RT2856H RICHTEK | Alldatasheet
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Technical content
Features
Low RDS(ON) Power MOSFET Switches 26mΩ ΩΩ ΩΩ/19mΩ ΩΩ ΩΩ Input Voltage Range : 4.5V to 18V Adjustable Switching Frequency : 200kHz to 1.6MHz Current-Mode Control Synchronous to External Clock : 200kHz to 1.6MHz to 85° °° °°C Monotonic Start-Up into Pre-biased Outputs Adjustable Soft-Start Power Good Indicator Under-Voltage and Over-Voltage Protection Input Under-Voltage Lockout RoHS Compliant and Halogen Free Marking Information Simplified Application Circuit 01= : Product Code YMDNN : Date Code VIN RT2856H VIN PVIN BOOT FB COUT VOUT CIN PGOOD COMPRT/SYNC L EN PGOOD SS/TR CSS ROSC CBOOT LX GND RCOMP1 CCOMP1 Enable CCOMP2 01=YM DNN
DS2856H-07 June 2019www.richtek.com ©Copyright 2019 Richtek Technology Corporation. All rights reserved. is a registered trademark of Ric htek Technology Corporation. Functional Pin Description Pin No. Pin Name Pin Function
1 RT/SYNC
Oscillator Resistor and External Frequency Synchronization Input. Connecting a resistor from this pin to GND sets the switching frequency or connecting an external clock to this pin changes the switching frequency. 2, 3, 15 (Exposed Pad) GND System Ground. Provide the ground return path for the control circuitry and low-side power MOSFET. The exposed pad must be soldered to a large PCB and connected to GND for minimum power dissipation. 4, 5 PVIN Power Input. Supplies the power switches of the device. 6 VIN Supply Voltage Input. Supplies the control circuitry and internal reference of the device. 7 FB Feedback Voltage Input. This pin is used to set the desired output voltage via an external resistive divider. The feedback reference voltage is 0.8V typically.
8 COMP
Compensation Node. The current comparator threshold increases with this control voltage. Connect external compensation elements to this pin to stab ilize the control loop.
9 SS/TR
Soft-Start and Tracking Control Input. Connect a capacitor from SS to GND to set the soft-start period. The soft-start period can be used to track and sequence when the external voltage on this pin overrides the internal reference. 10 EN Enable Control Input. Floating this pin or connecting this pin to logic high can enable the device and connecting this pin to GND can disable the device. 11, 12 LX Switch Node. LX is the switching node that supplies power to the output and connect the output LC filter from LX to the output load. 13 BOOT Bootstrap Supply for High-Side Gate Driver. Connect a 100nF or greater capacitor from LX to BOOT to power the high-side switch.
14 PGOOD
Power Good Indicator Output. This pin is an open-drain logic output that is pulled to ground when the output voltage is lower or higher than its specified threshold under the conditions of OVP, OTP, dropout, EN shutdown, or during slow start.
