LTC3856 LINER [Linear Technology], LTC3856 Datasheet
LTC3856
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LTC3856 Summary of contents
Page 1
... Power loss and supply noise are minimized by operating the two controller output stages out-of-phase and up to 12-phase operation can be achieved. The LTC3856 monitors the output current by sensing the voltage drop across the output inductor (DCR using a sense resistor. DCR temperature compensation maintains an accurate current sense threshold over a broad temperature range ...
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... LTC3856 absoluTe MaxiMuM raTings Input Supply Voltage (V ) ......................... 40V to –0.3V IN Topside Driver Voltages (BOOSTn) ............ 46V to –0.3V Switch Voltage (SWn) ................................... 40V to –5V INTV , RUN, PGOOD, EXTV , CC CC (BOOSTn – SWn) ......................................... 6V to –0.3V SENSEn Voltages ...................................... 5.5V to –0.3V MODE, PLLIN, ILIM, TK/SS, AVP , FREQ, ISET Voltages ............................. INTV DIFFP , DIFFN, DIFFOUT, PHASMD, ITEMP Voltages ...
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... LTC3856EUH#PBF LTC3856EUH#TRPBF LTC3856IUH#PBF LTC3856IUH#TRPBF Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container. Consult LTC Marketing for information on non-standard lead based finish parts. For more information on lead free part marking, go to: ...
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... LTC3856 elecTrical characTerisTics junction temperature range, otherwise specifications are at T SYMBOL PARAMETER TG Transition Time TG1,2 t Rise Time r TG1,2 t Fall Time f BG Transition Time BG1,2 t Rise Time r BG1,2 t Fall Time f TG/BG t Top Gate Off to Bottom Gate On Delay 1D Synchronous Switch-On Delay Time BG/TG t Bottom Gate Off to Top Gate On Delay ...
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... SENSE = 1.2V O Note 4: The LTC3856 is tested in a feedback loop that servos V specified 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 the Applications Information section. Note 6: Rise and fall times are measured using 10% and 90% levels. Delay times are measured using 50% levels ...
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... LTC3856 Typical perForMance characTerisTics Load Step: Burst Mode Operation V = 3.6V BAT 200µA LOAD CPO 40A/DIV C = 2.2 F CPO I L1 20A/DIV I L2 20A/DIV V OUT 200mV/DIV 100µs/DIV V = 12V 1.5V OUT 40A LOAD Efficiency vs Output Current and Mode 100 Burst Mode ...
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... Foldback) 100 INTV LIM FLOAT LIM GND LIM 100 0 0.1 0.2 0.3 0.4 FEEDBACK VOLTAGE (V) LTC3856 Quiescent Current vs Input Voltage without EXTV CC 4.5 4.3 4.1 54mV 3.9 3.7 3.5 3.3 3.1 2.9 3856 G07a 2.7 2 INPUT VOLTAGE (V) Maximum Current Sense Threshold vs Common Mode Voltage INTV LIM ...
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... LTC3856 Typical perForMance characTerisTics Shutdown (RUN) Threshold vs Temperature 1.25 ON 1.20 1.15 OFF 1.10 –50 – 100 125 TEMPERATURE (°C) 3856 G15 Undervoltage Lockout Threshold (INTV ) vs Temperature CC 4.0 ON 3.8 3.6 3.4 OFF 3.2 3.0 –50 – 100 TEMPERATURE (°C) 3856 G18 Shutdown Current vs Temperature ...
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... EXTV (Pin 28/Pin 20): External Power Input Internal Switch Connected to INTV and supplies the IC power, bypassing the internal low dropout regulator, whenever EXTV Do not exceed 6V on this pin and ensure V at all times. LTC3856 , CC through set the maximum current ...
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... Schottky diode (external) voltage drop below ground and CC CLKOUT (Pin 37/Pin 27): Clock output with phase change- able by PHASMD to enable usage of multiple LTC3856 ICs in multiphase systems. PLLIN (Pin 38/Pin 28): External Synchronization Pin clock on the pin synchronizes the internal oscillator with CC IN the clock on this pin ...
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... TEMPSNS F 0.6V – BURSTEN FCNT ON SWITCH LOGIC AND ANTISHOOT- THROUGH RUN OV ISET SS RUN 1.25µA – + – + 0.5V 1.22V RUN TK/ LTC3856 REG INTV CC BOOST SENSE – L1 SENSE PGND VCC PGOOD DIFFOUT + + 0.54V 40k R2 UV DIFFAMP ...
