LP2951A 150mA Adjustable Voltage Regulator POWER MANAGEMENT Description Features u u u u u u The LP2951A is an improved version of the LP2951 and features tighter tolerance on the output voltage and reference voltage specifications. Both the LP2951 and LP2951A feature 150mA output current capability. Guaranteed 150mA current Adjustable output voltage - 1.24V to 29V Accurate 5V output @ 150mA Low dropout voltage - 350 to 400mV @ 150mA Regulator or reference functions Direct replacement for LP2951AC, MIC2951-02, AS2951AC u Full industrial temperature range u SO-8 package The LP2951 series of low power voltage regulators have low quiescent current and low dropout voltage. The quiescent current increases minimally during dropout conditions thereby extending battery life. Available in the 8 lead SOIC package, the LP2951 series includes features such as shutdown and low output voltage detect (typically due to low battery conditions). This function may also be used as a power on reset function when triggered by CMOS or TTL inputs. Applications u u u u u u u u The circuit can be used as a fixed voltage 5 volt regulator or adjusted between 1.24 volts and 29 volts using external resistor pairs. Microcontroller supplies Linear regulators Adjustable Supplies Switching power supplies - post-regulation Portable modems Battery powered systems Cellular telephones Voltage references Typical Application Circuits C1 R1 VOUT = VREF 1 + R 2 10nF R1 U1 1 VOUT = 1.24V to 30V 2 3 SHUTDOWN INPUT 4 + C2 3.3uF LP2951A OUT IN SENSE FB SHDN TAP GND ERRORB 8 VIN 7 6 5 ERROR OUTPUT R2 R3 100k Revision 1, January 2001 1 www.semtech.com LP2951A POWER MANAGEMENT Absolute Maximum Ratings Parameter Supply Voltage Shutdown Input Voltage Sy mbol Maximum U nits VIN -0.3 to 30 V VSHDN -0.3 to 30 V -0.3 to 30 V Error C omp. Output Voltage Power D i ssi pati on PD Internally Li mi ted W Thermal Resi stance Juncti on to C ase q JC 47 C /W Thermal Resi stance Juncti on to Ambi ent(1) q JA 65 C /W Operati ng Juncti on Temperature Range TJ -40 to 125 C Storage Temperature Range TSTG -65 to 150 C Lead Temperature (Solderi ng) 5 Sec. TLEAD 300 C ESD Rati ng (Human Body Model) ESD 2 kV Note: (1) 2 inch square of 1/16 FR4, double sided, 1oz. minimum copper weight. Electrical Characteristics Unless specified: VIN = VOUT(NOM) + 1V, IOUT = 100A, COUT = 1F, limits are over operating temperature range (TJ = TA). Parameter Sy mbol C onditions Min Ty p Max U nits VO UT TJ = 25C , IOUT = 100A 4.975 5.000 5.025 V TC 0C TJ 70C 20 120 ppm/C Li ne Regulati on REG(LINE) 6V VIN 30V 0.1 0.5 % Load Regulati on REG(LOAD) 100A IOUT 150mA 0.1 0.4 % D ropout Voltage VD IOUT = 100A 80 150 mV IOUT = 150mA 380 600 IOUT = 100A 120 160 A IOUT = 150mA 8 14 mA IGND(D) VIN = 4.5V, IOUT = 100A 110 250 A ISC VOUT = 0V 200 250 mA VREF VREF VOUT (VIN - 1V), TJ = 25C , 100A IOUT 100mA 1.235 1.250 V 20 60 nA Output Voltage Temp C oeffi ci ent (1) Ground Pi n C urrent D ropout Ground Pi n C urrent Short C i rcui t C urrent Li mi t Reference Voltage Feedback Bi as C urrent a 2001 Semtech Corp. IGND IFB 2 1.220 www.semtech.com LP2951A POWER MANAGEMENT Electrical Characteristics (Cont.) Unless specified: VIN = VOUT(NOM) + 1V, IOUT = 100A, COUT = 1F, limits are over operating temperature range (TJ = TA). Parameter Sy mbol C onditions Output Hi gh Leakage C urrent IL(OH) VOH = 30V Output Low Voltage VOL VIN = 4.5V, IOL = 400A Threshold Voltage VTH Upper Min Ty p Max U nits 2 A 400 mV Error C omparator 150 25 Lower Hysteresi s 60 75 mV 140 15 VHYST mV Shutdown Input Input Logi c Voltage VSHDN Low Hi gh Input C urrent Regulator Shutdown Output C urrent ISHDN IOUT(SHDN) 0.6 2.0 V V VSHDN = 2.4V 100 VSHDN = 30V 750 VSHDN 2V, VIN 30V, VOUT = 0V, Feedback pi n to Tap 20 A A Note: (1) Temperature coefficient is defined as the worst case voltage change divided by total temperature range. a 2001 Semtech Corp. 3 www.semtech.com LP2951A POWER MANAGEMENT Pin Configuration Ordering Information D ev ice(1) Output Voltage P ackag e LP2951AC M.TR 5V/AD J SO-8 Notes: (1) Only available in tape and reel packaging. A reel contains 2500 devices. Block Diagram a 2001 Semtech Corp. 4 www.semtech.com LP2951A POWER MANAGEMENT Applications Information (LP2951(A)) Setting the Output Voltage The LP2951(A) can be set to deliver any output voltage from 1.24V to 30V by using an external voltage divider. In addition, an internal voltage divider is provided if a 5V (or 3.3V for LP2951-3.3) output is desired. To use the internal voltage divider, simply connect the sense pin to the output and the tap pin to the feedback pin (see block diagram). When