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Technical content
Features
Multi-Phase PWM Controller Two Embedded MOSFET Drivers and Embedded Switching Boot Diode External Reference Input Control PWM-VID Dynamic Voltage Control Dynamic Phase Number Control Lossless RDS(ON) Current Sensing for Current Balance Adjustable Current Limit Threshold Adjustable Switching Frequency Shoot Through Protection and Short Pulse Free Technology Support an Ultra-Low Output Voltage as Standby Voltage Thermal Alert Indicator in 2/1 Active Phase Application Power Good Indicator RoHS Compliant and Halogen Free
Applications
CPU/GPU Core Power Supply Notebook PC Memory Power Supply Chipset/RAM Power Supply Generic DC/DC Power Regulator Marking Information 4E= : Product Code YMDNN : Date Code4E=YM DNN Pin Configuration (TOP VIEW) WQFN-24L 4x4 BOOT1 UGATE1 EN PSI VID REFADJ ILIM REFIN VREF TON VSNS RGND BOOT2 UGATE2 VCC/ISEN1 TALERT/ISEN2 TSNS/ISEN3 PGOOD PVCC PHASE2 PHASE1 LGATE1 PWM3 LGATE2 GND 789 1 0 1 2 11 21 20 1924 2223
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. Package Type QW : WQFN-24L 4x4 (W-Type) (Exposed Pad-Option 1) Lead Plating System G : Green (Halogen Free and Pb Free) RT8813D
DS8813D-00 September 2016www.richtek.com ©Copyright 2016 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 BOOT1 Bootstrap supply for PWM 1. This pin powers the high side MOSFET driver. 2 UGATE1 High side gate driver of PWM 1. This pin provides the gate drive for the converter's high side MOSFET. Connect this pin to the Gate of high side MOSFET. 3 EN Enable control input. Active high input.
4 PSI
Power saving interface. When the voltage is pulled below 0.4V, the device will operate into 1 phase DEM. When the voltage is between 0.8V to 1V, the device will operate into 1 phase force CCM. When the voltage is between 1.4V to 5.5V, the device will operate into active phase force CCM (only for 2 or 3 phase). 5 VID Programming output voltage control input. Refer to PWM-VID Dynamic Voltage Control. 6 REFADJ Reference adjustment output. Refer to PWM-VID dynamic voltage control. 7 REFIN External reference input. 8 VREF Reference voltage output. This is a high precision voltage reference (2V) from VREF pin to RGND pin. 9 TON On-time/switching frequency adjustment input. Connect a 100pF capacitor between CTON and ground is optional for noise immunity enhancement. 10 RGND Negative remote sense input. Connect this pin to the ground of output load. 11 VSNS Positive remote sense input. Connect this pin to the positive terminal of output load. 12 ILIM Current limit setting. Connect a resistor from ILIM pin to GND to set the current limit threshold. 13 TSNS Temperature sensing input for 2/1 phase operation. ISEN3 Phase 3 current sense input for 3 phase operation. 14 TALERT Thermal alert. Active low open drain output for 2/1 Phase Operation. ISEN2 Phase 2 current sense input for 3 phase operation. 15 VCC Supply voltage input for 2/1 phase operation. (Connect to PVCC) ISEN1 Phase 1 current sense input for 3 phase operation. (Connect to PHASE1) 16 PGOOD Power good indicator output. Active high open drain output. 17 UGATE2 High side gate driver of PWM 2. This pin provides the gate drive for the converter's high side MOSFET. Connect this pin to the Gate of high side MOSFET. 18 BOOT2 Bootstrap supply for of PWM 2. This pin powers the high side MOSFET driver.
19 PHASE2
Switch node for PWM2. This pin is return node of the high side driver of PWM 2. Connect this pin to the Source of high side MOSFET together with the Drain of low side MOSFET and the inductor. 20 LGATE2 Low side gate driver of PWM 2. This pin provides the gate drive for the converter's low side MOSFET. Connect this pin to the Gate of low side MOSFET. 21 PVCC Supply voltage input. Connect this pin to a 5V bias supply. Place a high quality bypass capacitor from this pin to GND. 22 PWM3 Third phase PWM control signal output to driver for 3 phase operation. In 2/1 Phase Operation, this pin is high impedance. 23 LGATE1 Low side gate driver of PWM 1. This pin provides the gate drive for the converter's low side MOSFET. Connect this pin to the Gate of low side MOSFET.
