RT9202 Single Synchronous Buck PWM DC-DC Controller General Description Features The RT9202 is a single power supply PWM DC-DC converter controller designed to drive N-channel MOSFET in a synchronous buck topology. The IC integrates the control, output adjustment, monitoring and protection functions in a small 8-pin package. z The RT9202 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 RT9202 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. z z z z z z z z z z Operate from 5V 0.8V Internal Reference Drive Two N-channel MOSFET Voltage Mode PWM Control Fast Transient Response Fixed 300kHz Oscillator Frequency Full 0~100% Duty Cycle Internal Soft Start Adaptive Non-overlapping Gate Driver Over-current Monitor Uses MOSFET RDS(ON) Over-voltage Protection Uses Low-side MOSFET Pin Configurations Part Number Pin Configurations RT9202CS (Plastic SOP-8) TOP VIEW Applications z z z z z z z z z 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 DS9202-02 August 2002 BOOT 1 8 PHASE UGATE 2 7 OCSET GND 3 6 FB LGATE 4 5 VCC Ordering Information RT9202 Package type S : SOP-8 Operating temperature range C: Commercial standard www.richtek.com 1 RT9202 Typical Application Circuit R1 5V R4 20K 10 D1 8 SHDN H: shutdown BOOT OCSET UGATE MA732 C2 1 0.1µF 7 Q2 2N7002 PHASE RT9202 6 GND FB 5 LGATE VCC C4 1µF 2 3 MU VOUT 2.5V + C3 4 R2 120 255 C6 + C1 470µF 5µH 1000µF R3 C5 1µF L2 ML 10nF Fig.1 RT9202 powered from 5V only R4 12V 10 R1 5V 20K H: shutdown SHDN 8 Q1 2N7002 7 6 PHASE OCSET C2 1µF BOOT 1 UGATE RT9202 GND FB 2 3 MU VOUT 2.5V C5 1µF L1 + C1 470µF 5µH + C3 5 C4 1µF VCC LGATE 4 1000µF R3 R2 120 250 C6 ML 10nF Fig.2 RT9202 powered from 12V www.richtek.com 2 DS9202-02 August 2002 RT9202 MU D + COUT 1000µF CVCC 1µF RT9202 G S CIN1 1µF GND VCC L 5µH + CIN2 470µF CBOOT ML BOOT D 0.1µF G S GND Return Layout Placement Layout Notes 1. Put CIN1 & CIN2 to be near the MU drain and ML source nodes. 2. Put RT9202 to be near the COUT 3. Put CBOOT as close as to BOOT pin 4. Put CVCC as close as to VCC pin DS9202-02 August 2002 www.richtek.com 3 RT9202 Function Block Diagram 6.0V VCC BOOT Regulator Power on Reset Bias 40µA 0.8V Reference Soft Start + OCSET OC_ _ 1V UGATE + OVP _ + Control PWM VCC _ Error Amp PHASE Logic 35dB + _ FB 0.8V Error UVP + 0.5V LGATE GND www.richtek.com 4 300kHz Oscillator DS9202-02 August 2002 RT9202 Absolute Maximum Ratings Supply Voltage VCC 7V BOOT & UGATE to GND 15V z Input, Output or I/O Voltage GND−0.3V ~ 7V z Power Dissipation, PD @ TA = 25°C SOP-8 0.625W z Package Thermal Resistance SOP-8, θJA 160°C/W z Ambient Temperature Range 0°C ~ +70°C z Junction Temperature Range -40°C ~ +125°C z Storage Temperature Range -65°C ~ +150°C z Lead Temperature (Soldering, 10 sec.) 260°C CAUTION: Stresses beyond the ratings specified in “Absolute Maximum Ratings” may cause permanent damage to the device. This is a stress only rating and operation of the device at these or any other conditions above those indicated in the operational sections of this specification is not implied. z z 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 ICC UGATE, LGATE open -- 3 6 mA Regulated Voltage from BOOT VCC VBOOT = 12V 5 6 7 V Power-On Reset Rising VCC Threshold VOCSET = 4.5V 3.85 4.1 4.35 V VCC Threshold Hysteresis VOCSET1 = 4.5V 0.3 0.5 0.7 