AS2954 250 mA Low Drop Out Voltage Regulator FEATURES APPLICATIONS • Output Accuracy 5V, 3.3V,@ 250mA Output • Very Low Quiescent Current • Low Dropout Voltage • Extremely Tight Load And Line Regulation • Very Low Temperature Coefficient • Current & Thermal Limiting • Improved Replacement With Hight IOUT For LP2954 Sockets • Battery Powered Systems • Cordless Telephones • Radio Control Systems • Portable/Palm Top/Notebook Computers • Portable Consumer Equipment • Portable Instrumentation • Automotive Electronics • SMPS Post-Regulator • Voltage Reference • Avionics AS2954 Version Over LP2954 • Error Flag Warns Of Output Dropout • Logic-Controlled Electronic Shutdown • Output Programmable From 1.24V to 29V • Input Can Withstand -20V Reverse Battery & +60 Positive Transient PRODUCT DESCRIPTION The AS2954 is a low power voltage regulator. This device is an excellent choice for use in battery-powered applications such as cordless telephones, radio control systems, and portable computers. The AS2954 features very low quiescent current (75µA Typ.) and very low dropout voltage. This includes a tight initial tolerance of ± 0.5% max and ± 1% max., and very low output temperature coefficient, making the AS2954 useful as a low-power voltage reference. The key AS2954 features include protection against reversed battery, fold-back current limiting, and automotive load dump protection (60V positive transient). The error flag output feature is used as power-on reset for warning of a low output voltage, due to falling voltage input of batteries. Another feature is the logic compatible shutdown input which enables the regulator to be switched on and off. The AS2954 is offered in a 3-pin TO-92and TO-263 package compatible with other 5 volt regulators, in 8-Pin plastic, SO-8, (same pin out as AS2951), TO220 and TO-263. The regulator output voltage (of the 8-pin) may be pin-strapped for a 5Vand 3.3V or programmed from 1.24V to 29V with an external pair of resistors. Look for AS2951 for 150mA and LP2951 for 100mA applications. PIN CONNECTIONS TO-263-3 Package 2 VADJ VOUT Top View 8-Pin Surface Mount (S) AS2954 AS2954 1 TO-263-5 Package 3 1 2 3 4 5 1) INPUT 2) 3) 4) 5) VIN OUTPUT OUTPUT 1 SENSE 2 SHUTDOWN 3 GND 4 GND AS2954 SOT-223 Package 7 FEEDBACK 6 5V, 3.3V TAP 5 ERROR ERROR 1 2 2 3 AS2954 1) INPUT 2) OUTPUT GND VOUT 3) GND 4) SHUTDOWN 5) ERROR 1 2 3 VIN GND VOUT 3 Front View OUTPUT AS2954 Front View TO-92 (N) Top View TO-220-5 Package AS2954 1 VIN Top View SHUTDOWN TO-220-3 Package INPUT 8 1 2 3 4 5 Front View INPUT GND Bottom View Rev.9/29/00 AS2954 ORDERING INFORMATION TO-263 3-PIN AS2954YT3-X TO-263 5-PIN AS2954YT5-X TO-92 3 PIN AS2954YN-X TO-220 3 PIN AS2954YU3-X TO-220 5 PIN AS2954YU5-X PLASTIC SOIC 8 PIN AS2954YS-X SOT-223 3 PIN AS2954YM3-X OPER.TEMP. RANGE -40°C to +125°C X= Output Voltage: (3.3 for 3.3V, 5.0 for 5.0V) Y= Output Tolerance (A = 0.5%, Blank = 1%; B = 2%) ABSOLUTE MAXIMUM RATINGS Power Dissipation..........................................Internally Limited Lead Temp. (Soldering, 5 Seconds) ................................ 260°C Storage Temperature Range ............................ -65° to +150°C Operating Junction Temperature Range (Note 9) AS2954 .................................................. -40C° to +125°C Input Supply Voltage .......................................-20V to +60V Feedback Input Voltage .....................................-1.5 to +30V Shutdown Input Voltage.....................................-0.3 to +30V Error Comparator Output ...................................-0.3 to +30V ESD Rating ............................................................ 