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LM2931 Series Low Dropout Regulators
April 1998
LM2931 Series Low Dropout Regulators
General Description
The LM2931 positive voltage regulator features a very low quiescent current of 1 mA or less when supplying 10 mA loads. This unique characteristic and the extremely low input-output differential required for proper regulation (0.2V for output currents of 10 mA) make the LM2931 the ideal regulator for standby power systems. Applications include memory standby circuits, CMOS and other low power processor power supplies as well as systems demanding as much as 100 mA of output current. Designed originally for automotive applications, the LM2931 and all regulated circuitry are protected from reverse battery installations or 2 battery jumps. During line transients, such as a load dump (60V) when the input voltage to the regulator can momentarily exceed the specified maximum operating voltage, the regulator will automatically shut down to protect both internal circuits and the load. The LM2931 cannot be harmed by temporary mirror-image insertion. Familiar regulator features such as short circuit and thermal overload protection are also provided. The LM2931 family includes a fixed 5V output (3.8% tolerance for A grade) or an adjustable output with ON/OFF pin. Both versions are available in a TO-220 power package, TO-263 surface mount package, and an 8-lead surface mount package. The fixed output version is also available in the TO-92 plastic package.
Features
n n n n n n n n n n n Very low quiescent current Output current in excess of 100 mA Input-output differential less than 0.6V Reverse battery protection 60V load dump protection -50V reverse transient protection Short circuit protection Internal thermal overload protection Mirror-image insertion protection Available in TO-220, TO-92, TO-263 or SO-8 packages Available as adjustable with TTL compatible switch
Output Voltage Options
Output Number 5V LM2931T-5.0, LM2931AT-5.0 LM2931S-5.0, LM2931AS-5.0 LM2931Z-5.0, LM2931AZ-5.0 LM2931M-5.0, LM2931AM-5.0 Adjustable, 3V to 24V LM2931CT LM2931CS LM2931CM Part Number Package Type 3-Lead TO-220 3-Lead TO-263 TO-92 8-Lead SO 5-Lead TO-220 5-Lead TO-263 8-Lead SO
Typical Applications
LM2931 Fixed Output
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*Required if regulator is located far from power supply filter. **C2 must be at least 100 F to maintain stability. May be increased without bound to maintain regulation during transients. Locate as close as possible to
the regulator. This capacitor must be rated over the same operating temperature range as the regulator. The equivalent series resistance (ESR) of this capacitor is critical; see curve.
(c) 1998 National Semiconductor Corporation
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Typical Applications
(Continued) LM2931 Adjustable Output
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Note: Using 27k for R1 will automatically compensate for errors in VOUT due to the input bias current of the ADJ pin (approximately 1 A).
Connection Diagrams and Ordering Information
FIXED 5V OUTPUT TO-220 3-Lead Power Package TO-263 Surface-Mount Package
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Front View Order Number LM2931T-5.0 or LM2931AT-5.0 See NS Package Number T03B
Top View
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Side View Order Number LM2931S-5.0 or LM2931AS-5.0 See NS Package Number TS3B 8-Pin Surface Mount TO-92 Plastic Package
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*NC = Not internally connected
Top View Order Number LM2931M-5.0 or LM2931AM-5.0 See NS Package Number M08A
Bottom View Order Number LM2931Z-5.0 or LM2931AZ-5.0 See NS Package Number Z03A
