FR9885S6CTR

FR9885 /a85T 18V, 2A, 500KHz Synchronous Step-Down fitipower integrated technology lnc. DC/DC Converter Description Features The FR9885 is a synchronous step-down DC/DC converter that provides wide 4.5V to 18V input voltage range and 2A load current capability. At light load condition, the FR9885 can operate at power saving mode to support high efficiency and reduce power loss.  The FR9885 fault protection includes cycle-by-cycle current limit, UVLO and thermal shutdown. The internal soft-start function prevents inrush current at turn-on. This device uses current mode control scheme which provides fast transient response. Internal compensation function reduces external compensation components and simplifies the design process. In shutdown mode, the supply current is about 1μA. The FR9885 is offered in SOT-23-6 package, which provides a very compact system solution.            Low RDS(ON) Integrated Power MOSFET (170mΩ/135mΩ) Internal Compensation Function Wide Input Voltage Range: 4.5V to 18V Adjustable Output Voltage Down to 0.6V 2A Output Current 500kHz Switching Frequency Internal Soft-Start time: 0.8ms Cycle-by-Cycle Current Limit Hiccup Short Circuit Protection Over-Temperature Protection with Auto Recovery Input Under Voltage Lockout SOT-23-6 Package Applications     STB (Set-Top-Box) LCD Display, TV Distributed Power System Networking, XDSL Modem Pin Assignments Ordering Information S6 Package (SOT-23-6) FR9885□□□ LX VIN SHDN 6 5 TR: Tape/Reel C: Green 4 (Marking) 1 2 Package Type S6: SOT-23-6 3 BST GND FB Figure 1. Pin Assignment of FR9885 FR9885-Preliminary 0.3-SEP-2014 SOT-23-6 Marking Part Number Product Code FR9885S6CTR A9A 1 FR9885 /a85T fitipower integrated technology lnc. Typical Application Circuit C3 0.1μF R3 100kΩ 4 1 SHDN 5 VIN BST LX 6 VIN L1 2.2μH VOUT 1.2V 4.5V to 18V FR9885 C1 FB C5 10μF/25V CERAMIC 10μF/25V CERAMIC 3 GND 2 R1 4.99kΩ 1% C4 (optional) C2 22μF/6.3V CERAMIC x 2 R2 4.99kΩ 1% Figure 2. CIN /COUT use Ceramic Capacitors Application Circuit C3 0.1μF R3 100kΩ 4 1 SHDN 5 VIN 4.5V to 18V BST LX VIN 6 FR9885 FB C5 0.1μF/25V CERAMIC x 1 C1 100μF/25V EC x 1 3 GND 2 L1 2.2μH VOUT 1.2V R1 4.99kΩ 1% C4 (optional) C2 100μF/6.3V EC x 1 R2 4.99kΩ 1% Figure 3. CIN /COUT use Electrolytic Capacitors Application Circuit VIN=12V, the recommended BOM list is as below. VOUT C1 R1 R2 C5 C4 L1 C2 1.2V 10μF MLCC 4.99kΩ 4.99kΩ 10μF MLCC 10pF~10nF 2.2uH 22μF MLCC x2 1.8V 10μF MLCC 30.9kΩ 15.4kΩ 10μF MLCC 10pF~10nF 3.3uH 22μF MLCC x2 2.5V 10μF MLCC 30.9kΩ 9.76kΩ 10μF MLCC 10pF~10nF 4.7uH 22μF MLCC x2 3.3V 10μF MLCC 30kΩ 6.65kΩ 10μF MLCC 10pF~10nF 4.7uH 22μF MLCC x2 5V 10μF MLCC 30.9kΩ 4.22kΩ 10μF MLCC 10pF~10nF 6.8uH 22μF MLCC x2 1.2V 100μF EC 4.99kΩ 4.99kΩ 0.1μF -- 2.2uH 100μF EC 1.8V 100μF EC 30.9kΩ 15.4kΩ 0.1μF -- 3.3uH 100μF EC 2.5V 100μF EC 30.9kΩ 9.76kΩ 0.1μF -- 4.7uH 100μF EC 3.3V 100μF EC 30kΩ 6.65kΩ 0.1μF -- 4.7uH 100μF EC 5V 100μF EC 30.9kΩ 4.22kΩ 0.1μF -- 6.8uH 100μF EC Table 1. Recommended Component Values FR9885-Preliminary 0.3-SEP-2014 2 FR9885 /a85T fitipower integrated technology lnc. Functional Pin Description Pin Name Pin No. Pin Function BST 1 High side gate drive boost pin. A capacitance between 10nF to 100nF must be connected from this pin to LX. It can boost the gate drive to fully turn on the internal high side NMOS. GND 2 Ground pin. FB 3 Voltage feedback input pin. Connect FB and VOUT with a resistive voltage divider. feedback voltage via FB and regulates it at 0.6V. This IC senses 4 Enable input pin. This pin is a digital control input that turns the converter on or off. a 100KΩ resistor for self-startup. Connect to VIN with VIN 5 Power supply input pin. Placed input capacitors as close as possible from VIN to GND to avoid noise influence. LX 6 Power switching node. Connect an external inductor to this switching node. Block Diagram VIN UVLO & POR SHDN ISEN Internal Regulator VCC OTP VCC 1M Oscillator BST High-Side MOSFET S FB Internal Soft Start Current Comp Vref R OTP Control Logic Driver Logic LX