NCP3231A High Current Synchronous Buck Converter The NCP3231A is a high current, high efficiency, voltage−mode synchronous buck converter which operates from 4.5 V to 18 V input and generates output voltages down to 0.6 V at up to 25 A. www.onsemi.com Features • • • • • • • • • • • • • Wide Input Voltage Range from 4.5 V to 18 V 0.6 V Internal Reference Voltage 500 kHz Switching Frequency External Programmable Soft−start Lossless Low−side FET Current Sensing Output Over−voltage Protection and Under−voltage Protection System Over−temperature Protection using a Thermistor or Sensor Hiccup Mode Operation for All Faults Pre−bias Start−up Adjustable Output Voltage Power Good Output Internal Over−temperature Protection This is a Pb−Free Device* MARKING DIAGRAM 1 1 40 NCP3231A AWLYYWWG QFN40 6x6, 0.5P CASE 485CM NCP3231A = Specific Device Code A = Assembly Location WL = Wafer Lot YY = Year WW = Work Week G = Pb−Free Package AGND ISET SS OTS FB PG VIN VIN VIN 4 1 5 3 6 2 8 7 9 VIN 11 VIN 12 VIN 13 VIN 14 37 PGND VSWH 15 36 BST PGND 16 PGND 17 PGND 18 PGND 19 32 VSWH PGND 20 31 VSWH 40 EN VIN EP42 39 VCC GND EP41 38 VB 35 VSW 34 VSWH 27 28 29 PGND PGND VSWH 30 26 PGND VSWH 25 33 VSWH PGND 23 PGND 24 22 PGND 21 PGND VSWH EP43 PGND Cellular Base Stations ASIC, FPGA, DSP and CPU Core and I/O Supplies Telecom and Network Equipment Server and Storage System 10 • • • • COMP PIN CONNECTIONS Typical Applications (TOP VIEW) ORDERING INFORMATION Device Package Shipping† NCP3231AMNTXG QFN40 (Pb−Free) 2500 / Tape & Reel †For information on tape and reel specifications, including part orientation and tape sizes, please refer to our Tape and Reel Packaging Specification Brochure, BRD8011/D. *For additional information on our Pb−Free strategy and soldering details, please download the ON Semiconductor Soldering and Mounting Techniques Reference Manual, SOLDERRM/D. © Semiconductor Components Industries, LLC, 2015 May, 2015 − Rev. 3 1 Publication Order Number: NCP3231A/D NCP3231A VB VCC LDO VCC VB VB VB BST VIN OSC COMP VDD VREF FB Control Logic Ramp Generator PWM Logic + E/A − − and − VSWH SS Soft Start VCC 2 mA EN VB UVLO OVP, UVP Power Good OCP, TSD Protection VSW PVDD Enable Logic 1.2 V POR PGND PG VB + − VREF OTS ISET AGND Figure 1. NCP3231A Block Diagram www.onsemi.com 2 NCP3231A PIN DESCRIPTION Pin No. Symbol 1 SS A capacitor from this pin to GND allows the user to adjust the soft−start ramp time. Description 2 FB Output voltage feedback. 3 COMP 4 ISET 5 AGND 6 OTS 7 PG Power good indicator of the output voltage. Open−drain output. Connect PG to VDD with an external resistor. 8−14, EP42 VIN The VIN pin is connected to the internal power NMOS switch. The VIN pin has high di/dt edges and must be decoupled to ground close to the pin of the device. 15, 29−34, EP43 VSWH The VSWH pin is the connection of the drain and source of the internal NMOS switches. At switch off, the inductor will drive this pin below ground as the body diode and the NMOS conducts with a high dv/dt. 16−28, 37 PGND Ground reference and high−current return path for the bottom gate driver and low- side NMOS. 35 VSW IC connection to the switch node between the top MOSFET and bottom MOSFET. Return path of the high− side gate driver. 