LTC3806 Linear Technology, LTC3806 Datasheet
LTC3806
Available stocks
Related parts for LTC3806
LTC3806 Summary of contents
Page 1
... Power Over Ethernet supplies. Low start-up current reduces power dissipation in the start-up resistor and reduces the size of the external start- up capacitor. The LTC3806 is available in a 12-pin, exposed pad DFN package. , LTC and LT are registered trademarks of Linear Technology Corporation ...
Page 2
... TH I Pin Load = 5 A (Note SENSE SENSE INFORMATION TOP VIEW ORDER PART NUMBER 12 SENSE 11 NC LTC3806EDE GND DE PART MARKING DE12 PACKAGE 3806 = 125 C/W JA MIN TYP MAX 10 1000 140 1 ...
Page 3
... Note 4: The minimum operating voltage is allowed once operation begins. To begin operation, V threshold with V Note 5: The dynamic input supply current is higher due to power MOSFET gate charging (Q Note 6: The LTC3806 is tested in a feedback loop which servos V reference voltage with the I and power A (the no load to full load operating voltage range for the I 1 ...
Page 4
... LTC3806 W U TYPICAL PERFOR A CE CHARACTERISTICS Shutdown Mode (V) IN 3806 G04 G1 Rise and Fall Time 250 200 150 100 4000 8000 12000 ...
Page 5
... INTV LOAD (mA) CC Efficiency vs Output Power 3806 G16 LTC3806 INTV Line Regulation CC 7.020 7.015 7.010 7.005 7.000 6.995 6.990 (V) IN 3806 G14 FIGURE 8 CIRCUIT ...
Page 6
... LTC3806 CTIO S RUN (Pin 1): The RUN pin provides the user with an accurate means for sensing the input voltage and pro- gramming the start-up threshold for the converter. The falling RUN pin threshold is nominally 1.14V and the comparator has 91mV of hysteresis for noise immunity. ...
Page 7
... GND 7 NC: PINS 4 AND 11 SLOPE OSC COMPENSATION PWM LATCH + – CURRENT COMPARATOR R LOOP I LOOP SOFT-START 1.230V BIAS AND V REF START-UP CONTROL LTC3806 INTV CC Q LOGIC INTV CC RUN COMPARATOR + C2 – – UV2 + REGULATOR + – + 6.9V UV1 – 3806 ...
Page 8
... TH peak currents to be supplied to the primary of the trans- former. Soft-start is completed when the voltage on the SS pin exceeds the voltage on the I The nominal operating frequency of the LTC3806 is 250kHz. is OUT2 Since forced continuous operation is used, the noise spectrum over all operating conditions is well controlled with virtually all noise occurring at the operating frequency and its harmonics ...
Page 9
... In an actual application, most of the IC supply current is used to drive the gate capacitances of the power MOSFETs result, high input voltage applications with large power MOSFETs can cause the LTC3806 to exceed its maximum junction temperature rating. The junction tem- perature can be estimated using the following equations: ...
Page 10
... Programming Turn-On and Turn-Off Thresholds with the RUN Pin The LTC3806 leaves a comparator detection circuit and the voltage reference active even when the device is shut down (Figure 3). This allows users to accurately program an input voltage at which the converter will turn on and off. ...
Page 11
... Maximum Rating for this pin! The RUN pin can be connected to the input voltage through an external 1M resistor, as shown in Figure 3c, for “always on” operation. Application Circuits A basic LTC3806 application circuit is shown in Figure 1. External component selection is driven by the character- istics of the load and the input supply. Duty Cycle Considerations ...
Page 12
... LTC3806 U U APPLICATIO S I FOR ATIO Some common secondary turns ratios: V OUT 2.5 3.3 3.3 5.0 1.8 3.3 1.8 2.5 2.5 3.3 5.0 For example, assume we need a regulator that operates with a nominal 48V input to produce one 3.3V output and one 5V output. The ideal turns ratio for the 3.3V (master) output is 06875 . IDEAL1 48 We select a turns ratio of 1/ 0.066… ...
Page 13
... I RMS Low effective series resistance and inductance is also important in the input capacitor since it affects the electro- magnetic interference suppression. In some instances high ESR can also produce stability problems because flyback converters exhibit a negative input resistance LTC3806 to determine MAX V DROP I PK 200 ...
Page 14
... LTC3806 U U APPLICATIO S I FOR ATIO characteristic. Refer to Application Note 19 for more information. The output capacitor is sized to handle the ripple current and to insure acceptable output voltage ripple. The output capacitor should have a ripple current rating greater than: D MAX I I RMS OUT 1– ...
Page 15
... The flat portion of the curve is the result of the Miller (gate-to-drain) capacitance as the drain voltage drops. The upper sloping line is due to the gate-to-drain accumulation capacitance and the gate-to-source capacitance. The Miller LTC3806 V L OUT MAX ( ...
Page 16
... PC Board Layout Checklist voltages the curve 1. In order to minimize switching noise and improve out- DS term, take put load regulation, the GND pin of the LTC3806 should MILLER be connected directly to 1) the negative terminal of the INTV . the output decoupling capacitors, 3) the bottom ter- ...
Page 17
... LTC3806 is not shared with other converters. AC input current from CC another converter could cause substantial input voltage ripple and this could interfere with the operation of the LTC3806. A few inches of PC trace or wire (L 100nH) between the C V should be sufficient to prevent current sharing IN problems ...
Page 18
... Synchronous Forward Application C1 1 220 R11 D1 LTC3806 100 1 12 1N4148 RUN SENSE 3. ...
Page 19
... U UE/DE Package 12-Lead Plastic DFN (4mm 3mm) (Reference LTC DWG # 05-08-1695) 0.65 0.05 PACKAGE OUTLINE 0.25 0.05 0.50 BSC 3.30 0.05 (2 SIDES) 4.00 0.10 (2 SIDES 0.20 TYP 1.70 0.10 3.00 0.10 (2 SIDES) (2 SIDES) 0.75 0.05 0.00 – 0.05 LTC3806 0.38 0. 0.115 TYP 7 12 PIN 1 NOTCH (UE12/DE12) DFN 0603 6 1 0.25 0.05 0.50 BSC 3.30 0.10 (2 SIDES) BOTTOM VIEW—EXPOSED PAD 19 3806f ...
Page 20
... Linear Technology Corporation 20 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 FAX: (408) 434-0507 D1 1A 60V T1 B260A SMA XFMR EFD20 Si4490 LTC3806 C12 RUN SENSE 0.033 220nF 2 11 1206 0603 1nF 4 ...