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Connection Diagrams and Ordering Information
ADJUSTABLE OUTPUT VOLTAGE TO-220 5-Lead Power Package
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TO-263 5-Lead Surface-Mount Package
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Front View Order Number LM2931CT See NS Package Number T05A
Top View
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Side View Order Number LM2931CS See NS Package Number TS5B 8-Pin Surface Mount
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Top View Order Number LM2931CM See NS Package Number M08A
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Absolute Maximum Ratings (Note 1)
If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. Input Voltage Operating Range Overvoltage Protection LM2931A, LM2931C (Adjustable) LM2931 26V 60V 50V
Internal Power Dissipation (Note 2) (Note 4) Operating Ambient Temperature Range Maximum Junction Temperature Storage Temperature Range Lead Temp. (Soldering, 10 seconds) ESD Tolerance (Note 5)
Internally Limited -40C to +85C 125C -65C to +150C 230C 2000V
Electrical Characteristics for Fixed 5V Version
VIN = 14V, IO = 10 mA, TJ = 25C, C2 = 100 F (unless otherwise specified) (Note 2) Parameter Conditions LM2931A-5.0 Typ Output Voltage 6.0V VIN 26V, IO = 100 mA -40C Tj 125C Line Regulation Load Regulation Output Impedance Quiescent Current 9V VIN 16V 6V VIN 26V 5 mA IO 100 mA 100 mADC and 10 mArms, 100 Hz-10 kHz IO 10 mA, 6V VIN 26V -40C Tj 125C IO = 100 mA, VIN = 14V, Tj = 25C Output Noise Voltage Long Term Stability Ripple Rejection Dropout Voltage Maximum Operational Input Voltage Maximum Line Transient Reverse Polarity Input Voltage, DC Reverse Polarity Input Voltage, Transient T = 1 ms, 100 ms, RL = 500 -80 -50 -80 -50 VMIN RL = 500, VO 5.5V, T = 1 ms, 100 ms VO -0.3V, RL = 500 70 fO = 120 Hz IO = 10 mA IO = 100 mA 10 Hz-100 kHz, COUT = 100 F 0.4 15 500 20 80 0.05 0.3 33 26 60 70 55 0.2 0.6 1.0 30 5 500 20 80 0.05 0.3 33 26 50 0.2 0.6 0.4 15 1.0 mAMAX mAMAX mAMIN VrmsMAX mV/1000 hr dBMIN VMAX VMAX VMAX VMIN VMIN 2 4 14 200 5 Limit (Note 3) 5.19 4.81 5.25 4.75 10 30 50 2 4 14 200 LM2931-5.0 Typ Limit (Note 3) 5.25 4.75 5.5 4.5 10 30 50 VMAX VMIN VMAX VMIN mVMAX mVMAX mVMAX mMAX Units Limit
-30
-15
-30
-15
VMIN
Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Electrical specifications do not apply when operating the device beyond its rated operating conditions. Note 2: See circuit in Typical Applications. To ensure constant junction temperature, low duty cycle pulse testing is used. Note 3: All limits are guaranteed for TJ = 25C (standard type face) or over the full operating junction temperature range of -40C to +125C (bold type face). Note 4: The maximum power dissipation is a function of maximum junction temperature TJmax, total thermal resistance JA, and ambient temperature TA. The maximum allowable power dissipation at any ambient temperature is PD = (TJmax - TA)/JA. If this dissipation is exceeded, the die temperature will rise above 150C and the LM2931 will go into thermal shutdown. For the LM2931 in the TO-92 package, JA is 195C/W; in the SO-8 package, JA is 160C/W, and in the TO-220 package, JA is 50C/W; and in the TO-263 package, JA is 73C/W. If the TO-220 package is used with a heat sink, JA is the sum of the package thermal resistance junction-to-case of 3C/W and the thermal resistance added by the heat sink and thermal interface. If the TO-263 package is used, the thermal resistance can be reduced by increasing the P.C. board copper area thermally connected to the package: Using 0.5 square inches of copper area, JA is 50C/W; with 1 square inch of copper area, JA is 37C/W; and with 1.6 or more square inches of copper area, JA is 32C/W. Note 5: Human body model, 100 pF discharged through 1.5 k.