36 BST Top gate driver input supply, a bootstrap capacitor connection between the switch node and this pin. 38 VB 39 VCC 40 EN EP41 GND Output of the error amplifier. A resistor from this pin to ground sets the over−current protection (OCP) threshold. Analog ground. Negative input of internal thermal comparator. Tie this pin to ground if not in use. The internal LDO output and input supply for the NCP3231A. Connect a minimum of 4.7 mF ceramic capacitor from this pin to ground. Input Supply for IC. This pin must be connected to VIN. Logic control for enabling the switcher. An internal pull−up enables the device automatically. The EN pin can also be driven high to turn on the device, or low to turn off the device. A comparator and precision reference allow the user to implement this pin as an adjustable UVLO circuit. Exposed Pad. Connect GND to a large copper plane at ground potential to improve thermal dissipation. www.onsemi.com 3 NCP3231A VIN VIN BST VCC VOUT VSWH VSW VB PGND NCP3231A ISET AGND VPG EN FB OTS PG COMP SS Figure 2. Typical Application Circuit ABSOLUTE MAXIMUM RATINGS (measured vs. GND pad, unless otherwise noted) Symbol Value Unit VIN, VCC 20.5 −0.3 V VSW to GND VSWH, VSW 26 −0.6 (DC) +35 (t < 50 ns) −5 (t < 100 ns) V BST to GND BST 30 (DC) −0.6 (DC) +40 (t < 50 ns) V 6.0 −0.3 V Rating Power Supply to GND All other pins Operating Ambient Temperature Range (Note 1) TA −40 to +90 °C Operating Junction Temperature Range (Note 1) TJ −40 to +150 °C TJ(MAX) +150 °C Tstg −55 to +150 °C Electrostatic Discharge − Human Body Model HBM 1.0 kV Electrostatic Discharge − Charge Device Model CDM 2.0 kV HS FET Junction-to-Case Thermal Resistance (Note 2) RqJC−HS 1.3 °C/W LS FET Junction-to-Case Thermal Resistance (Note 2) RqJC−LS 0.6 °C/W Maximum Junction Temperature Storage Temperature Range THERMAL INFORMATION Stresses exceeding those listed in the Maximum Ratings table may damage the device. If any of these limits are exceeded, device functionality should not be assumed, damage may occur and reliability may be affected. 1. The maximum package power dissipation limit must not be exceeded. PD + T J(MAX) * T A R qJA 2. RqJC thermal resistance is obtained by simulating a cold plate test on the exposed power pad. No specific JEDEC standard test exists, but a close description can be found in the ANSI SEMI standard G30−88. www.onsemi.com 4 NCP3231A ELECTRICAL CHARACTERISTICS (−40°C < TJ < +125°C, VCC = 12 V, for min/max values unless otherwise noted, TJ = +25°C for typical values) Parameter Symbol Test Conditions Min Typ Max Units 18 V POWER SUPPLY VIN/VCC Operation Voltage VIN/VCC 4.5 VB UVLO Threshold (Rising) 4.1 4.2 4.3 V VB UVLO Threshold (Falling) 3.4 3.66 3.8 V 4.9 5.15 5.45 V IB = 25 mA, VCC = 4.5 V 36 110 mV EN = H, COMP = H, no switching; PG open; no switching 4.7 6.4 mA NCP3231A; EN = 0; VCC = 18 V; PG open 100 140 mA NCP3231A; EN = 0; VCC = 4.5 V; PG open 53 75 mA mV VB Output Voltage VB VB Dropout Voltage VCC Quiescent Current Shutdown Supply Current VCC = 6 V, 0 ≤ IB ≤ 40 mA FEEDBACK VOLTAGE FB Input Voltage VFB Feedback Input Bias Current IFB TJ = 25°C, 4.5 V ≤ VCC ≤ 18 V 597 600 603 −40°C ≤ TJ ≤ 125°C; 4.5 V ≤ VCC ≤ 18 V 594 600 606 VFB = 0.6 V 75 nA ERROR AMPLIFIER Guaranteed by Design Open Loop DC Gain Open Loop Unity Gain Bandwidth 60 F0dB,EA Open Loop Phase Margin Slew Rate COMP pin to GND = 10 pF COMP Clamp Voltage, High COMP Clamp Voltage, Low 85 dB 24 MHz 60 ° 2.5 V/m 3.46 V 465 mV Output Source Current VFB = 0 V 15 mA Output