RT9202B

RT9202B Single Synchronous Buck PWM DC-DC Controller General Description The RT9202B is a single power supply PWM DC-DC converter controller designed to drive N-MOSFET in a synchronous buck topology. The IC integrates the control, output adjustment, monitoring and protection functions in a small 8-pin package. The RT9202B uses a low gain voltage mode PWM control for simple application design. An internal 0.8V reference allows the output voltage to be precisely regulated to low voltage requirement. A fixed 300kHz oscillator reduces the component size for saving board space. The RT9202B features over current protection, over voltage protection, and under voltage lock-out. The output current is monitored by sensing the voltage drop across the MOSFET's RDS(ON), which eliminates the need for a current sensing resistor. Features l l l l l l l l l l l l Operate From 5V 0.8V Internal Reference Drive Two N-MOSFETs Voltage Mode PWM Control Fast Transient Response Fixed 300kHz Oscillator Frequency Full 0 to 100% Duty Cycle Internal Soft Start Adaptive Non-Overlapping Gate Driver Over-Current Monitor Uses MOSFET RDS(ON) Over-Voltage Protection Uses Low-Side MOSFET RoHS Compliant and 100% Lead (Pb)-Free Applications l l Ordering Information RT9202B Package Type S : SOP-8 Operating Temperature Range P : Pb Free with Commercial Standard G : Green (Halogen Free with Commercial Standard) Note : RichTek Pb-free and Green 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. }100% matte tin (Sn) plating. l l l l l l l Motherboard Power Regulation for Computers Subsystems Power Supplies Cable Modems, Set Top Box, and DSL Modems DSP and Core Communications processor Supplies Memory Power Supplies Personal Computer Peripherals Industrial Power Supplies 5V-Input DC-DC Regulators Low Voltage Distributed Power Supplies Pin Configurations (TOP VIEW) BOOT UGATE GND LGATE 2 3 4 8 7 6 5 PHASE OCSET FB VCC SOP-8 DS9202B-03 March 2007 www.richtek.com 1 RT9202B Typical Application Circuit R1 20K R4 10 D1 MA732 5V C2 8 7 SHND H : shutdown Q1 2N7002 6 5 C4 1uF PHASE BOOT 1 2 3 4 0.1uF VOUT 2.5V OCSET UGATE FB GND L2 + 5uH C3 1000uF MU + C5 1uF C1 470uF LGATE VCC RT9202B R3 120 ML R2 255 C6 10nF Figure 1. RT9202B powered from 5V only R4 R1 20K 10 12V 5V 8 7 SHND H : shutdown Q1 2N7002 5V 6 5 C4 1uF PHASE BOOT 1 2 3 4 C2 1uF MU + C5 1uF C1 470uF OCSET UGATE FB GND VOUT 2.5V + L1 5uH C3 1000uF LGATE VCC RT9202B R3 120 ML R2 250 C6 10nF Figure 2. RT9202B powered from 12V and 5V www.richtek.com 2 DS9202B-03 March 2007 RT9202B MU COUT 1000uF GND CBOOT VCC BOOT 0.1uF RT9202B G S GND Return ML D D L 5uH G S + CIN1 1uF CIN2 470uF + CVCC 1uF Layout Placement Layout Notes 1. Put CIN1 & CIN2 to be near the MU drain and ML source nodes. 2. Put RT9202B to be near the COUT 3. Put CBOOT as close as to BOOT pin 4. Put CVCC as close as to VCC pin Function Block Diagram VCC Power on Reset 6.0V Regulation Bias BOOT 0.8 Reference Soft Start 20uA + OC 1.1V OVP + OCSET UGATE 0.5V UVP + 0.8V FB Error + Error Amplifier + PWM - Control Logic VCC PHASE LGATE GND 300kHz Oscillator DS9202B-03 March 2007 www.richtek.com 3 RT9202B Functional Pin Description BOOT (Pin 1) This pin provides ground referenced bias voltage to the upper MOSFET driver. A bootstrap circuit is used to create a voltage suitable to drive a logic-level N-Channel MOSFET when operating at a single 5V power supply. This pin also could be powered from ATX 12V, in this OCSET (Pin 7) Connect a resistor from this pin to the drain of the upper MOSFET. This resistor, an internal 20µA current source, and the upper MOSFET on-resistance set the converter over-current trip point. An over-current trip cycles the softstart function. The voltage at this pin is monitored for power-on reset (POR) purpose and pulling this pin low with an open drain device will shut down the IC. I × R OCSET IPEAK = OCSET RDS(ON) situation, an internal 6.0V regulator will supply to VCC pin for internal voltage bias. UGATE (Pin 2) Connect UGATE pin to the PWM converter's upper MOSFET gate. This pin provides the gate drive for the upper MOSFET. GND (Pin 3) Signal and power ground for the IC. All voltage levels are measured with respect to this pin. LGATE (Pin 4) Connect LGATE to the PWM converter's lower