24 PHASE1
Switch node for PWM1. This pin is return node of the high side driver of PWM 1. Connect this pin to the Source of high side MOSFET together with the Drain of low side MOSFET and the inductor. (Exposed Pad) GND Ground. The Exposed pad should be soldered to a large PCB and connected to GND for maximum thermal dissipation.
DS8813D-00 September 2016 www.richtek.com ©Copyright 2016 Richtek Technology Corporation. All rights reserved. is a registered trademark of Ric htek Technology Corporation. Functional Block Diagram LGATE2 PHASE2 UGATE2 BOOT2 LGATE1 PVCC PHASE1 UGATE1 BOOT1 VSNS TON REFIN VREF EN Driver Logic Boot-Phase Detection 2 Boot-Phase Detection 1 S/H S/HCurrent Balance Control & Protection Logic TON Gen 1 TON Gen 2 TON Gen 3 PWM1 PWM2To Power On Reset VIN Detection To Protection Logic PWM CMP To Driver Logic To Power On Reset Enable Logic 40% REFIN Power On Reset & Central Logic Reference Output Gen. Soft-Start & Slew Rate Control UV OV Threshold Select Current Limit VB VB PGOOD VID PSI REFADJ Mode Select GM GM ILIM PWM3 S/H VB GM ISEN3 TALERT/ ISEN2 -1V TSNS/ ISEN3 VCC/ ISEN1 Phase Select RGND To Driver LogicZCDPHASE1 Internal OTP To Central Logic IOCSET 10µ
DS8813D-00 September 2016www.richtek.com ©Copyright 2016 Richtek Technology Corporation. All rights reserved. is a registered trademark of Ric htek Technology Corporation. Operation The RT8813D is a 3/2/1 phase synchronous Buck PWM controller with integrated drivers which are optimized for high performance graphic microprocessor and computer applications. The IC integrates a COT (Constant-On-Time) PWM controller with two MOSFET drivers, as well as output current monitoring and protection functions. Referring to the function block diagram of TON Genx, the synchronous UGATE driver is turned on at the beginning of each cycle. After the internal one-shot timer expires, the UGATE driver will be turned off. The pulse width of this one-shot is determined by the converter's input voltage and the output voltage to keep the frequency fairly constant over the input voltage range and output voltage. Another one-shot sets a minimum off-time. The RT8813D also features a PWM-VID dynamic voltage control circuit driven by the pulse width modulation method. This circuit reduces the device pin count and enables a wide dynamic voltage range. Soft-Start (SS) For internal soft-start function, an internal current source charges an internal capacitor to build the soft-start ramp voltage. The output voltage will track the internal ramp voltage during soft-start interval. PGOOD The power good output is an open drain architecture. When the soft-start is finished, the PGOOD open drain output will be high impedance. Current Balance The RT8813D implements internal current balance mechanism in the current loop. The RT8813D senses per phase current and compares it with the average current. If the sensed current of any particular phase is higher than average current, the on-time of this phase will be adjusted to be shorter. Current Limit The current limit circuit employs a unique “valley” current sensing algorithm. If the magnitude of the current sense signal at PHASE is above the current limit threshold, the PWM is not allowed to initiate a new cycle. Thus, the current to the load exceeds the average output inductor current, the output voltage falls and eventually crosses the under voltage protection threshold, inducing IC shutdown. Over Voltage Protection (OVP) & Under Voltage Protection (UVP) The output voltage is continuously monitored for over voltage and under voltage protection. When the output voltage exceeds its set voltage threshold (If V REFIN ≤ 1.33V, OV = 2V, or VREFIN > 1.33V, OV = 1.5 x VREFIN), UGATE goes low and LGATE is forced high; when it is less than 40% of its set voltage, under voltage protection is triggered and then both UGATE and LGATE gate drivers are forced low. The controller is latched until PVCC is re-supplied and exceeds the POR rising threshold voltage or EN is reset.
