capacitor. Noise can be reduced fourfold by a bypass capacitor across R1, since it reduces the high frequency gain from 4 to unity. Pick 1 C BYPASS ----------------------------------2R 1 * 200Hz or about 0.01 F. When doing this, the output capacitor must be increased to 3.3 F to maintain stability. These changes reduce the output noise from 430 V to 100 V rms for a 100 kHz bandwidth at 5V output. With the bypass capacitor added, noise no longer scales with output voltage so that improvements are more dramatic at higher output voltages. V REF V OUT ------------- = -----------------R2 R1 + R2 V OUT R1 + R2 = V REF ------------------ R2 R1 = V REF 1 + ----- R 2 V OUT Adding the error term, R1 V OUT = V REF 1 + ----- + I FB R 2 R 2 where VREF is the nominal 1.235 reference voltage and IFB is the feedback pin bias current, nominally -20 nA. The minimum recommended load current of 1 A forces an upper limit of 1.2 M on the value of R2, if the regulator must work with no load (a condition often found in CMOS in standby). IFB will produce a 2% typical error in VOUT which may be eliminated at room temperature by trimming R1. For better accuracy, choosing R2 = 100k reduces this error to 0.17% while increasing the resistor program current to 12 A. Since the RC2951 typically draws 60 A at no load with Pin 2 open-circuited, this is a small price to pay. 6 REV. 1.0.1 4/8/02 PRODUCT SPECIFICATION RC2951 Typical Applications Unregulated Input 1F 10k 8 6 IN VTAP SENSE RC2951 7 FB GND 4 OUT 1 2k 0.002F IQ 400A 2 + 0.01F Supertex VP12C Output 5V1%@ 0 to 1A 220F 1M Figure 3. 1A Regulator with 1.2V Dropout Unregulated Input 8 IN RC2951 6 VTAP FB 7 SENSE GND 4 2 + 4.7F 5V Output Load 50mA to 300mA OUT 1 330 27k 2N5432 (2) Error Output 5 +VIN 8 +VIN ERROR VOUT 1 *VOUTVIN RC2951 **Shutdown 3 SD Input GND 4 FB 4 Figure 4. 300 mA Regulator with 0.75 Dropout *Minimum input-output voltage ranges from 40 mV to 400 mV, depending on load current. Current limit is typically 160 mA. +V = 2 30V Figure 5. Wide Input Voltage Range Current Limiter 1.23 R IL Load IL= 8 VIN VOUT RC2951 Shutdown 3 SD Input GND 4 R 1% FB 7 1 F + 0.1F 1 2950-12 Figure 6. Low Drift Current Source REV. 1.0.1 4/8/02 7 RC2951 PRODUCT SPECIFICATION Typical Applications (continued) +VIN 8 +VIN 6 VTAP 2 SENSE VOUT 1 D2 5V Memory Supply 20 + 1F 3.6V Nicad 2N3906 4.7M 8 +VIN ERROR 27k 3 2.7M D3 D4 EARLY WARNING 220 20k Q1 8 +VIN 6 7 3 VTAP 2 SENSE VOUT 1 RESET 330k Main 5V Output D1 Current Limit Section +VIN = VOUT +5.0V 0.05 680 RC2951 #1 5 FB ERROR 7 GND 4 470 MJE2955 10k 5 Error Flag R1 + FB VOUT 1 47 4 .033 7 1% R2 4.7 TANT. + 100 F +VOUT @ 2A RC2951 SD GND P VDD VOUT = 1.23V 1 + FB RC2951 #2 5 SD ERROR GND 4 R1 R2 For 5VOUT,use internal resistors. Wire pin 6 to 7, & wire pin 2 +VOUT Buss. ( ) + 1F Figure 9. 2 Ampere Low Dropout Regulator +VIN C-MOS GATE *Sleep Input * Early warning flag on low input voltage * Main output latches of f at lower input voltages * Battery backup on auxillary output Operation Reg. #1's VOUT is programmed one diode drop above 5V. Its error flag becomes active when Vin 5.7V. WhenVin drops below 5.3V, the error flag of Reg. #2 becomes active and via Q1 latches the main output off. When Vin again exceeds 5.7V Reg. #1 is back in regulation and the early warning signal rises unlatching Reg. #2 via D3. Error Output 47k 8 +VIN 5 ERROR VOUT 470k 1 100 pF 2N3906 FB 7 +VOUT RC2951 Shutdown 3 SD Input GND 4 200k + 3.3F 1% 100k 1% 100k Figure 7. Regulator with Early Warning and Auxillary Output +VIN *High input lowers VOUT to 2.5V. 8 470k 5 470k RC2951 3 Reset SD GND 4 1N 4001 FB 7 R2 R1 + 1F 4 20mA 8 VIN VOUT RC2951 FB 0.1F GND 4 1N457 360 7 2 4 * High for IL < 3.5mA 1 1 +VIN ERROR 1 VOUT +5V 4.7k Output* 5 VOUT Figure 10. 