2KV Min ELECTRICAL CHARACTERISTICS at VS=±15V, TA=25°C, unless otherwise noted. Boldface applies over the full operating temperature range. Parameter 3.3V Version Output Voltage Output Voltage 5V Version Output Voltage Output Voltage Conditions Typical TJ =25°C -25°C ≤ TJ ≤ +85°C -40°C ≤ TJ ≤ +125°C 1mA ≤IL ≤ 250mA TJ ≤TJMAX 3.3 TJ =25°C -25°C ≤ TJ ≤ +85°C -40°C ≤ TJ ≤ +125°C 1mA ≤IL ≤ 250mA TJ ≤TJMAX AS2954A Min Max AS2954 Min Max AS2954B Min Max Units 3.317 3.333 3.340 3.350 3.267 3.251 3.234 3.201 3.333 3.350 3.366 3.399 3.234 3.201 3.194 3.168 3.366 3.399 3.432 3.432 V 3.3 3.284 3.267 3.260 3.251 5.0 5.0 5.0 5.0 4.975 4.95 4.94 4.925 5.025 5.050 5.06 5.075 4.95 4.925 4.90 4.85 5.05 5.075 5.10 5.15 4.90 4.85 4.84 4.80 5.10 5.15 5.20 5.20 V V V All Voltage Options Output Voltage Temperature Coefficient Line Regulation (Note 3) Load Regulation (Note 3) Dropout Voltage (Note 5) Ground Current Current Limit (Note 1) 6V ≤VIN ≤30V (Note 4) 20 100 150 180 ppm/°C 0.03 0.10 0.20 0.16 0.20 100 150 250 420 300 450 450 600 150 180 2 2.5 6 8 14 16 550 600 0.2 0.20 0.40 0.20 0.30 100 150 250 420 300 450 450 600 150 180 2 2.5 6 8 20 22 550 600 0.2 0.40 0.60 0.30 0.40 100 150 250 420 300 450 450 600 150 180 2 2.5 6 8 26 28 550 600 0.2 %max IL = 1 to 250 mA IL = 0.1 to 1 mA IL = 1mA 0.04 IL = 50mA 220 IL= 100mA 250 IL= 250 mA 375 IL = 1mA 90 IL = 50mA 1 IL = 100mA 4.5 IL = 250 mA 21 60 VOUT = 0 Thermal Regulation 0.05 Output Noise, 10Hz to 100khz IL = 100mA 8-Pin Versions only Reference Voltage CL = 2.2µF 400 CL = 33 µF 260 Typical 1.235 Reference Voltage Over Temperature (Note 6) Feedback Pin Bias Current Reference Voltage Temperature Coefficient Feedback Pin Bias Current Temperature Coefficient 20 %max mV µA mA mA %/w µV rms AS2954A 1.220 1.250 1.200 1.260 1.190 1.27 40 60 AS2954 1.210 1.200 1.185 1.260 1.270 1.285 40 60 AS2954B 1.200 1.270 1.190 1.280 1.180 1.295 40 60 V V nA ppm/°C (Note 7) 50 nA/°C 0.1 Rev.9/29/00 AS2954 (Continued) Parameter Conditions (Note 2) Typical AS2954A Min Max AS2954 Min Max AS2954B Min Max Units Applies for AS2954YT5-X, AS2954YU5-X and AS2954YS-X Error Comparator Output Leakage Current VOH = 30V 0.01 Output Low Voltage VIN = 4.5V IOL = 400µA 150 Upper Threshold Voltage (Note 8) 240 Lower Threshold Voltage (Note 8) 350 Hysteresis (Note 8) 60 Shutdown Input VSD 100 2.00 250 400 -320 -380 -450 -640 -320 -380 -450 -640 100 2.00 250 400 -150 -100 230 160 -320 -380 -450 -640 VIN(SD) = 0V to 5V mV -150 -100 230 160 mV mV 1.155 1.140 1.305 1.320 1.155 1.140 1.305 1.320 1.155 1.140 1.305 1.320 -30 -50 -30 -50 -30 -50 -30 -50 -30 -50 -30 -50 6 Input Bias Current(IB) µA mV Output Turn-On Threshold Voltage Hysteresis(HYST) -150 -100 230 160 100 2.00 250 400 10 V mV nA Note 1: Output or reference voltage temperature coefficients defined as the worst case voltage change divided by the total temperature range. Note 2: Unless otherwise specified all limits are guaranteed for TJ = 25°C, VIN = 6V, IL = 100 µA and CL = 1µF. Additional conditions for the 8-pin versions are feedback tied to 5V tap and output tied to output sense (VOUT = 5V) and VSHUTDOWN ≤ 0.8V. Note 3: 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. Note 4: Line regulation for the AS2954 is tested at 150°C for IL = 1 mA. For IL = 100µA and TJ = 125°C, line regulation is guaranteed by design to 0.2%. See typical performance characteristics for line regulation versus temperature and load current. Note 5: 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. Note 6: VREF ≤VOUT ≤ (VIN - 1V), 2.3 ≤VIN≤30V, 100µA≤IL≤ 250 mA, TJ ≤ TJMAX. Note 7: Comparator thresholds are expressed in terms of a voltage differential at the feedback terminal below the nominal reference voltage measured at 6V input. 