RT2859BHGQW

Reference Design Design Tools Sample & Buy ® RT2859A/B 3A, 18V, 650kHz, ACOT® Synchronous Step-Down Converter General Description The RT2859A/B are high-performance 650kHz 3A stepdown regulators with internal power switches and synchronous rectifiers. They feature quick transient response using their Advanced Constant On-Time (ACOT®) control architecture that provides stable operation with small ceramic output capacitors and without complicated external compensation, among other benefits. The input voltage range is from 4.5V to 18V and the output is adjustable from 0.765V to 7V. to avoid low-frequency interference while the RT2859A features a power-saving discontinuous operating mode at light loads. Features    ® The proprietary ACOT control improves upon other fastresponse constant on-time architectures, achieving nearly constant switching frequency over line, load, and output voltage ranges. Since there is no internal clock, response to transients is nearly instantaneous and inductor current can ramp quickly to maintain output regulation without large bulk output capacitance. The RT2859A/B are stable with and optimized for ceramic output capacitors. With internal 70mΩ switches and 70mΩ synchronous rectifiers, the RT2859A/B display excellent efficiency and good behavior across a range of applications, especially for low output voltages and low duty cycles. Cycle-bycycle current limit, input under-voltage lockout, externallyadjustable soft-start, output under- and over-voltage protection, and thermal shutdown provide safe and smooth operation in all operating conditions. The RT2859A and RT2859B are each available in the WQFN-16L 3x3 package, with exposed thermal pads. The RT2859B switches continuously even at light loads                Fast Transient Response Steady 650kHz Switching Frequency at all Load Current (RT2859B) Discontinuous Operating Mode at Light Load (RT2859A) 3A Output Current Advanced Constant On-Time (ACOT®) Control Optimized for Ceramic Output Capacitors 4.5V to 18V Input Voltage Range Internal 70mΩ Ω Switch and 70mΩ Ω Synchronous Rectifier 0.765V to 7V Adjustable Output Voltage Externally-Adjustable, Pre-Biased Compatible SoftStart Cycle-by-Cycle Current Limit Optional Output Discharge Function Output Over- and Under-voltage Shut Down Latched (RT2859ALGQW/RT2859BLGQW Only) With Hiccup Mode (RT2859AHGQW/RT2859BHGQW Only) Input Under-Voltage Lockout Thermal Shutdown RoHS Compliant and Halogen Free Simplified Application Circuit VIN RT2859A/B VIN SW VCC Power Good VREG5 Input Signal PGOOD BOOT VS FB EN SS VREG5 GND PGND Copyright © 2022 Richtek Technology Corporation. All rights reserved. DS2859A/B-06 July 2022 VOUT is a registered trademark of Richtek Technology Corporation. www.richtek.com 1 RT2859A/B Applications      Industrial and Commercial Low Power Systems Computer Peripherals LCD Monitors and TVs Green Electronics/Appliances Point of Load Regulation for High-Performance DSPs, FPGAs, and ASICs Ordering Information RT2859A/B Package Type QW : WQFN-16L 3x3 (W-Type) Lead Plating System G : Green (Halogen Free and Pb Free) H : Hiccup Mode OVP & UVP L : Latched OVP & UVP A : PSM B : PWM Marking Information RT2859AHGQW 48= : Product Code 48=YM DNN YMDNN : Date Code Note : Richtek products are :  RoHS compliant and compatible with the current requirements of IPC/JEDEC J-STD-020.  Suitable for use in SnPb or Pb-free soldering processes. RT2859ALGQW 45= : Product Code YMDNN : Date Code Pin Configuration (TOP VIEW) VS VCC VIN VIN 45=YM DNN 16 15 14 13 RT2859BHGQW 3Z= : Product Code YMDNN : Date Code 3Y= : Product Code GND 3 10 17 4 6 7 9 BOOT SW SW SW 8 WQFN-16L 3x3 YMDNN : Date Code Copyright © 2022 Richtek Technology Corporation. All rights reserved. www.richtek.com 2 11 5 RT2859BLGQW 3Y=YM DNN 12 2 PGOOD EN PGND PGND 3Z=YM DNN FB VREG5 SS GND 1 is a registered trademark of Richtek Technology Corporation. DS2859A/B-06 July 2022 RT2859A/B Functional Pin Description Pin No. Pin Name Pin Function 1 FB Feedback voltage input. Connect FB to the midpoint of the external feedback resistive divider to sense the output voltage. Place the resistive divider within 5mm from the FB pin. The IC regulates VFB at 0.765V (typical). 2 VREG5 Internal regulator output. Connect a 1F capacitor to GND to stabilize output voltage. 