Sink Current VFB = 1 V 20 mA CURRENT LIMIT Low−side ISET Current Source LS_ISET Low−side ISET Current Source Temperature Coefficient TC_LS_I− SET Low−side OCP Switch−over Threshold Low−side Fixed OCP Threshold LS_OCPth Low−side Programmable OCP Range LS_OCPth LS OCP Blanking time LS_Tblnk 34 mA +0.31 %/°C Guaranteed by Design 600 mV Guaranteed by Design 300 Sourced from ISET pin, before SS, TJ = 25°C mV < 600 mV Guaranteed by Design 150 ns Maximum duty cycle fsw = 500 kHz, VFB = 0 V 4.5 V < VCC < 18 V 92 % Minimum duty cycle VCOMP < PWM Ramp Offset Voltage 0 % Minimum GH on−time Guaranteed by Characterization 60 ns PWM Ramp Amplitude Guaranteed by Characterization VCC/8.6 VCC/6.6 VCC/5.6 V PWM Ramp Offset Guaranteed by Characterization 0.64 V PWM OSCILLATOR Oscillator Frequency Range fsw fsw = 500 kHz 4.5 V < VCC < 18 V www.onsemi.com 5 450 500 550 kHz NCP3231A ELECTRICAL CHARACTERISTICS (−40°C < TJ < +125°C, VCC = 12 V, for min/max values unless otherwise noted, TJ = +25°C for typical values) Parameter Symbol Test Conditions Min Typ Max Units thiccup tss < 1 ms, fsw = 500 kHz 4 ms tss > 1 ms, fsw = 500 kHz 4 x tss ms OSCILLATOR Hiccup Timer ENABLE INPUT (EN) EN Input Operating Range Enable Threshold Voltage V_EN VEN rising Enable Hysteresis 1.11 VEN falling Deep Disable Threshold 1.2 5.5 V 1.29 V 144 0.7 Enable Pull−up Current 0.78 mV 0.9 V 2 mA SOFTSTART INPUT (SS) SS Startup Delay tSSD 1.33 ms SS End Threshold SSEND 0.6 V SS Source Current ISS 2.15 2.5 2.8 mA 10 20 30 mA 665 675 685 mV 500 525 550 mV VOLTAGE MONITOR PG = 0.15 V Power Good Sink Current Output Overvoltage Rising Threshold Overvoltage Fault Blanking Time ms 20 Output Under−Voltage Trip Threshold Under−voltage Protection Blanking Time 20 ms OVP and UVP Enable Delay tSS s POWER STAGE High−side On Resistance RDSONH VIN/VCC = 5 V, ID = 2 A 7 9.9 mW Low−side On Resistance RDSONL VIN/VCC = VB, ID = 2 A 1.5 2.9 mW IBOOT = 2 mA 0.28 VFBOOT V THERMAL MONITOR (OTS) 0.59 OTS comparator reference voltage (Rising Threshold) OTS comparator reference voltage (Falling Hysteresis) 0.6 0.61 50 V mV THERMAL SHUTDOWN Thermal Shutdown Threshold Guaranteed by design Thermal Shutdown Hysteresis Guaranteed by design 135 150 25 165 °C °C Product parametric performance is indicated in the Electrical Characteristics for the listed test conditions, unless otherwise noted. Product performance may not be indicated by the Electrical Characteristics if operated under different conditions. www.onsemi.com 6 NCP3231A fSW, SWITCHING FREQUENCY (kHz) 0.602 0.601 0.600 0.599 0.598 0.597 0.596 −40 −25 −10 5 20 35 50 65 80 95 110 125 503 VCC = 12 V 502 501 500 VCC = 4.5 V 499 498 −40 −25 −10 5 20 35 50 65 80 95 110 125 TJ, JUNCTION TEMPERATURE (°C) Figure 3. Reference Voltage vs. Temperature Figure 4. Switching Frequency vs. Temperature 1.23 1.22 1.21 1.20 1.19 −40 −25 −10 5 20 35 50 65 80 95 110 125 1.10 1.09 1.08 1.07 1.06 −40 −25 −10 5 20 35 50 65 80 95 110 125 TJ, JUNCTION TEMPERATURE (°C) TJ, JUNCTION TEMPERATURE (°C) Figure 5. Rising Enable Threshold vs. Temperature Figure 6. Falling Enable Threshold vs. Temperature 7 100 90 IQ, QUIESCENT CURRENT (mA) ISD, SHUTDOWN CURRENT (mA) 504 TJ, JUNCTION TEMPERATURE (°C) VEN, FALLING ENABLE THRESHOLD (V) VEN, RISING ENABLE THRESHOLD (V) VFB, FEEDBACK REFERENCE VOLTAGE (V) TYPICAL CHARACTERISTICS 80 70 60 50 40 30 20 VCC = 12 V 10 0 −40 −25 −10 5 20 35 50 65 80 6 5 4 3 2 1 VCC = 12 V, No Switching 0 −40 −25 −10 95 110 125 5 20 35 50 65 80 95 110 125 TJ, JUNCTION TEMPERATURE (°C) TJ, JUNCTION TEMPERATURE (°C) Figure 7. Shutdown Current vs. Temperature Figure 8. Quiescent Current vs. Temperature www.onsemi.com 7 NCP3231A TYPICAL CHARACTERISTICS 50 ISET, LSOCP SET CURRENT (mA) ISS, SOFT−START CURRENT (mA) 2.70 2.65 2.60 2.55 2.50 2.45 2.40 2.35 2.30 −40 −25 −10 5 20 35 50 65 80 40 35 30 25 20 −40 −25 −10 95 110 125 5 20 35 50 65 80 95 110 125 TJ, JUNCTION TEMPERATURE (°C) TJ, JUNCTION TEMPERATURE (°C) Figure 9. Soft−start Current vs. Temperature Figure 10. ISET Current vs. Temperature 9.5 2.5 9.0 LOW−SIDE FET RDS(on) (mW) HIGH−SIDE FET RDS(on) (mW) 45 8.5 VIN/VCC = 4.5 V 8.0 7.5 VIN/VCC = 12 V 7.0 6.5 6.0 5.5 5.0 −40 −25 −10 5 20 35 50 65 80 95 2.0 VIN/VCC = 4.5 V 1.5 VIN/VCC = 12 V 1.0 0.5 0 −40 −25 −10 110 125 5 20 35 50 65 80 95 110 125 TJ, JUNCTION TEMPERATURE (°C) TJ, JUNCTION TEMPERATURE (°C) Figure 11. High−side RDS(on) vs. Temperature Figure 12. Low−side RDS(on) vs. Temperature 100 100 VOUT = 3.3 V 95 VOUT = 3.3 V 95 85 EFFICIENCY (%) EFFICIENCY (%) 90 VOUT = 1.0 V 80 VOUT = 2.5 V 75 VOUT = 1.8 V 70 VOUT = 1.2 V 65 90 85 VOUT = 2.5 V VOUT = 1.0 V VOUT = 1.8 V 80 VOUT = 1.2 V 75 70 60 VIN/VCC = 12 V TA = 25°C 55 50 VIN/VCC = 5 V TA = 25°C 65 60 0 2.5 5.0 0 7.5 10.0 12.5 15.0 17.5 20.0 22.5 25.0 2.5 5.0 7.5 10.0 12.5 15.0 17.5 20.0 22.5 25.0 IOUT, LOAD CURRENT (A) IOUT, LOAD CURRENT (A) Figure 13. Efficiency vs. Iout (Vin = 12 V) Figure 14. Efficiency vs. Iout (Vin = 5 V) www.onsemi.com 8 NCP3231A TYPICAL CHARACTERISTICS 0.61 4.30 0.60 0.59 0.58 0.57 0.56 Falling Threshold 0.55 0.54 −40 −25 −10 5 20 35 50 65 80 4.26 4.22 4.18 4.14 4.10 −40 −25 −10 95 110 125 5 20 35 50 65 80 95 110 125 TJ, JUNCTION TEMPERATURE (°C) TJ, JUNCTION TEMPERATURE (°C) Figure 15. OTS Threshold vs. Temperature Figure 16. VB UVLO Rising Threshold vs. Junction Temperature OVP, OVERVOLTAGE THRESHOLD (V) 3.80 3.76 3.72 3.68 3.64 3.60 −40 −25 −10 5 20 35 50 65 80 95 110 125 680 679 678 677 676 675 674 673 672 671 670 −40 −25 −10 5 20 35 50 65 80 95 110 125 TJ, JUNCTION TEMPERATURE (°C) TJ, JUNCTION TEMPERATURE (°C) Figure 17. VB UVLO Falling Threshold vs. Junction Temperature Figure 18. Output OVP vs. Junction Temperature UVP, UNDERVOLTAGE THRESHOLD (V) VB UVLO, FALLING THRESHOLD VOLTAGE (V) VB UVLO RISING THRESHOLD VOLTAGE (V) OTS, OVERTEMPERATURE THRESHOLD VOLTAGE (V) Rising Threshold 560 558 556 554 552 550 548 546 544 542 540 −40 −25 −10 5 20 35 50 65 80 95 110 125 TJ, JUNCTION TEMPERATURE (°C) Figure 19. Output UVP vs. Junction Temperature www.onsemi.com 9 NCP3231A TYPICAL CHARACTERISTICS CH1 (Blue): EN CH2 (Aqua): COMP CH3 (Purple): Vout CH4 (Green): SS CH1 (Blue): VSW CH2 (Aqua): COMP CH3 (Purple): Vout CH4 (Green): SS Figure 20. Typical Startup Waveforms (Vin = 12 V, Iout = 25 V, Vout = 1 V) Figure 21. Typical Short Circuit Waveforms (Vin = 12 V) www.onsemi.com 10 NCP3231A OPERATION DESCRIPTION Overview drive signal to avoid shoot through. During the dead time, the body diode of the low side FET freewheels the current. The body diode has much higher voltage drop than that of the MOSFET, which reduces the efficiency significantly. The longer the body diode conducts, the lower the efficiency. NCP3231A implements adaptive dead time control to minimize the dead time, as