UVLO Low-Side MOSFET Current Limit GND Figure 4. Block Diagram of FR9885 FR9885-Preliminary 0.3-SEP-2014 3 fitipower integrated technology lnc. Absolute Maximum Ratings (Note 1) FR9885 /a85T ● Supply Voltage VIN ------------------------------------------------------------------------------------------- -0.3V to +20V ● Enable Voltage ------------------------------------------------------------------------------------- -0.3V to +20V ● LX Voltage VLX ----------------------------------------------------------------------------------------------- -1V to VIN+0.3V ● Dynamic LX Voltage in 15ns Duration------------------------------------------------------------------- -5V to VIN+5V ● BST Pin Voltage VBST --------------------------------------------------------------------------------------- VLX-0.3V to VLX+6V ● All Other Pins Voltage -------------------------------------------------------------------------------------- -0.3V to +6V ● Maximum Junction Temperature (T J) ------------------------------------------------------------------- +150°C ● Storage Temperature (TS) --------------------------------------------------------------------------------- -65°C to +150°C ● Lead Temperature (Soldering, 10sec.) ----------------------------------------------------------------- +260°C ● Package Thermal Resistance (θJA) SOT-23-6 -------------------------------------------------------------------------------------------- 250°C/W ● Package Thermal Resistance (θJC) SOT-23-6 -------------------------------------------------------------------------------------------- 110°C/W Note 1：Stresses beyond this listed under “Absolute Maximum Ratings" may cause permanent damage to the device. Recommended Operating Conditions ● Supply Voltage VIN ------------------------------------------------------------------------------------------- +4.5V to +18V ● Operation Temperature Range --------------------------------------------------------------------------- -40°C to +85°C FR9885-Preliminary 0.3-SEP-2014 4 FR9885 /a85T fitipower integrated technology lnc. Electrical Characteristics (VIN=12V, TA=25°C, unless otherwise specified.) Parameter Symbol Conditions Min Typ 4.5 Max Unit 18 V VIN Input Supply Voltage VIN VIN Quiescent Current IDDQ =2V, VFB=1.0V 2 VIN Shutdown Supply Current ISD =0V 1 10 μA Feedback Voltage VFB 4.5V≦VIN≦18V 0.6 0.615 V 0.585 mA High-Side MOSFET RDS(ON) (Note2) RDS(ON) 170 mΩ Low-Side MOSFET RDS(ON) (Note2) RDS(ON) 135 mΩ High-Side MOSFET Leakage Current ILX(leak) High-Side MOSFET Current Limit ILIMIT(HS) (Note2) Oscillation Frequency Short Circuit Oscillation Frequency FOSC(short) DMAX Minimum On Time TMIN 10 Minimum Duty FOSC Maximum Duty Cycle (Note2) =0V, VLX=0V 3.2 400 500 μA A 600 kHz VFB=0V 150 kHz VFB=0.4V 90 % 100 ns 4.3 V Input Supply Voltage UVLO Threshold VUVLO(Vth) Input Supply Voltage UVLO Threshold Hysteresis VUVLO(HYS) 400 mV TSS 0.8 ms Internal Soft-Start Period Input Low Voltage 0.4 (L Input High Voltage 2 ( =2V Input Current Thermal Shutdown Threshold (Note2) VIN Rising TSD V V 2 μA 160 °C Note 2：Not production tested. FR9885-Preliminary 0.3-SEP-2014 5 FR9885 /a85T fitipower integrated technology lnc. Typical Performance Curves VIN=12V, VOUT=3.3 , C1=10μF×2, C2=22μF×2, L1=4.7uH, TA=+25°C, unless otherwise noted. IOUT=0A IOUT=2A VOUT 10mV/div. VOUT 10mV/div. IL IL 1A/div. VLX 5V/div. 1A/div. VLX 5V/div. 2ms/div. 2μs/div. Figure 5. Steady State Waveform IOUT=0A Figure 6. Steady State Waveform IOUT=2A VEN 5V/div. VEN VOUT 2V/div. VOUT 2V/div. IOUT 1A/div. VLX 5V/div. 2ms/div. 5V/div. IOUT 1A/div. VLX 5V/div. 2ms/div. Figure 7. Power On through Waveform IOUT=0A Figure 8. Power On through Waveform IOUT=2A VEN 2V/div. VOUT 2V/div. IOUT 1A/div. IOUT 1A/div. VLX 5V/div. 5V/div. 10ms/div. FR9885-Preliminary 0.3-SEP-2014 5V/div. VOUT VLX Figure 9. Power Off through VEN 5V/div. 400us/div. Waveform Figure 10. Power Off through Waveform 6 FR9885 /a85T fitipower integrated technology lnc. Typical Performance Curves (Continued) VIN=12V, VOUT=3.3 , C1=10μF×2, C2=22μF×2, L1=4.7uH, TA=+25°C, unless otherwise noted. IOUT=0A IOUT=2A VIN 5V/div. VIN VOUT 2V/div. VOUT 2V/div. IOUT 1A/div. VLX 5V/div. 5V/div. IOUT 1A/div. VLX 5V/div. 2ms/div. 2ms/div. Figure 11. Power On through VIN Waveform Figure 12. Power On through VIN Waveform IOUT=0A IOUT=2A VIN VIN 5V/div. 5V/div. VOUT 2V/div. VOUT 2V/div. IOUT 1A/div. IOUT 1A/div. VLX 5V/div. VLX 5V/div. 100ms/div. 100ms/div. Figure 13. Power Off through VIN Waveform Figure 14. Power Off through VIN Waveform IOUT=1A to 2A, C4=1nF VOUT IOUT VOUT 1V/div. IL 1A/div. 200mV/div. 1A/div. VLX 5V/div. 200μs/div. 4ms/div. Figure 15. Load Transient Waveform Figure 16. Short Circuit Test FR9885-Preliminary 0.3-SEP-2014 7 FR9885 /a85T fitipower integrated technology lnc. Typical Performance Curves (Continued) VOUT=1.2V VOUT=3.3V 90 80 80 70 70 Efficiency (%) 100 90 Efficiency (%) 100 60 50 40 30 VIN=5V VIN=12V VIN=18V 20 10 0 0.01 60 50 40 30 10 0.1 1 Load Current (A) 0 0.01 10 Figure 17. Efficiency vs. Load Current 0.1 1 Load Current (A) 10 Figure 18. Efficiency vs. Load Current VOUT=5V IOUT=700mA 0.615 100 Feedback Voltage (V) 90 80 Efficiency (%) VIN=5V VIN=12V VIN=18V 20 70 60 50 40 30 20 VIN=12V VIN=18V 10 0 0.01 0.61 0.605 0.6 0.595 0.59 0.585 0.1 1 10 Load Current (A) Figure 19. Efficiency vs. Load Current -40 -30 -20 -10 0 10 20 30 40 50 60 70 80 90 Temperture (°C) Figure 20. Feedback Voltage vs. Temperature Switching Frequency (kHz) IOUT=700mA 600 580 560 540 520 500 480 460 440 420 400 -40 -30 -20 -10 0 10 20 30 40 50 60 70 80 90 Temperture (°C) Figure 21. Switching Frequency vs. Temperature FR9885-Preliminary 0.3-SEP-2014 8 fitipower integrated technology lnc. Function Description The FR9885 is a high efficiency, internal compensation, and constant frequency current mode step-down synchronous DC/DC converter. It has integrated high-side (170mΩ, typ and low-side (135mΩ, typ) power switches, and provides 2A load current. It regulates input voltage from 4.5V to 18V, and down to an output voltage as low as 0.6V. Control Loop Under normal operation, the output voltage is sensed by FB pin through a resistive voltage divider and amplified through the error amplifier. The voltage of error amplifier output is compared to the switch current to control the RS latch. At the beginning of each clock cycle, the high-side NMOS turns on when the oscillator sets the RS latch, and turns off when current comparator resets the RS latch. Then the low-side NMOS turns on until the clock period ends. Internal Compensation Function The stability of the feedback circuit is controlled through internal compensation circuits. This internal compensation function is optimized for most applications and this function can reduce external R, C components. Enable The FR9885 pin provides digital control to turn on/turn off the regulator. When the voltage of exceeds the threshold voltage, the regulator starts the soft start function. If the pin voltage is below than the shutdown threshold voltage, the regulator will turn into the shutdown mode and the shutdown current will be smaller than 1μA. For auto start-up operation, connect to VIN through a 100KΩ resistor. FR9885 /a85T Over Current Protection The FR9885 over current protection function is implemented using cycle-by-cycle current limit architecture. The inductor current is monitored by measuring the high-side MOSFET series sense resistor voltage. When the load current increases, the inductor current also increases. When the peak inductor current reaches the current limit threshold, the output voltage starts to drop. When the over current condition is removed, the output voltage returns to the regulated value. Short Circuit Protection The FR9885 provides short circuit protection function to prevent the device damage from short condition. When the short condition occurs and the feedback voltage drops lower than 0.4V, the oscillator frequency will be reduced to 150kHz and hiccup mode will be triggered to prevent the inductor current increasing beyond the