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/1.235 = 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. Note 8: VSHUTDOWN ≥ 2V, VIN ≤ 30V, VOUT =0, feedback pin tied to 5V Tap. Note 9: The junction -to-ambient thermal resistance of the TO-92 package is 180°C/ W with 0.4” leads and 160°C/ W with 0.25” leads to a PC board. The thermal resistance of the 8-Pin DIP package is 105°C/W junction-to-ambient when soldered directly to a PC board. Junction-to-ambient thermal resistance for the SOIC (S) package is 160°C/W. UNREGULATED DC VO 7 + 1 8 INPUT FEEDBACK 5V @ 250mA MAX OUTPUT 2 SENSE + _ FROM CMOS OR TTL 3 180k Ω .. 6 ERROR AMPLIFIER 330kΩ .. 5V TAP SHUTDOWN 60k Ω .. + 60 mV + _ + 1.23V ERROR COMPARATOR 5 ______ ERROR + 1µF.. TO CMOS OR TTL 4 REFERENCE GROUND AS2954 Block Diagram Rev.9/29/00 AS2954 APPLICATION HINTS EXTERNAL CAPACITORS For the stability of the AS2954 requires a 2.2µF or greater capacitor between output and ground. Oscillation could occur without this capacitor. Most types of tantalum or aluminum electrolytic works fine here. For operations of below -25°C solid tantalum is recommended since the many aluminum types have electrolytes the freeze at about -30°C. The ESR of about 5Ω or less and resonant frequency above 500kHz are the most important parameters in the value of the capacitor. The capacitor value can be increased without limit. At lower values of output current, less output capacitance is required for stability. For the currents below 10mA the value of the capacitor can be reduced to 0.5µF and 0.15µF for 1mA. More output capacitance needed for the 8-pin version at voltages below 5V since it runs the error amplifier at lower gain. At worst case 5µF or greater must be used for the condition of 250mA load at 1.23V output. The AS2954, unlike other low dropout regulators will remain stable and in regulation with no load in addition to the internal voltage divider. This feature is especially important in application like CMOS RAM keep-alive. When setting the output voltage of the AS2954, a minimum load of 1µA is recommended 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 then a 1µA tantalum or aluminum electrolytic capacitor should be placed from the input to the ground. Instability can occur if there is stray capacitance to the AS2954 feedback terminal (pin 7). This could cause more problems when using a higher value of external resistors to set the output voltage. This problem can be fixed by adding a 100pF capacitor between output and feedback and increasing the output capacitor to at least 3.3µF. ERROR DETECTION COMPARATOR OUTPUT The Comparator produces a logic low output whenever the AS2954 output falls out of regulation by more than around 5%. This is around 60mV offset divided by the 1.235 reference voltage. This trip level remains 5% below normal regardless of the programmed output voltage of the regulator. Figure 1 shows the timing diagram depicting the ERROR signal and the regulator output voltage as the AS2954 input is ramped up and down. The ERROR signal becomes low at around 1.3V input, and goes high around 5V input (input voltage at which VOUT = 4.75. Since the AS2954’s dropout voltage is load dependent, the input voltage trip point (around 5V) will vary with the load current. The output voltage trip point (approx. 