FC3470 FS | Alldatasheet
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Applications
**** 2018. 12. 27 1/8Revision No : 0 SEMICONDUCTOR TECH NIC AL DATA FC3470 SOT-23-6
Typical Application Circuit 2018. 12. 27 2/8Revision No : 0 FC3470 Typical Application Circuit of FC3470 Functional Block Diagram of FC3470
Parameter Symbol Rating Unit V e g a t l o V n i V DD -0.3 to 20 V V e g a t l o V X L M -0.3 to (Vin+0.5V) V V e g a t l o V N E CO -0.3 to 20 V V e g a t l o V B F DO -0.3 to 6 V T e g a t l o V S B opr -0.3 to (VLX+5V) V T e r u t a r e p m e T n o i t c n u Jstg 150 °C C ° 5 8 + o t C ° 0 4 - e r u t a r e p m e T g n i t a r e p O Parameter Symbol Test Conditions Min Typ Max Unit Input Voltage Range VDD V 8 1 5 . 4 UVLO Threshold CO 3.0 V Supply Current in Operation V st VEN=2.0V, VFB=1.1V 0.4 0.6 mA Supply Current in Shutdown R short VEN =0 or EN = GND 1 uA Regulated Feedback Voltage TA = 25°C, 0.588 0.6 0.612 V m 0 9 e c n a t s i s e R - n O h c t i w S e d i S - h g i H Ω m 0 7 e c n a t s i s e R - n O h c t i w S e d i S - w o L Ω High-Side Switch Leakage Current VEN=0V , VLX=0V 0 10 uA Upper Switch Current Limit I DD Minimum Duty Cycle 3 A Oscillation Frequency Ist1 z H M 6 . 0 Maximum Duty Cycle VFB=0.6V 92 % S n 0 6 e m i T - n O m u m i n i M 0 6 1 n w o d t u h S l a m r e h T ℃ Electrical Characteristics (Ta=25 ℃ unless otherwise noted) Absolute Maximum Ratings (Ta=25 ℃ unless otherwise noted) 4.5V≤VIN≤18V 2018. 12. 27 3/8Revision No : 0 FC3470
The FC3470 is a current mode step down DC/DC converter that provides excellent transient response with no extra external compensation components. This device contains an internal, low resistance, high voltage power MOSFET, and operates at a high 600KHz operating frequency to ensure a compact, high efficiency design with excellent AC and DC performance. Error Amplifier The error amplifier compares the FB pin voltage with the internal FB reference (VFB) and outputs a current proportional to the difference between the two. This output current is then used to charge or discharge the internal compensation network to form the COMP voltage, which is used to control the power MOSFET current. The optimized internal compensation network minimizes the external component counts and simplifies the control loop design. Internal Soft-Start The soft-start is implemented to prevent the converter output voltage from overshooting during startup. When the chip starts, the internal circuitry generates a soft-start volt age (SS) ramping up from 0V to 0.6V. When it is lower than the internal reference (REF), SS overrides REF so the error amplifier uses SS as the reference. When SS is higher than REF, REF regains control. The SS time is internally fixed to 1 ms. Over-Current-Protection and Hiccup The FC3470 has cycle-by-cycle over current limit when the inductor current peak value exceeds the set current limit threshold. Meanwhile, output voltage starts to drop until FB is below the Under-Voltage (UV) threshold, typically 30% below the reference. Once a UV is trigger ed, the FC3470 enters hiccup mode to periodically restart the part. This protection mode is especially useful when the output is dead-short to ground. The average short circuit current is great ly reduced to alleviate the thermal issue and to protect the regulator. The FC3470 exits the hiccup mode once the over current condition is removed. Startup and Shutdown If both VIN and EN are higher than their appropriate thresholds, the chip starts. The reference block starts first, generating stable reference voltage and currents, and then the internal regulator is enabled. The regulator provides stable supply for the remaining circuitries. Three events can shut down the chip: EN low, VIN low and thermal shutdown. In t he shutdown procedure, the signaling path is first blocked to avoid any fault triggering. The COMP volt age and the internal supply rail are then pulled down. The floating driver is not subject to this shutdown command. Function Description 2018. 12. 27 4/8Revision No : 0 FC3470
