LTC3834 Linear Technology, LTC3834 Datasheet
LTC3834
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LTC3834 Summary of contents
Page 1
... The TRACK/SS pin ramps the output voltage during start-up. Current foldback limits MOSFET heat dissipa OUT tion during short-circuit conditions. A reduced feature set version of the part (LTC3834-1) is available in a smaller, lower pin count package. Comparison of LTC3834 and LTC3834-1 PART # LTC3834 LTC3834-1 L, LT, LTC, LTM, Burst Mode, PolyPhase and OPTI-LOOP are registered trademarks of Linear Technology Corporation ...
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... LTC3834IFE#PBF LTC3834IFE#TRPBF LTC3834EUFD#PBF LTC3834EUFD#TRPBF LTC3834IUFD#PBF LTC3834IUFD#TRPBF Consult LTC Marketing for parts specifi ed with wider operating temperature ranges. *The temperature grade is identifi label on the shipping container. Consult LTC Marketing for information on non-standard lead based fi nish parts. For more information on lead free part marking, go to: For more information on tape and reel specifi ...
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... V = 8.5V CC EXTVCC EXTV Ramping Positive Connect PLLLPF PLLLPF V = INTV PLLLPF CC PLLIN/MODE = External Clock; V PLLLPF PLLLPF f < f PLLIN/MODE OSC f > f PLLIN/MODE OSC LTC3834 MIN TYP MAX l 0.792 0.800 0.808 –5 –50 0.002 0.02 l 0.1 0.5 l –0.1 –0 ...
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... FB V Ramping Positive FB Note 4: The LTC3834 is tested in a feedback loop that servos V specifi ed voltage and measures the resultant V Note 5: Dynamic supply current is higher due to the gate charge being delivered at the switching frequency. See Applications Information. Note 6: Rise and fall times are measured using 10% and 90% levels. Delay times are measured using 50% levels. Note 7: The minimum on-time condition is specifi ...
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... EXTV RISING CC 4.8 4.6 EXTV FALLING CC 4.4 4.2 4.0 35 –45 –25 – TEMPERATURE (°C) 3834 G10 LTC3834 T = 25°C, unless otherwise noted. A Load Step (Pulse Skipping Mode) V OUT 100mV/DIV AC COUPLED I L 2A/DIV 3834 G05 20μs/DIV V = 3.3V OUT FIGURE 11 CIRCUIT Tracking Start-Up 3834 G08 20ms/DIV ...
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... LTC3834 TYPICAL PERFORMANCE CHARACTERISTICS Maximum Current Sense Voltage vs I Voltage Cycle TH www.datasheet4u.com 100 FORCED CONTINUOUS Burst Mode OPERATION 80 (RISING) Burst Mode OPERATION 6O (FALLING) PULSE SKIPPING –20 10% DUTY CYCLE –40 0 0.2 0.4 0.6 0.8 1.0 1.2 I PIN VOLTAGE (V) TH Foldback Current Limit 120 100 ...
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... FLOAT PLLLPF V = GND PLLLPF 3834 G24 V = 12V IN EXTV = 3834 G26 LTC3834 T = 25°C, unless otherwise noted. A Shutdown Current vs Input Voltage 3. INPUT VOLTAGE (V) 3834 G22 Undervoltage Lockout Threshold vs Temperature 4 ...
Page 8
... In this case, an R-C fi lter must be connected to the PLLLPF pin. When not synchronizing to an external clock, this input determines how the LTC3834 operates at light loads. power, CC Pulling this pin below 0.7V selects Burst Mode operation. ...
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... BOT FC TOP FB1 BURSTEN B + 0.4V SLEEP – SHDN ICMP + – – – – + 6mV 0.45V 2 SLOPE COMP OV 0.5μA 6V RUN LTC3834 INTV BOOST TOP SW SWITCH INTV CC LOGIC BG BOT PGND SENSE – SENSE – EA TRACK/ ...
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... C Shutdown and Start-Up (RUN and TRACK/SS Pins) The LTC3834 can be shut down using the RUN pin. Pulling this pin below 0.7V shuts down the main control loop of the controller. A low disables the controller and most internal circuits, including the INTV LTC3834 draws only 4μ ...
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... OPERATION (Refer to Functional Diagram) When the RUN pin is pulled low to disable the LTC3834, or when V drops below its undervoltage lockout threshold IN of 3.7V, the TRACK/SS pin is pulled low by an internal www.datasheet4u.com MOSFET. When in undervoltage lockout, the controller is disabled and the external MOSFETs are held off. ...
Page 12
... PLLIN/MODE pin. In this case, a series R-C should be connected between the PLLLPF pin and SGND to serve as the PLL’s loop fi lter. The LTC3834 phase detector adjusts the voltage on the PLLLPF pin to align the turn-on of the external top MOSFET to the rising edge of the synchronizing signal. The typical capture range of the LTC3834’ ...
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... However, lower frequency operation requires more inductance for a given amount of ripple current. The internal oscillator of the LTC3834 runs at a nominal 400kHz frequency when the PLLLPF pin is left fl oating and the PLLIN/MODE pin low or high. Pulling the PLLLPF to INTVCC selects 530kHz operation ...
