AS2850 5A Low Dropout Voltage Regulator Adjustable & Fixed Output, Fast Response FEATURES APPLICATIONS • Adjustable Output Down To 1.2V • Fixed Output Voltages 1.5V, 2.5V, 3.3V & 5.0V • Output Current Of 5A • Low Dropout Voltage 1.1V Typ @ 5A. • Extremely Tight Load And Line Regulation • Current & Thermal Limiting • Standard 3-Terminal Low Cost TO-220 & TO-263 • Similar To Industry Standard LT1085/LT1585 • Powering VGA & Sound Card • Power PCSupplies • SMPS Post-Regulator • High Efficiency “Green” Computer Systems • High Efficiency Linear Power Supplies • Portable Instrumentation • Constant Current Regulators • Adjustable Power Supplies • Battery charger PRODUCT DESCRIPTION The AS2850 are low power 5A adjustable and fixed voltage regulators that are very easy to use. It requires only 2 external resistors to set the output voltage for adjustable version. The AS2850 are designed for low voltage applications that offers lower dropout voltage and faster transient response. This device is an excellent choice for use in powering low voltage microprocessor that require a lower dropout, faster transient response to regulate from +2.5V to 3.8V supplies and as a post regulator for switching supplies applications. The AS2850 features low dropout of a maximum 1.2 volts. The AS2850 offers full protection against over-current faults, reversed input polarity, reversed load insertion, and positive and negative transient voltage. On-Chip trimming adjusts the reference voltage to 1%. The IQ of this device flows into the load, which increases efficiency. The AS2850 are offered in a 3-pin TO-220 and TO-263 package compatible with other 3 terminal regulators. For a 8A low dropout regulator refer to the AS2880 data sheet. ORDERING INFORMATION TO-220 3-PIN DD PLASTIC 3-PIN AS2850YU-X AS2850YT-X PIN CONNECTIONS X= Output Voltage (i.e. 1.5 for 1.5V, 2.5 for 2.5V etc.) Y= Output Tolerance, A for 1% Blank for 2% Consult factory for other fixed voltages. TO-263-3 (T) 3 AS2850 2 1 Top View TO-220-3 (U) VIN VOUT 3 AS2580 2 1 VIN VOUT ADJ/GND ADJ/GND Front View Rev. 10/11/00 AS2850 ABSOLUTE MAXIMUM RATINGS Lead Temp. (Soldering, 10 Seconds) .............................. 300°C Storage Temperature Range ............................ -65° to +150°C Operating Junction Temperature Range AS2850 Control Section ............................ -45°C +125°C AS2850 Power Transistor...........................-45°C +150°C Input Voltage........................................................ 10V Input to Output Voltage Differential .................... 10V ELECTRICAL CHARACTERISTICS (NOTE 1) at IOUT = 10mA, TA=25°C, unless otherwise specified. PARAMETER CONDITIONS Typ AS2850A AS2850 UNITS Min Max Min Max 1.485 1.515 1.47 1.53 1.47 1.53 1.455 1.545 2.475 2.525 2.45 2.55 2.45 2.55 2.425 2.575 1.5V Version Output Voltage (Note 2) AS2850-1.5V, 0 < IOUT < 5A, 3.3V<VIN<10V 1.5 V 2.5V Version Output Voltage (Note 2) AS2850-2.5V, 0 < IOUT < 5A, 4.0V<VIN<10V 2.5 V 3.3V Version Output Voltage (Note 2) AS2850-3.3V, 0 < IOUT< 5A, 4.8V<VIN<10V 3.3 3.267 3.333 3.234 3.366 3.234 3.366 3.069 3.399 V 4.950 5.050 4.9 5.1 4.900 5.100 4.65 5.15 1.225 1.270 1.225 1.270 V 5.0V Version Output Voltage (Note 2) AS2850-5.0V, 0 ≤ IOUT ≤ 5A, 6.5V≤VIN≤12V 5 V All Voltage Options Reference Voltage (Vref) VIN≤ 7V, P≤ PMAX 1.5V≤ (VIN -VOUT)≤5.75V, 10mA≤IOUT≤5A Min. Load Current (Note 3) 1.5V≤ (VIN –VOUT)≤5.75V Line Regulation (∆Vref(Vin)) 2.75V≤VIN ≤7V, Iout=10mA, TJ=25ºC (Note 3) VIN ≤7V, IOUT=0mA, TJ=25ºC (Note 2) Load Regulation(∆Vref(Iout)) 1.250 5 10 10 V 0.005 0.2 0.2 % 0.005 0.2 0.2 10mA≤IOUT ≤5A, (VIN-VOUT)=3V, TJ=25ºC (Note 3) 0.05 0.3 0.3 0≤IOUT ≤5A, VIN=7V, TJ=25ºC (Note 2) 0.05 0.3 0.3 Dropout Voltage ∆VREF=1% 1.1 1.2 1.2 Current Limit Iout(MAX) VIN=7V IOUT = 5A (Note 3) IOUT < 5A (Note 2) 6 5.2 5.2 % A 1.4V ≤ (VIN - VOUT) (Note3) Long Term Stability TA=125ºC, 1000 Hrs. 0.3 (Note 2) 0.01 Thermal Regulation (∆Vout(Pwr)) Temperature Stability (∆Vout(T)) Output Noise, RMS TA=25ºC, 20 ms pulse 10Hz to 10kHz Thermal Resistance TO-220 Junction to Tab Junction to Ambient 3.0 60 60 DD Package Junction to Tab Junction to Ambient 3.0 3.0 60 60 TA=25ºC 1 1 % 0.020 0.020 %/W 0.25 % 0.003 % Vo 3.0 ºC/W The Bold specifications apply to the full operating temperature range. Note 1: Changes in output voltage due to heating effects are covered under the specification for thermal regulation. Note 2: Fixed Version Only Note 3: Adjustable Version Only Rev. 10/11/00 AS2850 APPLICATION HINTS The AS2850 incorporates protection against over-current faults, reversed load insertion, over temperature operation, and positive and negative transient voltage. However, the use of an output capacitor is required in order to insure the stability and the performances. Reducing parasitic resistance and inductance One solution to minimize parasitic resistance and inductance is to connect in