RT2805AGSP

® RT2805A 5A, 36V, 500kHz Current Mode Asynchronous Step-Down Converter General Description Features The RT2805A is a current mode asynchronous step-down converter that achieves excellent load and line regulation. Over a wide input voltage range from 5.5V to 36V and supports output current up to 5A. The Current mode operation provides fast transient response and eases loop stabilization.       An adjustable soft-start reduces the stress on the input source at startup. In shutdown mode, the regulator draws only 25μA of supply current. The RT2805A requires a minimum number of readily available external components, providing a compact solution. The RT2805A provides protection functions inducing input under voltage lockout, cycle-by-cycle current limit, short circuit protection and thermal shutdown protection.        The RT2805A is available in the SOP-8 (Exposed Pad) package. Applications   Ordering Information  RT2805A  Package Type SP : SOP-8 (Exposed Pad-Option 2) Distributive Power Systems Battery Charger DSL Modems Pre-regulator for Linear Regulators Marking Information Lead Plating System G : Green (Halogen Free and Pb Free) RT2805AGSP : Product Number RT2805A GSPYMDNN Note : Richtek products are :  5A Output Current Wide Operating Input Range 5.5V to 36V Adjustable Output Voltage from 1.222V to 26V High Efficiency up to 90% Internal Compensation Minimizes External Parts Count Internal Soft-Start 110mΩ Ω Internal Power MOSFET Switch 25μ μA Shutdown Mode Fixed 500kHz Frequency Thermal Shutdown Cycle-by-Cycle Current Limit Available In an SOP-8 (Exposed Pad) Package RoHS Compliant and Halogen Free YMDNN : Date Code RoHS compliant and compatible with the current requirements of IPC/JEDEC J-STD-020.  Suitable for use in SnPb or Pb-free soldering processes. Simplified Application Circuit VIN VIN CIN BOOT RT2805A L1 SW D1 Chip Enable EN VOUT R1 COUT FB GND Copyright © 2015 Richtek Technology Corporation. All rights reserved. DS2805A-03 August 2015 CBOOT R2 is a registered trademark of Richtek Technology Corporation. www.richtek.com 1 RT2805A Pin Configurations (TOP VIEW) BOOT NC 2 NC 3 FB 4 GND 9 8 SW 7 VIN 6 GND 5 EN SOP-8 (Exposed Pad) Functional Pin Description Pin No. Pin Name Pin Function BOOT Bootstrap Input for High Side Gate Driver. Connect a 10nF or greater capacitor from SW to BOOT to power the high side switch. 2, 3 NC No Internal Connection. 4 FB Feedback Input. The feedback threshold is 1.222V. 5 EN Enable Input. EN is a digital input that turns the regulator on or off. Drive EN higher than 1.4V to turn on the regulator, lower than 0.4V to turn it off. For automatic startup, leave EN unconnected. 6, 9 (Exposed Pad) GND Ground. The exposed pad must be soldered to a large PCB and connected to GND for maximum power dissipation. 7 VIN Power Input. A suitable large capacitor should be connected from the VIN to GND to eliminate noise on the input to the IC. 8 SW Switch Node. Note that a capacitor is required from SW to BOOT to power the high side switch. 1 Function Block Diagram VIN Current Sense Amplifier - Ramp Generator + BOOT EN Regulator Oscillator 500kHz S + Reference FB 12k Error + Amplifier - 400k 30pF Q Driver R Current Comparator SW Bootstrap Control GND 13pF Copyright © 2015 Richtek Technology Corporation. All rights reserved. www.richtek.com 2 is a registered trademark of Richtek Technology Corporation. DS2805A-03 August 2015 RT2805A Operation The RT2805A is a constant frequency, current mode asynchronous step-down converter. In normal operation, the high side N-MOSFET is turned on when the S-R latch is set by the oscillator and is turned off when the current comparator resets the S-R latch. While the N-MOSFET is turned off, the inductor current conducts through the external diode. Error Amplifier The error amplifier adjusts its output voltage by comparing the feedback signal (V FB) with the internal 1.222V reference. When the load current increases, it causes a drop in the feedback voltage relative to the reference, the error amplifier's output voltage then rises to allow higher inductor current to match the load current. Oscillator The internal oscillator runs at