Ordering Information
Note : Richtek products are : RoHS compliant and compatible with the current require- ments of IPC/JEDEC J-STD-020. Suitable for use in SnPb or Pb-free soldering processes. Pin Configurations (TOP VIEW) WQFN-14AL 3.5x3.5 Package Type QW : WQFN-14AL 3.5x3.5 (W-Type) RT2856H Lead Plating System G : Green (Halogen Free and Pb Free) GND GND PVIN PVIN VIN FB COMP BOOT LX EN SS/TR LX PGOOD RT/SYNC 141 GND
DS2856H-07 June 2019 www.richtek.com ©Copyright 2019 Richtek Technology Corporation. All rights reserved. is a registered trademark of Ric htek Technology Corporation. Function Block Diagram Operation UV Comparator If the feedback voltage (VFB) is lower than threshold voltage (91% of V REF), the UV Comparator's output goes high and the logic control circuit is allowed to turn on the MOSFET to pull PGOOD pin to low. OV Comparator If the feedback voltage (V FB) is higher than threshold voltage (109% of VREF), the OV Comparator's output goes high and the logic control circuit is allowed to turn on the MOSFET to pull PGOOD pin to low. Voltage Reference The converter produces a precise ±1% voltage reference over-temperature by scaling the output of a temperature stable bandgap circuit. Error Amplifier The device uses a transconductance error amplifier. The error amplifier compares the FB pin voltage with the SS/ TR pin voltage and the internal reference voltage which is 0.8V. The transconductance of the error amplifier is 1300μA/V during normal operation. The compensation network should be connected between the COMP pin and ground. Oscillator with RT/SYNC function The switching frequency is adjustable by an external resistor connected between the RT/SYNC pin and GND. The available frequency range is from 200kHz to 1.6MHz. An internal synchronized circuit has been implemented to switch from RT mode to SYNC mode. To implement the synchronization function, connect a square wave clock signal to the RT/SYNC pin with a duty cycle between 10% to 90%. The switching cycle is synchronized to the falling edge of the external clock at RT/SYNC pin. Power Stage Control Logic, Driver, and Boot UVLO Regulator Voltage Reference Slope Compensation BOOT GND LXSS/TR Current Comparator RT/SYNC FB UVLOThermal Detector Shutdown Logic ShutdownHigh-Side Current Sense IhysIP PVINVINEN VEN = 1.21V Low-Side Current Sense Oscillator with RT/SYNC Function ISS -+VREF PGOOD Logic UV Comparator OV Comparator 91% VREF 109% VREF PGOOD COMP
DS2856H-07 June 2019www.richtek.com ©Copyright 2019 Richtek Technology Corporation. All rights reserved. is a registered trademark of Ric htek Technology Corporation. Absolute Maximum Ratings (Note 1) Power Dissipation, PD @ TA = 25°C Package Thermal Resistance (Note 2) ESD Susceptibility (Note 3)
Electrical Characteristics
(VIN = 4.5V to 18V, VPVIN = 1.6V to 18V, TA = −40°C to 85°C, unless otherwise specified) Recommended Operating Conditions (Note 4) Parameter Symbol Test Conditions Min Typ Max Unit Supply Voltage PVIN Power Input Operating Voltage VPVIN 1.6 -- 18 VIN Supply Input Operating Voltage VIN 4.5 -- 18 Under-Voltage Lockout Threshold VUVLO V IN Rising -- 4 4.5 V Under-Voltage Lockout Threshold Hysteresis VUVLO -- 150 -- mV VIN Shutdown Current V EN = 0V -- 3 9 VIN Quiescent Current V FB = 0.83V, Not Switching -- 600 1000 Enable Voltage VIH V EN Rising -- 1.21 1.26 EN Threshold Voltage VIL V EN Falling 1.1 1.17 -- V Pull-Up Current V EN = 1.1V -- 1 -- Hysteresis Current V EN = 1.3V -- 3 --
