RT5785BGJ8F

® RT5785A/B 2A, 6V, 1.5MHz, 25μ μA IQ, ACOTTM Synchronous Step-Down Converter General Description Features The RT5785A/B is a high-performance, Advanced Constant On-Time (ACOTTM) monolithic synchronous step-down DC/DC converter that can deliver up to 2A output current from a 2.5V to 6V input supply. The proprietary ACOT control architecture features quick transient response and provides stable operation with small ceramic output capacitors and without complicated external compensation. The switching ripple voltage is easily smoothed–out by small package filtering elements due to a constant switching frequency of 1.5MHz and the maximum duty cycle of 100% allows the device to operate at low dropout use. With internal low on-resistance power switches and extremely low quiescent current, the RT5785A/B displays excellent efficiency and good behavior across a range of applications.               Dramatically Fast Transient Response Steady 1.5MHz ±200kHz Switching Frequency Very Low Input Quiescent and Shutdown Currents Advanced COT Control Loop Design Optimized for Ceramic Output Capacitors 2.5V to 6V Input Voltage Range Accurate Voltage Reference 0.6V ±2% Integrated 100mΩ Ω/60mΩ Ω MOSFETs Internal Start-Up into Pre-biased Outputs Power Good Indicator Enable Control Over-Current and Over-Temperature Protections Under-Voltage Protection with Hiccup Mode RoHS Compliant and Halogen Free Applications Cycle-by-cycle current limit provides protection against shorted outputs, input under-voltage lock-out, output under-voltage protection, and thermal shutdown provide safe and smooth operation in all operating conditions. The RT5785A/B is available in the TSOT-23-8 (FC) package.     Mobile Phones and Handheld Devices STB, Cable Modem, and xDSL Platforms WLAN ASIC Power / Storage (SSD and HDD) General Purpose for POL LV Buck Converter Simplified Application Circuit VIN VIN RPGOOD PGOOD Enable LX L VOUT CIN R1 RT5785A/B PGOOD CFF COUT FB R2 EN VOUT PGND Copyright © 2015 Richtek Technology Corporation. All rights reserved. DS5785A/B-01 December 2015 AGND is a registered trademark of Richtek Technology Corporation. www.richtek.com 1 RT5785A/B Ordering Information Pin Configurations AGND VOUT 8 7 6 5 2 3 4 LX PGND Note : PGOOD PSM/PWM A : PSM/PWM B : Force-PWM FB Lead Plating System G : Green (Halogen Free and Pb Free) VIN Package Type J8F : TSOT-23-8 (FC) EN (TOP VIEW) RT5785 Richtek products are : TSOT-23-8 (FC)  RoHS compliant and compatible with the current requirements of IPC/JEDEC J-STD-020.  Suitable for use in SnPb or Pb-free soldering processes. Marking Information RT5785AGJ8F 0N= : Product Code 0N=DNN DNN : Date Code RT5785BGJ8F 0M= : Product Code 0M=DNN DNN : Date Code Functional Pin Description Pin No. Pin Name Pin Function 1 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 UVP, OTP, dropout, EN shutdown, or during slow start. 2 VIN Supply Input. Supplies the power to the internal control circuit as well as the power switches of the device. Drive VIN with a 2.5V to 6V power source and bypass VIN to PGND with a suitably large capacitor to eliminate noise on the input to the IC. 3 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. 4 PGND Power Ground. This pin must be soldered to a large PCB and connected to analog ground for maximum power dissipation. 5 VOUT Output Voltage Sense Input. This pin is used to monitor and adjust output voltage for superior load transient regulation. 6 AGND Analog Ground. Provides the ground return path for control circuitry and internal reference. 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 0.6V typically. 8 EN Enable Control Input. Connecting this pin to logic high can enable the device and connecting this pin to GND can disable the device. Copyright © 2015 Richtek Technology Corporation. All rights reserved. www.richtek.com 2 is a registered trademark of Richtek Technology Corporation. DS5785A/B-01 December 2015 RT5785A/B Function Block Diagram EN UVLO AGND Shutdown Control OTP FB VOUT Error Amplifier + + VREF TON Comparator + - Ramp Generator Logic Control Current Limit Detector PGOOD + AZC VFB LX VIN Driver LX LX LX PGND - Operation The RT5785A/B is a low voltage synchronous step-down converter that can support input voltage ranging from 2.5V to 6V and the output current can be up to 2A. The RT5785A/ B uses ACOTTM mode control. To achieve good stability with low-ESR ceramic capacitors, the 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. In steady-state operation, 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 on-time, 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 Copyright © 2015 Richtek Technology Corporation. All rights reserved. DS5785A/B-01 December 2015 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 so that rapidly-repeated on-times can raise the inductor current quickly when needed. Under-Voltage Protection (UVLO) The UVLO continuously monitors the VCC voltage to make sure the device works properly. When the VCC is high enough to reach the UVLO high threshold voltage, the step-down converter softly starts or pre-bias to its regulated output voltage. When the VCC decreases to its low threshold voltage, the device shuts down. Power Good When the output voltage is higher than PGOOD rising threshold, the PGOOD flag is high. Output Under-Voltage Protection (UVP) When the output voltage is lower than 66% reference voltage after soft-start, the UVP is triggered. is a registered trademark of Richtek Technology Corporation. www.richtek.com 3 RT5785A/B Over-Current Protection (OCP) The RT5785A/B senses the current signal when the highside and low-side MOSFET turns on. As a result, The OCP is a cycle-by-cycle current limit. If an over-current condition occurs, the converter turns off the next on pulse until inductor current drops below the OCP limit. The delay time of high-side MOSFET OCP trigger is 100ns. If the OCP is continually activated and the load current is larger than the current provided by the converter, the output voltage drops. Also, when the output voltage triggers the UVP also, the current will drop to ZC and trigger the resoft-start sequence. Soft-Start An internal current source charges an internal capacitor to build the soft-start ramp voltage. The typical soft-start time is 1.5ms. Over-Temperature Protection (OTP) The RT5785A/B has an over-temperature protection. When the device triggers the OTP, the device shuts down until the temperature is back to normal. PWM Frequency and Adaptive On-Time Control The on-time can be roughly estimated by the equation : TON = VOUT 1  where fOSC is nominal 1.5MHz VIN fOSC Copyright © 2015 Richtek Technology Corporation. All rights reserved. www.richtek.com 4 is a registered trademark of Richtek Technology Corporation. DS5785A/B-01 December 2015 RT5785A/B Absolute Maximum Ratings          (Note 1) Supply Input Voltage, VIN ----------------------------------------------------------------------------------------LX Pin Switch Voltage ---------------------------------------------------------------------------------------------