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| AS2885 5A Low Dropout Voltage Regulator Adjustable & Fixed Output, Fast Response FEATURES * Adjustable Output Down To 1.2V * Fixed Output Voltages 1.5, 2.5, 3.3 & 5.0V * Output Current Of 5A * Low Dropout Voltage 1.1V Typ. * Extremely Tight Load And Line Regulation * Current & Thermal Limiting * Standard 3-Terminal Low Cost TO-220 & TO-263 * Similar To Industry Standard LT1085/LT1585 APPLICATIONS * 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 AS2885 are low power 5A adjustable and fixed voltage regulators with 30V maximum VIN. They are very easy to use. It requires only 2 external resistors to set the output voltage for adjustable version. The AS2885 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 AS2885 features low dropout of a maximum of 1.2 volts. The AS2885 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 load, which increases efficiency. The AS2885 are offered in 3-pin TO-220 and TO-263 packages compatible with other 3 terminal regulators. For a similar 5A low dropout voltage regulator refer to the AS2850 datasheet. Also for higher current requirements, refer to the AS2880 datasheet. ORDERING INFORMATION TO-220 3-PIN AS2885YU AS2885YU-X TO-263 3-PIN AS2885YT AS2885YT-X PIN CONNECTIONS TO-263-3 (T) TO-220-3 (U) 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 with factory for other fixed output voltages AS2885 1 2 3 AS2885 1 2 3 ADJ/GND VOUT VIN Top View ADJ/GND VOUT VIN Front View Rev. 9/29/00 AS2885 ABSOLUTE MAXIMUM RATINGS Lead Temp. (Soldering, 10 Seconds) .............................. 300C Storage Temperature Range ............................ -65 to +150C Operating Junction Temperature Range AS2885 Control Section ............................ -45C +125C AS2885 Power Transistor...........................-45C +150C Input Voltage........................................................ 30V Input to Output Voltage Differential .................... 30V ELECTRICAL CHARACTERISTICS (NOTE 1) at IOUT = 10mA, Ta=25C, unless otherwise specified. PARAMETER 1.5V Version Output Voltage (Note 2) 2.5V Version Output Voltage (Note 2) 3.3V Version Output Voltage (Note 2) 5.0V Version Output Voltage (Note 2) Adjustable Version Reference Voltage (VREF) All Voltage Options Min. Load Current (Note 3) Line Regulation (VREF(Vin)) 1.5V (VIN -VOUT)25V 2.75VVIN 25V, IOUT=10mA, TJ=25C (Note 3) VIN 25V, IOUT=0mA, TJ=25C (Note 2) 10mAIOUT 5A, (VIN-VOUT)=3V, TJ=25C (Note 3) 0IOUT 5A, VIN=7V, TJ=25C (Note 2) VREF=1% VIN=7V 1.4V (VIN - VOUT) (Note3) TA=125C, 1000 Hrs. TA=25C, 20 ms pulse 10Hz to 10kHz TO-220 DD Package TA=25C Junction to Tab Junction to Ambient Junction to Tab Junction to Ambient IOUT = 5A (Note 3) IOUT < 5A (Note 2) 5 0.005 0.005 0.05 0.05 1.2 6 0.3 (Note 2) 0.01 0.25 0.003 3.0 60 3.0 60 5.2 1 0.020 10 0.2 0.2 0.7 0.3 1.5 5.2 1 0.020 10 0.2 0.2 0.7 0.3 1.5 A % %/W % % VO C/W % V % AS2885-5.0V, 0 IOUT 5A, 6.5VVIN25V 5 4.950 4.900 1.250 1.250 1.238 1.225 5.050 5.100 1.262 1.270 4.9 4.65 1.225 1.212 5.1 5.15 1.270 1.288 V V AS2885-3.3V, 0 < IOUT < 5A, 4.8V Load Regulation(VREF(IOUT)) Dropout Voltage Current Limit IOUT(MAX) Long Term Stability Thermal Regulation(VOUT(Pwr)) Temperature Stability (VOUT(T)) Output Noise, RMS Thermal Resistance 3.0 60 3.0 60 3.0 60 3.0 60 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. 9/29/00 AS2885 APPLICATION HINTS The AS2885 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 220F aluminum electrolytic capacitor or a 47F 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 (220F for an aluminum electrolytic capacitor, or 47F for a solid tantalum capacitor). If the ADJ pin is not bypass, the value of the output capacitor can be lowered to 100F for an electrolytic aluminum capacitor or 15F 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 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 AS2885 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: VIN = 7V, VOUT = 5V, IOUT = 1.5A, TA = 50C/W, Heatsink Case= 6C/W, Heatsink Case = 0.5C/W, JC = 3C/W Power dissipation under this condition PD = (VIN - VOUT) * IOUT = 7.5W Junction Temperature TJ = TA + PD * ( Case- HS + HS + JC) For the Control Sections TJ = 50 + 7.5*(0.5+6=3) = 121.25C 121.25C < TJ(max) for the Control & Power Sections. In both case reliable operation is insured by adequate junction temperature. Rev. 9/29/00 AS2885 Basic Adjustable Regulator VIN AS2885 VREF I ADJ VOUT R1 50A R2 VOUT = VREF * ( 1 + R /R1) + IADJ * R2 2 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 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. VIN R P Parasitic Line Resistance AS2885 Connect R 1 to Case of Regulator R1 RL R2 Connect R 2 to Load Fig.3 Basic Adjustable Regulator Rev. 9/29/00 AS2885 TYPICAL APPLICATIONS VIN C1 IN AS2885 ADJ OUT R1 VIN C1 IN AS2885 ADJ OUT C2 R1 VOUT LOAD VOUT = VREF (1 + R2 ) + IADJ R2 R1 R2 Fig. 4 5A Current output Regulator Fig. 5 Typical Adjustable Regulator (Note A) VIN IN 5V + 10F AS2885 ADJ OUT VOUT R1 121 1% 150F VIN (Note A) + IN AS2885 ADJ OUT 5V 121 1% + 100F 10F 1k 2N3904 1k 365 1% *C 1 improves ripple rejection. Xc should be ~ R 1 at ripple frequency. R2 365 1% TTL Input + C1 10F* Note A: V IN(MIN) = (Intended V OUT) + (VDROPOUT (MAX)) Note A: VIN(MIN)= (Intended V ) + (VDROPOUT (MAX)) OUT Fig. 6 Improving Ripple Rejection Fig.7 5V Regulator with Shutdown Rev. 9/29/00 |
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