LM2925T

Low Dropout Regulator with Delayed Reset LM2925 FEATURES ● Externally set delay for reset ● 5V/750mA output ● Very low dropout voltage 0.6V at 0.5A ● Reverse battery protection ● 60V load dump protection ● −50V reverse transient protection ● Internal thermal over load protection ● Short circuit protection ● Available in plasticTO-220 ● Long delay times available ● P+ Product Enhancementtested ● Moisture Sensitivity Level 3 TO - 220 PKG 1.Vin 2.Vout 3.Gnd 4.Delay 5.Reset ORDERING INFORMATION Device LM2925T Marking LM2925 Package TO-220 DESCRIPTION The LM2925 features a low dropout, high current regulator. Also included on-chip is a reset function with an externally set delay time. Upon power up, or after the detection of anyerror in the regulated output, the reset pin remains in the ac-tive low state for the duration of the delay. Types of errors de-tected include any that cause the output to become unregu- lated: low input voltage, thermal shutdown, short circuit,input transients, etc. No external pull-up resistor is neces-sary. The current charging the delay capacitor is very low, al-lowing long delay times. Designed primarily for automotive applications, the LM2925 and all regulated circuitry are protected from reverse battery installations or two-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 0.75A regulator will automatically shut down to protect both internal circuits and theload. The LM2925 cannot be harmed by temporary mirror-image inser-tion. Familiar regulator features such as short circuit and thermal overload protection are also provided. 2008 - Ver 1.0 −1− HTC Low Dropout Regulator with Delayed Reset LM2925 ABSOLUTE MAXIMUM RATING Internal Power Dissipation(Note 2*) Internally Limited Supply Voltage (Vin) Operating Range 26 [V] Over voltage Protaction 37 [V] Impulse Voltage(fall=100mS, rise=10mS) 60 [V] Reverse Input Voltage -18 [V] Impulse Voltage(fall=100mS ) - 40 [V] Operation Temperature Range Maximum Junction Temperature Storage Temperature Range Lead Temperature (Soldering, max 10 sec) -40 ~ +125 °C 150 °C -65 ~ +150 °C 260 °C TYPICAL APPLICATION CIRCUIT Vout=5V/750 mA C1 0.1u C2 10u RESET FLAG C3 0.1uF C1/C2 Required if regulator is located far from power supply filter. C2 must be at least 10µF 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. −2− HTC Low Dropout Regulator with Delayed Reset LM2925 Note1: 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. Note2: Thermal resistance without a heat sink for junction to case temperature is 3°C/W(TO-220). Thermal resistance for TO-220 case to ambient temperature is 50°C/W. −3− HTC Low Dropout Regulator with Delayed Reset FUNCTIONAL BLOCK DIAGRAM LM2925 TIPICAL CRICUIT WAVEFORMS −4− HTC Low Dropout Regulator with Delayed Reset TYPICAL PERFORMANCE CHARACTERISTICS LM2925 −5− HTC Low Dropout Regulator with Delayed Reset TYPICAL PERFORMANCE CHARACTERISTICS LM2925 −6− HTC Low Dropout Regulator with Delayed Reset LM2925 DETAILED DESCRIPTION Dropout Voltage: Th input-output voltage differential at which the circuit ceases to regulate against further reduction in input voltage. Measured when the outpu voltage has dropped 100mV from the nominal value obtained at 14V in-put, 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 volt-age for which the regulator will operate. Line Regulation The change in output voltage for a change in the input voltage. The measurement is made under condi-tions of low dissipation or by using pulse techniques such that the average chip temperature is not significantly af-fected. Load Regulation The change inoutput voltage for a change in load current at constant chip temperature. Long Term Stability Output voltage stability under acceler-ated 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 inpu ripple, measured over aspecified frequency range. Quiescent Current The 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. Temperature Stability of VO The percentage change in ou-put voltage for a thermal variation from room temperature to either temperature extreme. −7− HTC Low Dropout Regulator with Delayed Reset LM2925 APPLICATION HINT EXTERNAL CAPACITORS The LM2925 output capacitoris required for stability. Without it, the regulator output will oscillate, sometimes by many volts. Though the 10µF shown is the minimum recom-mended value,actual size and type may vary depending upon the application load and temperature range. Capacitor effective series resistance (ESR) also effects the IC stability. Since ESR varies from one brand to the next, some bench work may be required to determine the minimum capacitor value to use in production. Worst-case is usually determined at the minimum junction and ambient temperature and maxi- mum load expected. Output capacitors can be increased in size to any desired value above the minimum. One possible purpose of this would be to maintain the output voltages during brief condi-tions of negative input transients that might be characteristic of a particular system. Capacitors must also be rated at all ambient temperatures expected in the system. Many aluminum type electrolytics will freeze at temperatures less than −30°C, reducing their effective capacitance to zero. To maintain regulator stability down to −40°C, capacitors rated at that temperature (such as tantalums) must be used. RESET OUTPUT The range of values for the delay capacitor is limited only by stray capacitances on the lower extreme and capacitance leakage on the other. Thus, delay times from microseconds to seconds are possible. The low charging current, typically 2.0 microamps, allows the use of small, inexpensive disc capacitors for the nominal range of 100 to 500 milliseconds. This is the time required in many microprocessor systems for the clock oscillator to stabilize when initially powered up. The RESET output of the regulator will thus prevent erroneous data and/or timing functions to occur during this part of op-eration The same delay is incorporated after any other fault condition in the regulator output is corrected. −8− HTC