DS2856H-07 June 2019 www.richtek.com ©Copyright 2019 Richtek Technology Corporation. All rights reserved. is a registered trademark of Ric htek Technology Corporation. Parameter Symbol Test Conditions Min Typ Max Unit Reference Voltage Reference Voltage V REF 0A ILOAD 6A 0.792 0.8 0.808 V Timing Resistor and External Clock ROSC = 27k 1440 1600 1760 ROSC = 110k 400 480 560 Switching Frequency f OSC ROSC = 270k 160 200 240 Switching Frequency Range Include Sync mode and RT mode set point 200 -- 1600 kHz Minimum Sync Pulse Width -- 20 -- ns High-Level -- -- 2 SYNC Threshold Voltage Low-Level 0.8 -- -- V SYNC Falling Edge to LX Rising Edge Delay Measure at 500kHz with ROSC resistor in series -- 66 -- ns Internal MOSFET High-Side On-Resistance R DS(ON)_H V BOOT VLX = 5.5V -- 26 40 Low-Side On-Resistance R DS(ON)_L V IN = 12V -- 19 30 LX and BOOT Minimum On-Time Measured at 90% to 90% of VLX, Minimum Off-Time V BOOT VLX 3V -- 0 -- ns BOOTLX UVLO V BL-UVLO -- -- 3 V Soft-Start and Tracking Internal Charge Current -- 2 -- A SS to Feedback Offset V SS = 0.4V -- 20 60 mV Current Limit High-Side Switch Current Limit 8 11 -- Low-Side Switch Sourcing Current Limit 7 10 -- Low-Side Switch Sinking Current Limit -- 2.3 -- A Error Amplifier Error Amplifier Trans-conductance gm 2A < ICOMP < 2A, VCOMP = 1V -- 1300 -- A/V Error Amplifier DC Gain V FB = 0.8V 1000 3100 -- V/V Error Amplifier Sink/Source Current VCOMP = 1V, 100mV input overdrive -- 110 -- A COMP to Iswitch gm -- 16 -- A/V Power Good VFB Rising (Good) -- 94 -- Power Good Rising Threshold VFB Rising (Fault) -- 109 -- %VREF
DS2856H-07 June 2019www.richtek.com ©Copyright 2019 Richtek Technology Corporation. All rights reserved. is a registered trademark of Ric htek Technology Corporation. Note 1. Stresses beyond those listed “Absolute Maximum Ratings ” may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions may affect device reliability. Note 2. θ JA is measured at T A = 25 °C on a high effective thermal conductivity four-layer test board per JEDEC 51-7. θJC is measured at the exposed pad of the package. Note 3. Devices are ESD sensitive. Handling precaution is recommended. Note 4. The device is not guaranteed to function outside its operating conditions. Parameter Symbol Test Conditions Min T yp Max Unit V FB Falling (Fault) -- 91 -- Power Good Falling Threshold V FB Falling (Good) -- 106 - %VREF Power Good Sink Current Capability PGOOD signal fault, IPGOOD sinks 2mA -- -- 0.3 V Power Good Leakage Current PGOOD signal good, V PGOOD = 5.5V -- 30 100 nA Minimum VIN for Indicating PGOOD V PGOOD 0.5V, IPGOOD sinks 100A -- 0.6 1 Minimum SS/TR Voltage for Indicating PGOOD -- -- 2.6 V Over-Temperature Protection Thermal Shutdown T SD 160 175 -- Thermal Shutdown Hysteresis TSD -- 10 --
©Copyright 2019 Richtek Technology Corporation. All rights reserved. is a registered trademark of Ric htek Technology Corporation. Table 1. Suggested Component Values
