LT3686 LINER [Linear Technology], LT3686 Datasheet
LT3686
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LT3686 Summary of contents
Page 1
... Soft-start and frequency foldback eliminate input current surge during start-up. An optional internal regulated active load at the output via the BD pin keeps the LT3686 at full switching frequency at light loads, resulting in low, predictable output ripple above the audio and AM bands. Internal compensation and an internal boost diode reduce external component count ...
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... EN/UVLO Voltage ......................................................55V BD Voltage ................................................................25V RT Voltage ..................................................................6V SS Voltage ...............................................................2.5V MODE Voltage .............................................................6V Operating Junction Temperature Range (Note 2) LT3686E ............................................ –40°C to 125°C LT3686I ............................................. –40°C to 125°C Storage Temperature Range .................. –65°C to 150°C orDer inForMAtion LEAD FREE FINISH TAPE AND REEL LT3686EDD#PBF LT3686EDD#TRPBF ...
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... Specifications over the –40°C to 125°C operating junction temperature range are assured by design, characterization and correlation with statistical process controls. The LT3686I is guaranteed over the full –40°C to 125°C operating junction temperature range. The ...
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... LT3686 typicAl perForMAnce chArActeristics 3.3V Efficiency (2MHz) OUT 90 80 MODE > 0. MODE < 0. 12V 3.3V OUT 6.8µ 2MHz 0 600 800 0 200 400 1000 LOAD CURRENT (mA) 3686 G01 5V Maximum Load Current OUT 2.0 1.8 TYPICAL 1.6 1.4 MINIMUM 1.2 1.0 0.8 0.6 0 OUT L = 10µH 0 2MHz 0 10 ...
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... OUT IN Frequency (2MHz) 25 MODE > 0.8 20 MODE < 0 OUT L = 6.8µ 2MHz 0 100 0 500 1000 LOAD CURRENT (mA) LT3686 T = 25°C unless otherwise noted. A Soft-Start/Track vs Frequency (1MHz) 1200 1000 800 600 400 200 0 0 500 1000 1500 150 SS (mV) 3686 G10 Switch Current Limit vs Temperature 3 ...
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... LT3686 typicAl perForMAnce chArActeristics 3.3V Typical Minimum Input OUT Voltage 7 6 MODE < 0 MODE > 0 3.3V OUT 15µ 1MHz 100 1000 I (mA) LOAD 3686 G18 Light Load Discontinuous Mode Waveform V SW 2V/DIV I L 200mA/DIV 200ns/DIV V = 10V 3.3V OUT L = 6.8µ 2MHz C = 22µ ...
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... Do not drive the EN/UVLO pin above V MODE (Pin 7): The MODE pin acts as mode select for the BD active load; when it is tied high, the LT3686 will prevent pulse skipping at light loads by regulating an active load on the BD pin. To disable the active load, tie MODE to GND ...
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... LT3686 block DiAgrAM INT REG EN/ULVO UVLO OFF ON OVLO R5 1.27V – ACTIVE LOAD + SLOPE C COMP 0.8V OSC FREQUENCY FOLDBACK RT MODE R3 BOOST Q1 C3 DRIVER GND 3686 BD V OUT C1 3686fa ...
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... The LT3686 is a current mode step-down regulator. The EN/UVLO pin is used to place the LT3686 in shutdown. The 1.27V threshold on the EN/UVLO pin can be programmed by an external resistor divider (R4, R5) to disable the LT3686. When the EN/UVLO pin is driven above 1.27V, an internal regulator provides power to the control circuitry. ...
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... Figure EN/UVLO 0 Input Voltage Range The input voltage range for the LT3686 applications depends on the output voltage and on the absolute maximum ratings of the determined by either the LT3686’s minimum operating voltage of 3.6V its maximum duty cycle. The duty cycle is the fraction of time that the internal ...
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... V Minimum On Time As the input voltage is increased, the LT3686 is required to switch for shorter periods of time. Delays associated with turning off the power switch dictate the minimum on time of the part. The minimum on time for the LT3686 is 100ns (Figure 3 10V/DIV ...
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... Finite transistor bandwidth limits the speed at which the power switch can be turned on and off, effectively setting the minimum on-time of the LT3686. For a given output voltage, the minimum on-time determines the maximum input voltage to remain in con- tinuous mode operation outlined in the Minimum On Time section of the data sheet ...
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... EMI. A 2.2μF capacitor is capable of this task, but only placed close to the LT3686 and the catch diode (see the PCB Layout section). A second precaution regarding the ceramic input capacitor concerns the maxi- mum input voltage rating of the LT3686 ...
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... Output Capacitor The output capacitor has two essential functions. Along with the inductor, it filters the square wave generated by the LT3686 to produce the DC output. In this role it deter- mines the output ripple so low impedance at the switching frequency is important. The second function is to store energy in order to satisfy transient loads and stabilize the LT3686’ ...
