LTC3705 LINER [Linear Technology], LTC3705 Datasheet
LTC3705
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LTC3705 Summary of contents
Page 1
... The on-chip rectifier and the same pulse transformer provide gate drive bias power. Alternatively, the LTC3705 can be used as a standalone voltage mode controller in a primary-side control architec- ture with optoisolator feedback. Voltage feedforward pro- vides excellent line regulation and transient response. ...
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... Rising (Linear Regulator Rising (Trickle Charger Falling CC Rising Falling U W ORDER PART TOP VIEW NUMBER LTC3705EGN 14 BOOST LTC3705IGN PART MARKING PGND 3705 GN PACKAGE 3705I = 125°C, θ = 110°C/W JA http://www.linear.com/leadfree 25°C, unless ...
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... Note the sum of current into NDRV and V CC Note 4: The LTC3705EGN is guaranteed to meet performance specifications from 0°C to 85°C. Specifications over the –40°C to 85°C operating temperature range are assured by design, characterization and correlation with statistical process controls. The LTC3705IGN is guaranteed and tested over the – ...
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... LTC3705 W U TYPICAL PERFOR A CE CHARACTERISTICS Supply Current 2.0 TRICKLE CHARGER 1.5 LINEAR REGULATOR 1.0 0 (V) CC 3705 G01 UVLO Hysteresis Current vs Temperature 5.05 5.00 4.95 4.90 4.85 4.80 –40 – – 100 TEMPERATURE (°C) 3705 G10 Shunt Regulator Current 14.00 14.25 14.50 14.75 15.00 V ...
Page 5
... TEMPERATURE (°C) 3705 G14 Gate Drive Encoding TG FB/IN 10V/DIV FS/IN – 3705 G07 1µs/DIV LTC3705 = 25°C unless otherwise specified) Gate Drive Peak Pull-Up Current vs Temperature 2.0 1.9 1.8 1.7 1.6 1.5 –40 – – TEMPERATURE (°C) Fault Operation BG 10V/DIV SSFLT ...
Page 6
... This pin has several functions. The two terminals of one pulse transformer winding are connected + – to the FB/IN and FS/IN pins. The other pulse transformer winding is connected to the LTC3706. The LTC3705 automatically detects when the LTC3706 applies a pulse- + encoded signal to the FB/IN and FS/IN 6 duty cycle information for control of the primary-side gate drives (see Operation below) ...
Page 7
... LINE OFF TIME SOFT-START FAULT UVVIN PWM SECONDARY CONTROL PWM RECEIVER DET – PWM 400mV PRIMARY CONTROL RAMP V P OSCILLATOR P-P CLOCK I OSC LTC3705 SHUNT REGULATOR + REGULATOR 5V – 14.25V + 5.3V/4.7V UVINT – – 300mV LEVEL SHIFT SW DET BOOTSTRAP DRIVE REFRESH LOGIC – ...
Page 8
... LTC3705 U OPERATIO Mode Setting The LTC3705 is a controller and gate driver designed for use in a 2-switch forward converter. When used in con- junction with the LTC3706 PolyPhase secondary-side synchronous forward controller it forms a complete 2-switch forward converter with secondary-side regula- tion, galvanic isolation between input and output, and synchronous rectification ...
Page 9
... In normal operation, at some point before this, the LTC3705 makes a transition to controlling duty cycle using closed- loop regulation of the converter output voltage. The SSFLT pin is also used to indicate a fault. The LTC3705 recognizes faults from four origins overcurrent fault caused by the current sense voltage on the IS pin exceed- ...
Page 10
... FB/IN bias circuit which eliminates the need for external components The LTC3705 also has 16mV of voltage hysteresis on the UVLO pin so that the UVLO threshold for V V rising is 1.242V UVLO FALLING ( To implement external Run/Stop control, connect a small NMOS to the UVLO pin as shown in Figure 2 ...
Page 11
... R pin and CC Although the exact start-up frequency on the primary side is not critical generally a good practice to set it approximately equal to the operating frequency on the secondary side. In this mode the start-up frequency of the LTC3705 is approximately PRI pin. The CC In the event that the LTC3706 fails to start up properly and assume control of switching, there are several fail-safe mechanisms to help avoid overvoltage conditions ...
Page 12
... If the LTC3706 fails to start, the LTC3705 quickly times out the linear regulator once the voltage on the SSFLT pin reaches 2.8V. Fault Lockout The LTC3705 indicates a fault by pulling the SSFLT pin to within restart. Optionally, the user can prevent restart and “lock is very nearly NDRV out” ...
Page 13
... The auxiliary supply is connected in parallel with V linear regulator maintains V produces more than 8V, it turns off the external NMOS before the LTC3705 can time out the linear regulator. If the auxiliary supply produces less than 8V, the linear regulator times out and then the voltage on the V the voltage produced by the auxiliary supply ...
Page 14
... RUN/SS pins. The LTC3706 is put into slave mode by tying the FB pin Standalone Primary-Side Operation The LTC3705 can be used to implement a standalone forward converter using optoisolator feedback and a secondary-side voltage reference. Alternately the LTC3705 can be used to implement an open-loop forward converter using the VSLMT pin to regulate against changes in V ...
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... V CC – FS/IN PT SS/FLT RUN/SS LTC3705 (MASTER) V RUN/SS NDRV + SS/FLT FB/IN • • – UVLO FS/IN PT LTC3705 (SLAVE) Figure 4. Connections for PolyPhase LTC3705 + V OUT NDRV FS/SYNC + FB ITH – LTC3706 (MASTER) NDRV FS/SYNC FB + ITH – PHASE LTC3706 (SLAVE) 3705 F04 3705fb 15 ...
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... LTC3705 U U APPLICATIO S I FOR ATIO BOOST IN LT3705 BOOST TG TS UVLO – FS/IN BG GND PGND SIGNAL GROUND PLANE Figure 5. High-Current Transient Return Paths V IN POWER GROUND PLANE 3705 F05 3705fb ...
Page 17
... T2 FB/IN PT • • 1µF 0.1µF 100Ω 470pF 5k – – FS/IN PT 2:1 RUN/SS 162k 33nF 3705 F06b 80 0 LTC3705 10Ω L2 1.2µH 1nF 1.2Ω Si7336ADP 1µF ×2 CMPSH1-4 10µF 25V CZT3019 2.2µF 16V NDRV FS/SYNC FB LTC3706 ITH GND PGND PHASE SLP MODE REGSD ...
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... LTC3705 U TYPICAL APPLICATIO S 18 3705fb ...
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... TYP .008 – .012 (0.203 – 0.305) TYP LTC3705 .189 – .196* (4.801 – 4.978) .009 (0.229 REF .150 – .157** (3.810 – 3.988) ...
Page 20
... TYPICAL APPLICATIO 36V TO 0.82µH 72V 1µF 100V 1µF 1µF 100V 100V P2 – 365k 301k 100Ω 1% 330pF 301k 1 16 GND LTC3705 BOOT SLMT 4 13 220pF UVLO SSFLT 1000pF NDRV FB/IN BG 15k 8 9 – ...