well as preventing shoot through. The NCP3231A is a 500 kHz, high efficiency, high current PWM synchronous buck converter. It operates with a single supply voltage from 4.5 to 18 V and can provide output current as high as 25 A. NCP3231A utilizes voltage mode with voltage feed−forward control to respond instantly to Vin changes and provide for easier compensation over the supply range of the converter. The device also includes pre−bias startup capability to allow monotonic startup in the event of a pre−biased output condition. Protection features include overcurrent protection (OCP), output over and under voltage protection (OVP, UVP), and power good. The enable function is highly programmable to allow for adjustable startup voltages at higher input voltages. There is also an adjustable soft−start, an over− temperature/over−voltage comparator, and internal thermal shutdown. Precision Enable (EN) The ENABLE block allows the output to be toggled on and off and is a precision analog input. When the EN voltage exceeds V_EN, the controller will initiate the soft-start sequence as long as the input voltage and sub-regulated voltage have exceeded their UVLO thresholds. V_EN_hyst helps to reject noise and allow the pin to be resistively coupled to the input voltage or sequenced with other rails. If the EN voltage is held below typically 0.8 V, the NCP3231A enters a deep disable state where the internal bias circuitry is off. As the voltage at EN continues to rise, the Enable comparator and reference are active and provide a more accurate EN threshold. The drivers are held off until the rising voltage at EN crosses V_EN. An internal 2 mA pullup automatically enables the device when the EN pin is left floating. Reference Voltage The NCP3231A incorporates an internal reference that allows output voltages as low as 0.6 V. The tolerance of the internal reference is guaranteed over the entire operating temperature range of the controller. The reference voltage is trimmed using a test configuration that accounts for error amplifier offset and bias currents. Oscillator Ramp The ramp waveform is a saw tooth formed at the PWM frequency with a peak−to−peak amplitude of VCC/6.6, offset from GND by typically 0.64 V. The PWM duty cycle is limited to a maximum of 92%, allowing the bootstrap capacitor to charge during each cycle. INPUT SUPPLY / VCC VDD 2 mA EN Error Amplifier The error amplifier’s primary function is to regulate the converter’s output voltage using a resistor divider connected from the converter’s output to the FB pin of the controller, as shown in the Applications Schematic. A type III compensation network must be connected around the error amplifier to stabilize the converter. It has a bandwidth of greater than 24 MHz, with open loop gain of at least 60 dB. 1.2 V Figure 22. Enable Functional Block Diagram Pre−bias Startup In some applications the controller will be required to start switching when its output capacitors are charged anywhere from slightly above 0 V to just below the regulation voltage. This situation occurs for a number of reasons: the converter’s output capacitors may have residual charge on them or the converter’s output may be held up by a low current standby power supply. NCP3231A supports pre−bias start up by holding off switching until the feedback voltage and thus the output voltage rises