RT6257AHGJ6F

Reference Design Sample & Buy ® RT6257A/B 18V, 6A, 500kHz, ACOTTM Step-Down Converter in 6 pin TSOT-23 General Description Features The RT6257A/B is a high-performance, synchronous stepdown DC-DC converter that can deliver up to 6A output current from a 4.5V to 18V input supply. The device integrates low RDS(ON) power MOSFETs, accurate 0.6V reference and an integrated diode of bootstrap circuit to offer a very compact solution.  The RT6257A/B adopts Advanced Constant On-Time (ACOTTM) control architecture that provides ultrafast transient response and further reduces the externalcomponent count. In steady states, the ACOTTM operates in nearly constant switching frequency over line, load and output voltage ranges and makes the EMI filter design easier.           The device offers Independent enable control input pin for easily sequence control. To control the inrush current during the startup, the device provides a fixed 1.5ms softstart up. Fully protection features are also integrated in the device including the cycle-by-cycle current limit control, UVP, input UVLO and OTP. The RT6257A/B is available in the TSOT-23-6 (FC) package.  Internal Soft-Start (1.5ms typ.) Built-In UVP/OTP Input Under Voltage Lockout TSOT23-6 (FC) Package Applications     Ordering Information 4.5V to 18V Input Voltage Range 6A Output Current Constant-On-Time Mode to Enables Fast Transient Response Low Output Ripple and Allows Ceramic Output Capacitor 500kHz Switching Frequency High Efficient Internal Power MOSFET Switch Optimized for Lower Duty Cycle Applications Integrated 30mΩ Ω/20mΩ Ω MOSFETs Adjustable Output Voltage from 0.6V to 5V  Set Top Box Portable TV Access Point Router DSL Modem LCD TV RT6257A/B Package Type J6F : TSOT-23-6 (FC) Lead Plating System G : Green (Halogen Free and Pb Free) Pin Configuration (TOP VIEW) BOOT LX 6 UVP Option H : Hiccup PSM/PWM A : PSM/PWM B : Force-PWM FB VIN 5 4 2 3 EN GND TSOT-23-6 (FC) 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. Copyright © 2018 Richtek Technology Corporation. All rights reserved. DS6257A/B-03 October 2018 is a registered trademark of Richtek Technology Corporation. www.richtek.com 1 RT6257A/B Marking Information RT6257AHGJ6F 2K= : Product Code 2K=DNN DNN : Date Code RT6257BHGJ6F 2J=DNN 2J= : Product Code DNN : Date Code Typical Application Circuit VIN 4.5V to 18V 4 C1 10µF/50V C2 10µF/50V 2 Enable 3 VIN RT6257A/B 6 BOOT LX EN GND FB 5 CBOOT 0.1µF L 3.3µH 1 RT 4.99k R1 147k CFF 47pF C3 22µF/25V C4 22µF/25V VOUT 5V R2 20k Table 1. Suggested Component Values VOUT (V) R1 (k) R2 (k) L (H) COUT (F) RT (k) CFF (pF) 1 13.3 20 1.2 44 4.99 -- 1.2 20 20 1.2 44 4.99 -- 1.8 40.2 20 1.5 44 4.99 -- 2.5 63.4 20 2.2 44 4.99 47 to 82 3.3 90.9 20 2.8 44 4.99 47 to 82 5 147 20 3.3 44 4.99 47 to 82 Note : (1) All the input and output capacitors are the suggested values, referring to the effective capacitances, subject to any de-rating effect, like a DC bias. (2) Considering the noise immunity, it is necessary to add RT = 4.99k between feedback network and chip FB pin. Copyright © 2018 Richtek Technology Corporation. All rights reserved. www.richtek.com 2 is a registered trademark of Richtek Technology Corporation. DS6257A/B-03 October 2018 RT6257A/B Functional Pin Description Pin No. Pin Name Pin Function 1 FB Feedback voltage input. This pin is used to set the desired output voltage via an external resistive divider. 2 EN Enable control input. Connecting this pin to logic high can enable the device and connecting this pin to GND can disable the device. 3 GND System ground. Provides the ground return path for the control circuitry and low-side power MOSFET. 4 VIN Power input. Supplies the power switches of the device. 5 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. 