MOSFET gate. This pin provides the gate drive for the lower MOSFET. VCC (Pin 5) This is the main bias supply for the RT9202B. This pin also provides the gate bias charge for the lower MOSFET gate. The voltage at this pin is monitored for power-on reset (POR) purpose. This pin is also the internal 6.0V regulator output powered from BOOT pin when BOOT pin is directly powered from ATX 12V. FB (Pin 6) This pin is connected to the PWM converter's output divider. This pin also connects to internal PWM error amplifier inverting input and protection monitor. PHASE (Pin 8) This pin is used to monitor the voltage drop across the upper MOSFET for over-current protection. www.richtek.com 4 DS9202B-03 March 2007 RT9202B Absolute Maximum Ratings l l l l (Note 1) 7V 15V GND − 0.3V to 7V 0.625W 160°C/W 0°C to +70°C 260°C −65°C to +150°C 2kV 200V l l l l l Supply Input Voltage, VCC ----------------------------------------------------------------------------------------BOOT & UGATE to GND -------------------------------------------------------------------------------------------Input, Output or I/O Voltage ---------------------------------------------------------------------------------------Power Dissipation, PD @ TA = 25°C SOP-8 ------------------------------------------------------------------------------------------------------------------Package Thermal Resistance (Note 4) SOP-8, θJA -------------------------------------------------------------------------------------------------------------Ambient Temperature Range --------------------------------------------------------------------------------------Lead Temperature (Soldering, 10 sec.)--------------------------------------------------------------------------Storage Temperature Range ---------------------------------------------------------------------------------------ESD Susceptibility (Note 2) HBM (Human Body Mode) -----------------------------------------------------------------------------------------MM (Machine Mode) ------------------------------------------------------------------------------------------------(Note 3) Recommended Operating Conditions l Junction Temperature Range --------------------------------------------------------------------------------------- −40°C to +125°C Electrical Characteristics (VCC = 5V, TA = 25° C, Unless otherwise specified.) Parameter Symbol Test Conditions Min Typ Max Units VCC Supply Current / Regulated Voltage Nominal Supply Current Regulated Voltage from BOOT Power-On Reset Rising VCC Threshold VCC Threshold Hysteresis Rising VOCSET Threshold Reference Reference Voltage Oscillator Free Running Frequency Ramp Amplitude Error Amplifier DC gain PWM Controller Gate Driver Upper Drive Source Upper Drive Sink Lower Drive Source Lower Drive Sink RUGATE RUGATE RLGATE RLGATE BOOT= 12V BOOT-VUGATE = 1V VUGATE = 1V VCC - VLGATE = 1V, VLGATE = 1V ----7 5 4 2 11 7.5 6 4 Ω Ω Ω Ω 32 35 38 dB ∆ VOSC 250 -300 1.75 350 -k Hz VP-P 0.784 0.8 0.816 V VOCSET = 4.5V VOCSET = 4.5V 3.85 0.3 0.8 4.1 0.5 1.25 4.35 0.7 2.0 V V V ICC VCC UGATE, LGATE open VBOOT = 12V -5 3 6 6 7 mA V To be continued DS9202B-03 March 2007 www.richtek.com 5 RT9202B Parameter Protection FB Over-Voltage Trip FB Under-Voltage Trip OCSET Current Source Soft-Start Interval IOCSET FB Rising FB Falling VOCSET = 4.5V 1.0 -17 1 1.1 0.5 20 2 -0.6 23 4 V V µA ms Symbol Test Conditions Min T yp Max Units Note 1. S tresses listed as the above "Absolute Maximum Ratings" may cause permanent damage to the device. These are for stress ratings. 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 for extended periods may remain possibility to affect device reliability. Note 2. D evices are ESD sensitive. Handling precaution recommended. Note 3. T he device is not guaranteed to function outside its operating conditions. Note 4. θJA is measured in the natural convection at T A = 2 5 ° C on a low effective thermal conductivity test board of JEDEC 51-3 thermal measurement standard. www.richtek.com 6 DS9202B-03 March 2007 RT9202B Typical Operating Characteristic Dead Time VCC = 5V UGATE UGATE Dead Time VCC = 5V LGATE LGATE Time (50ns/Div) Time (50ns/Div) Power On VCC = 5V VOUT = 2.2V VCC Power Off VCC VCC = 5V VOUT = 2.2V VOUT VOUT Time (2.5ms/Div) T ime (50ms/Div) Load