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Bay Linear
Inspire the Linear Power
250mA Low Dropout Voltage Regulators
ON/OFF & BYPASS
B4251
Description
The B4251 series are a group of positive output voltage, five-pin regulators, which provide a high current even when the input/output voltage differential is small. Low power consumption and high accuracy is achieved though CMOS and programmable fuse technologies. Output voltage: 2.0V to 6.0V in 0.1V increments. The B4251 consists of a high-precision voltage reference, an error correction circuit, and a current limited output driver. Key features include a Shutdown Pin that reduces supply current to 0.5A max and a 470pF Bypass input to ground reduces noise present on the internal reference, which in turn significantly reduce output noise. If output noise is not concern, this input maybe left unconnected. Larger capacitor values cap be used, but results in longer time period to rated output voltage when power initially applied. The ON/OFF pin enables the output to be turned off, resulting in reduced power consumption. Provided in SOT-25 (150mW) packages minimizes the usage of board real state.
Features
* * * * * * * * * * Maximum Output Current: 250 mA. Highly Accurate Output Voltage +/- 1.4% Only 19A Power Consumption MAX Shutdown Supply Current 1A Ground Current of Less than 5A Very Low Dropout 0.12V at 100mA 0.23V at 250mA Shutdown Mode for Power Savings With ON/OFF & BYPASS Features Offered in SOT-89 & SOT-25 Packages PIN-to-PIN S-818
Applications
* * * * * Battery Powered Equipment Notebook PC, Palmtops, PDA Portable Cameras and Video Recorders Reference Voltage Sources Cellular / GSM / PCS Phones
Pin Connection
Ordering Information
Package
SOT-25 SOT-89
Part No.
B4251CK5-X.X B4251CR-X.X
SOT-25 (K5)
SOT-89 (R)
X.X = Fixed Output Voltages from 2.0V to 6.0V
Vout
5 1 2
Bypass
4 3
Vout
5
Vss
4
ON/OFF (Enable) Function
Part No B4251 ON/Off High Low VOUT ON OFF
1
2
3
Vin
ON/OFF GND
NC
Vin On/Off
Top View
Top View
Bay Linear, Inc
2478 Armstrong Street, Livermore, CA 94550 Tel: (925) 606-5950, Fax: (925) 940-9556
www.baylinear.com
B4251
Absolute Maximum Ratings
Parameter Input Voltage Output Current Output Voltage On/Off Voltage Continual Total Power Dissipation Operating Ambient Temperature Storage Temperature Symbol VIN IOUT VOUT On/Off SOT-25 SOT-89 Pd TOPR TSTG Ratings 12 500 VSS -0.3 to VIN 0.3 VSS -0.3 to VIN+ 0.3 150 300 -30 to 80 -40 to 125 Units V mA V V mW C C
Electrical Characteristics (Ta = 25C, VIN = VOUT + 0.5V; unless otherwise noted)
Parameter Output Voltage Accuracy Line Regulation VOUT/VIN-VOUT Load Regulation Maximum Output Current Current Limit Shutdown Supply Current Shutdown Input Bias Current Shutdown Exit Delay Shutdown Input Threshold Low Shutdown Input Threshold High Ground Pin Current Dropout Voltage Thermal Shutdown Temperature Conditions IO = 1mA IO = 0 to 150mA IO= 100mA, (VOUT + 0.1V)2 5 250 280
Marking Format SOT-25
FXWW
F = B4251
Variables
X = Voltage Codes
B = 2.0 C = 2.5 D = 2.8 E = 3.0 F= G= H= 3.3 3.5 5.0
WW = Work Week Code SOT-25 = 01 to 99
Bay Linear, Inc
2478 Armstrong Street, Livermore, CA 94550 Tel: (925) 606-5950, Fax: (925) 940-9556
www.baylinear.com
B4251
PRODUCT DESCRIPTION
The B4251 is precision fixed output voltage regulator. Unlike bipolar regulators, the B4251 supply current does not increase with load current. In addition, Vout remains stable and within regulator at very low load currents (an important consideration in RTC and CMOS RAM battery back-up application). Figure 1 shows a typical application circuit. The regulator is enabled any time the shutdown input is at or above VIH. And shutdown (disabled) when SHDN is at or below VIL. SHDN maybe controlled by a CMOS logic gate, or I/O port of a micro controller. If the SHDN input is not. Required, it should be connected directly to the supply. While in shutdown, supply current decreases to 0.05A (typical) and Vout falls to zero volts. Power Dissipation The amount of power the regulator dissipates is primarily a function of input and output voltage, and output current. The following equation is used to calculate worst case power dissipation: PD=(VINMAX-VOUTMIN)ILOADMAX Where: PD= worst case actual power dissipation VINMAX= Maximum voltage on VIN VOUTMIN=Minimum regulator output voltage ILOADMAX= maximum output (LOAD) Current The maximum allowable power dissipation is function of the maximum ambient temperature (TAMAX). The maximum allowable die temperature (125C) and the thermal resistance from junction-to-air (JA). The 5pin SOT-23A package has a JA of approximately 220C/Watt when mounted on a single layer FR4 dielectric copper clad PC board. PDMAX=(TJMAX-TAMAX)/ JA Where all terms are previously defined This can be caused in conjunction with other equation to ensure regulator thermal operation is within limit. For example: Given: VINMAX=3.0V+10% VOUTMIN=2.7V-2.5% ILOADMAX=40 mA TJMAX=125C TAMAX=55C Find: 1. Actual power dissipation 2. Maximum allowable dissipation Actual power dissipation: PD=(VINMAX-VOUTMIN)ILOADMAX =[(3.0 x 1.1)-(2.7 x 0.975)]40 x 10-3 =26.7mW Maximum allowable power dissipation: PDMAX=(TJMAX-TAMAX) =(125-55)/220 =318Mw These equations can be used to calculate maximum current and/or input voltage limits.