fixed frequency 500kHz. In short circuit condition, the frequency is reduced to 150kHz for low power consumption. Enable The converter is turned on when the EN pin is higher than 1.4V and turned off when the EN pin is lower than 0.4V. When the EN pin is open, it will be pulled up to logic-high by 1μA current internally. Soft-Start (SS) An internal current source charges an internal capacitor to build a soft-start ramp voltage. The FB voltage will track the internal ramp voltage during soft-start interval. The typical soft-start time is 5ms. Thermal Shutdown The over temperature protection function will shut down the switching operation when the junction temperature exceeds 150°C. Once the junction temperature cools down by approximately 30°C, the converter will automatically resume switching. Internal Regulator The regulator provides low voltage power to supply the internal control circuits and the bootstrap power for high side gate driver. Copyright © 2015 Richtek Technology Corporation. All rights reserved. DS2805A-03 August 2015 is a registered trademark of Richtek Technology Corporation. www.richtek.com 3 RT2805A Absolute Maximum Ratings           (Note 1) Supply Voltage, VIN ----------------------------------------------------------------------------------------Switching Voltage, SW ------------------------------------------------------------------------------------BOOT Voltage ------------------------------------------------------------------------------------------------Other Pins -----------------------------------------------------------------------------------------------------Power Dissipation, PD @ TA = 25°C SOP-8 (Exposed Pad) -------------------------------------------------------------------------------------Package Thermal Resistance (Note 2) SOP-8 (Exposed Pad), θJA --------------------------------------------------------------------------------SOP-8 (Exposed Pad), θJC -------------------------------------------------------------------------------Junction Temperature ---------------------------------------------------------------------------------------Lead Temperature (Soldering, 10 sec.) -----------------------------------------------------------------Storage Temperature Range ------------------------------------------------------------------------------ESD Susceptibility (Note 3) HBM (Human Body Model) --------------------------------------------------------------------------------- Recommended Operating Conditions    −0.3V to 40V −0.3V to (VIN + 0.3V) (VSW − 0.3V) to (VSW + 6V) −0.3V to 6V 2.04W 49°C/W 15°C/W 150°C 260°C −65°C to 150°C 2kV (Note 4) Supply Voltage, VIN ----------------------------------------------------------------------------------------- 5.5V to 36V 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 Reference Voltage VREF High Side Switch-On Resistance RDS(ON)1 Low Side Switch-On Resistance Current Limit Oscillator Frequency Short Circuit Frequency Maximum Duty Cycle Minimum On-Time Under Voltage Lockout Threshold Rising Under Voltage Lockout Threshold Hysteresis Logic-High EN Threshold Voltage Logic-Low Enable Pull Up Current Test Conditions Typ Max T A = 25°C 1.202 1.222 1.239 I OUT = 0A to 5A 1.196 1.222 1.245 Bias Gate Driver at VIN = 5.5V -- RDS(ON)2 Bias Gate Driver at VIN = 5.5V I LIM f OSC Voltage Mode Test VFB = 0.8V VFB = 0V DMAX t ON Unit V 110 230 m -- 10 15  6 400 -- 7.5 500 150 9 600 -- A kHz kHz VFB = 0.8V Come from Maximum Duty Cycle 85 -- 90 100 95 150 % ns VIN Rising, Check Switching -- 5.2 5.5 V VIN Falling, Check Switching -- 700 -- mV 1.4 --- --1 -0.4 -- A --3 25 0.6 5 -1 10 A mA ms -- 160 -- C VIH VIL Let EN = 1.4V, Check I Q Let EN = 0.4V, Check I Q Shutdown Current Quiescent Current Soft-Start Period I SHDN IQ VEN = 0V VEN = 2V, VFB = 1.5V Thermal Shutdown T SD Copyright © 2015 Richtek Technology Corporation. All rights reserved. www.richtek.com 4 Min V is a registered trademark of Richtek Technology Corporation. DS2805A-03 August 2015 RT2805A 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 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. The EVB board copper area is 70mm2. Note 3. Devices are ESD sensitive. Handling