3 SS Soft-start control. Connect an external capacitor between this pin and GND to set the soft-start time. 4 GND Ground. 5 PGOOD Open-drain power-good output. PGOOD connects to PGND whenever VFB is less than 90% of its regulation threshold (typical). 6 EN Enable control input. A logic-high enables the converter; a logic-low forces the IC into shutdown mode reducing the supply current to less than 10A. PGND Power ground. PGND connects to the Source of the internal N-channel MOSFET synchronous rectifier and to other power ground nodes of the IC. The exposed pad and the 2 PGND pins should be well soldered to the input and output capacitors and to a large PCB area for good power dissipation. SW Switch node. SW is the Source of the internal N-channel MOSFET switch and the Drain of the internal N-channel MOSFET synchronous rectifier. Connect SW to the inductor with a wide short PCB trace and minimize its area to reduce EMI. BOOT Bootstrap supply for high-side gate driver. Connect a 0.1F capacitor between BOOT and SW to power the internal gate driver. 13, 14 VIN Power input. The input voltage range is from 4.5V to 18V. Must bypass with a suitably large (10F x 2) ceramic capacitors at this pin. 15 VCC Internal linear regulator supply input. VCC supplies power for the internal linear regulator that powers the IC. Connect VIN to the input voltage and bypass to ground with a 0.1F ceramic capacitor. 16 VS Output voltage sense input. 7, 8, 17 (Exposed pad) 9, 10, 11 12 Copyright © 2022 Richtek Technology Corporation. All rights reserved. DS2859A/B-06 July 2022 is a registered trademark of Richtek Technology Corporation. www.richtek.com 3 RT2859A/B Functional Block Diagram BOOT VCC VREG5 POR & Reg EN VBIAS Min. Off-Time VREG5 2µA SS VIN FB VS VIN VREF OC UV & OV VREG5 Control Driver SW PGND SW ZC Ripple Gen. FB + + Comparator GND FB 0.9 x VREF Comparator - PGOOD + On-Time Detailed Description The RT2859A/B are high-performance 650kHz 3A stepdown regulators with internal power switches and synchronous rectifiers. They feature an Advanced Constant On-Time (ACOT®) control architecture that provides stable operation with ceramic output capacitors without complicated external compensation, among other benefits. The input voltage range is from 4.5V to 18V and the output is adjustable from 0.765V to 7V. The proprietary ACOT® control scheme improves upon other constant on-time architectures, achieving nearly constant switching frequency over line, load, and output voltage ranges. The RT2859A/B are optimized for ceramic output capacitors. Since there is no internal clock, response to transients is nearly instantaneous and inductor current can ramp quickly to maintain output regulation without large bulk output capacitance. Constant On-Time (COT) Control The heart of any COT architecture is the on-time oneshot. Each on-time is a pre-determined “fixed” period that is triggered by a feedback comparator. This robust arrangement has high noise immunity and is ideal for low Copyright © 2022 Richtek Technology Corporation. All rights reserved. www.richtek.com 4 duty cycle applications. After the on-time one-shot period, there is a minimum off-time period before any further regulation decisions can be considered. This arrangement avoids the need to make any decisions during the noisy time periods just after switching events, when the switching node (SW) rises or falls. Because there is no fixed clock, the high-side switch can turn on almost immediately after load transients and further switching pulses can ramp the inductor current higher to meet load requirements with minimal delays. Traditional current mode or voltage mode control schemes typically must monitor the feedback voltage, current signals (also for current limit), and internal ramps and compensation signals, to determine when to turn off the high-side switch and turn on the synchronous rectifier. Weighing these small signals in a switching environment is difficult to do just after switching large currents, making those architectures problematic at low duty cycles and in less than ideal board layouts. Because no switching decisions are made during noisy time periods, COT architectures are preferable in low duty cycle and noisy applications. However, traditional