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... IC operates at low frequency during the dropout transition to ensure C Shutdown and Start-Up (RUN and TK/SS Pins) The LTC3856 can be shut down using the RUN pin. Pulling the RUN pin below 1.22V shuts down the main control loop for the controller and most internal circuits, including the INTV regulator ...
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... Functional Diagram) Light Load Current Operation (Burst Mode Operation, Stage Shedding or Continuous Conduction) The LTC3856 can be enabled to enter high efficiency Burst Mode operation, Stage Shedding mode or forced continuous conduction mode. To select forced continuous operation, tie the MODE pin voltage below 0.6V (e ...
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... FB ±10% of the 0.6V reference voltage. The PGOOD pin is also pulled low when the RUN pin is below 1.22V or when the LTC3856 is in the soft-start or tracking phase. When the V pin voltage is within the ±10% regulation window, FB the MOSFET is turned off and the pin is allowed to be pulled external resistor to a source ...
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... Care must be taken not to float these pins during normal operation. Filter components mutual to the sense lines should be placed close to the LTC3856, and the sense lines should run close together to a Kelvin con- nection underneath the current sense element (shown in Figure 1) ...
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... LTC3856 applicaTions inForMaTion Low Value Resistors Current Sensing A typical sensing circuit using a discrete resistor is shown in Figure 2a chosen based on the required SENSE output current. The current comparator has a maximum threshold determined by the I SENSE(MAX) The input common mode range of the current compara- tor ...
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... Kelvin connected to the sense resistor. Inductor DCR Sensing For applications requiring the highest possible efficiency at high load currents, the LTC3856 is capable of sensing the voltage drop across the inductor DCR, as shown in Figure 2b. The DCR of the inductor represents the small amount of DC winding resistance of the copper, which can be less than 1mΩ ...
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... As the temperature of the inductor rises, its DCR value increases. The current limit of the controller is therefore reduced. The LTC3856 offers a method to counter this inaccuracy by allowing the user to place an NTC temperature sensing resistor near the inductor to actively correct this error. ...
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... C 25 ° • 100 1000 ) equations with Figure 5. Resistance vs Temperature for the ITEMP Pin Network and the 100k NTC LTC3856 • exp B • − 273 T ...
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... It is accomplished internally by adding a compensating ramp to the inductor current signal at duty cycles in excess of 40%. Normally, this results in a reduction of maximum inductor peak current for duty cycles greater than 40%. However, the LTC3856 100 120 uses a scheme that counteracts this compensating ramp, ...
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... DUTY FACTOR ( OUT IN 3856 F08 Figure 8. Normalized Peak Output Current vs Duty Factor [I = 0.3(I )] RMS OP-P LTC3856 = , ,..., – >> the top MOSFETs’ IN OUT 3856f ...
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... LTC3856 applicaTions inForMaTion The peak-to-peak MOSFET gate drive levels are set by the voltage requiring the use of logic-level threshold CC MOSFETs in most applications. Pay close attention to the BV specification for the MOSFETs as well; many of the DSS logic-level MOSFETs are limited to 30V or less. Selection ...
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... DUTY FACTOR ( OUT IN Figure 10. Normalized Input RMS Ripple Current vs Duty Factor for One to Six Output Stages LTC3856 ), is approximately equal to the OUT , or where ,..., – – 1 where ,..., N N 0.9 3856 F10 3856f ...
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... L Differential Amplifier assuming: The LTC3856 has a true remote voltage sense capability. The sensing connections should be returned from the load, back to the differential amplifier’s inputs through a common, tightly coupled pair of PC traces. The differential amplifier rejects common mode signals capacitively or inductively radiated into the feedback PC traces as well as ground loop disturbances ...
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... AVP the Stage Shedding mode threshold comparator. Programmable Burst Mode Operation When the MODE pin is floating, the LTC3856 enters Burst Mode operation. This means that both channels will stop switching when I The Burst Mode clamp, which sets the current limit when bursting, can be programmed through V ...
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... CC CC The LTC3856 features a true PMOS LDO that supplies power to INTV from the V CC the gate drivers and much of the LTC3856’s internal cir- cuitry. The LDO regulates the voltage at the INTV to 5V when V is greater than 5.5V. EXTV IN to INTV through a P-channel MOSFET and can supply CC the needed power when its voltage is higher than 4 ...
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... MOSFET gate drivers and to prevent interaction between the channels. High input voltage applications in which large MOSFETs are being driven at high frequencies may cause the maxi- mum junction temperature rating for the LTC3856 to be exceeded. The INTV current, which is dominated by the CC ...