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Electrical Characteristics for Adjustable Version
VIN = 14V, VOUT = 3V, IO = 10 mA, TJ = 25C, R1 = 27k, C2 = 100 F (unless otherwise specified) (Note 2) Parameter Reference Voltage IO 100 mA, -40C Tj 125C, R1 = 27k Measured from VOUT to Adjust Pin Output Voltage Range Line Regulation Load Regulation Output Impedance Quiescent Current VOUT + 0.6V VIN 26V 5 mA IO 100 mA 100 mADC and 10 mArms, 100 Hz-10 kHz IO = 10 mA IO = 100 mA During Shutdown RL = 500 Output Noise Voltage Long Term Stability Ripple Rejection Dropout Voltage Maximum Operational Input Voltage Maximum Line Transient Reverse Polarity Input Voltage, DC Reverse Polarity Input Voltage, Transient On/Off Threshold Voltage On Off On/Off Threshold Current VO = 3V 2.0 2.2 20 1.2 3.25 50 VMAX VMIN AMAX T = 1 ms, 100 ms, RL = 500 -80 -50 VMIN IO = 10 mA, Reference Voltage 1.5V T = 1 ms, 100 ms VO -0.3V, RL = 500 -30 -15 VMIN 33 70 26 60 VMIN VMIN fO = 120 Hz IO 10 mA IO = 100 mA 10 Hz-100 kHz 0.2 0.3 40 0.4 15 0.8 100 0.4 0.02 0.05 0.3 0.2 0.6 1 1 Conditions Typ 1.20 Limit 1.26 1.14 1.32 1.08 24 3 1.5 1 Units Limit VMAX VMIN VMAX VMIN VMAX VMIN mV/VMAX %MAX m/V mAMAX mA mAMAX Vrms/V %/1000 hr %/V VMAX VMAX
Typical Performance Characteristics
Dropout Voltage Dropout Voltage Low Voltage Behavior
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Typical Performance Characteristics
Output at Voltage Extremes
(Continued) Load Transient Response
Line Transient Response
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Peak Output Current
Quiescent Current
Quiescent Current
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Quiescent Current
Ripple Rejection
Ripple Rejection
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Typical Performance Characteristics
Output Impedance
(Continued) Reference Voltage
Operation During Load Dump
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Maximum Power Dissipation (SO-8)
Maximum Power Dissipation (TO-220)
Maximum Power Dissipation (TO-92)
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Maximum Power Dissipation (TO-263) (Note 4)
On/Off Threshold
Output Capacitor ESR
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Schematic Diagram
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Application Hints
One of the distinguishing factors of the LM2931 series regulators is the requirement of an output capacitor for device stability. The value required varies greatly depending upon the application circuit and other factors. Thus some comments on the characteristics of both capacitors and the regulator are in order. High frequency characteristics of electrolytic capacitors depend greatly on the type and even the manufacturer. As a result, a value of capacitance that works well with the LM2931 for one brand or type may not necessary be sufficient with an electrolytic of different origin. Sometimes actual bench testing, as described later, will be the only means to determine the proper capacitor type and value. Experience has shown that, as a rule of thumb, the more expensive and higher quality electrolytics generally allow a smaller value for regulator stability. As an example, while a high-quality 100 F aluminum electrolytic covers all general application circuits, similar stability can be obtained with a tantalum electrolytic of only 47 F. This factor of two can generally be applied to any special application circuit also. Another critical characteristic of electrolytics is their performance over temperature. While the LM2931 is designed to operate to -40C, the same is not always true with all electrolytics (hot is generally not a problem). The electrolyte in many aluminum types will freeze around -30C, reducing their effective value to zero. Since the capacitance is needed for regulator stability, the natural result is oscillation (and lots of it) at the regulator output. For all application circuits where cold operation is necessary, the output capacitor must be rated to operate at the minimum temperature. By coinciwww.national.com 8
dence, worst-case stability for the LM2931 also occurs at minimum temperatures. As a result, in applications where the regulator junction temperature will never be less than 25C, the output capacitor can be reduced approximately by a factor of two over the value needed for the entire temperature range. To continue our example with the tantalum electrolytic, a value of only 22 F would probably thus suffice. For high-quality aluminum, 47 F would be adequate in such an application. Another regulator characteristic that is noteworthy is that stability decreases with higher output currents. This sensible fact has important connotations. In many applications, the LM2931 is operated at only a few milliamps of output current or less. In such a circuit, the output capacitor can be further reduced in value. As a rough estimation, a circuit that is required to deliver a maximum of 10 mA of output current from the regulator would need an output capacitor of only half the value compared to the same regulator required to deliver the full output current of 100 mA. If the example of the tantalum capacitor in the circuit rated at 25C junction temperature and above were continued to include a maximum of 10 mA of output current, then the 22 F output capacitor could be reduced to only 10 F. In the case of the LM2931CT adjustable regulator, the minimum value of output capacitance is a function of the output voltage. As a general rule, the value decreases with higher output voltages, since internal loop gain is reduced. At this point, the procedure for bench testing the minimum value of an output capacitor in a special application circuit should be clear. Since worst-case occurs at minimum oper-
Application Hints
(Continued)
ating temperatures and maximum operating currents, the entire circuit, including the electrolytic, should be cooled to the minimum temperature. The input voltage to the regulator should be maintained at 0.6V above the output to keep internal power dissipation and die heating to a minimum. Worst-case occurs just after input power is applied and before the die has had a chance to heat up. Once the minimum value of capacitance has been found for the brand and type of electrolytic in question, the value should be doubled for actual use to account for production variations both in the capacitor and the regulator. (All the values in this section and the remainder of the data sheet were determined in this fashion.)
