LTC3805 Linear Technology, LTC3805 Datasheet
LTC3805
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LTC3805 Summary of contents
Page 1
... The LTC3805 provides ±1.5% output voltage accuracy and consumes only 360μA of quiescent current during normal operation and only 40μA during micropower start- up. Using a 9.5V internal shunt regulator, the LTC3805 can be powered from a high V be powered directly from a low impedance DC voltage less. ...
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... OC, I SENSE Operating Ambient Temperature Range ...–40°C to 85°C Operating Junction Temperature ........................... 125° Storage Temperature Range ...................–65°C to 125°C Lead Temperature (Soldering, 10 sec) LTC3805EMSE Only .......................................... 300°C *LTC3805 internal clamp circuit regulates V 10 GATE SENSE ...
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... Maximum Rating condition for extended periods may affect device reliability and lifetime. Note 2: The LTC3805E is guaranteed to meet specifi cations from 0°C to 85°C. Specifi cations over the –40°C to 85°C operating temperature range are assured by design, characterization and correlation with statistical process controls ...
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... LTC3805 TYPICAL PERFORMANCE CHARACTERISTICS Reference Voltage vs Temperature www.datasheet4u.com 812 808 804 800 796 792 788 –50 – TEMPERATURE (°C) Oscillator Frequency vs Supply Voltage 203 202 201 R = 124kΩ FS 200 199 198 197 196 (V) CC RUN Hysteresis Current vs Temperature 5 ...
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... G09 Overcurrent Threshold vs Temperature 104 102 100 100 125 –50 – TEMPERATURE (°C) 3805 G12 100 125 TEMPERATURE (°C) 3805 G15 LTC3805 V Shunt Regulator Voltage CC vs Temperature 9.60 9.55 V CLAMP25mA 9.50 9.45 9.40 9.35 9.30 V CLAMP1mA 9.25 9.20 75 100 125 –50 – TEMPERATURE (°C) ...
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... LTC3805 PIN FUNCTIONS SSFLT (Pin 1): Soft-Start Pin. A capacitor placed from this pin to GND (Exposed Pad) controls the rate of rise of converter output voltage during start-up. This capacitor is www.datasheet4u.com also used for time out after a fault prior to restart. I (Pin 2): Error Amplifi er Compensation Point. Normal TH operating voltage range is clamped between 0 ...
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... GND SOFT-START RAMP SHUTDOWN SOFT-START FAULT OVERCURRENT COMPARATOR + – CURRENT COMPARATOR – ERROR AMPLIFIER + 20mV OSCILLATOR 1. LTC3805 4 RUN UNDERVOLTAGE LOCKOUT GATE SWITCHING R DRIVER LOGIC AND Q BLANKING S CIRCUIT SLOPE COMP CURRENT RAMP ISENSE SYNC 6 GATE 10 7 3805 BD 3805fb 7 ...
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... LTC3805 OPERATION The LTC3805 is a programmable-frequency current mode controller for fl yback, boost and SEPIC DC/DC converters. The LTC3805 is designed so that none of its pins need to www.datasheet4u.com come in contact with the input or output voltages of the power supply circuit of which part, allowing the conversion of voltages well beyond the LTC3805’ ...
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... Figure 1. Operation in fault timeout is discussed in a subsequent section. During shutdown the LTC3805 draws only a small 40μA current. The undervoltage lockout (UVLO) mechanism prevents the LTC3805 from trying to drive the external MOSFET gate with insuffi cient voltage on the V at the V pin must initially exceed V CC enable LTC3805 operation ...
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... V as the shunt regulator is not forced to sink more than 25mA. The shunt regulator is always active, even when the LTC3805 is in shutdown, since it serves the vital func- tion of protecting the V regulator permits the use of a wide variety of powering schemes for the LTC3805 even from high voltage sources that exceed the LTC3805’ ...
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... Proper supply bypassing is necessary to supply the high transient currents required by the MOSFET gate driver. For maximum fl exibility, the LTC3805 is designed so that it can be operated from voltages well beyond the LTC3805’s absolute maximum ratings. Figure 2 shows the simplest ...
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... Note that this topology is very power- ful because, by appropriate choice of transformer turns ratio, the output voltage can be chosen without regard to the value of the input voltage or the V the LTC3805. The number of turns in the bias winding is chosen according ...
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... RUNOFF hysteresis that helps eliminate false trips. To introduce further user-programmable hysteresis, the LTC3805 sources 5μA out of the RUN pin when operation of LTC3805 is enabled result, the falling threshold for the RUN pin also depends on the value of R1 and can be programmed by the user. The falling threshold for V ...
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... This stabilizes the control loop against subharmonic oscillation. The amount of reduction in the current comparator threshold (ΔV can be calculated using the following equation: ΔV Note: LTC3805 enforces 6% < Duty Cycle < 80%. A good starting value for R ISOLATION BARRIER in current comparator threshold at 80% duty cycle. ...
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... If that is a problem, output capacitor charging can GATE LTC3805 R I SLOPE SLOPE I SENSE 10μ GND Figure 6. Circuit to Decrease Overcurrent Threshold LTC3805 to calculate ΔV IN(MIN) Δ SENSE VIN(MIN) = 10µA 100mV − ΔV ( SENSE VIN(MIN SENSE ) . Again, the calculation depends ...
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... function of the soft-start SS(EXT) is therefore SS 2.25 − 0. 6µA less than 5.8nF has SS less than the mandatory minimum SS(EXT) GATE LTC3805 R I SLOPE SLOPE I SENSE 10μ GND 3805 F08 Figure 8. Circuit to Increase the Overcurrent ...
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... C can be valuable to limit jitter SS in the oscillator. www.datasheet4u.com If there is an overcurrent fault detected on the OC pin, the LTC3805 enters a shutdown mode while a 2μA current discharges the voltage on the SSFLT pin from 4.75V to about 0.7V. The fault timeout t FTO(EXT) 4.75V − 0.7V t ...
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... LTC3805 PACKAGE DESCRIPTION www.datasheet4u.com 3.50 ±0.05 2.15 ±0.05 RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS TOP MARK (SEE NOTE Package 10-Lead Plastic DFN (3mm × 3mm) (Reference LTC DWG # 05-08-1699) 0.675 ±0.05 1.65 ±0.05 (2 SIDES) PACKAGE OUTLINE 0.25 ± 0.05 0.50 BSC 2.38 ±0.05 (2 SIDES) 3.00 ±0.10 (4 SIDES) PIN 1 0.75 ± ...
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... TYP 0.53 ± 0.152 (.021 ± .006) DETAIL “A” SEATING PLANE 0.17 – 0.27 (.007 – .011) TYP LTC3805 BOTTOM VIEW OF EXPOSED PAD OPTION 2.06 ± 0.102 (.081 ± .004) 1 1.83 ± 0.102 (.072 ± .004) 10 0.497 ± 0.076 (.0196 ± .003) ...
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... TYPICAL APPLICATION + V IN 36V TO 72V C C IN1 IN2 www.datasheet4u.com 2.2μF 2.2μF 100V 100V – C25 100pF C26 R24 470pF 20k C23, 0.1μ LTC3805EMSE IN 1 SSFLT GATE 221k RUN SENSE 5 FS GND SYNC R8 R20 11 8.66k ...