current limit. Once the short condition is removed, the frequency will return to normal. Over Temperature Protection The FR9885 incorporates an over temperature protection circuit to protect itself from overheating. When the junction temperature exceeds the thermal shutdown threshold temperature, the regulator will be shutdown. And the hysteretic of the over temperature protection is 40°C (typ). Soft Start The FR9885 employs internal soft start function to reduce input inrush current during start up. The typical value of internal soft start time is 0.8ms. Input Under Voltage Lockout When the FR9885 is power on, the internal circuits are held inactive until VIN voltage exceeds the input UVLO threshold voltage. And the regulator will be disabled when VIN is below the input UVLO threshold voltage. The hysteretic of the UVLO comparator is 400mV (typ). FR9885-Preliminary 0.3-SEP-2014 9 FR9885 /a85T fitipower integrated technology lnc. Application Information Output Voltage Setting The output voltage VOUT is set using a resistive divider from the output to FB. The FB pin regulated voltage is 0.6V. Thus the output voltage is: T =0. 1 R1 R2 Output Capacitor Selection Table 2 lists recommended values of R1 and R2 for most used output voltage. Table 2 Recommended Resistance Values VOUT R1 A low ESR capacitor is required to keep the noise minimum. Ceramic capacitors are better, but tantalum or low ESR electrolytic capacitors may also suffice. When using tantalum or electrolytic capacitors, a 0.1μF ceramic capacitor should be placed as close to the IC as possible. R2 5V 30.9kΩ 4.22kΩ 3.3V 30kΩ 6.65kΩ 2.5V 30.9kΩ 9.76kΩ 1.8V 30.9kΩ 15.4kΩ 1.2V 4.99kΩ 4.99kΩ The output capacitor is used to keep the DC output voltage and supply the load transient current. When operating in constant current mode, the output ripple is determined by four components: R PPLE t = R PPLE C t R PPLE(E L R PPLE E R t E t t The following figures show the form of the ripple contributions. VRIPPLE(ESR)(t) Place resistors R1 and R2 close to FB pin to prevent stray pickup. Input Capacitor Selection The use of the input capacitor is filtering the input voltage ripple and the MOSFETS switching spike voltage. Because the input current to the step-down converter is discontinuous, the input capacitor is required to supply the current to the converter to keep the DC input voltage. The capacitor voltage rating should be 1.25 to 1.5 times greater than the maximum input voltage. The input capacitor ripple current RMS value is calculated as: C = (RM = + VRIPPLE(ESL) (t) (t) + VRIPPLE(C) (t) (t) + VNOISE (t) (t) 1 T T Where D is the duty cycle of the power MOSFET. This function reaches the maximum value at D=0.5 and the equivalent RMS current is equal to I OUT/2. The following diagram is the graphical representation of above equation. 1.25 2A IIN(RMS) (A) 1 0.75 = VRIPPLE(t) 1.5A 1A 0.5 (t) 0.25 0 10 20 30 40 50 60 70 80 90 D (%) FR9885-Preliminary 0.3-SEP-2014 10 FR9885 /a85T fitipower integrated technology lnc. Application Information (Continued) R PPLE(E R = R PPLE(E L = R PPLE(C = T F C T 1 L E R E L L E L L= T F C 2 That will lower ripple current and result in lower output ripple voltage. The Δ L is inductor peak-to-peak ripple current: L C 1 T F C T T The following diagram is an example to graphical represent Δ L equation. Where FOSC is the switching frequency, L is the inductance value, VIN is the input voltage, ESR is the equivalent series resistance value of the output capacitor, ESL is the equivalent series inductance value of the output capacitor and the COUT is the output capacitor. 