above the set regulated voltage. If the pre−bias voltage is higher than the set regulated voltage, switching does not occur until the output voltage drops back to the regulation point. Programmable Soft−Start An external capacitor connected from the SS pin to ground sets up the soft start period, which can limit the start−up inrush current. The soft start period can be programmed based on the Equation 1. t SS + V ref C SS I SS Enable Logic (eq. 1) OCP is the only fault that is active during a soft−start. Adaptive Non−Overlap Gate Driver In a synchronous buck converter, a certain dead time is required between the low side drive signal and high side www.onsemi.com 11 NCP3231A Power Good (PG) Operation Power Good Pullup Voltage LSOCP Trip Level Inductor Current Start Reset/Start Reset/Start Backup Counter Start Hiccup Hiccup Counter 1 2 3 tHiccup = 4xtSS Skipped Pulses showing Skip Count Figure 23. LSOCP Function with Counters and Power Good Shown (exaggerated for informational purposes) PROTECTION FEATURES Hiccup Mode will turn on at that point as well, thus pulling PG low. Once VFB has fallen below the Undervoltage Protection Threshold (UVP), the device will enter hiccup mode. The NCP3231A utilizes hiccup mode for all of its fault conditions. Upon entering hiccup mode after a fault detection, the NCP3231A turns off the high side and low side FET’s and PG goes low. It waits for tHICCUP ms before reinitiating a soft−start. tHiccup is defined as four soft start timeouts (tss). And if the soft−start time tss is set to be less than 1 ms, the hiccup time will be 4 ms. The equation for tss is shown in Equation 1. OCP is the only active fault detection during the hiccup mode soft start. Under Voltage Protection (UVP) A UVP circuit monitors the VFB voltage to detect an under voltage event. If the VFB voltage is below this threshold for more than 20 ms, a UVP fault is set and the device will enter hiccup mode. Over Current Protection (OCP) The NCP3231A over current protection scheme senses the peak freewheeling current in the low−side FET (LSOCP) after a blanking time of 150 ns as shown in Figure 23. The low−side FET drain−to−source voltage, VDS, is compared against the voltage of a fixed, internal current source, ISET and a user−selected resistor, RSET. Voltage across the low−side FET is sensed from the VSW pin to GND. After an OCP detection, the NCP3231A keeps the high−side FET off until the Low−side FET current falls below the trip point again and the next clock cycle occurs. An internal OCP counter will count up to 3 consecutive LSOCP events. After the third consecutive count, the device enters hiccup mode. Over Temperature Comparator (OTS) The NCP3231A provides an over−temperature shutdown (OTS) comparator with 50 mV hysteresis and a 0.6 V reference in order to remotely sense an external temperature detector or thermistor. When the voltage at the OTS pin rises above 0.6 V, the drivers stop switching and both FET’s remain off. When this voltage drops below typically 0.55 V, a new soft−start cycle is generated automatically. Tie the OTS pin to ground if this function is not required. Over Voltage Protection (OVP) When the voltage at the FB pin (VFB) is above the OVP threshold for greater than 20 ms (typical), an OVP fault is set. The high side FET (HSFET) will turn off and the low side FET (LSFET) will turn on. The open-drain