DS8813D-00 September 2016 www.richtek.com ©Copyright 2016 Richtek Technology Corporation. All rights reserved. is a registered trademark of Ric htek Technology Corporation. Absolute Maximum Ratings (Note 1) BOOTx to GND PHASEx to GND (Note 6) UGATEx to PHASEx LGATEx to GND Power Dissipation, PD @ TA = 25°C Package Thermal Resistance (Note 2) ESD Susceptibility (Note 3) Recommended Operating Conditions (Note 4)
Electrical Characteristics
Parameter Symbol Test Cond itions Min Typ Max Unit PWM Controller PVCC Supply Voltage V PVCC 4.5 -- 5.5 V PVCC Supply Current I SUPPLY EN = 3.3V, Not Switching -- 1.5 2 mA PVCC Shutdown Current I SHDN EN = 0V -- -- 10 A PVCC POR Threshold 3.8 4.1 4.4 V POR Hysteresis -- 0.3 -- V (TA = 25°C unless otherwise specified)
DS8813D-00 September 2016www.richtek.com ©Copyright 2016 Richtek Technology Corporation. All rights reserved. is a registered trademark of Ric htek Technology Corporation. Parameter Symbol Test Conditions Min Typ Max Unit Switching Frequency f SW R TON = 500k (Note 5) 270 300 330 kHz Minimum On-Time t ON(MIN) -- 70 -- ns Minimum Off-Time t OFF(MIN) -- 300 -- ns EN Threshold EN Input Voltage Logic-High V ENH 1.2 -- -- V Logic-Low V ENL -- -- 0.6 V Mode Decision PSI High Threshold V PSIH Enables Full Phases with FCCM 1.4 -- -- V PSI Intermediate Threshold V PSIM Enables One Phases with FCCM 0.8 -- 1 V PSI Low Threshold V PSIL Enables One Phases with DEM -- -- 0.4 V VID Input Voltage Logic-High V VIDH 1.2 -- -- V Logic-Low V VIDL -- -- 0.6 V Protection Function Zero Current Crossing Threshold 8 -- 8 mV Current Limit Setting Current I OCSET 9 10 11 A Current Limit Setting Current Temperature Coefficient IOCSET_TC -- 6300 -- ppm/ C Current Limit Threshold R OCSET = 10k -- 60 -- mV Absolute Over Voltage Protection Threshold VOVP, Absolute VREFIN 1.33V 1.9 2 2.1 V Relative Over Voltage Protection Threshold VOVP, Relative V REFIN > 1.33V 145 150 155 % OV Fault Delay FB forced above OV threshold -- 5 -- s Relative Under Voltage Protection Threshold VUVP UVP 35 40 45 % UV Fault Delay FB forced above UV threshold -- 3 -- s Thermal Shutdown Threshold T SD -- 150 -- C Minimum TM Threshold V TSEN (No Shutting Down) 0.98 1 1.02 V VOUT Startup Delay t INIT From EV to VOUT startup -- 250 -- s VOUT Startup Time t RAMP VOUT ramp up (V REFIN = 1V) -- 0.75 -- ms PGOOD Startup Delay t SS From EN to PGOOD assertion -- -- 2 ms Error Amplifier VSNS Error Comparator Threshold (Valley) V REFIN = 1V 17.5 12.5 7.5 mV