COT is a registered trademark of Richtek Technology Corporation. DS2859A/B-06 July 2022 RT2859A/B control schemes suffer from some disadvantages that preclude their use in many cases. Many applications require a known switching frequency range to avoid interference with other sensitive circuitry. True constant on-time control, where the on-time is actually fixed, exhibits variable switching frequency. In a step-down converter, the duty factor is proportional to the output voltage and inversely proportional to the input voltage. Therefore, if the on-time is fixed, the off-time (and therefore the frequency) must change in response to changes in input or output voltage. Modern pseudo-fixed frequency COT architectures greatly improve COT by making the one-shot on-time proportional to VOUT and inversely proportional to VIN. In this way, an on-time is chosen as approximately what it would be for an ideal fixed-frequency PWM in similar input/output voltage conditions. The result is a big improvement but the switching frequency still varies considerably over line and load due to losses in the switches and inductor and other parasitic effects. Another problem with many COT architectures is their dependence on adequate ESR in the output capacitor, making it difficult to use highly-desirable, small, low-cost, but low-ESR ceramic capacitors. Most COT architectures use AC current information from the output capacitor, generated by the inductor current passing through the ESR, to function in a way like a current mode control system. With ceramic capacitors, the inductor current information is too small to keep the control loop stable, like a current mode system with no current information. ACOT® Control Architecture Making the on-time proportional to VOUT and inversely proportional to VIN is not sufficient to achieve good constant-frequency behavior for several reasons. First, voltage drops across the MOSFET switches and inductor cause the effective input voltage to be less than the measured input voltage and the effective output voltage to be greater than the measured output voltage. As the load changes, the switch voltage drops change causing a switching frequency variation with load current. Also, at light loads if the inductor current goes negative, the switch dead-time between the synchronous rectifier turn-off and the high-side switch turn-on allows the switching node to Copyright © 2022 Richtek Technology Corporation. All rights reserved. DS2859A/B-06 July 2022 rise to the input voltage. This increases the effective ontime and causes the switching frequency to drop noticeably. One way to reduce these effects is to measure the actual switching frequency and compare it to the desired range. This has the added benefit eliminating the need to sense the actual output voltage, potentially saving one pin connection. ACOT® uses this method, measuring the actual switching frequency (at SW) and modifying the ontime with a feedback loop to keep the average switching frequency in the desired range. To achieve good stability with low-ESR ceramic capacitors, ACOT® uses a virtual inductor current ramp generated inside the IC. This internal ramp signal replaces the ESR ramp normally provided by the output capacitor's ESR. The ramp signal and other internal compensations are optimized for low-ESR ceramic output capacitors. ACOT® One-Shot Operation The RT2859A/B control algorithm is simple to understand. The feedback voltage, with the virtual inductor current ramp added, is compared to the reference voltage. When the combined signal is less than the reference the on-time one-shot is triggered, as long as the minimum off-time one-shot is clear and the measured inductor current (through the synchronous rectifier) is below the current limit. The on-time one-shot turns on the high-side switch and the inductor current ramps up linearly. After the ontime, the high-side switch is turned off and the synchronous rectifier is turned on and the inductor current ramps down linearly. At the same time, the minimum off-time one-shot is triggered to prevent another immediate on-time during the noisy switching time and allow the feedback voltage and current sense signals to settle. The minimum off-time is kept short (260ns typical) so that