Transient UGATE Load Transient UGATE VOUT VCC = 5V VOUT = 2.2V COUT = 3000uF VCC = 5V VOUT = 2.2V COUT = 3000uF VOUT Time (5us/Div) Time (5us/Div) DS9202B-03 March 2007 www.richtek.com 7 RT9202B Bootstrap Wave Form Short Circuit Hiccup VCC = 5V, VOUT = 2.2V UGATE VOUT LGATE PHASE UGATE VCC = 5V, VOUT = 2.2V Time (1us/Div) Time (5ms/Div) Reference vs. Temperature 0.803 0.802 0.801 29 27 25 23 21 19 17 IOCSET v s. Temperature Reference (V) 0.800 0.799 0.798 0.797 0.796 -50 0 50 100 150 I OCSET (uA ) -40 -10 20 50 80 110 140 Temperature (°C) Temperature (°C) POR (Rising/Falling) vs. Temperature 4.3 4.2 4.1 Oscillator Frequency vs. Temperature 315 310 Rising Frequency (kHz) A 305 300 295 290 285 280 275 270 POR (V) 4.0 3.9 3.8 3.7 3.6 -50 0 50 100 150 Falling -50 0 Temperature (°C) www.richtek.com 8 Temperature (°C) 50 100 150 DS9202B-03 March 2007 RT9202B Application Information The RT9202B operates at either single 5V power supply with a bootstrap UGATE driver or 5V/12V dual-power supply form the ATX SMPS. The dual- power supply is recommended for high current application, the RT9202B can deliver higher gate driving current while operating with ATX SMPS based on dual-power supply. The Bootstrap Operation LGATE 5V 6.0V Regulation BOOT C1 1uF UGATE R1 10 12V 5V + VCC VCC In a single power supply system, the UGATE driver of RT9202B is powered by an external bootstrap circuit, as the Figure 1. The boot capacitor, CBOOT , generates a floating reference at the PHASE pin. Typically a 0.1µF CBOOT is enough for most of MOSFETs used with the RT9202B. The voltage drop between BOOT and PHASE is refreshed to a voltage of VCC − diode drop (VD) while the low side MOSFET turning on. R1 VCC C2 1uF D1 5V 0.1uF + C2 1uF RT9202B Figure 2. Dual Power Supply Operation Power On Reset The Power-On Reset (POR) monitors the supply voltage (normal +5V) at the VCC pin and the input voltage at the OCSET pin. The VCC POR level is 4.1V with 0.5V hysteresis and the normal level at OCSET pin is 1.5V (see over-current protection). The POR function initiates soft-start operation after all supply voltages exceed their POR thresholds. Soft Start BOOT UGATE PHASE VCC LGATE RT9202B Figure 1. Single 5V power Supply Operation Dual Power Operation The RT9202B is designed to regulate a 6.0V at VCC pin automatically when BOOT pin is powered by 12V. In a system with ATX 5V/12V power supply, the RT9202B is ideal for higher current application due to the higher gate driving capability, VUGATE = 7V and VLGATE = 6.0V. A RC (10Ω/1µF) filter is also recommended at BOOT pin to prevent the ringing induced from fast power on, as shown in Figure 2. A built-in soft-start is used to prevent surge current from power supply input during power on. The soft-start voltage is controlled by an internal digital counter. It clamps the ramping of reference voltage at the input of error amplifier and the pulse-width of the output driver slowly. The typical soft-start duration is 2ms. Over-Current Protection The over current protection (OCP) function of the RT9202B is triggered when the voltage across the RDS(ON) of upper side MOSFET that developed by drain current exceeds over-current tripping level. An external resistor (ROCSET ) programs the over-current tripping level of the PWM converter. As shown on Figure 3 the internal 20µA current sink (IOCSET ) develops a voltage across ROCSET (VSET ) that is referenced to VIN. The DRIVE signal enables the over-current comparator (OC). When the voltage across the upper MOSFET (VDS(ON)) exceeds VSET , the overcurrent comparator trips to set the over-current latch. www.richtek.com 9 DS9202B-03 March 2007 RT9202B Both VSET and VDS are referenced to VIN and a small capacitor across ROCSET h elps V OCSET t racking the variations of VIN due to MOSFET switching. The overcurrent function will be tripped at a peak inductor current (IPEAK) determined by : I × R OCSET IPEAK = OCSET RDS(ON) COUNT = 1 COUNT = 2 COUNT = 3 In te rn a l SS INDU CTO R C UR RENT 4V 2V 0V OVERLOAD APPLIED The OC trip point varies with MOSFET's R DS(ON) temperature variations. The temperature coefficient of IOCSET is 2500ppm that is used to compensate RDS(ON) temperature variations. To avoid over-current tripping in the normal operating load