DS8813D-00 September 2016 www.richtek.com ©Copyright 2016 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. θJA is measured under natural convection (still air) at T A = 25 °C with the component mounted on a high effective- thermal-conductivity four-layer test board on a JEDEC 51-7 thermal measurement standard. 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. Note 5. Not production tested. Test condition is V IN = 8V, VOUT = 1V, IOUT = 20A using application circuit. Note 6. Snubber circuit is recommended to reduce the phase spike. Parameter Symbol Test Conditions Min Typ Max Unit Reference Reference Voltage V VREF Sourcing Current = 1mA, VID no Switching 1.98 2 2.02 V Driver On-Resistance UGATE Driver Source R UGATEsr BOOTx PHASEx Forced to 5V -- 2 4 UGATE Driver Sink R UGATEsk BOOTx PHASEx Forced to 5V -- 1 2 LGATE Driver Source R LGATEsr LGATEx, High State -- 1.5 3 LGATE Driver Sink R LGATEsk LGATEx, Low State -- 0.7 1.5 From LGATE Falling to UGATE Rising -- 30 -- Dead-Time From UGATE Falling to LGATE Rising -- 20 -- ns Internal Boost Charging Switch On-Resistance RBOOT PVCC to BOOTx, I BOOT = 10mA -- 40 80
©Copyright 2016 Richtek Technology Corporation. All rights reserved. is a registered trademark of Ric htek Technology Corporation. Figure 1. 3 Active Phase Configuration Figure 2. 2 Active Phase Configuration
16 PGOODPGOOD
15 VCC/ISEN1VPVCC
14 TALERT/ISEN25V
13 TSEN/ISEN3VREF
21 PVCC
9 TONVIN
4 PSIPSI
5 VIDVID
14 TALERT/ISEN2PHASE2
13 TSEN/ISEN3PHASE3 GND
©Copyright 2016 Richtek Technology Corporation. All rights reserved. is a registered trademark of Ric htek Technology Corporation. Figure 3. 1 Active Phase Configuration
DS8813D-00 September 2016www.richtek.com ©Copyright 2016 Richtek Technology Corporation. All rights reserved. is a registered trademark of Ric htek Technology Corporation. Inductor Current vs. Output Current 0 1 02 03 04 05 06 0 Output Current (A) Inductor Current (A) VIN = 19V, VPVCC = 5V Phase 1 Phase 2 VREF vs. Temperature 1.96 1.97 1.98 1.99 2.00 2.01 2.02 2.03 2.04 -50 -25 0 25 50 75 100 125 Temperature (°C) VREF (V) VIN = 19V, VPVCC = 5V, No Load TON vs. Temperature 165.0 167.5 170.0 172.5 175.0 177.5 180.0 182.5 185.0 -50 -25 0 25 50 75 100 125 Temperature (°C) TON (ns) VIN = 19V, VPVCC = 5V, No Load Typical Operating Characteristics Efficiency vs. Load Current 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% 0.01 0.1 1 10 Load Current (A) Efficiency (%) VIN = 19V, VPVCC = 5V, VOUT = 0.9V, 1 Phase with DEM Operation 100 Efficiency vs. Load Current 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% 0 5 10 15 20 25 30 35 40 45 50 55 60 Load Current (A) Efficiency (%) VIN = 19V, VPVCC = 5V, VOUT = 0.9V, 2 Phase Operation 100 OCP Time (20 μs/Div) UGATE1 (50V/Div) VIN = 19V, VPVCC = 5V LGATE1 (10V/Div) IL1 (20A/Div) IL2 (20A/Div)