rapidly-repeated ontimes can raise the inductor current quickly when needed. Discontinuous Operating Mode (RT2859A Only) After soft-start, the RT2859B operates in fixed frequency mode to minimize interference and noise problems. The RT2859A uses variable-frequency discontinuous switching at light loads to improve efficiency. During discontinuous switching, the on-time is immediately increased to add is a registered trademark of Richtek Technology Corporation. www.richtek.com 5 RT2859A/B “hysteresis” to discourage the IC from switching back to continuous switching unless the load increases substantially. The IC returns to continuous switching as soon as an ontime is generated before the inductor current reaches zero. The on-time is reduced back to the length needed for 650kHz switching and encouraging the circuit to remain in continuous conduction, preventing repetitive mode transitions between continuous switching and discontinuous switching. Current Limit The RT2859A/B current limit is cycle-by-cycle measuring the inductor current through the synchronous rectifier during the off-time while the inductor current ramps down. The current is determined by measuring the voltage between Source and Drain of the synchronous rectifier, adding temperature compensation for greater accuracy. If the current exceeds the current limit (ILIM) once minimum off-time end, the on-time one-shot is inhibited until the inductor current ramps down below the current limit with an additonal wide hysteresis band (IHYS) of about 0.6A to 1A. This arrangement prevents the average output current from greatly exceeding the guaranteed current limit value, as typically occurs with other valley-type current limits. If the output current exceeds the available inductor current (controlled by the current limit mechanism), the output voltage will drop. If it drops below the output under-voltage protection level (see next section) the IC will stop switching to avoid excessive heat. dissipation, and then resume normal operation as soon as the overload or short circuit is removed. During hiccup mode, the shutdown time is determined by the capacitor at SS. A 0.5μA current source discharges VSS from its starting voltage (normally VREG5). The IC remains shut down until VSS reaches 0.2V, about 38ms for a 3.9nF capacitor. At that point the IC begins to charge the SS capacitor at 2μA, and a normal start-up occurs. If the fault remains, OVP and UVP protection will be enabled when VSS reaches 2.2V (typical). The IC will then shut down and discharge the SS capacitor from the 2.2V level, taking about 16ms for a 3.9nF SS capacitor. Latch-Off Mode The RT2859ALGQW/ RT2859BLGQW, uses latch-off mode OVP and UVP. When the protection function is triggered, the IC will shut down. The IC stops switching, leaving both switches open, and is latched off. To restart operation, toggle EN or power the IC off and then on again. Input Under-Voltage Lockout In addition to the enable function, the RT2859A/B feature an under-voltage lockout (UVLO) function that monitors the internal linear regulator output (VREG5). To prevent operation without fully-enhanced internal MOSFET switches, this function inhibits switching when VREG5 drops below the UVLO-falling threshold. The IC resumes switching when VREG5 exceeds the UVLO-rising threshold. Shut-Down, Start-Up and Enable (EN) The RT2859B also includes a negative current limit to protect the IC against sinking excessive current and possibly damaging the IC. If the voltage across the synchronous rectifier indicates the negative current is too high, the synchronous rectifier turns off until after the next high-side on-time. The RT2859A does not sink current and therefore does not need a negative current limit. The enable input (EN) has a logic-low level of 0.4V. When VEN is below this level the IC enters shutdown mode and supply current drops to less than 10μA. When VEN exceeds its logic-high level of 2V the IC is fully operational. Hiccup Mode Soft-Start (SS) The RT2859AHGQW/ RT2859BHGQW, use hiccup mode OVP and UVP. When the protection function is triggered, the IC will shut down for a period of time and then attempt to recover automatically. Hiccup mode allows the circuit to operate safely with low input current and power The RT2859A/B