PG pull down www.onsemi.com 12 NCP3231A good pin is a high impedance output. If the NCP3231A detects an OCP, OVP, UVP, OTS, TSD or is in soft start, it pulls PG pin low. The PG pin is an open drain 10 mA pull down output. To prevent nuisance trips, there is a backup counter that will reset the OCP counter after 7 consecutive cycles without an LSOCP trigger. The backup counter is reset and then started again after each OCP trip until the third OCP count as stated above occurs. Layout Guidelines When laying out a power PCB for the NCP3231A there are several general key points and special key points to consider: General Layout Guide: these are the common techniques for high frequency high power board layout design. Base component placement: High current path components should be placed to keep the current path as tight as possible. Placement of components on the bottom of the board such as input or output decoupling can add loop inductance. Ground Return for Power and Signals: Solid, uninterrupted ground planes must be present and adjacent to the high current path. Copper Shapes on Component Layers: Large copper planes on one or multiple layers with adequate vias will increase thermal transfer, reduce copper conduction losses, and minimize loop inductance. Greater than 20 A designs require 2~3 layer shapes or more, increasing the number of layers will only improvement performance. Via Placement for Power and Ground: Place enough vias to adequately connect outer layers to inner layers for thermal transfer and to minimize added inductance in layer transition. Multiple vias should be placed near important components like input ceramics and output ceramic capacitors. Key Signal Routes: Do not route sensitive signals, such as FB near or under noisy nets such as the switch node VSW and BST node, to reduce noise coupling effects on the sensitive lines. Special Layout Guide: please pay attention to the special requirement of layout guide. To improve the High-side OCP accuracy, users should connect VCC and VIN directly and do not place any type of filter or resistor between these two pins. To improve the Low-side OCP accuracy, users should use single ground connection instead of separate analog ground and power ground. Make sure that the inner layers (at least 2nd layer, 3rd layer and 4th layer) are dedicated for ground plane. Do not use other copper planes to cut or interrupt the shape of ground plane, which may add more parasitic components to affect the sensing accuracy. Over Current Protection Threshold The NCP3231A allows the user to adjust the LSOCP threshold with an external resistor, RSET. This resistor, along with an internal temperature compensated current source, ISET, sets the current limit reference voltage for the LSOCP comparator. Internally, a current sense circuit samples the voltage from VSW to GND. This voltage is then multiplied by a factor of 2 and compared against the ISET*RSET voltage threshold. The basic design equation for LSOCP trip point selection is: RSET + 2 +2 ǒiLoad ) 0.5iLpk*pkǓ Rdson ISET 67 (eq. 2) ǒiLoad ) 0.5i Lpk*pkǓ In this equation, iLoad is the over current protection point of the load current, iLpk-pk is the peak to peak value of inductor current, and for example, when input voltage is 12 V, output voltage is 3.3 V, switching frequency is 500 kHz and inductor value is 330 nH, the