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... V SANYO OUT 50mV/DIV 4TPB100M AC 3686 F07g Figure 7. Transient Load Response of the LT3686 with Different Output Capacitors as the Load Current Is Stepped from 0.25A to 1A 12V 3.3V 6.8µH , Frequency = 2MHz IN OUT BOOST and BD Pin Considerations Capacitor C3 and the internal boost diode are used to generate a boost voltage that is higher than the input voltage. In most cases a 0.22μ ...
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... V load circuit is automatically disabled. is the CATCH The minimum operating voltage of an LT3686 applica- tion is limited by the undervoltage lockout (3.6V) and by the maximum duty cycle as outlined above. For proper start-up, the minimum input voltage is also limited by the boost circuit. If the input voltage is ramped slowly, or ...
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... ApplicAtions inForMAtion the LT3686 is turned on with its EN/UVLO pin when the output is already in regulation, then the boost capacitor may not be fully charged. Because the boost capacitor is charged with the energy stored in the inductor, the circuit will rely on some minimum load current to get the boost circuit running properly ...
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... The LT3686 achieves this goal by commanding the minimum load necessary to keep itself at full switching frequency, hence the circuitry is called an active load. As the LT3686 approaches minimum on time in discontinu- ous mode, its power switch transitions smoothly into a fixed on time, fixed frequency open loop current source. ...
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... An internal 2µA current source charges an external soft- start capacitor to generate a voltage ramp. FB voltage is 1.2nF Figure 12. To Soft-Start the LT3686, Add a Capacitor to the SS Pin regulated to the voltage at the SS pin until it exceeds 0.8V then regulated to the reference 0.8V. Soft-start also reduces the oscillator frequency to avoid hitting current limit during start-up ...
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... LT3686 will reduce its frequency until the valley current is 1.7A (Figure 13). There is another situation to consider in systems where the output will be held high when the input to the LT3686 is absent. This may occur in battery charging applications or in battery backup systems where a battery or some other supply is diode ORed with the LT3686’ ...
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... ApplicAtions inForMAtion supply, the input network should be designed to prevent this overshoot. Figure 15 shows the waveforms that re- sult when an LT3686 circuit is connected to a 24V supply through six feet of 24-gauge twisted pair. The first plot is the response with a 2.2μF ceramic capacitor at the input. ...
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... The LT3686 uses current mode control to regulate the output. This simplifies loop compensation. In particular, the LT3686 does not require the ESR of the output capaci- tor for stability allowing the use of ceramic capacitors to achieve low output ripple and small circuit size. Figure 16 shows an equivalent circuit for the LT3686 control loop ...
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... GND pad of the LT3686 to help remove heat from the LT3686 to the ground plane. High Temperature Considerations The die temperature of the LT3686 must be lower than the maximum rating of 125°C. For high ambient temperatures, care should be taken in the layout of the circuit to ensure good heat sinking of the LT3686 ...
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... ApplicAtions inForMAtion The die temperature is calculated by multiplying the LT3686 power dissipation by the thermal resistance from junction to ambient. Power dissipation within the LT3686 can be estimated by calculating the total power loss from an efficiency measurement and subtracting the catch diode loss. The resulting temperature rise at full load is nearly independent of input voltage. Thermal resistance depends on the layout of the circuit board, but 43° ...
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... TA02e LT3686 3.3V Step-Down Converter EN/UVLO BOOST 0.22µF LT3686 15µH SW MODE SS DA 31. GND 61.9k 10k BOOST 500k 0.22µF LT3686 EN/UVLO SW 100k DA MODE FB SS 10k 1nF RT GND 61.9k 5V Step-Down Converter EN/UVLO BOOST 0.22µF LT3686 MODE 52.3k 1nF RT FB GND 61 ...
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... LT3686 pAckAge Description 3.55 0.05 1.65 0.05 2.15 0.05 (2 SIDES) 0.25 0.05 RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS PIN 1 TOP MARK (SEE NOTE 6) 0.200 REF DD Package 10-Lead Plastic DFN (3mm × 3mm) (Reference LTC DWG # 05-08-1699 Rev B) 0.70 0.05 PACKAGE OUTLINE 0.50 BSC 2.38 0.05 (2 SIDES) 3.00 0.10 1.65 0.10 (4 SIDES) (2 SIDES) 0.75 0.05 0.00 – 0.05 NOTE: 1. DRAWING TO BE MADE A JEDEC PACKAGE OUTLINE M0-229 VARIATION OF (WEED-2). ...
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... Updated Electrical Characteristics (Feedback Voltage) Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no representa- tion that the interconnection of its circuits as described herein will not infringe on existing patent rights. LT3686 PAGE NUMBER 1 3 ...
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... LT3686 relAteD pArts PART NUMBER DESCRIPTION LT3689 36V, 60V Transient Protection, 800mA, 2.2MHz, High Efficiency MicroPower Step-Down DC/DC Converter with POR Reset and Watchdog Timer LT3682 36V, 60V , 1A, 2.2MHz, High Efficiency MicroPower MAX Step-Down DC/DC Converter LT3970 40V, 350mA (I ), 2.2MHz, High Efficiency Step-Down OUT DC/DC Converter with Only 2.5µ ...