soft-start uses an external pin (SS) to clamp the output voltage and allow it to slowly rise. After VEN is high and VREG5 exceeds its UVLO threshold, the IC begins to source 2μA from the SS pin. An external capacitor at SS is used to adjust the soft-start timing. Copyright © 2022 Richtek Technology Corporation. All rights reserved. www.richtek.com 6 EN is a high voltage input that can be safely connected to VIN (up to 18V) for automatic start-up. is a registered trademark of Richtek Technology Corporation. DS2859A/B-06 July 2022 RT2859A/B The available capacitance range is from 2.7nF to 220nF. Do not leave SS unconnected. During start-up, while the SS capacitor charges, the RT2859A/B operates in discontinuous mode with very small pulses. This prevents negative inductor currents and keeps the circuit from sinking current. Therefore, the output voltage may be pre-biased to some positive level before start-up. Once the VSS ramp charges enough to raise the internal reference above the feedback voltage, switching will begin and the output voltage will smoothly rise from the pre-biased level to its regulated level. After VSS rises above about 2.2V output over-and under-voltage protections are enabled and the RT2859B begins continuous-switching operation. An internal linear regulator (VREG5) produces a 5.1V supply from VIN that powers the internal gate drivers, PWM logic, reference, analog circuitry, and other blocks. If VIN is 6V or greater, VREG5 is guaranteed to provide significant power for external loads. PGOOD Comparator The PGOOD pin is an open-drain power-good indication which is connected to PVCC through a pull-up resistor. After PVCC raises up, the PGOOD is actively held low and only allowed to transition high after soft-start is over. If VFB rises above a power-good threshold V TH_PGH (typically 90% of the target value), the PGOOD pin will be in high impedance and VPGOOD will be held high. When VFB drops under a VFB falling threshold VTH_PGL (typically 85% of the target value) or exceeds OVP threshold VOVP (typically 120% of the target value), the PGOOD pin will be pulled low. Once being started-up, if any protection is triggered (UVP, OVP and OTP) or EN is from high to low, PGOOD will be pulled to GND. Over-Temperature Protection The RT2859A/B includes an over-temperature protection (OTP) circuitry to prevent overheating due to excessive power dissipation. The OTP will shut down switching operation when the junction temperature exceeds 150°C. Once the junction temperature cools down by approximately 20°C the IC will resume normal operation with a complete soft-start. For continuous operation, provide adequate cooling so that the junction temperature does not exceed 150°C. Output Discharge Control When EN pin is low, the RT2859A/B will discharge the output with an internal 50Ω MOSFET connected between VOUT to GND pin. OVP/UVP Protection The RT2859A/B detects over- and under-voltage conditions by monitoring the feedback voltage on FB pin. The two functions are enabled after approximately 1.7 times the soft-start time. When the feedback voltage becomes higher than 120% of the target voltage, the OVP comparator will go high to turn off both internal high-side and low-side MOSFETs for hiccup version, and the latched version is turn off the high-side MOSFET but turn on the low-side MOSFET to sink the over-voltage source current on output terminal to avoid the damage risk of connected device, the current limit function will shutdown after the the OVP function is triggered, it derestrict the maximum sinking current value from output terminal through the lowside MOSFET. When the feedback voltage is lower than 70% of the target voltage for 250μs, the UVP comparator will go high to turn off both internal high-side and low-side MOSFETs. External Bootstrap Capacitor Connect a 0.1μF low ESR ceramic capacitor between BOOT and SW. This bootstrap capacitor provides the gate driver supply voltage for the high side N-channel MOSFET switch. Copyright © 2022 Richtek Technology Corporation. All rights reserved. DS2859A/B-06 July 2022 is a registered trademark of Richtek Technology Corporation. www.richtek.com 7 RT2859A/B Absolute Maximum Ratings            (Note 1) Supply Voltage, VIN, VCC ---------------------------------------------------------------------------------------Switch Voltage, SW -----------------------------------------------------------------------------------------------< 10ns ----------------------------------------------------------------------------------------------------------------BOOT to SW --------------------------------------------------------------------------------------------------------VREG5 to VIN or VCC --------------------------------------------------------------------------------------------EN, VS Pin ----------------------------------------------------------------------------------------------------------Other Pins ------------------------------------------------------------------------------------------------------------Power Dissipation, PD @ TA = 25°C WQFN-16L 3x3 -----------------------------------------------------------------------------------------------------Package Thermal Resistance (Note 2) WQFN-16L 3x3, θJA ------------------------------------------------------------------------------------------------WQFN-16L 3x3, θJC -----------------------------------------------------------------------------------------------Junction Temperature Range -------------------------------------------------------------------------------------Lead Temperature (Soldering, 10 sec.) ------------------------------------------------------------------------Storage Temperature Range -------------------------------------------------------------------------------------- Recommended Operating Conditions    −0.3V to 20V −0.3V to (VIN + 0.3V) −5V to 25V −0.3V to 6V −17V to 0.3V −0.3V to 20V −0.3V to 6V 2.1W 47.4°C/W 7.5°C/W 150°C 260°C −65°C to 150°C (Note 3) Supply Voltage, VIN ------------------------------------------------------------------------------------------------ 4.5V to 18V Junction Temperature Range -------------------------------------------------------------------------------------- −40°C to 125°C Ambient Temperature Range -------------------------------------------------------------------------------------- −40°C to 85°C Electrical Characteristics (VIN = 12V, TA = −40°C to 85°C, unless otherwise specified) Parameter Symbol Test Conditions Min Typ Max Unit Supply Current Shutdown Current ISHDN TA = 25C, VEN = 0V -- 1 10 A Quiescent Current IQ TA = 25C, VEN = 5V, VFB = 0.8V -- 1 1.3 mA Logic-High 2 -- 18 Logic-Low -- -- 0.4 Logic Threshold EN Input Voltage V VFB Voltage and Discharge Resistance TA = 25C 0.757 TA = 40C to 85C 0.755 -- 0.775 VFB = 0.8V, TA = 25C -- 0.01 0.1 A RDIS VEN = 0V, VS = 0.5V -- 50 100  VREG5 TA = 25C, 6V  VIN  18V, 0 < IVREG5  5mA 4.8 5.1 5.4 V Feedback Threshold Voltage VFB Feedback Input Current IFB VOUT Discharge Resistance 0.765 0.773 V VREG5 Output VREG5 Output Voltage Line Regulation 6V  VIN  18V, IVREG5 = 5mA -- -- 20 mV Load Regulation 0  IVREG5  5mA -- -- 100 mV VIN = 6V, VREG5 = 4V, TA = 25C -- 70 -- mA Output Current IVREG5 Copyright © 2022 Richtek Technology Corporation. All rights reserved. www.richtek.com 8 is a registered trademark of Richtek Technology Corporation. DS2859A/B-06 July 2022 RT2859A/B Parameter Symbol Test Conditions Min Typ Max Unit RDS(ON) Switch On Resistance High-Side RDS(ON)_H TA = 25C (VBOOT  VSW ) = 5.5V -- 70 -- Low-Side RDS(ON)_L TA = 25C -- 70 -- 4 5 6 -- 150 -- -- 20 -- m Current Limit Current Limit ILIM A Thermal Shutdown Thermal Shutdown Threshold TSD Shutdown temperature Thermal Shutdown Hysteresis TSD C On-Time Timer Control On-Time tON VIN = 12V, VOUT = 1.05V -- 135 -- ns Minimum Off-Time tOFF(MIN) VFB = 0.7V, TA = 25C -- 260 310 ns VSS = 0V 1.4 2 2.6 A VSS = 0.5V (Latch Mode) 0.1 0.2 -- mA VSS = 0.5V (Hiccup Mode) -- 0.5 -- A 3.6 3.85 4.1 0.13 0.35 0.47 VFB rising 85 90 95 VFB falling -- 85 -- 2.5 5 -- mA 114 120 126 % OVP Prop Delay -- 5 -- s UVP Trip Threshold 65 70 75 UVP Hysteresis -- 10 -- UVP Prop Delay -- 250 -- s -- tSS x 1.7 -- ms Soft-Start SS Charge Current SS Discharge Current UVLO UVLO Threshold Wake up VREG5 Hysteresis V Power Good PGOOD Threshold PGOOD Sink Current PGOOD = 0.5V % Output Under-Voltage and Over-Voltage Protection OVP Trip Threshold UVP Enable Delay OVP detect tUVPEN Relative to soft-start time % Note 1. Stresses beyond those listed under “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 at TA = 