precaution is recommended. Note 4. The device is not guaranteed to function outside its operating conditions. Copyright © 2015 Richtek Technology Corporation. All rights reserved. DS2805A-03 August 2015 is a registered trademark of Richtek Technology Corporation. www.richtek.com 5 RT2805A Typical Application Circuit VIN 5.5V to 36V Chip Enable 7 CIN 4.7µF/ 50V x 2 BOOT VIN RT2805A 5 EN 1 SW 8 D1 B550A Open = Automatic Startup 6, 9 (Exposed Pad) CBOOT 10nF L1 VOUT CFF R1 COUT FB 4 GND R2 Table 1. Recommended Component Selection VOUT (V) R1 (k) R2 (k) CFF (pF) L (H) COUT (F) 2.5 100 100 82 6.8 22 x 2 3.3 100 58.6 82 10 22 x 2 5 100 31.6 82 15 22 x 2 8 100 18 82 22 22 x 2 Copyright © 2015 Richtek Technology Corporation. All rights reserved. www.richtek.com 6 is a registered trademark of Richtek Technology Corporation. DS2805A-03 August 2015 RT2805A Typical Operating Characteristics Efficiency vs. Output Current Reference Voltage vs. Input Voltage 100 1.230 90 VIN = 12V VIN = 32V VIN = 36V 70 Reference Voltage (V) Efficiency (%) 80 60 50 40 30 20 10 VOUT = 5V 0 0 1 2 3 4 1.226 1.222 1.218 1.214 VOUT = 5V, IOUT = 0A 1.210 4 5 8 12 16 Output Current (A) 24 28 32 36 Output Voltage vs. Output Current 5.008 1.228 5.004 5.000 1.226 Output Voltage (V) Reference Voltage (V) Reference Voltage vs. Temperature 1.230 1.224 1.222 VIN = 12V VIN = 24V VIN = 36V 1.220 1.218 1.216 1.214 VIN = 36V VIN = 24V VIN = 12V 4.996 4.992 4.988 4.984 4.980 4.976 4.972 4.968 1.212 IOUT = 0A 1.210 -50 -25 0 25 50 75 100 4.964 VOUT = 5V 4.960 0 125 1 2 3 4 Frequency vs. Input Voltage Frequency vs. Temperature 540 530 530 520 520 Frequency (kHz) 540 510 500 490 480 470 510 500 490 480 VIN = 12V VIN = 24V VIN = 36V 470 460 460 450 450 VOUT = 5V, IOUT = 0A 440 4 8 12 16 20 24 28 32 Input Voltage (V) Copyright © 2015 Richtek Technology Corporation. All rights reserved. DS2805A-03 August 2015 5 Output Current (A) Temperature (°C) Frequency (kHz) 20 Input Voltage (V) VOUT = 5V 440 36 -50 -25 0 25 50 75 100 125 Temperature (°C) is a registered trademark of Richtek Technology Corporation. www.richtek.com 7 RT2805A Shutdown Current vs. Input Voltage 60 11 50 Shutdown Current (μA) Current Limit (A) Current Limit vs. Temperature 12 10 9 8 7 6 VIN = 12V 5 -50 -25 0 25 50 75 100 40 30 20 10 VEN = 0V 0 4 125 8 12 16 20 24 28 Temperature (°C) Input Voltage (V) Quiescent Current vs. Temperature Load Transient Response 32 36 1 Quiescent Current (mA) 0.9 VOUT (200mV/Div) 0.8 0.7 0.6 VIN = 36V VIN = 24V VIN = 12V 0.5 0.4 0.3 0.2 IOUT (2A/Div) 0.1 VIN = 12V, VOUT = 5V, IOUT = 0.2A to 5A 0 -50 -25 0 25 50 75 100 Time (100μs/Div) 125 Temperature (°C) Switching Load Transient Response VOUT (200mV/Div) VOUT (10mV/Div) VSW (10V/Div) IOUT (2A/Div) VIN = 12V, VOUT = 5V, IOUT = 2.5A to 5A Time (100μs/Div) Copyright © 2015 Richtek Technology Corporation. All rights reserved. www.richtek.com 8 IL (5A/Div) VIN = 12V, VOUT = 5V, IOUT = 5A Time (1μs/Div) is a registered trademark of Richtek Technology Corporation. DS2805A-03 August 2015 RT2805A Power On from EN Power Off from EN VEN (5V/Div) VEN (5V/Div) VOUT (5V/Div) VOUT (5V/Div) IL (5A/Div) IL (5A/Div) VIN = 12V, VOUT = 5V, IOUT = 5A Time (2.5ms/Div) Copyright © 2015 Richtek Technology Corporation. All rights reserved. DS2805A-03 August 2015 VIN = 12V, VOUT = 5V, IOUT = 5A Time (2.5ms/Div) is a registered trademark of Richtek Technology Corporation. www.richtek.com 9 RT2805A Application Information The RT2805A is an asynchronous high voltage buck converter that can support the input voltage range from 5.5V to 32V and the output current can be up to 5A. Output Voltage Setting The resistive divider allows the FB pin to sense the output voltage as shown in Figure 1. VOUT R1 FB RT2805A R2 GND Figure 1. Output Voltage Setting The output voltage is set by an external resistive divider according to the following equation : VOUT = VREF  1 R1   R2  Where VREF is the reference voltage (1.222V typ.). Soft-Start The RT2805A contains an internal soft-start clamp that gradually raises the output voltage. The typical soft-start time is 5ms. Chip Enable Operation The EN pin is the chip enable input. Pull the EN pin low (1.4V,