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... If a change is made and the input current decreases, then the efficiency has improved. If there is no change in input current, then there is no change in efficiency VIN LTC3856 1Ω INTV INTVCC 4.7µF Figure 13. Set-Up for a 5V Input pins together and tie the combined pins ...
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... Foldback current limiting is disabled during the soft-start or tracking up. Under short-circuit conditions with very low duty cycles, the LTC3856 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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... Figure 15 and specified in the Electrical Characteristics table external clock is detected on the PLLIN pin, the internal switch mentioned above turns off and isolates the influence of the FREQ pin. Note that the LTC3856 can only be synchronized to an external clock whose frequency is within range of the LTC3856’s internal V anteed to be between 250kHz and 770kHz ...
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... Minimum On-Time Considerations Minimum on-time the smallest time duration ON(MIN) that the LTC3856 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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... LTC3856 applicaTions inForMaTion the topside MOSFET and the synchronous MOSFET. If the two MOSFETs have approximately the same R then the resistance of one MOSFET can simply be summed with the resistances of L and R 2 tain I R losses. For example, if each 10mΩ 5mΩ, then the total resistance is ...
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... C DS(ON) voltage with T temperature: P MAIN The worst-case power dissipated by the synchronous MOSFET under normal operating conditions at elevated ambient temperature and estimated 50°C junction temperature rise is: P SYNC LTC3856 : OUT = = = µ ...
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... LTC3856 applicaTions inForMaTion A short-circuit to ground will result in a folded back current of − SC Ω µ 0 002 . The worst-case power dissipated by the synchronous MOSFET under short-circuit conditions at elevated ambi- ent temperature and estimated 50°C junction temperature ...
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... PC trace since very high switched currents are present. External OPTI-LOOP – + and SENSE tion allows overcompensation for PC layouts which are not optimized, but this is not the recommended design procedure. LTC3856 connect to the drains of the PWR + , SENSE , ITEMP). Ideally the SWn, BOOSTn FB compensa- ® ...
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... LTC3856 applicaTions inForMaTion BOLD LINES INDICATE HIGH, SWITCHING CURRENT LINES. KEEP LINES TO A MINIMUM LENGTH. Figure 17. Instantaneous Current Path Flow in a Multiple Phase Switching Regulation SW1 L1 R SENSE1 D1 SW2 L2 R SENSE2 D2 V OUT C OUT + R L 3856 F17 3856f ...
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... BG1 INTV RJK0305DPB 4.7µF Q7 TG2 RJK0305DPB D2, CMDSH-3 INTV CC 0.1µF Q4 SW2 RJK0330DPB BG2 + 1nF – 100 100 Figure 18. 1.5V/50A Converter Using Sense Resistors LTC3856 180µF 16V 22µF 22µF L1 0.22µH 0.001 100µF Q6 6.3V + RJK0330DPB 330µ 22µ ...
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... LTC3856 package DescripTion 4.75 REF 6.60 ±0.10 4.50 REF SEE NOTE 4 RECOMMENDED SOLDER PAD LAYOUT 4.30 – 4.50* (.169 – .177) 0.09 – 0.20 0.50 – 0.75 (.0035 – .0079) (.020 – .030) NOTE: 1. CONTROLLING DIMENSION: MILLIMETERS 2. DIMENSIONS ARE IN MILLIMETERS (INCHES) 3. DRAWING NOT TO SCALE FE Package 38-Lead Plastic TSSOP (4.4mm) (Reference LTC DWG # 05-08-1772 Rev A) ...
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... UH Package 32-Lead Plastic QFN (5mm × 5mm) (Reference LTC DWG # 05-08-1693 Rev D) 0.57 0.05 PACKAGE OUTLINE 0.23 0.05 0.50 BSC 0.75 0.05 0.00 – 0.05 3.45 0.10 (4-SIDES) 0.200 REF LTC3856 BOTTOM VIEW—EXPOSED PAD R = 0.115 0.40 0.10 TYP (UH) QFN 0102 0.23 0.05 0.50 BSC 3856f ...
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... V IN 0.1µF 2.2 S 2.68k 47pF S S CLKOUT V SENSE1 IN PLLIN SENSE1 100k FREQ RUN 0.1µF TK/SS I BOOST1 TH 20k 49.9 LTC3856 AVP S ITEMP 100pF PHASMD 30.1k DIFFP S BOOST2 DIFFN DIFFOUT ISET EXTV CC INTV CC ILIM SENSE2 100 100k MODE PGOOD PGOOD PGND SGND SENSE2 S 3856 F19 relaTeD parTs ...