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AS2885AT-1.5 [ETC]

Analog IC ; 模拟IC\n
AS2885AT-1.5
型号： AS2885AT-1.5
厂家： ETC    ETC
描述：

Analog IC
模拟IC\n

模拟IC
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AS2885  
5A 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 5A  
• Powering VGA & Sound Card  
• Power PCSupplies  
• SMPS Post-Regulator  
• Low Dropout Voltage 1.1V Typ.  
• Extremely Tight Load And Line Regulation  
• Current & Thermal Limiting  
• High Efficiency “Green” Computer Systems  
• High Efficiency Linear Power Supplies  
• Portable Instrumentation  
• Standard 3-Terminal Low Cost TO-220 & TO-263  
• Similar To Industry Standard LT1085/LT1585  
• 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  
TO-263  
3-PIN  
AS2885YU  
AS2885YU-X  
AS2885YT  
AS2885YT-X  
PIN CONNECTIONS  
X= Output Voltage (i.e. 1.5 for 1.5V, 2.5 for 2.5V etc.)  
TO-263-3 (T)  
TO-220-3 (U)  
Y= Output Tolerance, A for 1%  
Blank for 2%  
Consult with factory for other fixed output voltages  
AS2885  
AS2885  
1
3
2
1
2
3
VIN  
ADJ/GND  
VOUT  
Top View  
VIN  
V
ADJ/GND  
OUT  
Front View  
Rev. 9/29/00  
AS2885  
ABSOLUTE MAXIMUM RATINGS  
Lead Temp. (Soldering, 10 Seconds) .............................. 300°C  
Storage Temperature Range ............................-65° to +150°C  
Operating Junction Temperature Range  
Input Voltage........................................................ 30V  
Input to Output Voltage Differential .................... 30V  
AS2885 Control Section............................ -45°C +125°C  
AS2885 Power Transistor...........................-45°C +150°C  
ELECTRICAL CHARACTERISTICS (NOTE 1) at IOUT = 10mA, Ta=25°C, unless otherwise specified.  
PARAMETER  
CONDITIONS  
Typ  
1.5  
2.5  
3.3  
5
AS2885A  
AS2885  
UNITS  
Min  
Max  
Min  
Max  
1.5V Version  
Output Voltage (Note 2)  
AS2885-1.5V, 0 < IOUT < 5A, 3.3V<VIN<25V  
AS2885-2.5V, 0 < IOUT < 5A, 4.0V<VIN<25V  
AS2885-3.3V, 0 < IOUT < 5A, 4.8V<VIN<25V  
AS2885-5.0V, 0 ≤ IOUT ≤ 5A, 6.5V≤VIN≤25V  
1.485  
1.47  
1.515  
1.53  
1.47  
1.53  
V
V
V
1.455  
1.545  
2.5V Version  
Output Voltage (Note 2)  
2.475  
2.45  
2.525  
2.55  
2.45  
2.55  
2.425  
2.575  
3.3V Version  
Output Voltage (Note 2)  
3.267  
3.234  
3.333  
3.366  
3.234  
3.366  
3.069  
3.399  
5.0V Version  
Output Voltage (Note 2)  
4.950  
5.050  
4.9  
5.1  
V
V
4.900  
5.100  
4.65  
5.15  
Adjustable Version  
Reference Voltage (VREF  
)
1.250  
1.238  
1.262  
1.225  
1.270  
1.5V≤ (VIN -VOUT)≤25V, 10mA≤IOUT≤5A  
1.5V≤ (VIN –VOUT)≤25V  
1.250  
1.225  
1.270  
1.212  
1.288  
All Voltage Options  
Min. Load Current (Note 3)  
V
5
10  
10  
0.005  
0.2  
0.2  
%
Line Regulation (∆VREF(Vin))  
2.75V≤VIN ≤25V, IOUT=10mA, TJ=25ºC  
(Note 3)  
0.005  
0.05  
0.2  
0.7  
0.2  
0.7  
V
IN ≤25V, IOUT=0mA, TJ=25ºC (Note 2)  
%
Load Regulation(∆VREF(IOUT))  
10mA≤IOUT ≤5A, (VIN-VOUT)=3V, TJ=25ºC  
(Note 3)  
0.05  
1.2  
0.3  
1.5  
0.3  
1.5  
0≤IOUT ≤5A, VIN=7V, TJ=25ºC (Note 2)  
Dropout Voltage  
∆VREF=1%  
IOUT = 5A (Note 3)  
I
OUT < 5A (Note 2)  
Current Limit IOUT(MAX)  
Long Term Stability  
VIN=7V  
1.4V ≤ (VIN – VOUT) (Note3)  
TA=125ºC, 1000 Hrs.  
6
5.2  
5.2  
A
0.3  
(Note 2)  
0.01  
0.25  
0.003  
1
1
%
TA=25ºC, 20 ms pulse  
0.020  
0.020  
%/W  
%
% VO  
ºC/W  
Thermal Regulation(∆VOUT(Pwr))  
Temperature Stability (∆VOUT(T))  
Output Noise, RMS  
10Hz to 10kHz TA=25ºC  
TO-220  
Thermal Resistance  
Junction to Tab  
3.0  
3.0  
60  
3.0  
60  
Junction to Ambient  
Junction to Tab  
60  
DD Package  
3.0  
60  
3.0  
60  
3.0  
60  
Junction to Ambient  
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  
Reducing parasitic resistance and inductance  
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.  
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  
Thermal Consideration  
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.  
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.  
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 (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.  
Assuming:  
V
IN = 7V, 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  
However the value of the ADJ-bypass capacitor should be  
chosen with respect to the following equation:  
Junction Temperature  
TJ = TA + PD * (θ Case- HS + θ HS + θ JC)  
C = 1 / ( 6.28 * FR * R1 )  
For the Control Sections  
Where C  
= value of the capacitor in Farads (select an  
TJ = 50 + 7.5*(0.5+6=3) = 121.25°C  
equal or larger standard value),  
FR = ripple frequency in Hz,  
R1 = value of resistor R1 in Ohms.  
121.25°C < TJ(max) for the Control & Power Sections.  
In both case reliable operation is insured by adequate junction  
temperature.  
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 = VOUT / VREF  
Where M = multiplier for the ripple seen when the ADJ pin  
is optimally bypassed.  
VREF = Reference Voltage  
Rev. 9/29/00  
AS2885  
Basic Adjustable Regulator  
VIN  
VOUT  
AS2885  
R1  
R2  
VREF  
IADJ  
50µA  
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.  
RP Parasitic Line  
Resistance  
VIN  
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  
VOUT  
VIN  
OUT  
IN  
AS2885  
OUT  
IN  
AS2885  
C2  
C1  
C1  
R1  
R2  
ADJ  
R1  
ADJ  
VOUT = VREF (1 + R ) + IADJ R2  
R21  
LOAD  
Fig. 5 Typical Adjustable Regulator  
Fig. 4 5A Current output Regulator  
(Note A)  
VIN  
5V  
VIN  
(Note A)  
IN  
OUT  
5V  
IN  
OUT  
VOUT  
AS2885  
ADJ  
AS2885  
+
10µF  
121Ω  
ADJ  
R1  
1%  
+
121Ω  
+
10µF  
1k  
1%  
100µF  
TTL  
Input  
150µF  
2N3904  
*C1 improves ripple rejection. Xc  
should be ~ R 1 at ripple frequency.  
365Ω  
R2  
365Ω  
1%  
1%  
+
C1  
10µF*  
1k  
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. 9/29/00  

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