FR9850S6

FR9850 17V, 2A Synchronous Step-Down 85T DC/DC Converter Description Features The FR9850 is a synchronous step-down DC/DC converter with fast constant on time (FCOT) mode control. The device provides 4.5V to 17V input voltage range and 2A continuous load current capability. Operation frequency depends on Input and output voltage condition. At light load condition, the FR9850 can operate at power saving mode to support high efficiency and reduce power loss.  The FR9850 fault protection includes cycle-by-cycle current limit, short circuit protection, UVLO and thermal shutdown. The soft-start function prevents inrush current at turn-on. The FR9850 use fast constant on time control that provides fast transient response, the noise immunity and all kinds of very low ESR output capacitor for ensuring performance stabilization.            Low RDS(ON) Integrated Power MOSFET (150mΩ/80mΩ) Wide Input Voltage Range: 4.5V to 17V Output Voltage Range: 0.6V to 8V 2A Output Current FCOT Mode Enables Fast Transient Response Pseudo 850kHz Frequency Input Under Voltage Lockout Internal 1ms Soft-Start Cycle-by-Cycle Current Limit Hiccup Short Circuit Protection Over Temperature Protection with Auto Recovery 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) FR9850□ Package Type S6: SOT-23-6 LX VIN SHDN 6 1 4 5 (Marking) 2 3 BST GND FB SOT-23-6 Marking Figure 1. Pin Assignments of FR9850 FR9850-Preliminary 0.2-MAY-2019 Part Number Product Code FR9850S6 FD2 1 FR9850 85T Typical Application Circuit C3 0.1μF R3 100kΩ 4 1 SHDN 5 VIN L1 1.5μH BST LX 6 VIN VOUT 1.2V 4.5V to 17V FR9850 C1 22μF/25V MLCC FB C5 3 R1 4.99kΩ 1% C4 (optional) C2 22μF/6.3V MLCC 0.1μF GND 2 R2 4.99kΩ 1% Figure 2. CIN /COUT use Ceramic Capacitors Application Circuit VIN=12V, the recommended BOM list is as below. VOUT C1 R1 R2 C4 L1 C2 1.05V 22μF MLCC 3.74kΩ 4.99kΩ 5pF~220pF 1.5μH 22μF MLCC 1.2V 22μF MLCC 4.99kΩ 4.99kΩ 5pF~220pF 1.5μH 22μF MLCC 1.8V 22μF MLCC 30.9kΩ 15.4kΩ 5pF~220pF 2.2μH 22μF MLCC 2.5V 22μF MLCC 30.9kΩ 9.76kΩ 5pF~220pF 3.3μH 22μF MLCC 3.3V 22μF MLCC 30kΩ 6.65kΩ 5pF~220pF 4.7μH 22μF MLCC 5V 22μF MLCC 30.9kΩ 4.22kΩ 5pF~220pF 4.7μH 22μF MLCC Table 1. Recommended Component Values FR9850-Preliminary 0.2-MAY-2019 2 FR9850 85T Functional Pin Description Pin Name Pin No. Pin Function BST 1 High side gate drive boost pin. A capacitor rating between 0.1uF~1uF 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. This IC senses feedback voltage via FB and regulates it at 0.6V. 4 Enable input pin. Pull high to turn on IC, and pull low to turn off IC. Connect VIN with a 100kΩ resistor for self-startup. 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 OTP Internal Regulator VCC VCC 1M Off Time Generator BST High-Side MOSFET FB Internal Soft Start On Time Generator OTP Vref Logic Control Driver Logic LX UVLO LX OCP Low-Side MOSFET Cycle by Cycle Current Limit GND Figure 3. Block Diagram of FR9850 FR9850-Preliminary 0.2-MAY-2019 3 Absolute Maximum Ratings (Note 1) FR9850 85T ● Supply Voltage VIN ------------------------------------------------------------------------------------------- -0.3V to +20V ● Enable Voltage H ------------------------------------------------------------------------------------- -0.3V to +20V ● LX Voltage VLX ------------------------------------------------------------------------------------------------ -0.3 to VIN +0.3V ● Dynamic LX Voltage in 15ns Duration------------------------------------------------------------------- -5V to VIN +5V ● BST Pin Voltage VBST --------------------------------------------------------------------------------------- -0.3V to VLX +6.5V ● All Other Pins Voltage -------------------------------------------------------------------------------------- -0.3V to +6V ● Maximum Junction Temperature (TJ) ------------------------------------------------------------------- +150°C ● Storage Temperature (TS) --------------------------------------------------------------------------------- -65°C to +150°C ● Lead Temperature (Soldering, 10sec.) ----------------------------------------------------------------- +260°C ● Package Thermal Resistance, (θJA) (Note 2) 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. Note 2: θJA is measured at 25°C ambient with the component mounted on a high effective thermal conductivity 4-layer board of JEDEC-51-7. The thermal resistance greatly varies with layout, copper thickness, number of layers and PCB size. Recommended Operating Conditions ● Supply Voltage VIN ------------------------------------------------------------------------------------------ +4.5V to +17V ● Operation Temperature Range --------------------------------------------------------------------------- -40°C