RY3831

RY3831 18V 2.5A 500KHz Synchronous Step-Down Regulator Features • • • • • • • • Wide 4V to 18V Operating Input Range 2A Continuous Output Current 500kHz Switching Frequency Short Protection with Hiccup-Mode Built-in Over Current Limit Built-in Over Voltage Protection Internal Power-Save Mode (PFM/PWM) Internal Soft-Start • 115mΩ/100mΩ Low RDS(ON) Internal Power MOSFETs • • • • • • Output Adjustable from 0.923V No Schottky Diode Required Integrated internal compensation Thermal Shutdown Available in ESOP8 Package -40°C to +85°C Temperature Range • • • • Digital Video Recorder (DVR) Portable Media Player (PMP) Cable Modem / XDSL General Purposes Applications • • • • Digital Set-top Box (STB) Tablet Personal Computer (Pad) Flat-Panel Television and Monitor Wi-Fi Router / AP General Description The RY3831 is a high frequency, synchronous, rectified, step-down, switch-mode converter with internal power MOSFETs. It offers a very compact solution to achieve a 3.5A peak output current over a wide input supply range, with excellent load and line regulation. The RY3831 requires a minimal number of readily available, external components and is available in a space saving ESOP8 package. Typical Application Circuit C1 1 VIN 8 CIN BST 2 ON/ OFF 3 IN SW NC NC 6 L1 VOUT R1 COUT CFF Opt. 7 EN FB GND/EPAD 4 5 R2 9 Figure 1. Basic Application Circuit Email: support@rychip.com ©RYCHIP Semiconductor Inc. http://www.rychip.com Page 1 / 7 RY3831 18V 2.5A 500KHz Synchronous Step-Down Regulator Absolute Maximum Ratings VIN, EN, Voltage …………………... -0.3V to 21V VSW Voltage ...………………...…...…. -0.3V to (VIN+0.5V) VFB Voltages ...………………………… -0.3 to 6V VBS Voltage …...………………...... (Vsw-0.3) to (Vsw+5V) Operating Temperature Range …...-40°C to +85°C Storage Temperature Range ………………. -65°C to 150°C Lead Temperature (Soldering, 10s) ……... +300°C Junction Temperature……….………………...….…+125°C ESD (Human Body Made) HMB…………….2KV ESD (Machine Made) MM…………………………... 200V Thermal Resistance (θJA) ………………50 °C/W Thermal Resistance（θJC）……………10 °C/W Note1: Exceeding these ratings may damage the device. Note2: The device is not guaranteed to function outside of its operating conditions. Pin Description BST 1 VIN 2 SW 3 GND 4 9 EP 8 NC 7 EN 6 NC 5 FB (ESOP8) Pin Name Function 1 BST Bootstrap. A capacitor connected between SW and BST pins is required to form a floating supply across the high-side switch driver. 2 VIN Power Supply Pin 3 SW Switching Pin 4/9 GND/ EPAD GROUND Pin 5 FB 6 NC 7 EN 8 NC Email: support@rychip.com ©RYCHIP Semiconductor Inc. Adjustable Version Feedback input. Connect FB to the center point of the external resistor divider Drive this pin to a logic-high to enable the IC. Drive to a logic-low to disable the IC and enter micro-power shutdown mode. http://www.rychip.com Page 2 / 7 RY3831 18V 2.5A 500KHz Synchronous Step-Down Regulator Electrical Characteristics Parameter Input Voltage Range Conditions Min 4 Supply Current in Operation VEN=3.0V, VFB=1.1V Supply Current in Shutdown VEN =0 or EN = GND Regulated Feedback Voltage TA = 25°C, 4V≤VIN ≤18V 0.905 Typ. Max 18 Unit V 0.4 0.6 mA 4 μA 0.940 V 0.923 High-Side Switch On-Resistance 115 mΩ Low-Side Switch On-Resistance 100 mΩ High-Side Switch Leakage Current VEN=0V, VSW=0V 0 Upper Switch Current Limit Minimum Duty Cycle μA 10 3.5 Oscillation Frequency A 500 Maximum Duty Cycle KHz VFB=0.923V 92 % Minimum On-Time 60 nS Minimum Off-Time 90 nS Soft Start 1.2 mS Thermal Shutdown 160 ℃ Thermal Hysteresis 20 ℃ Functional Block Diagram VIN + ∑ VCC REGULATOR RSEN - VCC CURRENT SENSE AMPLIFIER BOOST REGULATOR BS OSCILLATOR HS DRIVER + COMPARATOR - SW VCC REFERENCE EN ON TIME CONTROL CURRENT LIMIT COMPARATOR 1pF 1M 56pF LOGIC CONTROL 400k LS DRIVER + + FB GND ERROR AMPLIFIER Figure 2. RY3831 Block Diagram Email: support@rychip.com ©RYCHIP Semiconductor Inc. http://www.rychip.com Page 3 / 7 RY3831 18V 2.5A 500KHz Synchronous Step-Down Regulator Functions Description Internal Regulator The