6 BOOT Bootstrap supply for high-side gate driver. Connect a 0.1F ceramic capacitor from LX to BOOT to power the high-side switch. Copyright © 2018 Richtek Technology Corporation. All rights reserved. DS6257A/B-03 October 2018 is a registered trademark of Richtek Technology Corporation. www.richtek.com 3 RT6257A/B Functional Block Diagram BOOT VIN VIN VCC Reg Minoff VIBIAS VCC VREF UGATE OC Control LX Driver LGATE UV GND GND LX VCC LX Ripple Gen. EN + + - Comparator EN VIN On-Time LX FB Operation The RT6257A/B is a high-efficiency, monolithic synchronous step-down DC-DC converter that can deliver up to 6A output current from a 4.5V to 18V input supply. Using the ACOT control mode can reduce the output capacitance and perform fast transient response. It can minimize the component size without additional external compensation network. Current Limit The RT6257A/B current limit is a cycle-by-cycle “valley” type, 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, the on-time one-shot is inhibited until it drops below the current limit level. 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. Copyright © 2018 Richtek Technology Corporation. All rights reserved. www.richtek.com 4 Output Under-Voltage Protection and Hiccup Mode The RT6257A/B includes output under-voltage protection (UVP) against over-load or short-circuited condition by constantly monitoring the feedback voltage VFB. If VFB drops below the under-voltage protection trip threshold (typically 60% of the internal feedback reference voltage), the UV comparator will go high to turn off both the internal high-side and low-side MOSFET switches. If the output under-voltage condition continues for a period of time, the RT6257A/B will enter output under-voltage protection with hiccup mode. It is shown as Figure 1. During hiccup mode, the IC will shut down for tHICCUP_OFF (5ms), and then attempt to recover automatically for tHICCUP_ON (2.5ms). Upon completion of the soft-start sequence, if the fault condition is removed, the converter will resume normal operation; otherwise, such cycle for auto-recovery will be repeated until the fault condition is cleared. Hiccup mode allows the circuit to operate safely with low input current and power dissipation, and then resume normal operation as soon as the over-load or short-circuit condition is removed. is a registered trademark of Richtek Technology Corporation. DS6257A/B-03 October 2018 RT6257A/B Resume normal operation Abnormal case detected (UV) tHICCUP_ON = 2.5ms VOUT tHICCUP_OFF = 5ms External Bootstrap Capacitor Fault condition removed t 0.8ms Connect a 0.1μF low ESR ceramic capacitor between BOOT and LX. This bootstrap capacitor provides the gate driver supply voltage for the high-side N-channel MOSFET switch. Over-Temperature Protection VLX t Figure 1. UVP and Hiccup Mode Shut-Down, Start-Up and Enable (EN) The enable input (EN) has a logic-low level. When VEN is below this level the IC enters shutdown mode. When VEN exceeds its logic-high level the IC is fully operational. The RT6257A/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 15°C, the IC will resume normal operation. For continuous operation, provide adequate cooling so that the junction temperature does not exceed 150°C. UVP Protection The RT6257A/B detects under-voltage conditions by monitoring the feedback voltage on FB pin. When the feedback voltage is lower than 60% of the target voltage, the UVP comparator will go high to turn off both internal high-side and low-side MOSFETs. VUVLO VIN VENH VEN VOUT EN Delay ~0.5ms Soft Start time ~1.5ms Figure 2. Power Up Sequence Copyright © 2018 Richtek Technology Corporation. All rights reserved. DS6257A/B-03 October 2018 is a registered trademark of Richtek Technology Corporation. www.richtek.com 5 RT6257A/B Absolute Maximum Ratings (Note 1) Supply Input Voltage and EN Voltage, VIN, EN ---------------------------------------------------------------- −0.3V to 20V Switch Voltage, LX ---------------------------------------------------------------------------------------------------- −0.3V to 20V