LTC3831-1 Linear Technology, LTC3831-1 Datasheet
LTC3831-1
Related parts for LTC3831-1
LTC3831-1 Summary of contents
Page 1
... N-channel FET, providing an adjustable current limit without a current sense resistor. The LTC3831-1 operates with input supply voltage as low as 3V and with a maximum duty cycle of > 91%. It includes a fixed frequency PWM oscillator for low output ripple operation ...
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... LTC3831 ABSOLUTE AXI U RATI GS (Note 1) Supply Voltage V ....................................................................... ................................................................ 14V www.datasheet4u.com CC1,2 Input Voltage ............................................... – 0.3V to 14V FB MAX + – FB, SHDN, FREQSET ..... – 0. Junction Temperature (Note 9) ............................. 125 C Operating Temperature Range (Note 4) .. – Storage Temperature Range ................. – 150 C Lead Temperature (Soldering, 10 sec) ...
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... Note 3: Supply current in normal operation is dominated by the current needed to charge and discharge the external FET gates. This will vary with the LTC3831-1 operating frequency, operating voltage and the external FETs used. Note 4: The LTC3831EGN-1 is guaranteed to meet performance specifications from Specifications over the – operating temperature range are assured by design, characterization and correlation with statistical process controls ...
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... LTC3831-1 W TYPICAL PERFOR A CE CHARACTERISTICS Load Regulation 0.762 www.datasheet4u.com 0.760 REFER TO FRONT PAGE APPLICATION 0.758 NEGATIVE OUTPUT CURRENT INDICATES CURRENT SINKING 0.756 0.754 0.752 0.750 0.748 0.746 0.744 0.742 0.740 0.738 –8 –6 –4 – –10 6 OUTPUT CURRENT (A) Output Voltage Temperature Drift 0 ...
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... TEMPERATURE ( C) 3831 G14 V Operating Supply Current CC vs Temperature 1.6 FREQSET FLOATING 1.5 1.4 1.3 1.2 1.1 1.0 0.9 0.8 0.7 0.6 0.5 0.4 125 – –25 TEMPERATURE ( C) 3831 G17 LTC3831-1 Output Overcurrent Protection 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0 REFER TO FRONT PAGE APPLICATION 100 125 OUTPUT CURRENT (A) 3831 G12 Soft-Start Sink Current vs (V – ...
Page 6
... SHDN (Pin 8): Shutdown. A TTL compatible low level at . For normal SHDN for longer than 100 s puts the LTC3831-1 into GS(ON)(Q1 least shutdown mode. In shutdown, TG and BG go low, all CC internal circuits are disabled and the quiescent current drops max ...
Page 7
... CC I (Pin 12): Current Limit Threshold Set. I MAX threshold for the internal current limit comparator drops below I with TG on, the LTC3831-1 goes into MAX current limit. I has an internal 12 A pull-down to GND. MAX Connect this pin to the main V IN through an external resistor to set the current limit thresh- old ...
Page 8
... Using the LTC3831-1 to supply the interface ter- mination voltage allows large current sourcing and sink- ing through the termination resistors during bus transitions. The LTC3831-1 includes a current limit sensing circuit that uses the topside external N-channel power MOSFET as a current sensing element, eliminating the need for an external sense resistor ...
Page 9
... C, after which, the chip resumes normal operation. Soft-Start and Current Limit The LTC3831-1 includes a soft-start circuit that is used for start-up and current limit operation. The SS pin requires an external capacitor, CSS, to GND with the value deter- mined by the required soft-start time. An internal 12 A ...
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... The low period of this clock signal must not be >100 s or else the LTC3831-1 enters into the shutdown mode. Figure 3 describes the operation of the external synchro- nization function ...
Page 11
... In a typical low voltage DDR memory termination applica- RAMP SIGNAL tion, V WITH EXT SYNC supply for the LTC3831-1 is 3.3V, a tripling charge pump circuit can be added to power the PV This requires sub-logic level threshold power MOSFET with R Figure 5 shows a tripling charge pump circuit that powers ...
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... APPLICATIO S I FOR ATIO The charge pump capacitors for PV BG pin goes high and the switch node is pulled low by Q2. The BG on time becomes narrow when the LTC3831-1 www.datasheet4u.com operates at maximum duty cycle (95% typical) which can occur if the input supply rises more slowly than the soft- start capacitor or the input voltage droops during load transients ...
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... After the MOSFET threshold voltage is selected, choose the R DS(ON) allowable power dissipation and maximum output cur- rent typical LTC3831-1 circuit operating in continu- ous mode, the average inductor current is equal to the output load current. This current flows through either with the power dissipation split up according to the ...
Page 14
... A ) differential and the LTC3831-1’s maximum duty cycle typical 1.5V input 0.75V output application, the maximum values suggest large rise time will be: DC where L quency compensation, the combination of the inductor and output capacitor values determine the transient recov- values below 0 ...
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... This action causes a temporary voltage droop at the output. To minimize this effect, the inductor value should usually be in the range for most LTC3831-1 circuits. To optimize performance, different combinations of input and output voltages and expected loads may require different induc- tor values ...
Page 16
... RC network box to iterate toward the final values obtaining the optimum loop response using a network analyzer to find the actual loop poles and zeros. R Figure 7b. Bode Plot of the LTC3831-1 Overall Transfer Function )(C )] and C C )(C1)] respectively ...
Page 17
... When laying out the printed circuit board, the following checklist should be used to ensure proper operation of the LTC3831-1. These items are also illustrated graphically in the layout diagram of Figure 8. The thicker lines show the high current paths. Note that at 5A current levels or above, current density in the PC board itself is a serious concern ...
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... Do not connect these parts to the ground plane! 4. The close to the LTC3831-1 as possible. The 4.7 F and 2.2 F bypass capacitors shown at V will help provide optimum regulation performance. 5. The (+) plate of C possible to the drain of the upper MOSFET, Q1 ...
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... BSC .015 .004 45 .0532 – .0688 (0.38 0.10) (1.35 – 1.75) 0 – 8 TYP .008 – .012 (0.203 – 0.305) TYP INCHES (MILLIMETERS) LTC3831-1 .189 – .196* (4.801 – 4.978) .009 (0.229 REF .150 – .157** (3.810 – 3.988 ...
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... LTC3831-1 RELATED PARTS PART NUMBER DESCRIPTION LTC1628/LTC3728 Dual High Efficiency 2-Phase Synchronous Step-Down Controllers Constant Frequency, Standby 5V and 3.3V LDOs, 3.5V V www.datasheet4u.com LTC1702 Dual High Efficiency 2-Phase Synchronous Step-Down Controller 550kHz, 25MHz GBW Voltage Mode, V LTC1703 Dual 550kHz Synchronous 2-Phase Switching Regulator Controller with Mobile VID ...