parallel capacitors. This arrangement will improve the transient response of the power supply if your system requires rapidly changing current load condition. Stability The output capacitor is part of the regulator’s frequency compensation system. Either a 22µF aluminum electrolytic capacitor or a 10µF solid tantalum capacitor between the output terminal and ground guarantees stable operation for all operating conditions. However, in order to minimize overshoot and undershoot, and therefore optimize the design, please refer to the section ‘Ripple Rejection’. Thermal Consideration Although the AS2850 offers some limiting circuitry for overload conditions, it is necessary not to exceed the maximum junction temperature, and therefore to be careful about thermal resistance. The heat flow will follow the lowest resistance path, which is the Junction-to-case thermal resistance. In order to insure the best thermal flow of the component, a proper mounting is required. Note that the case of the device is electrically connected to the output. In case the case has to be electrically isolated, a thermally conductive spacer can be used. However do not forget to consider its contribution to thermal resistance. Ripple Rejection Ripple rejection can be improved by adding a capacitor between the ADJ pin and ground. When ADJ pin bypassing is used, the value of the output capacitor required increases to its maximum (220µF for an aluminum electrolytic capacitor, or 47µF for a solid tantalum capacitor). If the ADJ pin is not bypass, the value of the output capacitor can be lowered to 10µF for an electrolytic aluminum capacitor or 4.7µF for a solid tantalum capacitor. However the value of the ADJ-bypass capacitor should be chosen with respect to the following equation: C = 1 / ( 6.28 * FR * R1 ) Where C = value of the capacitor in Farads (select an equal or larger standard value), FR = ripple frequency in Hz, R1 = value of resistor R1 in Ohms. If an ADJ-bypass capacitor is use, the amplitude of the output ripple will be independent of the output voltage. If an ADJbypass capacitor is not used, the output ripple will be proportional to the ratio of the output voltage to the reference voltage: M = VOUT / VREF Where M = multiplier for the ripple seen when the ADJ pin is optimally bypassed. VREF = Reference Voltage Assuming: VIN = 10V, VOUT = 5V, IOUT = 1.5A, TA = 50°C/W, θHeatsink Case= 6°C/W, θHeatsink Case = 0.5°C/W, θ JC = 3°C/W Power dissipation under this condition PD = (VIN – VOUT) * IOUT = 7.5W Junction Temperature TJ = TA + PD * (θCase – HS + θ HS θ JC) For the Control Section TJ = 50 + 7.5*(0.5 + 6=3) = 121.25°C 121.25°C < TJ (max) for the Control & Power Sections. In both case reliable operation is insured by adequate junction temperature. Rev. 10/11/00 AS2850 Basic Adjustable Regulator VIN VOUT AS2850 ADJ VREF R1 Load Regulation Parasitic line resistance can degrade load regulation. In order not to affect the behavior of the regulator, it is best to connect directly the R1 resistance from the resistor divider to the case, and not to the load. For the same reason, it is best to connect the resistor R2 to the Negative side of the load. IADJ 50uA R2 VOUT = VREF * ( 1 + R2/R1) + IADJ * R2 VIN 5V VOUT 3.3V AS2850 Fig.2 Basic Adjustable Regulator Output Voltage Consider Figure 2. The resistance R1 generates a constant current flow, normally the specified load current of 10mA. This current will go through the resistance R2 to set the overall output voltage. The current IADJ is very small and constant. Therefore its contribution to the overall output voltage is very small and can generally be ignored R P Parasitic Line Resistance VIN VOUT AS2850 ADJ C2 10uF C1 10uF Basic Fixed Regulator Output Voltage The fixed voltage LDO voltage regulators are simple to use regulators since the VOUT is preset to the specifications. It is important however, to provide the proper output capacitance for stability and improvement. For most operating conditions a capacitance of 22uF tantalum or 100uF electrolytic will ensure stability and prevent oscillation. Connect R 1 to Case of Regulator R1 RL R2 Connect R 2 to Load Fig.3 Basic Adjustable Regulator Rev. 10/11/00 AS2850 TYPICAL APPLICATIONS VIN IN AS2850 VIN OUT Fig. 5 Typical Adjustable Regulator Fig. 4 5A Current output Regulator 5V IN + 10µF AS2850 *C 1 improves ripple rejection. Xc should be ~ R 1 at ripple frequency. VOUT OUT ADJ VIN C1 10µF* AS2850 TTL Input 5V OUT 121Ω 1% ADJ + 150µF + IN (Note A) R1 121Ω 1% R2 365Ω 1% R2 VOUT = VREF (1 + R2 ) + IADJ R2 R1 LOAD (Note A) R1 ADJ R1 ADJ VOUT OUT C2 C1 C1 VIN AS2850 IN + 10µF 100µF 1k 2N3904 1k 365Ω 1% Note A: VIN(MIN) = (Intended VOUT) + (VDROPOUT (MAX)) Note A: VIN(MIN)= (Intended VOUT) + (VDROPOUT (MAX)) Fig. 6 Improving Ripple Rejection Fig.7 5V Regulator with Shutdown Rev. 10/11/00 AS2850 TYPICAL CHARACTERISTICS Rev. 10/11/00