DS8813D-00 September 2016 www.richtek.com ©Copyright 2016 Richtek Technology Corporation. All rights reserved. is a registered trademark of Ric htek Technology Corporation. Power On from EN Time (500 μs/Div) PGOOD (5V/Div) VIN = 19V, VPVCC = 5V, IOUT = 30A EN (2V/Div) PHASE1 (20V/Div) VOUT (50mV/Div) Power Off from PVCC Time (500 μs/Div) PGOOD (5V/Div) VIN = 19V, VEN = 1.8V, IOUT = 30A PVCC (5V/Div) PHASE1 (20V/Div) VOUT (500mV/Div) VOUT PGOOD PVCC Power Off from EN Time (500 μs/Div) PGOOD (5V/Div) VIN = 19V, VPVCC = 5V, IOUT = 30A EN (2V/Div) PHASE1 (20V/Div) VOUT (500mV/Div) EN PGOOD VOUT Power On from PVCC Time (500 μs/Div) PHASE1 (20V/Div) VIN = 19V, VEN = 1.8V, IOUT = 30A PVCC (5V/Div) PGOOD (5V/Div) VOUT (500mV/Div) UVP Time (20 μs/Div) UGATE1 (20V/Div) VIN = 19V, VPVCC = 5V, IOUT = 40A VVSNS (1V/Div) LGATE1 (5V/Div) OVP Time (100 μs/Div) UGATE1 (20V/Div) VIN = 19V, VPVCC = 5V, No Load VVSNS (1V/Div) LGATE1 (5V/Div)
DS8813D-00 September 2016www.richtek.com ©Copyright 2016 Richtek Technology Corporation. All rights reserved. is a registered trademark of Ric htek Technology Corporation. Dynamic Output Voltage Control Time (50 μs/Div) PHASE1 (20V/Div) VID (2V/Div) PHASE2 (20V/Div) VOUT (500mV/Div) VREFIN = 1.2V to 0.6V, VID from high to low VIN = 19V, VPVCC = 5V, VEN = 1.8V, IOUT = 30A Dynamic Output Voltage Control Time (50 μs/Div) PHASE1 (20V/Div) VREFIN = 0.6V to 1.2V, VID from low to high VID (2V/Div) PHASE2 (20V/Div) VIN = 19V, VPVCC = 5V, VEN = 1.8V, IOUT = 30A VOUT (500mV/Div) Dynamic Output Voltage Control Time (50 μs/Div) PHASE1 (20V/Div) VREFIN = 0.9V to 1.2V, VID from floating to high VID (2V/Div) PHASE2 (20V/Div) VIN = 19V, VPVCC = 5V, VEN = 1.8V, IOUT = 30A VOUT (500mV/Div) Dynamic Output Voltage Control Time (50 μs/Div) PHASE1 (20V/Div) VREFIN = 0.9V to 0.6V, VID from floating to low VID (2V/Div) PHASE2 (20V/Div) VIN = 19V, VPVCC = 5V, VEN = 1.8V, IOUT = 30A VOUT (500mV/Div) Dynamic Output Voltage Control Time (50 μs/Div) PHASE1 (20V/Div) VID (2V/Div) PHASE2 (20V/Div) VOUT (500mV/Div) VREFIN = 1.2V to 0.9V, VID from high to floating VIN = 19V, VPVCC = 5V, VEN = 1.8V, IOUT = 30A Dynamic Output Voltage Control Time (50 μs/Div) PHASE1 (20V/Div) VID (2V/Div) PHASE2 (20V/Div) VOUT (500mV/Div) VREFIN = 0.6V to 0.9V, VID from low to floating VIN = 19V, VPVCC = 5V, VEN = 1.8V, IOUT = 30A
DS8813D-00 September 2016 www.richtek.com ©Copyright 2016 Richtek Technology Corporation. All rights reserved. is a registered trademark of Ric htek Technology Corporation. Load Transient Response Time (20 μs/Div) UGATE1 (50V/Div) VIN = 19V, VPVCC = 5V IOUT (50A/Div) UGATE2 (50V/Div) VOUT (100mV/Div) Load Transient Response Time (20 μs/Div) UGATE1 (50V/Div) VIN = 19V, VPVCC = 5V IOUT (50A/Div) UGATE2 (50V/Div) VOUT (100mV/Div)
DS8813D-00 September 2016www.richtek.com ©Copyright 2016 Richtek Technology Corporation. All rights reserved. is a registered trademark of Ric htek Technology Corporation.