using an external divider the sense and tap pins are left open, and the divider is installed from the output to ground, with its center connected to the feedback pin (see Adjustable Regulator figure below). When using an external voltage divider, resistances can be calculated from the following formula: 1 .235 Theoretically, it is also possible for the regulator to become unstable if very large capacitances (>10,000F) are connected to the output, but this has not been observed in practice. It is also important that the capacitance be mounted close (1cm or less) to the output pin of the regulator. -9 VOUT = R 2 + 20 x10 x R1 + 1 .235 V An upper limit of values for R2 occurs at ~1.2MW if the regulator is to be operated when completely unloaded, as this allows the feedback divider to provide the 1A minimum load recommended for the LP2951(A). If the regulator always has a load of 1A or more connected externally, higher resistor values can be used, but attention must be paid to the -20nA (typical) bias current required by the feedback pin. Using a 1.2MW resistor for R2, this bias current will already cause a 2% shift in output voltage between full load and no load. Larger values of R2 exacerbate the problem. Using a 120kW resistor for R2 reduces the error caused by feedback bias current to 0.2% while still only requiring 10A to feed the divider string. Figure 1: Adjustable Regulator If the lead inductance between the input of the LP2951(A) and its power source exceeds ~500nH (approximately 10/25cm of 0.031/0.78mm trace) it may also be necessary to add a filter capacitor between the input terminal and ground. A 1F tantalum or aluminum electrolytic capacitor is usually sufficient. Lower values can be used if load currents are small. Noise injection into the feedback terminal of the LP2951(A) from nearby noise sources can also upset the output. Generally this can be cured by the addition of 100pF or so from the feedback terminal to the output. Output Filtering An output filter capacitor is always necessary with the LP2951(A) in order to assure output stability. The size of this capacitor varies with output voltage (smaller at higher output voltages) and output current (smaller at lower output currents). For 5V operation 1F is sufficient. For regulator operation at minimum output voltage (1.24V) and output currents of 100mA, the required filter increases to 3.3F. Any type of capacitor may be used, although if aluminum electrolytics are chosen, the equivalent series resistance (ESR) should be held to 5W or less. For small load currents the capacitance can be reduced. 0.33F will be satisfactory for output currents of 10mA or less, and 0.1F will work if output current is below 1mA. a 2001 Semtech Corp. Reducing Output Noise In ultra-quiet systems, or when the LP2951(A) is being used as a reference, it may be desirable to perform additional output filtering to reduce noise. While this can be done by simply using larger capacitors on the output, that solution tends to be bulky and expensive, and eventually, with huge capacitors (>1,000F) may cause instability in the regulator. Generally, it is more costeffective to let the regulator regulate output noise away. 5 www.semtech.com LP2951A POWER MANAGEMENT Applications Information (Cont.) This can be done by bypassing the upper resistor in the feedback divider with a small capacitor to provide a more direct path for AC feedback. The size of this capacitor can be calculated from the formula: 1 CBYPASS = 2 R f 1 corner where R1 is the upper resistor of the feedback divider and fcorner is the frequency above which the increased AC feedback is to become active. Because the gain of the error amplifier in the LP2951(A) begins to roll off at about 300Hz, this is generally an optimum choice for corner frequency. The reduction of the output noise will be proportional to the ratio of the two resistors in the feedback divider: R1 R1 + R 2 and will increase at a rate of 20 dB per decade at frequencies above the corner frequency chosen, up to the frequency where the error amplifiers gain has rolled off to 1 (~100kHz). In order to maintain regulator stability when using a noise-reducing bypass capacitor, it will also be necessary to increase the size of the output filter capacitor by the ratio: R1 R1 + R 2 a 2001 Semtech Corp. 6 www.semtech.com LP2951A POWER MANAGEMENT Outline Drawing - SO-8 Land Pattern -SO-8 Contact Information Semtech Corporation Power Management Products Division 652 Mitchell Rd., Newbury Park, CA 91320 Phone: (805)498-2111 FAX (805)498-3804 a 2001 Semtech Corp. 7 www.semtech.com