DS2856H-07 June 2019www.richtek.com ©Copyright 2019 Richtek Technology Corporation. All rights reserved. is a registered trademark of Ric htek Technology Corporation. Typical Operating Characteristics Reference Voltage vs. Temperature 0.65 0.70 0.75 0.80 0.85 0.90 0.95 -50 -25 0 25 50 75 100 125 Temperature (°C) Reference Voltage (V) Efficiency vs. Output Current 100 0123456 Output Current (A) Efficiency (%) VIN = 9V VIN = 12V VIN = 17V VOUT = 3.3V Efficiency vs. Output Current 100 0123456 Output Current (A) Efficiency (%) VOUT = 5V VOUT = 3.3V VOUT = 1.2V VIN = 12V Output Voltage vs. Output Current 3.26 3.27 3.28 3.29 3.30 3.31 3.32 3.33 0123456 Output Current (A) Output Voltage (V) VIN = 12V, VOUT = 3.3V Switching Frequency vs. Temperature 350 400 450 500 550 600 650 700 - 5 0- 2 5 0 2 5 5 0 7 51 0 0 1 2 5 Temperature (°C) Switching Frequency (kHz) 1 ROSC = 100kΩ Output Voltage vs. Input Voltage 3.23 3.25 3.27 3.29 3.31 3.33 3.35 3.37 4 6 8 1 01 21 41 61 8 Input Voltage (V) Output Voltage (V) IOUT = 0A IOUT = 3A IOUT = 6A VOUT = 3.3V
DS2856H-07 June 2019 www.richtek.com ©Copyright 2019 Richtek Technology Corporation. All rights reserved. is a registered trademark of Ric htek Technology Corporation. Current Limit vs. Input Voltage 4 6 8 1 01 21 41 61 8 Input Voltage (V) Current Limit (A) Current Limit vs. Temperature -50 -25 0 25 50 75 100 125 Temperature (°C) Current Limit (A) Quiescent Current vs. Temperature 400 500 600 700 800 900 1000 1100 -50 -25 0 25 50 75 100 125 Temperature (°C) Quiescent Current (µA) VFB = 0.83V Quiescent Current vs. Input Voltage 400 500 600 700 800 900 1000 1100 4 6 8 1 01 21 41 61 8 Input Voltage (V) Quiescent Current (µA) VFB = 0.83V Shutdown Current vs. Temperature - 5 0- 2 5 0 2 5 5 0 7 51 0 0 1 2 5 Temperature (°C) Shutdown Current (µA) 1 VEN = 0V Shutdown Current vs. Input Voltage 3.0 3.3 3.6 3.9 4.2 4.5 4.8 5.1 4 6 8 1 01 21 41 61 8 Input Voltage (V) Shutdown Current (µA) 1 VEN = 0V
DS2856H-07 June 2019www.richtek.com ©Copyright 2019 Richtek Technology Corporation. All rights reserved. is a registered trademark of Ric htek Technology Corporation. EN Voltage vs. Temperature 1.05 1.10 1.15 1.20 1.25 1.30 1.35 -50 -25 0 25 50 75 100 125 Temperature (°C) EN Voltage (V) VIN = 3.3V Falling Rising Input Voltage vs. Temperature 3.9 4.0 4.1 4.2 4.3 4.4 4.5 -50 -25 0 25 50 75 100 125 Temperature (°C) Input Voltage (V) VEN = 3.3V Falling Rising Load Transient Response Time (100 μs/Div) IOUT (2A/Div) VOUT (1V/Div) VIN = 12V, VOUT = 3.3V, IOUT = 1A to 6A Time (100 μs/Div) Load Transient Response IOUT (2A/Div) VOUT (1V/Div) VIN = 12V, VOUT = 3.3V, IOUT = 0 to 6A Load Transient Response Time (100 μs/Div) IOUT (1A/Div) VOUT (500mV/Div) VIN = 12V, VOUT = 3.3V, IOUT = 0 to 3A Load Transient Response Time (100 μs/Div) IOUT (2A/Div) VOUT (500mV/Div) VIN = 12V, VOUT = 3.3V, IOUT = 3 to 6A
DS2856H-07 June 2019 www.richtek.com ©Copyright 2019 Richtek Technology Corporation. All rights reserved. is a registered trademark of Ric htek Technology Corporation. Voltage Ripple Time (1 μs/Div) VLX (20V/Div) VIN (20mV/Div) VIN = 12V, VOUT = 3.3V, IOUT = 0A VOUT (10mV/Div) Voltage Ripple Time (1 μs/Div) VLX (20V/Div) VIN (500mV/Div) VIN = 12V, VOUT = 3.3V, IOUT = 6A VOUT (10mV/Div) Power On from VIN Time (2.5ms/Div) IOUT (5A/Div) VIN (20V/Div) VIN = 12V, VOUT = 3.3V, IOUT = 6A VPGOOD (5V/Div) VOUT (2V/Div) Power Off from EN Time (2.5ms/Div) IOUT (5A/Div) VEN (5V/Div) VIN = 12V, VOUT = 3.3V, IOUT = 6A VPGOOD (5V/Div) VOUT (2V/Div) Power On from EN Time (2.5ms/Div) IOUT (5A/Div) VEN (5V/Div) VIN = 12V, VOUT = 3.3V, IOUT = 6A VPGOOD (5V/Div) VOUT (2V/Div) Power Off from VIN Time (10ms/Div) IOUT (5A/Div) VIN (20V/Div) VIN = 12V, VOUT = 3.3V, IOUT = 6A VPGOOD (5V/Div) VOUT (2V/Div)
DS2856H-07 June 2019www.richtek.com ©Copyright 2019 Richtek Technology Corporation. All rights reserved. is a registered trademark of Ric htek Technology Corporation.