1.8 1.6 ΔIL (A) 1.4 Low ESR capacitors are preferred to use. Ceramic, tantalum or low ESR electrolytic capacitors can be used depending on the output ripple requirement. When using the ceramic capacitors, the ESL component is usually negligible. It is important to use the proper method to eliminate high frequency noise when measuring the output ripple. The figure shows how to locate the probe across the capacitor when measuring output ripple. Removing the scope probe plastic jacket in order to expose the ground at the tip of the probe. It gives a very short connection from the probe ground to the capacitor and eliminating noise. Probe Ground L=3.3μ 1.2 1 L=4.7μ 0.8 0.6 L=6.8μ 0.4 0.2 5 6 7 8 9 10 11 12 13 14 15 16 17 18 VIN (V) VOUT=3.3V, FOSC=500kHz A good compromise value between size and efficiency is to set the peak-to-peak inductor ripple current Δ L equal to 30% of the maximum load current. But setting the peak-to-peak inductor ripple current Δ L between 20%~50% of the maximum load current is also acceptable. Then the inductance can be calculated with the following equation: L =0.3 GND FR9885-Preliminary 0.3-SEP-2014 PEAK = Load Current The output inductor is used for storing energy and filtering output ripple current. But the trade-off condition often happens between maximum energy storage and the physical size of the inductor. The first consideration for selecting the output inductor is to make sure that the inductance is large enough to keep the converter in the continuous current mode. F T C L To guarantee sufficient output current, peak inductor current must be lower than the FR9885 high-side MOSFET current limit. The peak inductor current is as below: Ceramic Capacitor Inductor Selection T(MA T L= VOUT T 1 L T(MA L 2 IPEAK IOUT(MAX) ∆IL Time 11 FR9885 /a85T fitipower integrated technology lnc. Application Information (Continued) Feedforward Capacitor Selection PCB Layout Recommendation Internal compensation function allows users saving time in design and saving cost by reducing the number of external components. The use of a feedforward capacitor C4 in the feedback network is recommended to improve the transient response or higher phase margin. The device’s performance and stability is dramatically affected by PCB layout. It is recommended to follow these general guidelines shown as below: VOUT R1 FR9885 C4 FB R2 1. Place the input capacitors and output capacitors as close to the device as possible. Trace to these capacitors should be as short and wide as possible to minimize parasitic inductance and resistance. 2. Place feedback resistors close to the FB pin. 3. Keep the sensitive signal (FB) away from the switching signal (LX). 4. Multi-layer PCB design is recommended. VOUT L1 VIN LX 6 5 4 R3 For optimizing the feedforward capacitor, knowing the cross frequency is the first thing. The cross frequency (or the converter bandwidth) can be determined by using a network analyzer. When getting the cross frequency with no feedforward capacitor identified, the value of feedforward capacitor C4 can be calculated with the following equation: C1 C2 GND C3 1 2 3 R2 C4= 2 1 FCR 1 R1 1 1 R1 R2 R1 C4 Figure 22. Recommended PCB Layout Diagram Where FCROSS is the cross frequency. To reduce transient ripple, the feedforward capacitor value can be increased to push the cross frequency to higher region. Although this can improve transient response, it also decrease phase margin and cause more ringing. In the other hand, if more phase margin is desired, the feedforward capacitor value can be decreased to push the cross frequency to lower region. In general, the feedforward capacitor range is between 10pF to 10nF. External Diode Selection For 5V input applications, it is recommended to add an external boost diode. This helps improving the efficiency. The boost diode can be a low cost one such as 1N4148. D1 1N4148 VIN 5V VIN BST FR9885 C3 LX FR9885-Preliminary 0.3-SEP-2014 12 FR9885 /a85T fitipower integrated technology lnc. Outline Information SOT-23-6 Package (Unit: mm) SYMBOLS UNIT DIMENSION IN MILLIMETER MIN MAX A 0.90 1.45 A1 0.00 0.15 A2 0.90 1.30 B 0.30 0.50 D 2.80 3.00 E 2.60 3.00 E1 1.50 1.70 e 0.90 1.00 e1 1.80 2.00 L 0.30 0.60 Note：Followed From JEDEC MO-178-C. Carrier Dimensions Life Support Policy Fitipower’s products are not authorized for use as critical components in life support devices or other medical systems. FR9885-Preliminary 0.3-SEP-2014 13