RY3831 is a current mode step down DC/DC converter that provides excellent transient response with no extra external compensation components. This device contains an internal, low resistance, high voltage power MOSFET, and operates at a high 500KHz operating frequency to ensure a compact, high efficiency design with excellent AC and DC performance. Error Amplifier The error amplifier compares the FB pin voltage with the internal FB reference (VFB) and outputs a current proportional to the difference between the two. This output current is then used to charge or discharge the internal compensation network, which is used to control the power MOSFET current. The optimized internal compensation network minimizes the external component counts and simplifies the control loop design. Internal Soft-Start The soft-start is implemented to prevent the converter output voltage from overshooting during startup. When the chip starts, the internal circuitry generates a soft-start voltage (SS) ramping up from 0V to 0.923V. When it is lower than the internal reference (REF), SS overrides REF so the error amplifier uses SS as the reference. When SS is higher than REF, REF regains control. The SS time is internally max to 1.2ms. Over Current Protection & Hiccup The RY3831 has cycle-by-cycle over current limit when the inductor current peak value exceeds the set current limit threshold. Meanwhile, output voltage starts to drop until FB is below the Under-Voltage (UV) threshold, typically 25% below the reference. Once a UV is triggered, the RY3831 enters hiccup mode to periodically restart the part. This protection mode is especially useful when the output is dead-short to ground. The average short circuit current is greatly reduced to alleviate the thermal issue and to protect the regulator. The RY3831 exits the hiccup mode once the over current condition is removed. Startup and Shutdown If both VIN and EN are higher than their appropriate thresholds, the chip starts. The reference block starts first, generating stable reference voltage and currents, and then the internal regulator is enabled. The regulator provides stable supply for the remaining circuitries. Three events can shut down the chip: EN low, VIN low and thermal shutdown. In the shutdown procedure, the signaling path is first blocked to avoid any fault triggering. The comp voltage and the internal supply rail are then pulled down. The floating driver is not subject to this shutdown command. Email: support@rychip.com ©RYCHIP Semiconductor Inc. http://www.rychip.com Page 4 / 7 RY3831 18V 2.5A 500KHz Synchronous Step-Down Regulator Applications Information Setting the Output Voltage RY3831 require an input capacitor, an output capacitor and an inductor. These components are critical to the performance of the device. RY3831 are internally compensated and do not require external components to achieve stable operation. The output voltage can be programmed by resistor divider. 𝑉𝑂𝑈𝑇 = 𝑉𝐹𝐵 × 𝑅1 + 𝑅2 𝑅2 VOUT R1 R2 L1MIN L1TYP L1MAX CIN COUT 1V 4.05KΩ 50KΩ 2.2μH 2.2μH 4.7μH 20-47uF 20-68uF 1.05V 6.76KΩ 50KΩ 2.2μH 2.2μH 4.7μH 20-47uF 20-68uF 1.2V 14.9KΩ 50KΩ 2.2μH 2.2μH 4.7μH 20-47uF 20-68uF 1.5V 31.1KΩ 50KΩ 2.2μH 2.2μH 4.7μH 20-47uF 20-68uF 3.3V 128.4KΩ 50KΩ 3.3μH 3.3μH 4.7μH 20-47uF 20-68uF 5.0V 220KΩ 50KΩ 3.3μH 4.7μH 4.7μH 20-47uF 20-68uF Selecting the Inductor The recommended inductor values are shown in the Application Diagram. It is important to guarantee the inductor core does not saturate during any foreseeable operational situation. The inductor should be rated to handle the peak load current plus the ripple current: Care should be taken when reviewing the different saturation current ratings that are specified by different manufacturers. Saturation current ratings are typically specified at 25°C, so ratings at maximum ambient temperature of the application should be requested from the manufacturer. 