range, determine the ROCSET resistor value from the equation above with: 1.The maximum R SD(ON) a t the highest junction temperature 2.The minimum IOCSET f rom the characteristics 3.Determine IPEAK for IPEAK > IOUT(MAX) + (∆I)/2 0A T0 T1 T2 TIME T3 Figure 4 Shutdown Pulling low the OCSET pin can shutdown the RT9202B PWM controller as shown in typical application circuit. Inductor Selection The RT9202B was designed for VIN = 5V, step-down application mainly. Figure 5 shows the typical topology and waveforms of step-down converter. The ripple current of inductor can be calculated as follows: where ∆I is the output inductor ripple current. OVER-CURRENT TRIP: VDS > VSET iD × RDS(ON) > IOCSET × ROCSET OCSET IOCSET 20uF DRIVE + OC PHASE GATE CONTROL VIN = +5V ROCSET VSET+ VCC UGATE VDS+ iD ILRIPPLE = (5V - VOUT )/L × TON Because operation frequency is fixed at 300kHz, TON = 3.33 × VOUT /5V The VOUT ripple is VOUT RIPPLE = ILRIPPLE × ESR ESR is output capacitor equivalent series resistor Table 1 shows the ripple voltage of VOUT : VIN = 5V PWM VPHASE = VIN - VDS VOCSET = VIN - VSET Figure 3 Under Voltage and Over Voltage Protection The voltage at FB pin is monitored and protected against OC (over current), UV (under voltage), and OV (over voltage). The UV threshold is 0.5V and OV-threshold is 1.0V. Both UV/OV detection have 30µs triggered delay. When OC or UV trigged, a hiccup re-start sequence will be initialized, as shown in Figure 4. Only 3 times of trigger are allowed to latch off. Hiccup is disabled during softstart interval. www.richtek.com 10 DS9202B-03 March 2007 RT9202B Table 1 VOUT Inductor 1000µF (ESR=53mΩ) 1500µF (ESR=33mΩ) 3000µF (ESR=21mΩ) 2 µH 100mV 62mV 40mV 3.3V 5µ H 40mV 25mV 16mV 2µ H 110mV 68mV 43mV 2.5V 5µ H 44mV 28mV 18mV 2µ H 93mV 58mV 37mV 1.5V 5µ H 37mV 23mV 15mV *Refer to Sanyo low ESR series (CE, DX, PX.....) The suggested L and C are as follows: 2µH with ≥ 1500µF COUT 5µH with ≥ 1000µF COUT Input / Output Capacitor High frequency/long life decoupling capacitors should be placed as close to the power pins of the load as physically possible. Be careful not to add inductance to the PCB trace, as it could eliminate the performance from utilizing these low inductance components. Consult with the manuf acturer of the load on specific decoupling requirements. The output capacitors are necessary for filtering output and stabilizing the close loop (see the PWM loop stability). For powering advanced, high-speed processors, it is required to meet with the requirement of fast load transient, high frequency capacitors with low ESR/ESL capacitors are recommended. Another concern is high ESR induced ripple may trigger UV or OV protections. uQ IL = IO Q L VL VI D C R VO C.C.M TS TON TOFF VI - VO VL - VO iL mIL PWM Loop Stability The RT9202B is a voltage mode buck controller designed for 5V step-down applications. The gain of error amplifier is fixed at 35dB for simplified design. The output amplitude of ramp oscillator is 1.75V, the loop gain and loop pole/zero are calculated as follows : iQ IQ DC loop gain GA = 35dB × 5 × 0.8 1.75 VOUT 1 LC filter pole PO = 2π LC Error Amp pole PA = 300kHz iD ID Figure 5 1 2π ESRC The RT9202B Bode plot as shown Figure 6 is stable in most of application conditions. ESR zero ZO = DS9202B-03 March 2007 www.richtek.com 11 RT9202B Feedback Divider VOUT = 3.3V COUT = 1500µF(33mΩ) L = 2µH 40 VOUT = 1.5V VOUT = 2.5V VOUT = 3.3V PO = 2.9kHz ZO = 3.2kHz 30 20 Loop Gain 10 The reference of RT9202B is 0.8V. The output voltage can be set using a resistor based divider as shown in Figure 9. Put the R1 and R2 as close as possible to FB pin and R2 should less than 1 kΩ to avoid noise coupling. The C1 capacitor is a speed-up capacitor for reducing output ripple to meet with the requirement of fast transient load. Typically a 1nF ~ 0.1µF is enough for C1. VIN 100 1k 10k 100k 1M L Figure 6 Reference Voltage Because RT9202B use a low 35dB gain error amplifier, shown in Figure 7. The voltage regulation is dependent on VIN & VOUT setting. The FB reference voltage of 0.8V were trimmed at VIN = 5V & VOUT = 2.5V condition. In a fixed VIN = 5V application, the FB reference voltage vs. VOUT v oltage can be calculated as Figure 8. R2 FB + R1 1K REP 0.8V + EA VOUT + COUT R1 R2