to +85°C FR9850-Preliminary 0.2-MAY-2019 4 FR9850 85T Electrical Characteristics (VIN=12V, TA=25°C, unless otherwise specified.) Parameter Symbol Conditions Min =2V, VFB=1V VIN Quiescent Current IDDQ H VIN Shutdown Supply Current ISD H Feedback Voltage VFB 4.5V≦VIN≦17V Feedback Input Current IFB VFB=1V Typ Max 0.3 =0V 0.591 Unit mA 1 10 μA 0.6 0.609 V 0.01 0.1 μA High-Side MOSFET RDS(ON) (Note 3) RDS(ON) 150 mΩ Low-Side MOSFET RDS(ON) (Note 3) RDS(ON) 80 mΩ ILIMIT(HS) 3.2 A VIN=12V, VOUT=1.05V 150 ns High-Side MOSFET Current Limit On Time (Note 3) (Note 3) TON Minimum Off Time TOFF(MIN) VFB=0.4V 180 ns Input Supply Voltage UVLO Threshold VUVLO(Vth) VIN Rising 4.3 V UVLO Threshold Hysteresis VUVLO(HYS) 0.35 V TSS 1 ms Internal Soft-Start Period H Input Low Voltage H Input High Voltage H Input Current Thermal Shutdown Threshold Thermal Shutdown Hysteresis H (L H (H (Note 3) 1.5 V V 2 μA TSD 160 °C THYS 30 °C H (Note 3) 0.5 H =2V Note 3: Not production tested. FR9850-Preliminary 0.2-MAY-2019 5 FR9850 85T Function Description The FR9850 is a synchronous step-down DC/DC converter with fast constant on time (FCOT) mode control. It has integrated high-side (150mΩ, typ) and low-side (80mΩ, typ) power switches, and provides 2A continuous load current. It regulates input voltage from 4.5V to 17V, and down to an output voltage as low as 0.6V. Using FCOT control scheme provides fast transient response, which can minimize the component size without additional external compensation network. Over Current Protection Enable Short Circuit Protection The FR9850 H pin provides digital control to turn on/turn off the regulator. When the voltage of H exceeds the threshold voltage, the regulator starts the soft start function. If the H 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 H to VIN through a 100kΩ resistor. The FR9850 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 0.33V, the oscillator frequency will be reduced naturally 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. Soft Start The FR9850 employs internal soft start function to reduce input inrush current during start up. The typical value of internal soft start time is 1ms. Input Under Voltage Lockout When the FR9850 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 350mV (typ). FR9850-Preliminary 0.2-MAY-2019 The FR9850 over current protection function is implemented using cycle-by-cycle current limit architecture. The inductor current is monitored by Low-side MOSFET. When the load current increases, the inductor current also increases. When the valley 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. Over Temperature Protection The FR9850 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 30°C (typ). 6 FR9850 85T 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 equation is: . T 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 1.05V 3.74kΩ 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 PPL t R PPL R PPL ( C t L R PPL t R 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) + VRIPPLE(C) (t) (t) + VNOISE (t) (t) 1 T 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 IOUT/2. The following diagram is the graphical representation of above equation. = VRIPPLE(t) ICIN(RMS) (A) 1.25 2A 1 0.75 1.5A 1A 0.5 (t) 0.25 0 10 20 30 40 50 60 70 80 90 D (%) FR9850-Preliminary 0.2-MAY-2019 7 FR9850 85T Application Information (Continued) R PPL ( R R PPL ( L T F C T 1 L R L R PPL (C That will lower ripple current and result in lower output ripple voltage. The Δ L is inductor peak-to-peak ripple current: L L T F C 2 L C 1 T F C T 1 L T T 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. 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. 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 . T(MA T L F T C L 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 FR9850 Probe Ground C3 LX VOUT GND Ceramic Capacitor Inductor Selection 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. FR9850-Preliminary 0.2-MAY-2019 8 FR9850 85T Application Information (Continued) PCB Layout Recommendation 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. VOUT L1 VIN LX 6 5 4 R3 The device’s performance and stability is dramatically affected by PCB layout. It is recommended to follow these general guidelines shown as below: C1 C2 GND C3 1 2 3 R2 R1 C4 Figure 4. Recommended PCB Layout Diagram 3. Keep the sensitive signal (FB) away from the switching signal (LX). 4. Multi-layer PCB design is recommended. FR9850-Preliminary 0.2-MAY-2019 9 FR9850 85T 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 4: 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. FR9850-Preliminary 0.2-MAY-2019 10