General Description The MIC2937A family are bulletproof efficient voltage regulators with very low dropout voltage (typically 40mV at light loads and 300mV at 500mA), and very low quiescent current (90uA typical). The quiescent current of the MIC2937A increases only slightly in dropout, thus prolonging battery life. Key MIC2937A features include protection against reversed battery, fold-back current limiting, and automotive "load dump" protection (60V positive transient). The MIC2937 is available in several configurations. The MIC2937A-xx devices are three pin fixed voltage regulators. The M!IC29371 is a fixed regulator offering logic compatible ON/OFF switching input and an error flag output. This flag may also be used as a power-on reset signal. A logic- compatible shutdown input is provided on the adjustable MIC29372, which enables the regulator to be switched on and off. The MIC29373 is a five pin adjustable version that includes an error flag output that warns of a low output voltage, which is often due to failing batteries on the input. MIC2937A,29371 ,29372,29373 750mA Low Drop Out Voltage Regulator Preliminary InformationProduction Q1 94 Features High output voltage accuracy Guaranteed 750mA output Low quiescent current Low dropout voltage Extremely tight load and line regulation Very iow temperature coefficient Current and thermal limiting Input can withstand -20V reverse battery and +60V positive transients Error flag warns of output dropout Logic-controlled electronic shutdown * Output programmable from 1.24V to 26V(MIC29372/ MIC29373) * Available in TO-220, TO-263, TO-220-5, and TO-263-5 packages. Applications Battery Powered Equipment Cellular Telephones Laptop, Notebook, and Palmtop Computers PCMCIA V,,, and V,,, Regulation/Switching Bar Code Scanners Automotive Electronics SMPS Post-Regulator/ DC to DC Modules High Efficiency Linear Power Supplies Pin Configuration i Cay INPUT GROUND OUTPUT TO-263 Package (MIC2937A-xxBU) ai TO-263-5 Package (MIC 2937 1/29372/29373BU) Five Lead Package Pin Functions: MiC29371 + MiC29372 MIC29373 1) Error Adjust Error 2) input Shutdown Adjust 3) Ground Ground Ground 4) Output Input Input 5) Shutdown Output Output The TAB is Ground on the TO-220 and TO-263 packages. O O \/ 1 2 3 INPUT GROUND OUTPUT TO-220 Package (MIC2937A-xxBT) TO-220-5 Package (MIC2937 1/29372/29373BT) 6-36MIC2937A/2937 1/29372/29373 Micrel Ordering Information Part Number Voltage | Temperature Range* | Package MIC2937A-3.3BU 3.3 40C to +125C TO-263-3 MIC2937A-3.3BT 3.3 40C to +125C TO-220 MIC2937A-5.0BU 5.0 ~40C to +125C TO-263-3 MIC2937A-5.0BT 5.0 40C to +125C TO-220 MiC2937A-12BU 12 40C to +125C TO-263-3 MIC2937A-12BT 12 40C to +125C TO-220 MIC2937A-15BU 15 40C to +125C TO-263-3 MIC2937A-15BT 15 40C to +125C TO-220 MIC29371-3.3BT 3.3 40C to +125C TOQ-220-5 MIC29371-3.3BU 3.3 -40C to +125C TO-263-5 MiC29371-5.0BT 5.0 40C to +125C TO-220-5 MIC29371-5.0BU 5.0 40C to +125C TO-263-5 MIC29371-12BT 12 40C to +125C TO-220-5 MIC29371-12BU 12 ~40C to +125C TO-263-5 MIC29371-15BT 15 ~40C to +125C TO-220-5 MIC29371-15BU 15 40C to +125C TO-263-5 MIC29372BT Adj 40C to +125C TO-220-5 MIC29372BU Adj ~40C to +125C TO-263-5 MIC29373BT Adj -40C to +125C TO-220-5 MIC29373BU Adj 40C to +125C TOQ-263-5 * Junction temperatures Absolute Maximum Ratings If Military/Aerospace specified devices are required, contact your local Micrel representative/distributor for availability and specifications. Power Dissipation (Note 1) Internally Limited Lead Temperature (Soldering, 5 seconds) 260C Storage Temperature Range 65C to +150C Operating Junction Temperature Range 40C to +125C Input Supply Voltage -20V to +60V Operating Input Supply Voltage 2V' to 26V Adjust Input Voltage (Notes 9 and 10) -1.5V to +26V Shutdown Input Voltage 0.3V to +30V Error Comparator Output Voltage 0.3V to +30V