www.baylinear.com
Bypass Input
A 470pF capacitor connected from the bypass input to ground reduces noise present on the internal reference, which in turn significantly reduces output noise. If output noise is not a concern, this input maybe left unconnected. Larger capacitor values maybe used, but it results in a longer time period to rated output voltage power is initially applied.
Output Capacitor
A 1F (min) capacitor from Vout to ground is required. Then output capacitor should have an effective series resistance of 5 or less. A 1A capacitor should be connected from Vin to GND if there is more than 10 inches of wire between the regulator and the AC filter capacitor, or if a battery is used as the power source. Aluminum electrolytic or tantalum capacitor types can be used. (since many aluminum electrolytic capacitors freeze at approximately- 30C, solid tantalums are recommended for applications operating below -25 C.) When operating from sources other than batteries, supply-noise rejection and transient response can be improved by increasing the value of the input and output capacitors and employing passive filtering techniques.
Thermal Considerations
Thermal Shutdown Integrated thermal protection circuitry shuts the regulator off when die temperature exceeds 160C. The regulator remaining off until the die temperature drops to approximately 150 C.
Bay Linear, Inc
2478 Armstrong Street, Livermore, CA 94550 Tel: (925) 606-5950, Fax: (925) 940-9556
B4251
SOT-25 Packaging Outline
D B (5 PLACES)
E
H
e e1
A
A2
A1 L
C
SYMBOL
MILLIMETERS
INCHES
MIN. 0.90 0 0.30 0.10 2.70 1.40 1.70 2.50
MAX 1.30 0.10
MIN. .035 0 .012 .004 .106 .055 .066 .098
MAX. .051 .004 .019 .0137 .122 .071 .082 .118
A A1 A2 B C D E e e1 H L
NOTE: 1. REFER TO APPLICABLE 2. CONTROLLING DIMENTION : MILLIMETER 3. PACKAGE SURFACE FINISHING TO BE SMOOTH FINISH.
0.80 REF 0.50 0.35 3.10 1.80 2.10 3.00
.0315 REF
0.95 BSC.
.037 BSC.
MIN 0.2
MIN .0078
Bay Linear, Inc
2478 Armstrong Street, Livermore, CA 94550 Tel: (925) 606-5950, Fax: (925) 940-9556
www.baylinear.com
Advance Information- These data sheets contain descriptions of products that are in development. The specifications are based on the engineering calculations, computer simulations and/ or initial prototype evaluation. Preliminary Information- These data sheets contain minimum and maximum specifications that are based on the initial device characterizations. These limits are subject to change upon the completion of the full characterization over the specified temperature and supply voltage ranges.
The application circuit examples are only to explain the representative applications of the devices and are not intended to guarantee any circuit design or permit any industrial property right to other rights to execute. Bay Linear takes no responsibility for any problems related to any industrial property right resulting from the use of the contents shown in the data book. Typical parameters can and do vary in different applications. Customer's technical experts must validate all operating parameters including " Typical" for each customer application.
LIFE SUPPORT AND NUCLEAR POLICY Bay Linear products are not authorized for and should not be used within life support systems which are intended for surgical implants into the body to support or sustain life, in aircraft, space equipment, submarine, or nuclear facility applications without the specific written consent of Bay Linear President.
Bay Linear, Inc
2478 Armstrong Street, Livermore, CA 94550 Tel: (925) 606-5950, Fax: (925) 940-9556
www.baylinear.com

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