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. The device is not guaranteed to function outside its operating conditions. Copyright © 2022 Richtek Technology Corporation. All rights reserved. DS2859A/B-06 July 2022 is a registered trademark of Richtek Technology Corporation. www.richtek.com 9 RT2859A/B Typical Application Circuit RT2859A/B VIN 13, 14 C1 10µF x 2 C2 0.1µF 15 SW VIN BOOT VCC Output Signal VREG5 VS R3 100k 5 PGOOD 6 EN Input Signal C5 3.3nF 9, 10, 11 12 L1 1.4µH C6 0.1µF R1 8.25k CFF 16 COUT 22µF x 2 VOUT 1.05V/3A FB 1 VREG5 2 C4 1µF 3 SS GND PGND 4 7, 8, 17 (Exposed Pad) R2 22.1k VREG5 Table 1. Suggested Component Values (VIN = 12V) VOUT (V) R1 (k) R2 (k) CFF (pF) L1 (H) COUT (F) 1 6.81 22.1 -- 1 22 to 68 1.05 8.25 22.1 -- 1 22 to 68 1.2 12.7 22.1 -- 1 22 to 68 1.8 30.1 22.1 5 to 22 1.5 22 to 68 2.5 49.9 22.1 5 to 22 2.2 22 to 68 3.3 73.2 22.1 5 to 22 2.2 22 to 68 5 124 22.1 5 to 22 3.3 22 to 68 7 180 22.1 5 to 22 3.3 22 to 68 Note : Considering the effective capacitance de-rated with biased voltage level and size, the effective capacitance of COUT should be above 22μF at targeted output level for stable and normal operation. Copyright © 2022 Richtek Technology Corporation. All rights reserved. www.richtek.com 10 is a registered trademark of Richtek Technology Corporation. DS2859A/B-06 July 2022 RT2859A/B Typical Operating Characteristics Efficiency vs. Output Current 100 Efficiency vs. Output Current 100 RT2859A 90 VOUT = 5V 80 VOUT = 1.05V 60 50 40 30 20 70 VOUT = 1.05V 60 50 40 30 20 10 10 VIN = 12V 0 0.001 0.01 0.1 1 VIN = 12V 0 0.001 10 0.01 Output Current (A) 10 RT2859B 1.09 1.08 Output Voltage (V) 1.08 Output Voltage (V) 1 Output Voltage vs. Output Current 1.10 RT2859A 1.09 0.1 Output Current (A) Output Voltage vs. Output Current 1.10 1.07 1.06 1.05 1.04 1.03 1.02 1.01 1.07 1.06 1.05 1.04 1.03 1.02 1.01 VIN = 12V, VOUT = 1.05V, IOUT = 0A to 3A 1.00 VIN = 12V, VOUT = 1.05V, IOUT = 0A to 3A 1.00 0.0 0.5 1.0 1.5 2.0 2.5 3.0 0.0 0.5 Output Current (A) RT2859A Switching Frequency (kHz)1 600 500 400 300 200 100 VIN = 12V, VOUT = 1.05V, IOUT = 0A to 3A 0 0.5 1 1.5 2 2.5 Output Current (A) Copyright © 2022 Richtek Technology Corporation. All rights reserved. DS2859A/B-06 July 2022 1.5 2.0 2.5 3.0 Switching Frequency vs. Output Current 800 700 0 1.0 Output Current (A) Switching Frequency vs. Output Current 800 Switching Frequency (kHz)1 VOUT = 5V 80 70 Efficiency (%) Efficiency (%) RT2859B 90 RT2859B 700 600 500 400 300 200 100 VIN = 12V, VOUT = 1.05V, IOUT = 0A to 3A 0 3 0 0.5 1 1.5 2 2.5 3 Output Current (A) is a registered trademark of Richtek Technology Corporation. www.richtek.com 11 RT2859A/B Feedback Voltage vs. Input Voltage Feedback Voltage vs. Temperature 0.80 VIN = 12V, VOUT = 0.765V, IOUT = 0.6A 0.79 VIN = 12V, VOUT = 0.765V, IOUT = 0.6A 0.775 0.78 Feedback Voltage (V) Feedback Voltage (V) 0.780 0.77 0.76 0.75 0.74 0.73 0.72 0.770 0.765 0.760 0.755 0.750 0.745 0.71 0.740 0.70 -50 -25 0 25 50 75 100 4 125 6 8 Temperature (°C) Shutdown Current vs. Temperature VIN = 12V, VOUT = 1.05V, IOUT = 0A 14 16 18 VIN = 12V, VOUT = 1.05V, IOUT = 0A 950 25 20 15 10 5 900 850 800 750 700 650 0 600 -50 -25 0 25 50 75 100 125 -50 -25 0 25 50 75 Temperature (°C) Temperature (°C) Current Limit vs. Temperature Output Ripple Voltage 5.5 VIN = 12V, VOUT = 1.05V 5.0 Current Limit (A) 12 Quiescent Current vs. Temperature 1000 Quiescent Current (µA) Shutdown Current (µA)1 30 10 Input Voltage (V) 100 125 VIN = 12V, VOUT = 1.05V, IOUT = 3A VOUT (10mV/Div) ILIM 4.5 ILIM−IHYS 4.0 3.5 VSW (5V/Div) 3.0 2.5 -50 -25 0 25 50 75 100 125 Time (500ns/Div) Temperature (°C) Copyright © 2022 Richtek Technology Corporation. All rights reserved. www.richtek.com 12 is a registered trademark of Richtek Technology Corporation. DS2859A/B-06 July 2022 RT2859A/B Load Transient Response Load Transient Response RT2859A RT2859B VOUT (50mV/Div) IOUT (1A/Div) VOUT (50mV/Div) VIN = 12V, VOUT = 1.05V, IOUT = 0A to 3A IOUT (1A/Div) VIN = 12V, VOUT = 1.05V, IOUT = 0A to 3A Time (100μs/Div) Time (100μs/Div) Power On from VIN Power Off from VIN VIN (20V/Div) VIN (20V/Div) VOUT (1V/Div) VOUT (1V/Div) VSW (10V/Div) VSW (10V/Div) IOUT (2A/Div) IOUT (2A/Div) VIN = 12V, VOUT = 1.05V, IOUT = 3A VIN = 12V, VOUT = 1.05V, IOUT = 3A Time (4ms/Div) Time (4ms/Div) Power On from EN Power Off from EN VEN (10V/Div) VEN (10V/Div) VOUT (1V/Div) VOUT (1V/Div) VSW (10V/Div) VSW (10V/Div) IOUT (2A/Div) IOUT (2A/Div) VIN = 12V, VOUT = 1.05V, IOUT = 3A Time (4ms/Div) Copyright © 2022 Richtek Technology Corporation. All rights reserved. DS2859A/B-06 July 2022 VIN = 12V, VOUT = 1.05V, IOUT = 3A Time (100μs/Div) is a registered trademark of Richtek Technology Corporation. www.richtek.com 13 RT2859A/B Applications Information Soft-Start (SS) VIN The RT2859A/B soft-start uses an external capacitor at SS to adjust the soft-start timing according to the following equation : Figure 2. Digital Enable Control Circuit VIN REN1 EN REN2 RT2859A/B GND Figure 3. Resistor Divider for Lockout Threshold Setting Enable Operation (EN) For automatic start-up the high-voltage EN pin can be connected to VIN, either directly or through a 100kΩ resistor. Its large hysteresis band makes EN useful for simple delay and timing circuits. EN can be externally pulled to VIN by adding a resistor-capacitor delay (REN and CEN in Figure 1). Calculate the delay time using EN's internal threshold where switching operation begins (1.4V, typical). An external MOSFET can be added to implement digital control of EN when no system voltage above 2V is available (Figure 2). In this case, a 100kΩ pull-up resistor, REN, is connected between VIN and the EN pin. MOSFET Q1 will be under logic control to pull down the EN pin. To prevent enabling circuit when VIN is smaller than the VOUT target value or some other desired voltage level, a resistive voltage divider can be placed between the input voltage and ground and connected to EN to create an additional input undervoltage lockout threshold (Figure 3). EN CEN RT2859A/B GND The soft-start timing is the output voltage rising time from 0V to settled level and can be programmed by the external capacitor between the SS and GND pins. The available capacitance range is from 2.7nF to 220nF. If a 3.9nF capacitor is used, the typical soft-start will be 1.5ms. Do not leave SS unconnected. REN EN Q1 Enable C (nF)  0.765V tSS (ms) = SS ISS (μA) VIN REN 100k EN RT2859A/B GND Figure 1. External Timing Control Output Voltage Setting Set the desired output voltage using a resistive divider from the output to ground with the midpoint connected to FB. The output voltage is set according to the following equation : R1 VOUT = 0.765  (1 ) R2 VOUT R1 FB RT2859A/B R2 GND Figure 4. Output Voltage Setting Place the FB resistors within 5mm of the FB pin. Choose R2 between 10kΩ and 100kΩ to minimize power consumption without excessive noise pick-up and calculate R1 as follows : R2  (VOUT  0.765V) 0.765V For output voltage accuracy, use divider resistors with 1% R1 = or better tolerance. Under-Voltage Lockout Protection The RT2859A/B feature an under-voltage lock-out (UVLO) function that monitors the internal linear regulator output Copyright © 2022 Richtek Technology Corporation. All rights reserved. www.richtek.com 14 is a registered trademark of Richtek Technology Corporation. DS2859A/B-06 July 2022 RT2859A/B (PVCC) and prevents operation if VPVCC is too low. In some multiple input voltage applications, it may be desirable to use a power input that is too low to allow VPVCC to exceed the UVLO threshold. External BOOT Bootstrap Diode When the input voltage is lower than 5.5V it is recommended to add an external bootstrap diode between VIN (or VINR) and the BOOT pin to improve enhancement of the internal MOSFET switch and improve efficiency. The bootstrap diode can be a low cost one such as 1N4148 or BAT54. 5V 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 : PD(MAX) = (TJ(MAX) − TA) / θJA Figure 5. External Bootstrap Diode External BOOT Capacitor Series Resistance The internal power MOSFET switch gate driver is optimized to turn the switch on fast enough for low power loss and good efficiency, but also slow enough to reduce EMI. Switch turn-on is when most EMI occurs since VSW rises rapidly. During switch turn-off, SW is discharged relatively slowly by the inductor current during the deadtime between high-side and low-side switch on-times. In some cases it is desirable to reduce EMI further, at the expense of some additional power dissipation. The switch turn-on can be slowed by placing a small (