ESD Rating >+2000V + Across the full operating temperature, the minimum input voltage range for full output current is 4.3V to 26V. Output will remain in-regulation at lower output voltages and low current loads down to an input of 2V at 25C. 6-37MIC2937A/2937 1/29372/29373 Micrel Electrical Characteristics Limits in standard typeface are for T, = 25C and limits in boldface apply over the full operating temperature range. Uniess otherwise specified, V,, = V,,, + 1V, |, = 5mA, C, = 10uF. The MIC29372 and MIC29373 are programmed for a OUT 5V output voltage, and Vip pown < 0-6V (MIC29372 only). Symbol Parameter Conditions Min Typical Max Units Vo Output Voltage 4.950 5.00 5.050 Vv (5.0 or adjustable 4.900 5.100 versions) 5mA <1, <500mA 4.880 5.00 5.120 Output Voltage Variation from designed V,,,, -1 1 % Accuracy ~2 2 5mA <1, < 500mA ~-2.5 2.5 AV, Output Voltage (Note 2) 20 100 | ppm/c AT Temperature Coef. AV, Line Regulation Vin = Vout + 1V to 26V 0.03 0.10 % Vo 0.40 AVo Load Regulation |. =5 to 750mA 0.04 0.16 % Vo 0.20 (Note 3) Vina Vo Dropout Voltage | = 5mA 60 100 mV (Note 4) 150 | = 100mA 150 200 320 |, = 500mA 300 450 600 | = 750mA 370 leno Ground Pin Current] |, = 5mA 90 150 HA (Note 5) 180 |, = 100mA 1 2 mA 3 |, = 500mA 8 13 16 I = 750mA 15 lsnooo Ground Pin Vy = 0.5V less than designed V,,,,, 180 300 pA Current at Dropout | (V,,, 2 3.3V) (Note 5) U nar Current Limit Vout = OV 1.0 1.5 A (Note 6) 2 AV, Thermal Regulation| (Note 7) 0.05 0.2 Sol AP, e, Output Noise C, = 2.2uF 400 yuV RMS Voltage (10Hz to 100kHz) C, = 33uF 260 1, = 100mA 6-38MIC2937A/2937 1/29372/29373 Micrel Electrical Characteristics (Continued) MIC29372/MIC 29373 Parameter Conditions Min | Typical; Max Units Reference Voltage 1.210 4.235 1.260 Vv 1.200 1.270 V max Reference Voltage (Note 8) 1.185 1.285 Vv Adjust Pin 20 40 nA Bias Current 60 Reference Voltage (Note 7) 20 ppm/C Temperature Coefficient Adjust Pin Bias 0.1 nAfeG Current Temperature Coefficient Error Comparator MIC29371/29373 Output Leakage Vou = 30V 0.01 1.00 HA Current 2.00 Output Low Vin =4.5V 150 250 mV Voltage lo, = 250HA 400 Upper Threshold (Note 9) 40 60 mV Voltage 25 Lower Threshold (Note 9) 75 95 mV Voltage 140 Hysteresis (Note 9) 15 mV Shutdown Input MIC29371/MIC29372 Input Logic Voltage 1.3 Vv Low (ON) 0.7 High (OFF) 2.0 Shutdown Pin Venutoown = 2-4 30 50 HA Input Current 100 Venutpown = SOV 450 600 HA 750 Regulator Output (Note 10) 3 10 HA Current in Shutdown 20 6-39MIC2937A/2937 1/29372/29373 Micrel Note 1: Absolute maximum ratings indicate limits beyond which damage to the component may occur. Electrical specifications do not apply when operating the device outside of its rated operating conditions. The maximum allowable power dissipation is a function of the maximum junction temperature, T, 44... the junction-to-ambient thermal resistance, 8,,, and the ambient temperature, T,. The maximum allowable power dissipation at any ambient temperature is calculated using: Pasay) = (Tymraxy~ Ta)/ Oy, Exceeding the maximum allowable power dissipation will result in excessive die temperature, and the regulator will go into thermal shutdown. Note 2: Output voltage temperature coefficient is defined as the worst case voltage change divided by the total temperature range. Note 3: Regulation is measured at constant junction temperature using low duty cycle pulse testing. Changes in output voltage due to heating effects are covered by the thermal regulation specification. Note 4: Dropout Voltage is defined as the input to output differential at which the output voltage drops 100 mV below its nominal value measured at 1V differential. At low values of programmed output voltage, the minimum input supply voltage of 4.3V over temperature must be taken into account. The MIiC2937A operates down to 2V of input at reduced output current at 25C. Note 