peak to peak value of inductor current is 14.5 A. ISET is temperature compensated current source proportional to the on-resistance of LS MOSFET, Rdson, the ratio of Rdson to ISET is about 67. In case RSET is not connected, the device switches the OCP threshold to a fixed 300 mV value: an internal safety clamp on ISET is triggered as soon as the ISET voltage reaches 600 mV, enabling the 300 mV fixed threshold. Thermal Shutdown (TSD) The NCP3231A protects itself from overheating with an internal thermal monitoring circuit. If the junction temperature exceeds the thermal shutdown threshold both the upper and lower MOSFETs will be shut OFF. Once the temperature drops below the falling hysteresis threshold, the voltage at the COMP pin will be pulled below the ramp valley voltage and a soft−start will be initiated. Power Good Monitor (PG) NCP3231A monitors the output voltage and signal when the output is out of regulation or during a non−regulated pre−bias condition, or fault condition. When the output voltage is within the OVP and UVP thresholds, the power www.onsemi.com 13 NCP3231A PACKAGE DIMENSIONS QFN40 6x6, 0.5P CASE 485CM ISSUE O A B D PIN ONE LOCATION 2X ÉÉÉ ÉÉÉ ÉÉÉ L1 DETAIL A ALTERNATE CONSTRUCTIONS E ÉÉ ÉÉ 0.15 C EXPOSED Cu 2X TOP VIEW 0.15 C (A3) DETAIL B 0.10 C DIM A A1 A3 b D D2 D3 E E2 E3 E4 e G K L L1 MOLD CMPD DETAIL B ALTERNATE CONSTRUCTION A 43X 0.08 C NOTES: 1. DIMENSIONING AND TOLERANCING PER ASME Y14.5M, 1994. 2. CONTROLLING DIMENSIONS: MILLIMETERS. 3. DIMENSION b APPLIES TO PLATED TERMINAL AND IS MEASURED BETWEEN 0.15 AND 0.30mm FROM TERMINAL 4. COPLANARITY APPLIES TO THE EXPOSED PAD AS WELL AS THE TERMINALS. 5. POSITIONAL TOLERANCE APPLIES TO ALL THREE EXPOSED PADS. L L SIDE VIEW A1 C NOTE 4 SEATING PLANE 0.10 C A B D3 D2 NOTE 5 G DETAIL A 40X L MILLIMETERS MIN MAX 0.80 1.00 −−− 0.05 0.20 REF 0.18 0.30 6.00 BSC 2.30 2.50 1.40 1.60 6.00 BSC 4.30 4.50 1.90 2.10 1.64 1.84 0.50 BSC 2.20 BSC 0.20 −−− 0.30 0.50 −−− 0.15 SOLDERING FOOTPRINT E3 6.30 E2 4.56 E4 1.66 1 G 40 K e 40X e/2 G BOTTOM VIEW 40X 0.63 2.56 1 b 0.10 C A B 0.05 C 2.16 NOTE 3 4.56 6.30 2.16 PKG OUTLINE 40X 0.50 PITCH 0.30 DIMENSIONS: MILLIMETERS ON Semiconductor and are registered trademarks of Semiconductor Components Industries, LLC (SCILLC). SCILLC owns the rights to a number of patents, trademarks, copyrights, trade secrets, and other intellectual property. A listing of SCILLC’s product/patent coverage may be accessed at www.onsemi.com/site/pdf/Patent−Marking.pdf. SCILLC reserves the right to make changes without further notice to any products herein. SCILLC makes no warranty, representation or guarantee regarding the suitability of its products for any particular purpose, nor does SCILLC assume any liability arising out of the application or use of any product or circuit, and specifically disclaims any and all liability, including without limitation special, consequential or incidental damages. “Typical” parameters which may be provided in SCILLC data sheets and/or specifications can and do vary in different applications and actual performance may vary over time. All operating parameters, including “Typicals” must be validated for each customer application by customer’s technical experts. SCILLC does not convey any license under its patent rights nor the rights of others. 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