LT1579 LINER [Linear Technology], LT1579 Datasheet
LT1579
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LT1579 Summary of contents
Page 1
... All of the circuitry needed to switch smoothly and automatically between inputs is incorporated. The LT1579 can supply 300mA of output current from either input at a dropout voltage of 0.4V. Quiescent current dropping shutdown. Two comparators are included to monitor input voltage status. Two addi- ...
Page 2
... T = 125 C, JMAX 157933 T = 125 C, JMAX 15795 ORDER PART NUMBER LT1579CS8-3 V POWER IN1 INPUTS V LT1579CS8-3.3 IN2 CONTROL SHDN LT1579CS8-5 INPUT GND S8 PART MARKING 15793 SEE APPLICATION INFORMATION SECTION 157933 T JMAX 15795 ORDER PART NUMBER TOP VIEW 16 GND LT1579CGN 15 OUT LT1579CS 14 ADJ ...
Page 3
... V IN1 4.3V < V LT1579 IN1 6V < V IN1 Adjust Pin Voltage LT1579 IN1 3.7V < V Line Regulation LT1579 3.5V to 20V, V IN1 LT1579-3 3.8V to 20V, V IN1 LT1579 5.5V to 20V, V IN1 LT1579 V = 3.2V to 20V, V IN1 Load Regulation LT1579 IN1 IN1 LT1579-3.3 V ...
Page 4
... In dropout, the output voltage will be equal to V Note 4: To meet the requirements for minimum input voltage, the LT1579 (adjustable version) is connected with an external resistor divider for a 3.3V output voltage (see curve of Minimum Input Voltage vs Temperature in the Typical Performance Characteristics) ...
Page 5
... 500k (ADJUSTABLE OPERATING 60 QUIESCENT 50 CURRENT 40 30 STANDBY 20 QUIESCENT 10 CURRENT 0 – 100 125 –25 TEMPERATURE ( C) 1579 G02 LT1579-3.3 Output Voltage 3. 1mA LOAD 3.36 3.34 3.32 3.30 2.28 2.26 2.24 2.22 – 100 125 – TEMPERATURE ( C) 1579 G04 Input Current 60 I IN2 I IN1 50 ...
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... LT1579 W U TYPICAL PERFORMANCE CHARACTERISTICS Input and Ground Pin Current 1 IN2 IN1 1.0 0.8 0.6 I GND 0.4 0.2 0 –0.2 –0.1 0 0.1 0.2 0.3 0.4 V – V (V) IN1 OUT Input and Ground Pin Current IN2 IN1 GND –0.2 –0.1 0 0.1 0.2 0.3 0.4 V – V (V) IN1 OUT Input and Ground Pin Current ...
Page 7
... TEMPERATURE ( C) 1579 G17 Logic Flag Output Voltage (Output Low) 1.0 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0 100 A 1mA 10mA LOGIC FLAG SINK CURRENT 1579 G20 LT1579 Shutdown Pin Threshold 1 1mA LOAD 0.8 0.6 0.4 0.2 0 – 50 – 100 125 TEMPERATURE ( C) 1579 G15 Secondary Select Threshold (Switch IN1 2 ...
Page 8
... Hysteresis SINK CURRENT ( A) LBO 1579 G23 Reverse Output Current IN1 IN2 (LT1579-3) OUT V = 3.3V (LT1579-3.3) OUT (LT1579-5) OUT – 50 – TEMPERATURE ( C) 1579 G26 Current Limit 0 ...
Page 9
... Larger output capacitors will be required for appli- cations with large transient loads to limit peak voltage . transients. IN2 ADJ: For the adjustable LT1579, this is the input to the error amplifier. This pin is internally clamped to 7V and – 0.6V (one V LT1579 LT1579-5 “Hot” Plugging and ...
Page 10
... The adjust pin voltage is 1.5V referenced to ground and the output voltage range is 1.5V to 20V. SHDN: The shutdown pin is used to put the LT1579 into a low power shutdown state. All functions are disabled if the shutdown pin is pulled low. The output will be off, all ...
Page 11
... BE this pin can be left open circuit. Device operation is unaffected if this pin is not connected. DROPOUT DETECT OUTPUT DRIVER E/A CONTROL WARNING + LB1 – + LB2 – LT1579 ). If unused OUT INTERNAL RESISTOR DIVIDER FOR FIXED VOLTAGE DEVICES ONLY – ADJ + BACKUP FLAGS DROPOUT LBO1 LBO2 1579 • ...
Page 12
... Internal bias circuitry powers the refer- ence, error amplifier, output driver controls, logic flags and low-battery comparators. The LT1579 aids power management with the use of two independent low-battery comparators and two status flags. The low-battery comparators can be used to monitor the input voltage levels ...
Page 13
... V Output Capacitance and Transient Response The LT1579 is designed to be stable with a wide range of output capacitors. The ESR of the output capacitor affects stability, most notably with small capacitors. A minimum output capacitor of 4.7 F with an ESR less is recommended to prevent oscillations. Smaller value ca- pacitors may be used, but capacitors which have a low ESR (i ...
Page 14
... A. A low-battery detector with the trip point set at the critical discharge point can signal the low battery condi- tion and force the switchover to the secondary as shown in Figure 2. The second low-battery comparator can be used to set a latch to shutdown the LT1579 (see the Typical Applications ...
Page 15
... The timing diagram is meant as a tool to help in understanding basic operation of the LT1579. Actual discharge rates will be a function of the load current and the type of batteries used. The load current used in the example was 100mA DC. ...
Page 16
... LB2. The trip threshold for LB2 is also set at 5.5V, slightly above where the secondary input reaches dropout. At time E, both inputs are low enough to cause the LT1579 to enter dropout, with the DROPOUT flag signaling the impending loss of output regulation. After time E, the output voltage drops out of regulation ...
Page 17
... JMAX 75 C/W 80 C/W Protection Features 95 C/W The LT1579 incorporates several protection features that make it ideal for use in battery-powered circuits. In addi- tion to the normal protection features associated with monolithic regulators, such as current limiting and ther- mal limiting, the device is protected against reverse input , with an ...
Page 18
... LT1579 U U APPLICATIONS INFORMATION The inputs of the device can withstand reverse voltages up to 20V. Current flow into the device will be limited to less than 1mA (typically less than 100 A) and no negative voltage will appear at the output. The device will protect both itself and the load. This provides protection against batteries which can be plugged in backwards ...
Page 19
... DWG # 05-08-1610 0.228 – 0.244 (5.791 – 6.197 0.053 – 0.069 (1.346 – 1.752) 0 – 8 TYP 0.014 – 0.019 (0.355 – 0.483) LT1579 0.150 – 0.157** (3.810 – 3.988 0.004 – 0.010 (0.101 – 0.254) 0.050 (1.270) TYP SO8 0996 0.386 – ...
Page 20
... LT1579 U TYPICAL APPLICATION Additional Logic Forces LT1579 Into Shutdown to Protect Input Batteries C1 IN1 D3: 1N4148 IN2 D3 R8 330k D4 C5 5.1V 0.1 F 1N751A RESET R9 1.5M RELATED PARTS PART NUMBER DESCRIPTION LT1175 500mA Negative Low Dropout Micropower Regulator ® TM LTC 1421 Hot Swap Controller ...