5: Ground pin current is the regulator quiescent current. The total current drawn from the source is the sum of the load current plus the ground pin current. Note 6: The MIC2937A features fold-back current limiting. The short circuit (V.., = OV) current limit is less than the maximum current with normal output voltage. Note 7: Thermal regulation is defined as the change in output voltage at a time T after a change in power dissipation is applied, excluding load or line regulation effects. Specifications are for a 200mA load pulse at V,, = 20V (a 4W pulse) for T = 10ms. Note 8: Vie S Voy, S (Vi 1: V), 4 3V SVS 26V, SMA <1, < 750 MA, T)< Ty yay Note 9: Comparator thresholds are expressed in terms of a voltage differential at the Adjust terminal below the nominal reference voltage measured at 6V input (for a 5V regulator). To express these thresholds in terms of output voltage change, multiply by the error amplifier gain = Viu7 Mace = (R1 + R2)/R2. For example, at a programmed output voltage of SV, the Error output is guaranteed to go low when the output drops by 95 mV x 5V/1.235 V = 384 mV. Thresholds remain constant as a percent of VouT as VouT is varied, with the dropout warning occurring at typically 5% below nominal, 7.5% guaranteed. Note 10: Circuit of Figure 3 with Rt 2 150kQ. Veuoown 2 2V and V,, < 26V,V,. 7 = 0. Note 11: When used in dual supply systems where the regulator load is returned to a negative supply, the output voltage must be diode clamped to ground. Note 12: Maximum positive supply voltage of 60V must be of limited duration (< 100ms) and duty cycle (< 1%). The maximum continuous supply voltage is 26V. Schematic Diagram Ric 1.4 ku 156 i Re 27.8 kD REI 60 Ky 324 [ro xs 6-40MIC2937A/2937 1/29372/29373 Micrel! Typical Characteristics Ground Pin Current Ground Pin Current Ground Pin Current vs. Input Voltage vs. Temperature vs. Load z 0 250 1 3 Z Z E = 4 ~ 200 5 z G ra > c < 150 3 zx eg z oO z a z a 100 IL= 2 4 g 3 3 g 3 fe & 50 o o 12 3 45 67 8 -75-50 -25 0 25 50 75 100 125150 o4 1 10. 100. 1000 INPUT VOLTAGE (V) TEMPERATURE (C) OUTPUT CURRENT (mA) Ground Pin Current Ground Pin Current 3 vs. Input Voltage vs. Temperature Output Noise Voltage 0 z ~ = < =1 ~ 25 = @ 2 5 E 20 2 3 5 s Ww Oo 15 3 g z Zz 5 oa a 10 8 3 5 Ww 3 5 3 | VIN= c = S 5 & g Vout = 012 3 45 6 7 8 -75 -50 -25 0 25 50 75 100125 150 01 1 10. 100 1000 INPUT VOLTAGE (V) JUNCTION TEMPERATURE (C) LOAD CURRENT (ma) Ripple Rejection Ripple Rejection vs. Frequency at vs. Frequency Medium Current at High Current Output Impedance 10 90 100 = 99 _ ~ i IN = g g C= 3 of yours 5 80 3 w L = 10p ~- 70 a 2 | B60 g 8 a a i, =500mA uw c 50 x 2 Bgl Vin=8 a Vin = 6V 5 0 45 Vout =5V a Vout = & Le x Cy= 10uF e Cy= 10pF 2 be p= 25mA Le 10u a 0 10 0.01 0.01 01 4 10 100 1000 0.01 01 + 10 100 1000 0.01 014 1 10 100 1000 FREQUENCY (kHz) FREQUENCY (kHz) FREQUENCY (kHz) Line Transient Response Line Transient Response ua uy SG =1 g =1 <S 400 _ <S = Be arom] SE I= 10m = = >S 0 Sw Vout bea ra >< at or fr 5S -400 55 6 6 lu EtG Eo ze 26 25 av 25 > > 0 02 04 06 08 1 0 1 2 3.04 5 TIME (ms) TIME (ms) 6-41MIC2937A/2937 1/29372/29373 Typical Characteristics, Continued Load Transient 800 VIN = 400 Vout = -400 OUTPUT VOLTAGE CHANGE (mV) Oo -800 500mA 100pA LOAD CURRENT o 10 20 30040 TIME (ms) 19 Enable Transient Cyst OUTPUT VOLTAGE {V) OUTPUT VOLTAGE (V) SHUTDOWN VOLTAGE (V) SHUTDOWN VOLTAGE (V) 0 1 2 3 4 5 TIME (ms) Thermal OUTPUT VOLTAGE CHANGE (V) POWER DISSIPATION (W) oO 10 20 30 40 TIME (ms) OUTPUT VOLTAGE CHANGE (mv) LOAD CURRENT OUTPUT CURRENT (mA) Load Transient Response 200 Vine 100 Vout = 5V. 0 = 100UF -100 -200 500mA 100pA 0 70 20 30 40 50 60 TIME (ms) Enable Transient 6 ce TIME (ms) Fold-Back Current Limiting 1200 1000 7 | 800 | LY 600 400 0 20 40 60 80 100 PERCENT OUTPUT VOLTAGE (%) OUTPUT CURRENT (mA) OUTPUT VOLTAGE (V) DROPOUT VOLTAGE (V) Characteristics 0 1 2 3 4 5 6 INPUT VOLTAGE (VOLTS) Short-Circuit Output Current and Maximum Output Current 600 550 500 450 400 350 300 250 MAX OUTPUT. Vout = SHORT CURRENT Vout = 0 200 -75-50 -25 0 25 5075 100 125150 JUNCTION TEMPERATURE (*C) Dropout Voltage 0 02 #04 06 O08 1.0 OUTPUT CURRENT (A) Micrel 6-42MIC2937A/2937 1/29372/29373 Micrel Applications Information External Capacitors A 10uF (or greater) capacitor is required between the MIC2937A output and ground to prevent oscillations due to instability. Most types of tantalum or aluminum electrolytics will be adequate; film types will work, but are costly and therefore not recommended. Many aluminum electrolytics have electrolytes that freeze at about30C, so solid tantalums are recommended for operation below 25C. The important parameters of the capacitor are an effective series resistance of about 5Q or less and a resonant frequency above 500kHz. The value of this capacitor may be increased without limit. At lower values of output current, less output capacitance is required for output stability. The capacitor can be reduced to 0.5uF for current below 10mA or 0.15uF for currents below 1 mA. Adjusting the MIC29372/29373 to voltages below 5V runs the error amplifier at lower gains so that more output capacitance is needed. For the worst-case situation of a 750mA load at 1.23V output (Output shorted to Adjust) a 22uF (or greater) capacitor should be used. The MiC2937A will remain stable and in regulation with no load in addition to the internal voltage divider, unlike many other voltage regulators. This is especially important in CMOS RAM keep-alive applications. When setting the output voltage of the MIC29372/29373 version with external resistors, a minimum load of 1mA is recommended. A 1pF capacitor should be placed from the input to ground if there is more than 10 inches of wire between the input and the AC filter capacitor or if a battery is used as the input. Stray capacitance to the MIC29372/29373 Adjust terminal (pin 7) can cause instability. This may especially be a problem when using high value external resistors to set the output voltage. Adding a 100pF capacitor between Output and Adjust and increasing the output capacitor to at least 22uF will remedy this. Error Detection Comparator Output (MIC29371/ MIC29373) A logic low output willbe produced by the comparator whenever the MIC29371/29373 output falls out of regulation by more than approximately 5%. This figure is the comparators built- in offset of about 6OmV divided by the 1.235V reference voltage. (Refer to the block diagram on Page 1). Thistrip level remains 5% below normal regardless of the programmed output voltage of the MIC29371/29373. For example, the error flag trip level is typically 4.75V for a 5V output or 11.4V fora 12V output. The out of regulation condition may be due either to low input voltage,extremely high input voltage, current limiting, or thermal limiting. Figure 1 is a timing diagram depicting the ERROR signal and the regulated output voltage as the MIC2937 1/29373 input is ramped up and down. The ERROR signal becomes valid (low) at about 1.3V input. It goes high at about 5V input (the input voltage at which V,,,,, = 4.75). Since the MIC29371/ 29373s dropout voltage is load-dependent (see curve in Typical Performance Characteristics), the input voltage trip point (about 5V) will vary with the load current. The output voltage trip point (approximately 4.75V) does not vary with load. The error comparator has an open-collector output which requires an external pull-up resistor. Depending on system requirements, this resistor may be returned to the 5V output or some other supply voltage. In determining a value for this resistor, note that while the output is rated to sink 250,/A, this sink current adds to