𝐿= 𝑉𝑂𝑈𝑇 × (𝑉𝐼𝑁 − 𝑉𝑂𝑈𝑇 ) 𝑉𝐼𝑁 × ∆𝐼𝐿 × 𝐹𝑂𝑆𝐶 Where ΔIL is the inductor ripple current. Choose inductor ripple current to be approximately 30% if the maximum load current. The maximum inductor peak current is: 𝐼𝐿(𝑀𝐴𝑋) = 𝐼𝐿𝑂𝐴𝐷 + ∆𝐼𝐿 2 Under light load conditions below 100mA, larger inductance is recommended for improved efficiency. Email: support@rychip.com ©RYCHIP Semiconductor Inc. http://www.rychip.com Page 5 / 7 RY3831 18V 2.5A 500KHz Synchronous Step-Down Regulator Selecting the Output Capacitor Special attention should be paid when selecting these components. The DC bias of these capacitors can result in a capacitance value that falls below the minimum value given in the recommended capacitor specifications table. The ceramic capacitor’s actual capacitance can vary with temperature. The capacitor type X7R, which operates over a temperature range of −55°C to +125°C, will only vary the capacitance to within ±15%. The capacitor type X5R has a similar tolerance over a reduced temperature range of −55°C to +85°C. Many large value ceramic capacitors, larger than 1uF are manufactured with Z5U or Y5V temperature characteristics. Their capacitance can drop by more than 50% as the temperature varies from 25°C to 85°C. Therefore X5R or X7R is recommended over Z5U and Y5V in applications where the ambient temperature will change significantly above or below 25°C. Tantalum capacitors are less desirable than ceramic for use as output capacitors because they are more expensive when comparing equivalent capacitance and voltage ratings in the 0.47uF to 44uF range. Another important consideration is that tantalum capacitors have higher ESR values than equivalent size ceramics. This means that while it may be possible to find a tantalum capacitor with an ESR value within the stable range, it would have to be larger in capacitance (which means bigger and more costly) than a ceramic capacitor with the same ESR value. It should also be noted that the ESR of a typical tantalum will increase about 2:1 as the temperature goes from 25°C down to −40°C, so some guard band must be allowed. PC Board Layout Consideration PCB layout is very important to achieve stable operation. It is highly recommended to duplicate EVB layout for optimum performance. If change is necessary, please follow these guidelines for reference. 1. Keep the path of switching current short and minimize the loop area formed by Input capacitor, high-side MOSFET and low-side MOSFET. 2. Bypass ceramic capacitors are suggested to be put close to the Vin Pin. 3. Ensure all feedback connections are short and direct. Place the feedback resistors and compensation components as close to the chip as possible. 4. VOUT, SW away from sensitive analog areas such as FB. 5. Connect IN, SW, and especially GND respectively to a large copper area to cool the chip to improve thermal performance and long-term reliability. Email: support@rychip.com ©RYCHIP Semiconductor Inc. http://www.rychip.com Page 6 / 7 RY3831 18V 2.5A 500KHz Synchronous Step-Down Regulator Package Description ESOP8 (EXPOSED PAD) 0.189(4.80) 0.197(5.00) 0.024(0.61) 0.050(1.27) 0.063(1.60) EXAMPLE TOP MARK AAAAA 0.150(3.80) 0.157(4.00) 0.228(5.80) 0.244(6.20) 0.103(2.62) 0.213(5.40) PIN 1 ID 0.138(3.51) RECOMMENDED PAD LAYOUT TOP VIEW 0.010(0.25) x45° 0.020(0.50) 0.051(1.30) 0.067(1.70) 0.013(0.33) 0.020(0.51) 0.050(1.27) BSC SEATING PLANE 0.000(0.00) 0.006(0.15) FRONT VIEW GAUGE PLANE 0.010(0.25) BSC 0°~8° 0.016(0.41) 0.050(1.27) 0.0075(0.19) 0.0098(0.25) SIDE VIEW 0.124(3.15) 0.136(3.45) 0.089(2.26) 0.101(2.56) NOTE: 1. CONTROL DIMENSION IS IN INCHES. DIMENSION IN BRACKET IS IN MILLIMETERS. 2. PACKAGE LENGTH DOES NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS. 3. PACKAGE WIDTH DOES NOT INCLUDE INTERLEAD FLASH OR PROTRUSIONS. 4. LEAD COPLANARITY (BOTTOM OF LEADS AFTER FORMING) SHALL BE 0.004" INCHES MAX. 5. DRAWING CONFORMS TO JEDEC MS-012, VARIATION BA. 6. DRAWING IS NOT TO SCALE. BOTTOM VIEW Email: support@rychip.com ©RYCHIP Semiconductor Inc. http://www.rychip.com Page 7 / 7