5V Regulator with 2.5V Sleep Function Figure 8. Latch Off When Error Flag Occurs Min. Voltages 4V 2950-13 Figure 11. Open Circuit Detector for 4mA to 20mA Current Loop 8 REV. 1.0.1 4/8/02 PRODUCT SPECIFICATION RC2951 Typical Applications (continued) 8 39k RESET 5 +VIN 2 SENSE VOUT 1 +VOUT = 5V + 1F FB VTAP 6 7 ERROR RC2951 - *C4 + 3 SD GND 39k 4 + 6V Lead-Acid Battery 1% 100 k - C1 + 100k < 5.8V** 100k < 6.0V** 1% 1k - C2 + C1-C4 LP339 1% 1k - C3 + 100k < 6.2V** 10k R3 1% 20k *Optional Latch off when drop out occurs. Adjust R3 for C2 Switching when Vin is 6.0V. **Outputs go low whenVin drops below designated thresholds. Figure 12. Regulator with State-of-Charge Indicator For values shown, Regulator shuts down when Vin < 5.5V and turns on again at 6.0V. Current drain in disconnected mode is 150 A. + 6V Sealed Lead-Acid Battery Source 120k 1.5k** 8 +VIN 1 VOUT RC2951 3 SENSE SD GND 4 FB VTAP 6 1F 2 7 20 + + Ni-cad Backup Battery Memory V+ Main V+ + FB LM385 - 1N457 400k* for 5.5V 100k *Sets disconnect Voltage **Sets disconnect Hysteresis 2950-14 Figure 13. Low Battery Disconnect REV. 1.0.1 4/8/02 9 RC2951 PRODUCT SPECIFICATION Mechanical Dimensions - 8 Lead SOIC Symbol A A1 B C D E e H h L N ccc Inches Min. Max. Millimeters Min. Max. Notes: Notes 1. Dimensioning and tolerancing per ANSI Y14.5M-1982. 2. "D" and "E" do not include mold flash. Mold flash or protrusions shall not exceed .010 inch (0.25mm). 3. "L" is the length of terminal for soldering to a substrate. 4. Terminal numbers are shown for reference only. 5 2 2 5. "C" dimension does not include solder finish thickness. 6. Symbol "N" is the maximum number of terminals. .053 .069 .004 .010 .013 .020 .008 .010 .189 .197 .150 .158 .050 BSC .228 .010 .016 8 0 -- 8 .004 .244 .020 .050 1.35 1.75 0.10 0.25 0.33 0.51 0.20 0.25 4.80 5.00 3.81 4.01 1.27 BSC 5.79 0.25 0.40 8 0 -- 8 0.10 6.20 0.50 1.27 3 6 8 5 E H 1 4 D A1 A SEATING PLANE B -C- LEAD COPLANARITY ccc C h x 45 C e L 10 REV. 1.0.1 4/8/02 RC2951 PRODUCT SPECIFICATION Ordering Information Product Number RC2951MT RC2951M33 Package 8-pin SOIC in tape and reel 8-pin SOIC DISCLAIMER FAIRCHILD SEMICONDUCTOR RESERVES THE RIGHT TO MAKE CHANGES WITHOUT FURTHER NOTICE TO ANY PRODUCTS HEREIN TO IMPROVE RELIABILITY, FUNCTION OR DESIGN. FAIRCHILD DOES NOT ASSUME ANY LIABILITY ARISING OUT OF THE APPLICATION OR USE OF ANY PRODUCT OR CIRCUIT DESCRIBED HEREIN; NEITHER DOES IT CONVEY ANY LICENSE UNDER ITS PATENT RIGHTS, NOR THE RIGHTS OF OTHERS. LIFE SUPPORT POLICY FAIRCHILD'S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT OF FAIRCHILD SEMICONDUCTOR CORPORATION. As used herein: 1. Life support devices or systems are devices or systems which, (a) are intended for surgical implant into the body, or (b) support or sustain life, and (c) whose failure to perform when properly used in accordance with instructions for use provided in the labeling, can be reasonably expected to result in a significant injury of the user. www.fairchildsemi.com 4/8/02 0.0m 001 Stock#DS30002951 2001 Fairchild Semiconductor Corporation 2. A critical component in any component of a life support device or system whose failure to perform can be reasonably expected to cause the failure of the life support device or system, or to affect its safety or effectiveness. |
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