150mA Adjustable Voltage Regulator Guaranteed 150mA current Adjus

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150mA Adjustable Voltage Regulator Guaranteed 150mA current Adjus

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LP2951A improved version LP2951 features tighter tolerance output voltage reference voltage specifications. Both LP2951 LP2951A feature 150mA output current capability. LP2951 series power voltage regulators have quiescent current dropout voltage. quiescent current increases minimally during dropout conditions thereby extending battery life. Available lead SOIC package, LP2951 series includes features such shutdown output voltage detect (typically battery conditions). This function also used power reset function when triggered CMOS inputs. circuit used fixed voltage volt regulator adjusted between 1.24 volts volts using external resistor pairs.
150mA Adjustable Voltage Regulator
Guaranteed 150mA current Adjustable output voltage 1.24V Accurate output 150mA dropout voltage 400mV 150mA Regulator reference functions Direct replacement LP2951AC, MIC2951-02, AS2951AC Full industrial temperature range SO-8 package
LP2951A
Applications
Microcontroller supplies Linear regulators Adjustable Supplies Switching power supplies post-regulation Portable modems Battery powered systems Cellular telephones Voltage references
Typical Application Circuits
10nF
VOUT VREF
VOUT 1.24V SHUTDOWN INPUT 3.3uF
LP2951A ERRORB ERROR OUTPUT
SENSE SHDN
100k
Revision January 2001
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LP2951A
POWER MANAGEMENT Absolute Maximum Ratings
Parameter Supply Voltage Shutdown Input Voltage Error omp. Output Voltage Power pati Thermal Resi stance Juncti Thermal Resi stance Juncti Ambi ent(1) Operati Juncti Temperature Range Storage Temperature Range Lead Temperature (Solderi Sec. Rati (Human Body Model) TSTG TLEAD mbol VSHDN Maximum -0.3 -0.3 -0.3 Internally nits
Note: inch square 1/16 FR4, double sided, 1oz. minimum copper weight.
Electrical Characteristics
Unless specified: VOUT(NOM) IOUT 100µA, COUT 1µF, limits over operating temperature range TA).
Parameter Output Voltage Temp oeffi Regulati Load Regulati ropout Voltage
mbol REG(LINE) REG(LOAD)
onditions 25°C IOUT 100µA 70°C 100µA IOUT 150mA IOUT 100µA IOUT 150mA
4.975
5.000
5.025 1.250
nits ppm/°C
Ground urrent
IGND
IOUT 100µA IOUT 150mA
ropout Ground urrent Short rcui urrent Reference Voltage Feedback urrent
IGND(D) VREF
4.5V, IOUT 100µA VOUT VREF VOUT (VIN 1V), 25°C 100µA IOUT 100mA 1.220
1.235
2001 Semtech Corp.
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LP2951A
POWER MANAGEMENT Electrical Characteristics (Cont.)
Unless specified: VOUT(NOM) IOUT 100µA, COUT 1µF, limits over operating temperature range TA).
Parameter Error omparator Output Leakage urrent Output Voltage Threshold Voltage
mbol
onditions
nits
IL(OH)
4.5V, 400µA Upper Lower
Hysteresi Shutdown Input Input Logi Voltage
VHYST
VSHDN
Input urrent
ISHDN
VSHDN 2.4V VSHDN
Regulator Shutdown Output urrent
IOUT(SHDN)
VSHDN 30V, VOUT Feedback
Note: Temperature coefficient defined worst case voltage change divided total temperature range.
2001 Semtech Corp.
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LP2951A
POWER MANAGEMENT Configuration Ordering Information
ice(1) LP2951AC M.TR Output Voltage 5V/AD ackag SO-8
Notes: Only available tape reel packaging. reel contains 2500 devices.
Block Diagram
2001 Semtech Corp.
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LP2951A
POWER MANAGEMENT Applications Information (LP2951(A))
Setting Output Voltage LP2951(A) deliver output voltage from 1.24V using external voltage divider. addition, internal voltage divider provided 3.3V LP2951-3.3) output desired. internal voltage divider, simply connect sense output feedback (see block diagram). When using external divider sense pins left open, divider installed from output ground, with center connected feedback (see Adjustable Regulator figure below). When using external voltage divider, resistances calculated from following formula:
VOUT .235 .235
Theoretically, also possible regulator become unstable very large capacitances (>10,000µF) connected output, this been observed practice. also important that capacitance mounted close (1cm less) output regulator.
upper limit values occurs ~1.2MW regulator operated when completely unloaded, this allows feedback divider provide minimum load recommended LP2951(A). regulator always load more connected externally, higher resistor values used, attention must paid -20nA (typical) bias current required feedback pin. Using 1.2MW resistor this bias current will already cause shift output voltage between full load load. Larger values exacerbate problem. Using 120kW resistor reduces error caused feedback bias current 0.2% while still only requiring 10µA feed divider string. Output Filtering output filter capacitor always necessary with LP2951(A) order assure output stability. size this capacitor varies with output voltage (smaller higher output voltages) output current (smaller lower output currents). operation sufficient. regulator operation minimum output voltage (1.24V) output currents 100mA, required filter increases 3.3µF. type capacitor used, although aluminum electrolytics chosen, equivalent series resistance (ESR) should held less. small load currents capacitance reduced. 0.33µF will satisfactory output currents 10mA less, 0.1µF will work output current below 1mA.
2001 Semtech Corp.
Figure Adjustable Regulator lead inductance between input LP2951(A) power source exceeds ~500nH (approximately 10/25cm 0.031/0.78mm trace) also necessary filter capacitor between input terminal ground. tantalum aluminum electrolytic capacitor usually sufficient. Lower values used load currents small. Noise injection into feedback terminal LP2951(A) from nearby noise sources also upset output. Generally this cured addition 100pF from feedback terminal output. Reducing Output Noise ultra-quiet systems, when LP2951(A) being used reference, desirable perform additional output filtering reduce noise. While this done simply using larger capacitors output, that solution tends bulky expensive, eventually, with huge capacitors (>1,000µF) cause instability regulator. Generally, more costeffective regulator regulate output noise away.
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LP2951A
POWER MANAGEMENT Applications Information (Cont.)
This done bypassing upper resistor feedback divider with small capacitor provide more direct path feedback. size this capacitor calculated from formula: CBYPASS corner where upper resistor feedback divider fcorner frequency above which increased feedback become active. Because gain error amplifier LP2951(A) begins roll about 300Hz, this generally optimum choice corner frequency. reduction output noise will proportional ratio resistors feedback divider:
will increase rate decade frequencies above corner frequency chosen, frequency where error amplifiers gain rolled (~100kHz). order maintain regulator stability when using noise-reducing bypass capacitor, will also necessary increase size output filter capacitor ratio:
2001 Semtech Corp.
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LP2951A
POWER MANAGEMENT Outline Drawing SO-8
Land Pattern -SO-8
Contact Information
Semtech Corporation Power Management Products Division Mitchell Rd., Newbury Park, 91320 Phone: (805)498-2111 (805)498-3804
2001 Semtech Corp.
www.semtech.com

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