AS2887 3A Low Dropout Voltage Regulator Adjustable & Fixed Output, Fast Response FEATURES APPLICATIONS • Adjustable Output Down To 1.2V • Fixed Output Voltages 1.5, 2.5, 3.3, 5.0V • Output Current Of 3A • Low Dropout Voltage 1.1V Typ. • Extremely Tight Load And Line Regulation • Current & Thermal Limiting • Standard 3-Terminal Low Cost TO-220, TO-263 & TO-252 • 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 AS2887 are low power 3A 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 AS2887 is designed for low voltage applications that offer 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 AS2887 features low dropout of a maximum of 1.5 volts. The AS2887 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 AS2887 are offered in a 3-pin TO-220, TO-263 & TO-252 packages compatible with other 3 terminal regulators. For a 8A low dropout regulator refer to the AS2880 data sheet. ORDERING INFORMATION TO-220 3-PIN AS2887YU AS2887YU-X DD PLASTIC 3-PIN AS2887YT AS2887YT-X TO-252 DPAK AS2887YR AS2887YR-X 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 PIN CONNECTIONS TO-263-3 (T) TO-220-3 (U) AS2887 1 2 TO-252 (R) AS2887 3 AS2887 1 2 1 2 3 3 ADJ/GND VOUT VIN Front View ADJ/GND VOUT VIN Top View ADJ/GND VOUT VIN Front View Rev. 10/11/00 AS2887 ABSOLUTE MAXIMUM RATINGS Lead Temp. (Soldering, 10 Seconds) .............................. 300°C Storage Temperature Range ............................ -65° to +150°C Operating Junction Temperature Range ...................... AS2887 Control Section ............................ -45°C +125°C AS2887 Power Transistor...........................-45°C +150°C Input Voltage........................................................ 30V Input to Output Voltage Differential Max ............ 30V ELECTRICAL CHARACTERISTICS (NOTE 1) at IOUT = 10mA, TA=25°C, unless otherwise specified. AS2887A PARAMETER CONDITIONS Typ Min Max AS2887 Min Max Units 1.5V Version Output Voltage (Note 2) AS2887-1.5V, 0 ≤IOUT≤3A, 2.75V≤VIN ≤29V 1.5 1.5 1.485 1.470 1.515 1.530 1.470 1.455 1.530 1.545 V 2.5V Version Output Voltage (Note 2) AS2887-2.5V,0 ≤IOUT≤3A, 3.5V≤VIN ≤29V 2.5 2.5 2.475 2.450 2.525 2.550 2.450 2.425 2.550 2.575 V 3.3V Version Output Voltage (Note 2) AS2887-3.3V, 0 ≤IOUT≤3A, 4.75V≤VIN ≤29V 3.3 3.3 3.270 3.240 3.330 3.360 3.230 3.201 3.370 3.399 V 5.0V Version Output Voltage (Note 2) AS2887-5.0V, 0 ≤IOUT≤3A, 5.5V≤VIN ≤29V 5.0 5.0 4.95 4.90 5.05 5.10 4.900 4.850 5.100 5.150 V 1.250 1.238 1.263 1.225 1.270 V Adjustable Version Reference Voltage (VREF) All Voltage Options Min. Load Current (Note 3) Line Regulation (∆VREF(VIN)) VIN≤ 7V, P≤ PMAX 1.5V≤ (VIN -VOUT)≤(VIN-VOUT)MAX, 10mA≤IOUT≤3A 5 10 10 mA 2.75V≤VIN ≤29V, IOUT=10mA, TJ=25°C (Note 3) 0.005 0.2 0.2 % VIN ≤29V, IOUT=0mA, TJ=25°C (Note 2) 0.005 0.2 0.2 % 10mA≤IOUT ≤3A, (VIN-VOUT)=3V, TJ=25°C (Note 3) 0.05 0.3 0.3 % 0≤IOUT ≤3A, VIN=7V, TJ=25°C (Note 2) 0.05 0.3 0.3 % Dropout Voltage ∆VREF=1% 1.1 1.5 1.5 V Current Limit IOUT(MAX) Long Term Stability VIN=7V 1.4V≤ (VIN- VOUT) (Note3) TA=125°C, 1000 Hrs. 0.3 (Note 2) 1 1 % Thermal Regulation (∆VOUT(Pwr)) Temperature Stability (∆VOUT(T)) Output Noise, RMS Thermal Resistance TA=25°C, 20 ms pulse 0.01 0.020 0.020 %/W Load Regulation(∆VREF(IOUT)) 1.5V≤ (VIN -VOUT)≤ (VIN-VOUT)MAX IOUT =3A (Note 3) IOUT≤ 3A (Note 2) A 4.0 3.2 3.2 0.25 10Hz to 10kHz TO-220 DD Package TA=25°C Junction to Tab Junction to Ambient Junction to Tab Junction to Ambient % 0.003 3.0 60 3.0 60 % VO 3.0 60 3.0 60 3.0 60 3.0 60 °C/W °C/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 AS2887 APPLICATION HINTS The AS2887 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 220µF aluminum electrolytic capacitor or a 47µF 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 AS2887 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 100µF for an electrolytic aluminum capacitor or 15µF 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 θ Heatsink = 6°C/W, θ Case-Heatsink = 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 Sections TJ = 50 + 7.5*(0.5 +6=3) = 121.25°C 121.25°C < TJ(max) for the control section. In both case reliable operation is insured by adequate junction temperature. Rev. 10/11/00 AS2887 Basic Adjustable Regulator VIN VOUT AS2887 VREF R1 IADJ 50µA R2 VOUT = VREF * ( 1 + R2/R1) + IADJ * R2 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 AS2887 Connect R 1 to Case of Regulator R1 RL R2 Connect R 2 to Load Fig.3 Basic Adjustable Regulator Rev. 10/11/00 AS2887 TYPICAL APPLICATIONS VIN IN AS2887 VIN OUT C2 Fig. 5 Typical Adjustable Regulator Fig. 4 3A Current output Regulator IN AS2887 + 10µF 5V *C 1 improves ripple rejection. Xc should be ~ R 1 at ripple frequency. VOUT OUT ADJ R2 VOUT = VREF (1 + R2 ) + IADJ R2 R1 LOAD (Note A) R1 ADJ R1 ADJ VOUT OUT C1 C1 VIN AS2887 IN VIN + 150µF + C1 10µF* AS2887 5V OUT 121Ω 1% ADJ R1 121Ω 1% R2 365Ω 1% IN (Note A) TTL Input + 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 AS2887 TYPICAL CHARACTERISTICS Rev. 10/11/00