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... Power MOSFET and Schottky Diode (Optional) Selection Two external power MOSFETs must be selected for the LTC3834: one N-channel MOSFET for the top (main) switch, and one N-channel MOSFET for the bottom (syn- chronous) switch. The peak-to-peak drive levels are set by the INTV This voltage is typically 5V during start-up (see EXTV Connection) ...
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... The output ripple is highest at maximum input voltage since I increases with input voltage. RIPPLE Setting Output Voltage The LTC3834 output voltage is set by an external feed- back resistor divider carefully placed across the output, as shown in Figure 1. The regulated output voltage is determined by: ⎛ ...
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... The start- controlled by the voltage on the OUT www.datasheet4u.com TRACK/SS pin. When the voltage on the TRACK/SS pin is less than the internal 0.8V reference, the LTC3834 regulates the V pin voltage to the voltage on the TRACK/SS pin FB instead of 0.8V. The TRACK/SS pin can be used to program an external soft-start function or to allow V another supply during start-up ...
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... EXTV is greater than 7. absolute maximum of 10V, INTV CC Using the EXTV control power to be derived from the LTC3834 switch- supply pin or the EXTV CC ing regulator output (4.7V ≤ V operation and from the V of regulation (e.g., start-up, short circuit). If more current ...
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... SW pin is low. 100mV to 30mV. Under short-circuit conditions with very low duty cycles, the LTC3834 will begin cycle skipping in order to limit the short-circuit current. In this situation the bottom MOSFET will be dissipating most of the power but less than in normal operation ...
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... PLLIN/MODE, is shown in Figure 7 and specifi the Electrical Characteristics table. Note that the LTC3834 can only be synchronized to an external clock whose frequency is within range of the LTC3834’s internal VCO, which is nominally 115kHz to 800kHz. This is guaranteed to be between 140kHz and 650kHz. A simplifi ed block diagram is shown in Figure 8 ...
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... Minimum On-Time Considerations Minimum on-time the smallest time duration ON(MIN) that the LTC3834 is capable of turning on the top MOSFET determined by internal timing delays and the gate charge required to turn on the top MOSFET. Low duty cycle applications may approach this minimum on-time ...
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... The discharged bypass capacitors are effectively put in parallel pin not only TH with C alter its delivery of current quickly enough to prevent this LTC3834 series R -C fi lter sets the dominant pole-zero C C pin waveforms that will ...
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... LTC3834 APPLICATIONS INFORMATION sudden step change in output voltage if the load switch resistance is low and it is driven quickly. If the ratio greater than 1:50, the switch rise time LOAD OUT www.datasheet4u.com should be controlled so that the load rise time is limited to approximately 25 • Thus a 10μF capacitor would LOAD require a 250μ ...
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... All of these nodes have very large and fast mov- ing signals and therefore should be kept on the “output side” of the LTC3834 and occupy minimum PC trace area. 7. Use a modifi ed “star ground” technique: a low imped- ...
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... In addition, investigate common ground path voltage pickup between these components and the SGND pin of the IC. An embarrassing problem, which can be missed in an otherwise properly working switching regulator, results C1 1nF Figure 9. LTC3834 Recommended Printed Circuit Layout Diagram BOLD LINES INDICATE HIGH SWITCHING CURRENT ...
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... PGOOD TRACK/SS BOOST LTC3834 D B 100pF CMDSH-3 SGND INTV CC 4.7μF PLLIN/MODE EXTV – SENSE + SENSE PGND LTC3834 V IN 10V TO 36V C IN 10μ 7.2μH 0.015Ω V OUT 9. OUT 150μF 4.7μF M2 3834 TA02 V IN 12V C IN 10μ ...
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... BG FB – SENSE + 39pF SENSE PGND High Effi ciency 1.2V, 5A Step-Down Converter CLKOUT V IN GND PLLLPF TG RUN C B 0.22μF PGOOD TRACK/SS BOOST LTC3834 D B 100pF CMDSH-3 SGND INTV CC 4.7μF PLLIN/MODE EXTV – SENSE + 390pF SENSE PGND V IN 5.5V TO 36V C IN 10μ ...
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... SIDES) 0.70 0.05 PIN 1 TOP MARK (NOTE 6) 5.00 0.10 (2 SIDES) PACKAGE OUTLINE 5. EXPOSED PAD SHALL BE SOLDER PLATED 6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION ON THE TOP AND BOTTOM OF PACKAGE LTC3834 6.40 – 6.60* (.252 – .260) 3.86 (.152 6.40 2.74 (.252) (.108) BSC ...
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... McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 FAX: (408) 434-0507 ● CLKOUT V IN PLLLPF RUN TG C PGOOD B TRACK/SS 0.22μF BOOST LTC3834 B 150pF CMDSH-3 SGND INTV CC 4.7μF PLLIN/MODE EXTV – SENSE + SENSE PGND 39pF Figure 11. High Effi ciency Step-Down Converter ...