Application Information
This IC is a single phase Buck PWM converter with two integrated N-MOSFETs. It provides good performance during load and line transients by implementing a single feedback loop, current-mode control, and external compensation. The integrated synchronous power switches can increase efficiency and it is suitable for lower duty cycle applications. The switching frequency can be externally set from 200kHz to 1.6MHz which allows for high efficiency and optimal size selection of output filter components. In additional, there is a synchronization mode control in this device which can be synchronized to the external clock frequency, and easily switched from internal switching mode to synchronization mode. The device contains a power good protection and an external soft-start function that is able to monitor the system output voltage for normal regulation and provides a programmable power up sequence for avoiding inrush currents efficiently. Furthermore, the device incorporates a lot of protections such as OVP, OCP, OTP and etc. Main Control Loop The device implements an adjustable fixed frequency with peak current-mode control which offers an excellent performance over various line and loading. During normal operation, the internal high-side power switch is turned on by the internal oscillator initiating. Current in the inductor increases until the high-side switch current reaches the current reference converted by the output voltage V COMP of the error amplifier. The error amplifier adjusts its output voltage by comparing the feedback signal from a resistive voltage divider on the FB pin with an internal 0.8V reference. When the load current increases, it causes a reduction in the feedback voltage relative to the reference. The error amplifier increases its current reference until the average inductor current matches the new load current. When the high-side power MOSFET turns off, the low- side synchronous power switch (N-MOSFET) turns on until the beginning of the next clock cycle. VIN and PVIN Pins The VIN and PVIN pins can be used together or separately for a variety of applications. In this device, the VIN pin is an input for supplying internal reference and control circuitry and the PVIN pin is an input for providing main power to device system and internal high-side power MOSFET. When the VIN and PVIN pins are tied together, both pins can operate from 4.5V to 18V. When the VIN and PVIN pins are used separately, VIN pin must be ranged from 4.5V to 18V, and the PVIN pin can be applied down to as low as 1.6V to 18V. The device incorporates an internal Under-Voltage Lockout (UVLO) circuitry on the VIN pin. If the VIN pin voltage exceeds the UVLO rising threshold voltage 4V, the converter resets and prepares the PWM for operation. If the VIN pin voltage falls below the falling threshold voltage 3.85V during normal operation, the device is disabled. Such wide internal UVLO hysteresis of 150mV can efficiently prevent noise caused reset. There is also an external UVLO circuitry which can be achieved by configuring a resistive voltage divider on EN pin for both input VIN and PVIN pins and it is able to provide either input pins an adjustable UVLO function to ensure a proper power up behavior. More discussions are located in the section of Enable Operation. Output Voltage Setting The resistive voltage divider allows the FB pin to sense the output voltage as shown in Figure 1. Figure 1. Setting the Output Voltage
©Copyright 2019 Richtek Technology Corporation. All rights reserved. is a registered trademark of Ric htek Technology Corporation. Table 2. Suggested Capacitors for CIN and COUT in short-circuit conditions efficiently.