Application Information
The RT8813D is a multi-phase synchronous Buck PWM controller with integrated drivers which is optimized for high-performance graphic microprocessor and computer applications. A COT (Constant-On-Time) PWM controller and two MOSFET drivers with internal bootstrap diodes are integrated so that the external circuit can be easily designed and the number of component is reduced. The topology solves the poor load transient response timing problems of fixed-frequency mode PWM and avoids the problems caused by widely varying switching frequencies in conventional constant on-time and constant off-time PWM schemes. The IC supports dynamic mode transition function with various operating states, which include multi-phase with CCM operation and single phase with diode emulation mode. These different operating states make the system efficiency as high as possible. The RT8813D provides a PWM-VID dynamic control operation in which the feedback voltage is regulated and tracks external input reference voltage. It also features complete fault protection functions including over voltage, under voltage and current limit. Remote Sense The RT8813D uses the remote sense path (VSNS and RGND) to overcome voltage drops in the power lines by sensing the voltage directly at the end of GPU. Normally, to protect remote sense path disconnecting, there are two resistors (R Local) connecting between local sense path and remote sense path. That is, in application with remote sense, the R Local is recommended to be 10Ω to 100Ω. If no need of remote sense, the RLocal is recommended to be 0Ω. OUTON TON IN 2 V 3.2pT = R V0 . 5 /SO U T I N O NF= V V T And then the switching frequency FS is : PWM Operation The RT8813D integrates a Constant-On-Time (COT) PWM controller, and the controller provides the PWM signal which relies on the output ripple voltage comparing with internal reference voltage as shown in Figure 5. Referring to the function block diagram of TON Genx, the synchronous UGATE driver is turned on at the beginning of each cycle. After the internal one-shot timer expires, the UGATE driver will be turned off. The pulse width of this one-shot is determined by the converter's input voltage and the output voltage to keep the frequency fairly constant over the input voltage and output voltage range. Another one-shot sets a minimum off-time. R TON is a resistor connected from the VIN to TON pin. The value of RTON can be selected according to Figure 6. The recommend operation frequency range is 150kHz to 600kHz.Figure 4. Output Voltage Sensing VOUT UGATE LGATE BOOT PHASE GPU-VSNS GPU+ VIN RGND RLocal+ RLocal- Local Sense Path Remote Sense Path On-Time Control The on-time one-shot comparator has two inputs. One input monitors the output voltage, while the other input samples the input voltage and converts it to a current. This input voltage proportional current is used to charge an internal on-time capacitor. The on-time is the time required for the voltage on this capacitor to charge from zero volts to V OUT, thereby making the on-time of the high side switch directly proportional to output voltage and inversely proportional to input voltage. The implementation results in a nearly constant switching frequency without the need for a clock generator. Figure 5. Constant On-Time PWM Control
©Copyright 2016 Richtek Technology Corporation. All rights reserved. is a registered trademark of Ric htek Technology Corporation. be the complement of the high side gate drive waveform. new initialization and soft-start cycle. signal as well as the input current at power up are limited. shows the internal soft-start sequence. Figure 8. Internal Soft-Start Sequence
DS8813D-00 September 2016 www.richtek.com ©Copyright 2016 Richtek Technology Corporation. All rights reserved. is a registered trademark of Ric htek Technology Corporation. Current Balance The RT8813D implements current balance mechanism in the current loop. The RT8813D senses per phase current signal and compares it with the average current. If the sensed current of any particular phase is higher than the average current, the on-time of this phase will be decreased. The current balance accuracy is major related with on- resistance of low side MOSFET (R LG,DS(ON)). That is, in practical application, using lower R LG,DS(ON) will reduce the current balance accuracy. Output Over Voltage Protection (OVP) The output voltage can be continuously monitored for over voltage protection. If REFIN voltage is lower than 1.33V, the over voltage threshold follows to absolute over voltage 2V. If REFIN voltage is higher than 1.33V, the over voltage threshold follows relative over voltage 1.5 x V REFIN. When OVP is triggered, UGATE goes low and LGATE is forced high. The RT8813D is latched once OVP is triggered and can only be released by PVCC or EN power on reset. A 5μs delay is used in OVP detection circuit to prevent false trigger. Output Under Voltage Protection (UVP) The output voltage can be continuously monitored for under voltage protection. When the output voltage is less than 40% of its set voltage, under voltage protection is triggered and then all UGATEx and LGATEx gate drivers are forced low. There is a 3μs delay built in the UVP circuit to prevent false transitions. During soft-start, the UVP blanking time is equal to PGOOD blanking time. VALLEY LGDS(ON) OCSET OCSET IR 4 0 m VR = I where IVALLEY represents the desired inductor limit current (valley inductor current) and IOCSET is current limit setting current which has a temperature coefficient