Line Regulation: The change in output voltage for a change in the input voltage. The measurement is made under conditions of low dissipation or by using pulse techniques such that the average chip temperature is not significantly affected. Load Regulation: The change in output voltage for a change in load current at constant chip temperature. Long Term Stability: Output voltage stability under accelerated life-test conditions after 1000 hours with maximum rated voltage and junction temperature. Output Noise Voltage: The rms AC voltage at the output, with constant load and no input ripple, measured over a specified frequency range. Quiescent Current: That part of the positive input current that does not contribute to the positive load current. The regulator ground lead current. Ripple Rejection: The ratio of the peak-to-peak input ripple voltage to the peak-to-peak output ripple voltage at a specified frequency. Temperature Stability of VO: The percentage change in output voltage for a thermal variation from room temperature to either temperature extreme.
Definition of Terms
Dropout Voltage: The input-output voltage differential at which the circuit ceases to regulate against further reduction in input voltage. Measured when the output voltage has dropped 100 mV from the nominal value obtained at 14V input, dropout voltage is dependent upon load current and junction temperature. Input Voltage: The DC voltage applied to the input terminals with respect to ground. Input-Output Differential: The voltage difference between the unregulated input voltage and the regulated output voltage for which the regulator will operate.
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Physical Dimensions
inches (millimeters) unless otherwise noted
8-Lead Surface Mount Package (M) Order Number LM2931AM-5.0, LM2931M-5.0 or LM2931CM NS Package Number M08A
3-Lead TO-220 Plastic Package (T) Order Number LM2931AT-5.0 or LM2931T-5.0 NS Package Number T03B
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Physical Dimensions
inches (millimeters) unless otherwise noted (Continued)
5-Lead TO-220 Power Package (T) Order Number LM2931CT NS Package Number T05A
3-Lead TO-263 Surface Mount Package Order Number LM2931S-5.0 or LM2931AS-5.0 NS Package Number TS3B
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Physical Dimensions
inches (millimeters) unless otherwise noted (Continued)
5-Lead TO-263 Surface Mount Package Order Number LM2931CS NS Package Number TS5B
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LM2931 Series Low Dropout Regulators
Physical Dimensions
inches (millimeters) unless otherwise noted (Continued)
3-Lead TO-92 Plastic Package (Z) Order Number LM2931AZ-5.0 or LM2931Z-5.0 NS Package Number Z03A
LIFE SUPPORT POLICY NATIONAL'S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT OF NATIONAL SEMICONDUCTOR CORPORATION. As used herein: 2. A critical component in any component of a life support 1. Life support devices or systems are devices or sysdevice or system whose failure to perform can be reatems which, (a) are intended for surgical implant into sonably expected to cause the failure of the life support the body, or (b) support or sustain life, and whose faildevice or system, or to affect its safety or effectiveness. ure to perform when properly used in accordance with instructions for use provided in the labeling, can be reasonably expected to result in a significant injury to the user.
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National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves the right at any time without notice to change said circuitry and specifications.

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