AS2850 SIPEX | Alldatasheet
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Rev. 10/11/00 AS2850 5A Low Dropout Voltage Regulator Adjustable & Fixed Output, Fast Response FEATURES APPLICATIONS
- Adjustable Output Down To 1.2V • Powering VGA & Sound Card
- Fixed Output Voltages 1.5V, 2.5V, 3.3V & 5.0V • Power PCSupplies
- Output Current Of 5A • SMPS Post-Regulator
- Low Dropout Voltage 1.1V Typ @ 5A. • High Efficiency “Green” Computer Systems
- Extremely Tight Load And Line Regulation • High Efficiency Linear Power Supplies
- Current & Thermal Limiting • Portable Instrumentation
- Standard 3-Terminal Low Cost TO-220 & TO-263 • Constant Current Regulators
- Similar To Industry Standard LT1085/LT1585 • 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 res istors 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 appli cations. 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 a nd negative transient voltage. On-Chip trimming adjusts the reference voltage to 1%. The I Q 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
Y= Output Tolerance, A for 1% Blank for 2% Consult factory for other fixed voltages. PIN CONNECTIONS Top View TO-263-3 (T) ADJ/GND VOUT VIN AS2850 Front View TO-220-3 (U) AS2580 VIN VOUT ADJ/GND
Rev. 10/11/00 AS2850 ABSOLUTE MAXIMUM RATINGS Operating Junction Temperature Range ELECTRICAL CHARACTERISTICS (NOTE 1) at IOUT = 10mA, TA=25°C, unless otherwise specified. PARAMETER CONDITIONS Typ AS2850A AS2850 UNITS Min Max Min Max 1.5V Version 1.47 1.53 1.455 1.545 2.5V Version 2.45 2.55 2.425 2.575 3.3V Version 3.234 3.366 3.069 3.399 5.0V Version 4.900 5.100 4.65 5.15 All Voltage Options VIN≤ 7V, P≤ PMAX 1.5V≤ (VIN -VOUT)≤5.75V, 10mA≤IOUT≤5A Min. Load Current (Note 3) 1.5V≤ (VIN –VOUT)≤5.75V 5 10 10 V Line Regulation (∆Vref(Vin)) 2.75V ≤VIN ≤7V, Iout=10mA, TJ=25ºC (Note 3) 0.005 0.2 0.2 VIN ≤7V, IOUT=0mA, TJ=25ºC (Note 2) 0.005 0.2 0.2 10mA≤IOUT ≤5A, (VIN-VOUT)=3V, TJ=25ºC (Note 3) 0.05 0.3 0.3 Load Regulation(∆Vref(Iout)) 0≤IOUT ≤5A, VIN=7V, TJ=25ºC (Note 2) 0.05 0.3 0.3 Dropout Voltage ∆VREF=1% I OUT = 5A (Note 3) I OUT < 5A (Note 2) 1.1 1.2 1.2 VIN=7V 6 5.2 5.2 A Current Limit Iout(MAX) 1.4V ≤ (VIN - VOUT) (Note3) Long Term Stability T A=125ºC, 1000 Hrs. 0.3 (Note 2) 1 1 % Thermal Regulation (∆Vout(Pwr)) TA=25ºC, 20 ms pulse 0.01 0.020 0.020 %/W Temperature Stability (∆Vout(T)) 0.25 % Output Noise, RMS 10Hz to 10kHz T A=25ºC 0.003 % Vo 3.0 3.0 TO-220 Junction to Tab Junction to Ambient 60 60 3.0 3.0 Thermal Resistance Junction to Ambient 60 60 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. Stability The output capacitor is part of the regulator’s frequency compensation system. Either a 22 µF aluminum electrolytic capacitor or a 10 µF 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’. 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 (220 µF 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 4.7 µF 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 * F R * R1 ) Where C = value of the capacitor in Farads (select an equal or larger standard value), F R = ripple frequency in Hz, R 1 = value of resistor R 1 in Ohms. If an ADJ-bypass capacitor is use, the amplitude of the output ripple will be independent of the output voltage. If an ADJ- bypass capacitor is not used, the output ripple will be proportional to the ratio of the output voltage to the reference voltage: M = V OUT / VREF Where M = multiplier for the ripple seen when the ADJ pin is optimally bypassed. V REF = Reference Voltage 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. Thermal Consideration Although the AS 2850 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. Assuming: V IN = 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 P D = (VIN – VOUT) * IOUT = 7.5W Junction Temperature T J = TA + PD * (θCase – HS + θ HS θ JC) For the Control Section T 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 Output Voltage Consider Figure 2. The resistance R 1 generates a constant current flow, normally the specified load current of 10mA. This current will go through the resistance R 2 to set the overall output voltage. The current I ADJ is very small and constant. Therefore its contribution to the overall output voltage is very small and can generally be ignored 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 R 1 resistance from the resistor divider to the case, and not to the load. For the same reason, it is best to connect the resistor R 2 to the Negative side of the load. Output Voltage The fixed voltage LDO voltage regulators are simple to use regulators since the V OUT 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. AS2850 Fig.2 Basic Adjustable Regulator VREF R1 VOUT = VREF * ( 1 + R2/R1) + IADJ * R2 IADJ ADJ VIN VOUT 50uA AS2850 Fig.3 Basic Adjustable Regulator VIN Connect R 2 to Load RL Connect R 1 to Case of Regulator RP Parasitic Line Resistance VOUT ADJ AS2850 Basic Fixed Regulator VIN VOUT 10uF 10uF 3.3V
Rev. 10/11/00 AS2850 TYPICAL APPLICATIONS IN OUT ADJ AS2850 VOUT Fig. 5 Typical Adjustable Regulator VIN LOAD ADJ AS2850 Fig. 4 5A Current output Regulator VIN OUTIN VOUT = VREF (1 + R2 ) + IADJ R2 Note A: VIN(MIN) = (Intended VOUT) + (VDROPOUT (MAX) ) AS2850 Fig. 6 Improving Ripple Rejection VIN 150µF 10µF* 121Ω 365Ω 10µF *C1 improves ripple rejection. Xc should be ~ R1 at ripple frequency. ADJ IN OUT (Note A) VOUT AS2850 Fig.7 5V Regulator with Shutdown VIN 100µF 121Ω 365Ω 10µF ADJ IN OUT (Note A) TTL Input 2N3904 Note A: VIN(MIN) = (Intended VOUT) + (VDROPOUT (MAX) )
Rev. 10/11/00 AS2850 TYPICAL CHARACTERISTICS