DS2856H-07 June 2019 www.richtek.com ©Copyright 2019 Richtek Technology Corporation. All rights reserved. is a registered trademark of Ric htek Technology Corporation. output voltage, so the low-side MOSFET is turned off long enough to reduce the inductor current to prevent a current runaway issue. With function of level frequency reducing, the switching frequency can reduce from 100%, 50%, then 25% as the voltage decreases from 0.8V to 0V on FB pin. The principle of level frequency reducing is also allowed to cover the soft-start sequence to increase the switching frequency as feedback voltage increases from 0V to 0.8V. Output Over-Voltage Protection The device provides an output Over-Voltage Protection (OVP) once the output voltage exceeds 109% of V OUT, the OVP function turns off the high-side power MOSFET to stop current flowing to the output which can only be released when the output voltage drops below 106% of V OUT. There is a 5μs delay also built into the over-voltage protection circuit to prevent false transition. Using this OVP feature can easily minimize the output overshoot. High-Side MOSFET Over-Current Protection The Over-Current Protection (OCP) of high-side MOSFET is implemented in this device, it adopts monitoring inductor current during the on-state to control the COMP pin voltage for turning off the high-side MOSFET. Each cycle the separated inductor current signal is compared through sensing the external inductor current to the COMP pin voltage from an error amplifier output. If the separated inductor current peak value exceeds the set current limit threshold, the high-side power switch is turned off. Low-Side MOSFET Over-Current Protection The device not only implements the high-side over-current protection but also provides the over sourcing current protection and over sinking current protection for low-side MOSFET. With these three current protections, the IC can easily control inductor current at both side power switches and avoid current runaway for short-circuit condition. For the sourcing current protection, there is a specific comparator in internal circuitry to compare the low-side MOSFET sourcing current to the internal set current limit at the end of every clock cycle. When the low-side sourcing current is higher than the set sourcing limit, the high-side power switch is not turned on and low-side power switch is kept on until the following clock cycle for releasing the above sourcing current to the load. It is allowed to turn on the high-side MOSFET again when the low-side current is lower than the set sourcing current limit at the beginning of a new cycle. For the sinking current protection, it is implemented by detecting the voltage across the low-side power switch. If the low-side reverse current exceeds the set sinking limit, both power switches are off immediately, and it is held to stop switching until the beginning of next cycle. By incorporating this additional protection, the device is able to prevent an excessive sinking current from the load during the condition of pre-biased output and the SS/TR pin is asserted high that is 2.1V or above. Over-Temperature Protection An Over-Temperature Protection (OTP) is contained in the device. The protection is triggered to force the device shutdown for protecting itself when the junction temperature exceeds 175°C typically. Once the junction temperature drops below the hysteresis 10 °C typically, the device is re-enable and automatically reinstates the power up sequence. Thermal Considerations For continuous operation, do not exceed absolute maximum junction temperature. The maximum power dissipation depends on the thermal resistance of the IC package, PCB layout, rate of surrounding airflow, and difference between junction and ambient temperature. The maximum power dissipation can be calculated by the following formula : P D(MAX) = (TJ(MAX) − TA) / θJA where TJ(MAX) is the maximum junction temperature, TA is the ambient temperature, and θJA is the junction to ambient thermal resistance. For recommended operating condition specifications, the maximum junction temperature is 125°C. The junction to ambient thermal resistance, θJA, is layout dependent. For WQFN-14AL 3.5x3.5 package, the thermal resistance, θJA, is 48°C/W on a standard JEDEC 51-7 four-layer thermal test board. The maximum power dissipation at TA = 25°C can be calculated by the following formula :
DS2856H-07 June 2019 www.richtek.com Richtek Technology Corporation 14F, No. 8, Tai Yuen 1st Street, Chupei City Hsinchu, Taiwan, R.O.C. Tel: (8863)5526789 Richtek products are sold by description only. Customers should obtain the latest relevant information and data sheets before p lacing orders and should verify that such information is current and complete. Richtek cannot assume responsibility for use of any circuitry other than circuit ry entirely embodied in a Richtek product. Information furnished by Richtek is believed to be accurate and reliable. However, no responsibility is assumed by Ric htek or its subsidiaries for its use; nor for any infringements of patents or other rights of third parties which may result from its use. No license is granted by i mplication or otherwise under any patent or patent rights of Richtek or its subsidiaries. Outline Dimension W-Type 14AL QFN 3.5x3.5 Package Min. Max. Min. Max. A 0.700 0.800 0.028 0.031 A1 0.000 0.050 0.000 0.002 A3 0.175 0.250 0.007 0.010 b 0.200 0.300 0.008 0.012 D 3.400 3.600 0.134 0.142 D2 2.000 2.100 0.079 0.083 E 3.400 3.600 0.134 0.142 E2 2.000 2.100 0.079 0.083 e K L 0.350 0.450 0.014 0.018 Symbol Dimensions In Millimeters Dimensions In Inches 0.200 0.008 0.325 0.013 0.500 0.020 1.500 0.059 0.350 0.014 Note : The configuration of the Pin #1 identifier is optional, but must be located within the zone indicated. DETAIL A Pin #1 ID and Tie Bar Mark Options 2 2