to compensate the temperature dependency of the R DS(ON). If ROCSET is not present, there is no current path for IOCSET to build the current limit threshold. In this situation, the current limit threshold is internally preset to 400mV (typical). Negative Current Limit The RT8813D supports cycle-by-cycle negative current limiting. The absolute value of negative current limiting threshold is the same with the positive current limit threshold. If negative inductor current is rising to trigger negative current limit, the low side MOSFET will be turned off and the current will flow to input side through the body diode of the high side MOSFET. At this time, output voltage tends to rise because this protection limits current to discharge the output capacitor. In order to prevent shutdown because of over voltage protection, the low side MOSFET is turned on again 400ns after it is turned off. If the device hits the negative over current threshold again before output voltage is discharged to the target level, the low side MOSFET is turned off and process repeats. It ensures maximum allowable discharge capability when output voltage continues to rise. On the other hand, if the output is discharged to the target level before negative current threshold is reached, the low side MOSFET is turned off, the high side MOSFET is then turned on, and the device keeps normal operation. Current Limit Setting Current limit threshold can be set by a resistor (R OCSET) between ILIM and GND. Once PVCC exceeds the POR threshold and chip is enabled, an internal current source I OCSET flows through ROCSET. The voltage across ROCSET is stored as the current limit protection threshold V OCSET. The threshold range of VOCSET is 50mV to 400mV. ROCSET can be determined using the following equation : Thermal Monitoring and Temperature Reporting The RT8813D provides thermal monitoring function in 2/1 phase operation via sensing the TSNS pin voltage, and which can indicate ambient temperature through the voltage divider R OTSET and RNTC shown in Figure 13. The voltage of VTSNS is typically set to be higher than 1V. When ambient temperature rises, VTSNS will fall and the TALERT signal will be pulled to low level if TSNS voltage drops below 1V.
©Copyright 2016 Richtek Technology Corporation. All rights reserved. is a registered trademark of Ric htek Technology Corporation. voltage is a conservatively safe design. reducing the input voltage ripple at heavy load. save board space especially when the height is limited. inductor current rising time increases with inductance value. ensure safe operation without sacrificing efficiency. drivers to obtain high efficiency power conversion. Figure 13. External OTP Setting
©Copyright 2016 Richtek Technology Corporation. All rights reserved. is a registered trademark of Ric htek Technology Corporation. MOSFET driver capability and the budget. Figure 14. Derating Curve of Maximum Power on the maximum power dissipation.
DS8813D-00 September 2016www.richtek.com ©Copyright 2016 Richtek Technology Corporation. All rights reserved. is a registered trademark of Ric htek Technology Corporation. Layout Considerations Layout is very important in high frequency switching converter design. If designed improperly, the PCB could radiate excessive noise and contribute to the converter instability. Following layout guidelines must be considered before starting a layout for RT8813D. Place the RC filter as close as possible to the PVCC pin. Keep current limit setting network as close as possible to the IC. Routing of the network should avoid coupling to high voltage switching node. Connections from the drivers to the respective gate of the high side or the low side MOSFET should be as short as possible to reduce stray inductance. All sensitive analog traces and components such as VSNS, RGND, EN, PSI, VID, PGOOD, VREF, TON VREFADJ, VREFIN and TSNS should be placed away from high voltage switching nodes such as PHASE, LGATE, UGATE, or BOOT nodes to avoid coupling. Use internal layer(s) as ground plane(s) and shield the feedback trace from power traces and components. Power sections should connect directly to ground plane(s) using multiple vias as required for current handling (including the chip power ground connections). Power components should be placed to minimize loops and reduce losses.
DS8813D-00 September 2016 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. Richtek reserves the right to change the circuitry and/or specifications without notice at any time. Customers should obtain the latest relevant information and data sheets before placing orders and should verify that such information is current and complete. Richtek cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Richtek product. Information furnish ed by Richtek is believed to be accurate and reliable. However, no responsibility is assumed by Richtek or its subsidiaries for its use; nor for any infringeme nts of patents or other rights of third parties which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of R ichtek or its subsidiaries. Outline Dimension A D E L be SEE DETAIL A 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 Dimensions In Millimeters Dimensions In Inches Symbol 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 0.180 0.300 0.007 0.012 D 3.950 4.050 0.156 0.159 Option 1 2.400 2.500 0.094 0.098 Option 2 2.650 2.750 0.104 0.108 E 3.950 4.050 0.156 0.159 Option 1 2.400 2.500 0.094 0.098 Option 2 2.650 2.750 0.104 0.108 e 0.500 0.020 L 0.350 0.450 0.014 0.018 W-Type 24L QFN 4x4 Package