battery drain in a low battery condition. Suggested values range from 100k to 1MQ. The resistor is not required if this output is unused. In shutdown mode, ERROR will go high if it has been pulled up to an external supply. To avoid this invalid response, ERROR should be pulled up to V,,,,,- Programming the Output Voltage (MIC29372/ MIC29373) The MIC29372/29373 may programmed for any output voltage between its 1.235V reference and its 26V maximum rating. An external pair of resistors is required, as shown in Figure 3. The complete equation for the output voltage is Vour = Var X{1+R/Ro} + hen R, where V__, is the nominal 1.235 reference voltage and I_, is the Adjust pin bias current, nominally 20nA. The minimum recommended load current of 1A forces an upper limit of 1.2MQ on the value of R,,, if the regulator must work with no load (a condition often found in CMOS in standby), |... will produce a 2% typical error in V,.,, which may be eliminated at room temperature by trimming R,. For better accuracy, choosing R, = 100k reduces this errorto0.17% while increasing the resistor program current to 12nA. Since the MIC29372/ 29273 typically draws 100uA at no load with SHUTDOWN open-circuited, this is a negligible addition. Reducing Output Noise In reference applications it may be advantageous to reduce the AC noise present at the output. One method is to reduce the regulator bandwidth by increasing the size of the output capacitor. This is relatively inefficient, as increasing the capacitor from 1pF to 220uF only decreases the noise from 430uV to 160UV,,,. for a 100kHz bandwidth at 5V output. Noise can be reduced by a factor of four with the adjustable 4.75V, OUTPUT VOLTAGE NOT VALID ERROR NOT VALID INPUT Vv VOLTAGE 8 1.3V * SEE APPLICATIONS INFORMATION Figure 1. ERROR Output Timing 6-43MIC 2937A/2937 1/29372/29373 regulators with a bypass capacitor across R,, since it reduces the high frequency gain from 4 to unity. Pick Ceypass = -1.- 27Ri 200 Hz or about 0.01p.F. When doing this, the output capacitor must be increased to 10uF to maintain stability. These changes reduce the output noise from 430yV to 100LV,,,, for a 100 kHz bandwidth at 5V output. With the bypass capacitor added, noise no longer scales with output voltage so that improvements are more dramatic at higher output voltages. Micrel Automotive Applications The MIC2937A is ideally suited for automotive applications for a variety of reasons. It will operate over a wide range of input voltages with very low dropout voltages (40myV at light loads), and very low quiescent currents (100A typical). These features are necessary for use in battery powered systems, such as automobiles. itis a bulletproof" device with the ability to survive both reverse battery (negative transients up to 20V below ground), and load dump (positive transients up to 60V) conditions. A wide operating temperature range with low temperature coefficients is yet another reason to use these versatile regulators in automotive designs. Typical Applications VIN +Vin OUT Vour = 5V + HE Oo HK Figure 2. MIC2937A-5.0 Fixed +5V Regulator +VIN VIN VOUT ~ VIN VOUT! GND ADJUST LoL MINIMUM INPUT-OUTPUT VOLTAGE RANGES FROM 40mV TO 400mvV, DEPENDING ON LOAD CURRENT. Figure 4. MIC29372/29373 Wide Input Voltage Range Current Limiter +VIN 100kQ MIN Vout ERROR ERROR Vv 1.2V 26V OUTPUT OUT | | EU SHUTDOWN ~ A 10pF OFF L Ry] .04 _f- GND ADJUST UF ON L 1.23V 5 = AY VREF Ra Vout = VREF x (1+ a L a ERROR OUTPUT ON MIC29373 ONLY SHUTDOWN INPUT ON MIC29372 ONLY Figure 3. MiC29372/29373 Adjustable Regulator +5V to +7V +VIN Veg OUT VouT| SHUTDOWN O INPUT 9 __| SHUTDOWN fT OFF ON + 300kQ 10uF 1% 100pF nL GND ADJUST I 220k2 180k 1% = 1% 2N2222 Sv SHUTDOWN PIN LOW= ENABLE OUTPUT. Q1 ON = 3.3V, Q1 OFF = 5.0V. Figure 5. MIC29372 5.0V or 3.3V Selectable Regulator with Shutdown. 6-44