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AP1187
1A Ultra Low Dropout Positive Adjustable Regulator
Features
* * * * * * *
General Description
AP1187 is a 1A regulator with extremely low dropout voltage. This product is specifically designed to provide well regulated supply for applications requiring 2.8V or lower voltages from 3.3V ATX power supplies where high efficiency of a switcher can be achieved without the cost and complexity associated with switching regulator. One such application is the new graphic chip sets that require anywhere from 2.4V to 2.7V supply.
Adjustable output voltage 0.6V Maximum Dropout voltage at 1.0A Load current Built-in Thermal Shutdown Output Current Limiting Fast transient response Good noise rejection Package: SOP-7L
Applications
* * * * * * * *
PC Motherboard LCD Monitor Graphic Card DVD-Video Player NIC/Switch Telecom Equipment ADSL Modem Printer and other Peripheral Equipment
Pin Assignments
Pin Descriptions
Name ADJ Description A resistor divider from this pin to the VOUT pin and ground sets the output voltage. This pin is the positive side of the reference that allows remote load sensing to achieve excellent load regulation. A minimum of 10uF capacitor must be connected from this pin to ground to insure stability. The input of the regulator. This pin is the supply pin for the internal control circuit as well as the base drive for the pass transistor. Not used. The output of the regulator.
( Top View ) ADJ 1 VSENSE 2 AP1187 VIN 3 VCTRL 4 SOP-7L 7 NC
6 VOUT
VSENSE
5 VIN
VIN VCTRL NC VOUT
This datasheet contains new product information. Anachip Corp. reserves the rights to modify the product specification without notice. No liability is assumed as a result of the use of this product. No rights under any patent accompany the sale of the product.
Rev.1.1 1/6
Aug 23, 2005
AP1187
1A Ultra Low Dropout Positive Adjustable Regulator
Ordering Information
AP 1187 X Low Dropout Regulator Package
S7:SOP-7L
X
X Lead Free Packing
Blank : Tube A : Taping& Reel
Blank : Normal L : Lead Free Package
Block Diagram
VIN VCTRL + + Current Limit Thermal Shutdown 1.25V + ADJ + VOUT VSENSE
Absolute Maximum Ratings (Note 1)
Symbol VIN VCTRL PD TST TOP Input Voltage Control Input Voltage Power Dissipation Storage Temperature Operating Junction Temperature Range Parameter Rating 16 18 Internally limited -65 to +150 0 to +150 oC oC Unit V V
NOTE1: AP1187-ADJ incorporates an internal thermal shutdown that protects the device when the junction temperature exceeds the allowable maximum junction temperature.
Anachip Corp. www.anachip.com.tw 2/6
Rev.1.1
Aug 23, 2005
AP1187
1A Ultra Low Dropout Positive Adjustable Regulator
Electrical Characteristics
Unless otherwise specified, these specifications apply over, CIN=1uF, COUT=10uF, and TJ=0 to 150 C. Typical value refer to TJ=25 C. VOUT = VSENSE.
o o
Sym.
Parameter
o
Test Condition
Min. Typ. Max. Unit 1.225 1.250 1.275 0.2 1 1.5 0.5 1.1 5 0.01 60 70 6 50 20 1 2 10 120
O
VREF Reference Voltage TJ=25 C,(VIN-VOUT)=0.5V, IO=10mA VCTRL =VIN+1V Line Regulation IO=10mA, VOUT+0.5VV % % V V A
1.7 0.6
10 0.02
mA %W dB mA A C/W W
Typical Application Circuit
3.3V + 470uF 121 ohm 121 ohm ADJ VSENSE VIN 5V + 470uF VCTRL AP1187 NC VOUT 2.5V/1A VOUT VIN + 470uF
Anachip Corp. www.anachip.com.tw 3/6
Rev.1.1
Aug 23, 2005
AP1187
1A Ultra Low Dropout Positive Adjustable Regulator
Function Description
Introduction The AP1187 regulator is a 7-terminal device designed specifically to provide extremely low dropout voltages comparable to the PNP type without the disadvantage of the extra power dissipation due to the base current associated with PNP regulators. This is done by bringing out the control pin of the regulator that provides the base current to the power NPN and connecting it to a voltage that is greater than the voltage present at the VIN pin. This flexibility makes the AP1187 ideal for applications where dual inputs are available such as a computer motherboard with an ATX style power supply that provides 5V and 3.3V to the board. One such application is the new graphic chip sets that require anywhere from 2.4V to 2.7V supply. The AP1187-ADJ can easily be programmed with the addition of two external resistors to any voltages within the range of 1.25V to 15.5V. Another major requirement of these graphic chips is the need to switch the load current from zero to several amps in tens of nanoseconds at the processor pins, which translates to an approximately 300 to 500ns of current step at the regulator. In addition, the output voltage tolerances are also extremely tight and they include the transient response as part of the specification. The AP1187 is specifically designed to meet the fast current transient needs as well as providing an accurate initial voltage, reducing the overall system cost with the need for fewer number of output capacitors. Another feature of the device is its true remote sensing capability that allows accurate voltage setting at the load rather than at the device. Output Voltage Setting The AP1187 can be programmed to any voltages in the range of 1.25V to 15.5V with the addition of R1 and R2 external resistors according to the following formula:
VOUT=VREF(1+R2/R1)+IADJ*R2 where: VREF=1.25V & IADJ=50uA Typically
VIN AP1187-ADJ VCTRL ADJ IADJ=50uA VSENSE VREF R1+ VOUT
The AP1187 keeps a constant 1.25V between the VSENSE pin and the ADJ pin. By placing a resistor R1 across these two pins and connecting the VSENSE and VOUT pin together, a constant current flows through R1, adding to the IADJ current and into the R2 resistor producing a voltage equal to the (1.25/R1)*R2 + IADJ*R2. This voltage is then added to the 1.25V to set the output voltage. This is summarized in the above equation. Since the minimum load current requirement of the AP1187 is 10mA, R1 is typically selected to be a 121 resistor so that it automatically satisfies this condition. Notice that since the IADJ is typically in the range of 50uA it only adds a small error to the output voltage and should be considered when very precise output voltage setting is required. Load Regulation Since the AP1187 has separate pins for the output (VOUT) and the sense (VSENSE), it is ideal for providing true remote sensing of the output voltage at the load. This means that the voltage drops due to parasitic resistance such as PCB traces between the regulator and the load are compensated for using remote sensing. Figure following shows a typical application of the AP1187 with remote sensing.
VIN VCTRL VIN AP1187-ADJ VCTRL VSENSE ADJ R1 R2 RL VOUT
R2+
Stability The AP1187 requires the use of an output capacitor as part of the frequency compensation in order to make the regulator stable. Typical designs for the microprocessor applications use standard electrolytic capacitors with typical ESR in the range of 50 to 100m and an output capacitance of 100uF to 1000uF. Fortunately as the capacitance increases, the ESR decreases resulting in a fixed RC time constant. The AP1187 takes advantage of the phenomena in making the overall regulator loop stable. For most applications a minimum of 100uF aluminum electrolytic capacitor insures both stability and good transient response.
Anachip Corp. www.anachip.com.tw 4/6
Rev.1.1 Aug 23, 2005
AP1187
1A Ultra Low Dropout Positive Adjustable Regulator
Function Description (Continued)
Thermal Design The AP1187 incorporates an internal thermal shutdown that protects the device when the junction temperature exceeds the allowable maximum junction temperature. Although this device can operate with junction temperatures in the range of 150, it is recommended that the selected heat sink be chosen such that during maximum continuous load operation the junction temperature is kept below this number. The example below shows the steps in selecting the proper surface mount package. Package SOP7 Copper Area 1.0" X 1.0" Assuming, the following conditions: VOUT =2.5V VIN =3.3V VCTRL=5V IOUT =1A DC Avg. Calculate the maximum power dissipation using the following equation: PD= IOUT *(VIN -VOUT) + (IOUT/60) * (VCTRL - VOUT) PD =1*(3.3-2.5) + (1/60)*(5-2.5) =0.84W Using table below select the proper package and the amount of copper board needed. Max Pd (Ta=25oC) 1.7W Max Pd (Ta=45oC) 1.4W
JA (oC / W) 65
o
Note: Above table is based on the maximum junction temperature of 135 C. As shown in the above table, any of the two packages will do the job. For low cost applications the SOP7 package is recommended.
Marking Information
(Top View) 7 5
Logo Part number
AP1187 YY WW X X
Blank: normal L: Lead Free Package ID code: internal Xth week: 01~52 Year: "01" =2001 "02" =2002 ~
1
4
SOP-7L
Anachip Corp. www.anachip.com.tw 5/6
Rev.1.1 Aug 23, 2005
AP1187
1A Ultra Low Dropout Positive Adjustable Regulator
Package Information
Package Type: SOP-7L
C2
C3
A
B1 B2
E C1 C
e D
F
Symbol A B1 B2 C C1 C2 C3 D E e F
Dimensions In Millimeters Min. 5.79 3.83 3.78 4.80 1.57 0.32 1.17 0.19 0.48 1.35 Nom. 5.99 3.91 3.86 4.87 1.67 0.4 1.27 0.22 1.04REF 0.68 1.45 7o Max. 6.19 3.99 3.94 4.94 1.77 0.48 1.37 0.25 0.88 1.55
Dimensions In Inches Min. 0.228 0.151 0.149 0.189 0.062 0.013 0.046 0.007 0.019 0.053 Nom. 0.236 0.154 0.152 0.192 0.066 0.016 0.050 0.009 0.041REF 0.027 0.057 7o Max. 0.244 0.157 0.155 0.194 0.070 0.019 0.054 0.010 0.035 0.061
Anachip Corp. www.anachip.com.tw 6/6
Rev.1.1 Aug 23, 2005

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