4.75V) does not vary with load. The error comparator has an open-collector output, which requires an external pull-up resistor. Depending on the system requirements the resistor may be returned to 5V output or other supply voltage. In determining the value of this resistor, note that the output is rated to sink 400µA, this value adds to battery drain in a low battery condition. Suggested values range from 100K to 1MΩ. If the output is unused this resistor is not required. PROGRAMMING THE OUTPUT VOLTAGE OF AS2954 The AS2954 may be pin-strapped for 5V using its internal voltage divider by tying Pin 1 (output) to Pin 2 (sense) and Pin 7 (feedback) to Pin 6 (5V Tap). +VIN 4.75V 8 100K OUTPUT VOLTAGE ERROR OUTPUT _______ ERROR* +VIN 5 ______ ERROR VOUT 1.2 to 30V 1 AS2954 SHUTDOWN INPUT +5.0V INPUT VOLTAGE +1.3V + 3 + R1 SD GND 4 3.3uF .01uF FB 7 1.23V + V REF R2 * See Application Info. _______ Figure 1. ERROR Output Timing Figure 2. Adjustable Regulator Rev.9/29/00 AS2954 Also, 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. Refer to the below equation for the programming of the output voltage: REDUCING OUTPUT NOISE It may be an advantage to reduce the AC noise present at the output. One way is to reduce the regulator bandwidth by increasing the size of the output capacitor. This is the only way that noise can be reduced on the 3 lead AS2954 but is relatively inefficient, as increasing the capacitor from 1µF to 220µF only decreases the noise from 430µV to 160µV rms for a 100kHz bandwidth at 5V output. Noise could also be reduced fourfold by a bypass capacitor across R1, since it reduces the high frequency gain from 4 to unity. Pick VOUT = VREF × ( 1 + R1\ R2 )+ IFBR1 The VREF is 1.235 and IFB is the feedback bias current, nominally -20nA. The minimum recommended load current of 1µA forces an upper limit of 1.2 MΩ on value of R2. If no load is presented the IFB produces an error of typically 2% in VOUT, which may be eliminated at room temperature by trimming R1. To improve the accuracy choose the value of R2 = 100k this reduces the error by 0.17% and increases the resistor program current by 12µA. Since the LP2951 typically draws 60µA at no load with Pin 2 opencircuited this is a small price to pay CBYPASS ≅ 1 / 2πR1 × 200 Hz or choose 0.01µF. When doing this, the output capacitor must be increased to 3.3µF to maintain stability. These changes reduce the output noise from 430µV to 100µVRMS for a 100kHz 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. HEATSINK REQUIREMENTS Depending on the maximum ambient temperature and maximum power dissipation a heatsink may be required with the AS2954. The junction temperature range has to be within the range specified under Absolute Maximum Ratings under all possible operating conditions. To find out if a heatsink is required, the maximum power dissipation of the device needs to be calculated. This is the maximum specific AC voltage that must be taken into consideration at input. Figure 3 shows the condition and power dissipation which should be calculated with the following formula: IIN IN VIN OUT 5V IL PTOTAL = (VIN - 5) IL + (VIN)IG AS2954 Next step is to calculate the temperature rise TR (MAX). TJ (MAX) maximum allowable junction temperature, TA (MAX) maximum ambient temperature : + GND TR (MAX) = TJ (MAX) - TA (MAX) Junction to ambient thermal resistance θ(j-A) can be calculated after determining of PTOTAL & TR (MAX): I IN= I L+ I G LOAD + 2.2 uF IG Figure 3. 5V Regulator Circuit θ(J-A) = TR (max)/P(MAX) If the θ(J-A) is 60°C/W or higher, the device could be operated without a heatsink. If the value is below 60°C/W then the heatsink is required and the thermal resistance of the heatsink can be calculated by the following formula, θ(J-C) junction to case, θ(C-H) case to heatsink, θ(H-A) heatsink to ambient: θ(J-A) = θ(J-C) + θ(C-H) + θ(H-A) Rev.9/29/00 AS2954 TYPICAL APPLICATIONS +VIN 8 ERROR 5 OUTPUT +VIN ______ ERROR VOUT 1 *VOUT = VIN AS2954 SHUTDOWN INPUT 3 SD GND 4 FB 7 *MINIMUM INPUT-OUTPUT VOLTAGE RANGES FROM 4mV TO 400mV. DEPENDING ON LOAD CURRENT. CURRENT LIMIT IS TYPICALLY 160mA Wide Input Voltage Range Current Limited +V IN +V IN *V V OUT AS2954 OUT = 5V + 10uF GND 4 AS2954 FIXED +5V REGULATOR Rev.9/29/00