Setting the Output Voltage The external resistor divider is used to set the output voltage (see Typical Application on page 1). The feedback resistor R1 also sets the feedback loop bandwidth with the internal compensation capacitor. Choose R1 to be around 100kΩ for optimal transient response. R2 is then given by: 1 / FB outV V RR Selecting the Inductor A 4.7μH to 22μH inductor with a DC current rating of at least 25% percent higher than the maximum load current is recommended for most applications. For highest efficiency, the inductor DC resistance should be less than 15mΩ. For most designs, the inductance value can be derived from the following equation. OSC L in out inout f I V V V VL ×△× − ×= ) ( Where ΔIL is the inductor ripple current. Choose inductor ripple current to be approximately 30% if the maximum load current, 2A. The maximum inductor peak current is: ) ( L LOADMAX L II I + = Under light load conditions below 100mA, larger inductance is recommended for improved efficiency. Selecting the Output Capacitor The output capacitor (C2) is required to maintain the DC output voltage. Ceramic, tantalum, or low ESR electrolytic capacitors are recommended. Low ESR capacitors are preferred to keep the output voltage ripple low. The output voltage ripple can be mated by:
11 C fRV
V L f VV S ESR IN OUT S OUT OUT Function Description(Cont.) 2018. 12. 27 5/8Revision No : 0 FC3470
Where L is the inductor value and RESR is the equivalent series resistance (ESR) value of the output capacitor. In the case of ceramic capacitors, the impedance at the switching frequency is dominated by the capacitance. The output voltage ripple is mainly caused by the capacitance. For simplification, the output voltage ripple can be mated by: ] [−×× × × IN OUT S OUT OUT V V C L f VV 1 8 2 In the case of tantalum or electrolytic capacitors, the ESR dominates the impedance at the switching frequency. For simplification, the output ripple can be approximated to: IN OUT S OUT OUT RV V L f The characterics of the output capacitor also affect the stability of the regulation system. The BC3470 can be optimized for a wide range of capacitance and ESR values. PCB Layout Guide PCB layout is very important to achieve stable operation. It is highly reco mmended to duplicate EVB layout for optimum performance. If change is necessary,please follow these guidelines and take for reference. 1) Keep the path of switching current short and minimize the loop area formed by Input capacitor, high-side MOSFET and low-side MOSFET. 2) Bypass ceramic capacitors are suggested to be put close to the Vin Pin. 3) Ensure all feedback connections are short and direct. Place the feedback resistors and compensation components as close to the chip as possible. 4) VOUT, LX away from sensitive analog areas such as FB. 5) Connect IN, LX, and especially GND respectively to a large copper area to cool the chip to improve thermal performance and long-term reliability. ESR Function Description(Cont.) 2018. 12. 27 6/8Revision No : 0 FC3470
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Temperature Profile for IR Reflow Soldering(Pb-Free) Note: 1.Preheating:150~180℃, Time:60~90sec. 2.Peak Temp.:245±5℃, Duration:5±0.5sec. 3. Cooling Speed: 2~10℃/sec. Resist ance to Soldering Heat Test Conditions Temp.:260±5℃ Time:10±1sec Packaging SPEC.(REEL) Package Type Units n o i s n e m i D (unit：mm ) Units/Reel R eels/Inner Box Un its/Inner Box Inner Boxes/Outer Box Units/Outer Box Reel Inner Box Outer Box SOT-23-5/6 3,000 10 30,000 4 120,000 7〞×8 210×205×205 445×230×435 2018. 12. 27 8/8Revision No : 0 FC3470