LM2931AZ-5.0 — Automotive-Grade 100mA 5.0V Low Dropout (LDO) Regulator

Overview

The LM2931AZ-5.0 (LM2931) is a specialized automotive-grade positive low-dropout (LDO) linear voltage regulator manufactured by Texas Instruments and onsemi. Packaged in a compact 3-pin through-hole TO-92 enclosure, it delivers a clean, regulated $+5.0\text{V}$ DC rail at up to $100\text{ mA}$ from noisy, harsh vehicular power networks.

Specifically engineered to withstand extreme automotive electrical transients, the LM2931 provides built-in protection against $+60\text{V}$ load-dump spikes, $-18\text{V}$ reverse battery connection, $-50\text{V}$ reverse inductive spikes, mirror-image pin insertion, and thermal overload. With an exceptionally low dropout voltage ( $160\text{ mV}$ typ at $10\text{mA}$ and $< 0.6\text{V}$ at $100\text{mA}$ ), it continues to maintain clean 5V regulation even during severe cold-cranking battery voltage sags.

Quick reference


Regulator Type	Automotive Low-Dropout (LDO) Positive Linear Regulator
Package	TO-92 (3-pin through-hole)
Output Voltage ( $V_{OUT}$ )	$+5.0\text{ V}$ DC ( $\pm 3.8\%$ over $-40^\circ\text{C} \dots 125^\circ\text{C}$ )
Operating Input Range ( $V_{IN}$ )	$6.0\text{ V}$ to $26.0\text{ V}$ DC
Transient Input Protection	$+60\text{ V}$ Load Dump / $-18\text{ V}$ Reverse Battery / $-50\text{ V}$ Transient
Dropout Voltage ( $V_{DROP}$ )	$160\text{ mV}$ typ at $10\text{mA}$ / $600\text{ mV}$ max at $100\text{mA}$
Quiescent Ground Current ( $I_Q$ )	$0.4\text{ mA}$ typical at $I_L = 10\text{mA}$
Operating Junction Temp	$-40^\circ\text{C}$ to $+125^\circ\text{C}$

Pinout (TO-92 Package)

Looking at the flat front face with leads pointing downwards:

text

        ┌─────────┐
        │  TO-92  │
        │ LM2931  │
        │ AZ-5.0  │
        └─┬───┬───┬─┘
          1   2   3
        VOUT GND VIN

Pin	Name	Type	Description
1	`VOUT`	Power Output	Regulated $+5.0\text{ V}$ DC output (Requires minimum $100\ \mu\text{F}$ electrolytic or $22\ \mu\text{F}$ tantalum)
2	`GND`	Ground	Common system ground reference ( $0\text{ V}$ )
3	`VIN`	Power Input	Automotive DC input ( $+6.0\text{ V}$ to $+26.0\text{ V}$ , withstands $+60\text{V}$ load dump)

Specifications

Parameter	Symbol	Min	Typ	Max	Unit	Conditions
Output Voltage ( $25^\circ\text{C}$ )	$V_{OUT}$	4.90	5.00	5.10	V	$I_L = 10\text{mA}$ (A-grade, $\pm 2\%$ )
Output Voltage (Full Temp)	$V_{OUT}$	4.81	5.00	5.19	V	$-40^\circ\text{C} \le T_J \le +125^\circ\text{C}$
Operating Input Voltage	$V_{IN}$	6.0	—	26.0	V	Normal operation
Max Input Transient Voltage	$V_{IN(trans)}$	—	—	60.0	V	$t < 100\text{ ms}$ (Load dump)
Reverse Battery Voltage	$V_{IN(rev)}$	—	—	-18.0	V	Continuous DC reverse voltage
Dropout Voltage ( $10\text{mA}$ )	$V_{DROP}$	—	160	300	mV	$I_L = 10\text{mA}$
Dropout Voltage ( $100\text{mA}$ )	$V_{DROP}$	—	300	600	mV	$I_L = 100\text{mA}$
Quiescent Current	$I_Q$	—	0.4	1.0	mA	$I_L = 10\text{mA}, V_{IN} = 14\text{V}$
Peak Output Current	$I_{OUT(pk)}$	150	250	—	mA	$V_{IN} = 14\text{V}$

Typical Automotive Application Circuit

text

  Vehicle 12V Battery Rail (9V - 16V, transients to 60V)
           │
           ├───[ C_IN: 0.1µF Ceramic ]────────────┐
           │                                      │
       [Pin 3: VIN]                               │
      LM2931AZ-5.0                                │
       [Pin 2: GND] ──────────────────────────────┼─── Vehicle Chassis GND
       [Pin 1: VOUT]                              │
           │                                      │
           ├───[ C_OUT: 22µF Tantalum or 100µF ]──┘
           │
  Protected +5.0V DC Rail (Automotive MCU / CAN Bus / Sensors)

Capacitor Selection & Stability

Input Capacitor: A $0.1\ \mu\text{F}$ ceramic capacitor from VIN to GND is recommended if the regulator is located more than a few inches from the supply source.
Output Capacitor: The LM2931 requires an output capacitor for stability. The minimum recommended value is $22\ \mu\text{F}$ (tantalum) or $100\ \mu\text{F}$ (aluminum electrolytic) with an ESR of $0.1\ \Omega \dots 1.0\ \Omega$ .

Common mistakes

Using insufficient output capacitance: Unlike modern CMOS LDOs, the LM2931 requires substantial output capacitance ( $\ge 22\ \mu\text{F}$ ) to prevent internal control loop oscillation.
Confusing with standard 78L05: Standard 78L05 regulators will blow instantly if exposed to a $40\text{V}\dots 60\text{V}$ automotive alternator load dump spike or reverse battery connection. Always use the LM2931 in vehicle-connected projects (CAN bus dongles, OBD-II gauges, motorcycle telemetry).

Notes

Pin-Compatible Drop-In Alternatives: LM2931Z-5.0 (standard grade), LP2950ACZ-5.0.

Interface	3-Terminal Passive (VOUT, GND, VIN)
Package	TO-92 (3-pin through-hole)