V 0.8 1.25 2.0 V 0.784 0.8 0.816 V 250 300 350 KHz -- 1.75 -- VP-P 32 35 38 dB Rising VOCSET Threshold Reference Reference Voltage Oscillator Free Running Frequency Ramp Amplitude ∆ VOSC Error Amplifier DC gain PWM Controller Gate Driver Upper Drive Source RUGATE BOOT= 12V BOOT-VUGATE = 1V -- 7 11 Ω Upper Drive Sink RUGATE VUGATE = 1V -- 5 7.5 Ω Lower Drive Source RLGATE VCC - VLGATE = 1V, -- 4 6 Ω Lower Drive Sink RLGATE VLGATE = 1V -- 2 DS9202-02 August 2002 Ω To be continued 4 www.richtek.com 5 RT9202 Parameter Symbol Test Conditions Min Typ Max Units Protection FB Over-Voltage Trip FB Rising 1.0 1.1 -- V FB Under-Voltage Trip FB Falling -- 0.5 0.6 V VOCSET= 4.5V 35 40 45 µA 1 2 4 mS OCSET Current Source IOCSET Soft-Start Interval 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 Nchannel MOSFET when operating at a single 5V power supply. This pin also could be powered from ATX 12V, in this situation, a 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. 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. OCSET (Pin 7) Connect a resistor from this pin to the drain of the respective upper MOSFET. This resistor, an internal 40µA current source, and the upper MOSFET onresistance set the converter over-current trip point. An over-current trip cycles the soft-start 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. IPEAK = IOCSET × ROCSET RDS(ON) PHASE (Pin 8) This pin is used to monitor the voltage drop across the upper MOSFET for over-current protection. VCC (Pin 5) This is the main bias supply for the RT9202. This pin also provides the gate bias charge for the lower MOSFETs gate. The voltage at this pin 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. www.richtek.com 6 DS9202-02 August 2002 RT9202 Typical Operating Charateristics Dead Time Dead Time VCC = 5V VCC = 5V UGATE UGATE LGATE LGATE Time Time Power On Power Off VCC = 5V VOUT = 2.2V VCC VCC VOUT VOUT VCC = 5V VOUT = 2.2V Time Time Load Transient Load Transient UGATE UGATE VCC = 5V VOUT = 2.2V COUT = 3000µF VOUT VCC = 5V VOUT = 2.2V COUT = 3000µF Time DS9202-02 August 2002 VOUT Time www.richtek.com 7 RT9202 Bootstrap Wave Form Short Hiccup VCC = 5V; VOUT = 2.2V VCC = 5V VOUT = 2.2V UGATE VOUT LGATE PHASE UGATE Time Time IOCSET vs. Temperature 55 0.802 50 0.801 45 IOCSET ( µ A) Reference (V) Reference vs. Temperature 0.803 0.800 0.799 40 35 0.798 30 0.797 25 0.796 20 -50 0 50 Temperature ( °C) 100 150 -40 -10 20 50 80 110 140 Temperature (° C) Oscillator Frequency vs. Temperature POR (Rising/Falling) vs. Temperature 4.3 315 4.2 310 Rising 305 Frequency (kHz) POR (V) 4.1 4.0 3.9 3.8 Falling 300 295 290 285 280 3.7 275 3.6 270 -50 0 50 100 Temperature (° C) www.richtek.com 8 150 -50 0 50 100 150 Temperature (° C) DS9202-02 August 2002 RT9202 Functional Description The RT9202 operates at either single 5V power supply with a bootstrap UGATE driver or 5V/12V dual-power supply form the ATX SMPS. The dualpower supply is recommended for high current application, the RT9202 can deliver higher gate driving current while operating with ATX SMPS based on dual-power supply. The Bootstrap Operation In a single power supply system, the UGATE driver of RT9202 is powered by an external bootstrap circuit, as the Fig.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 RT9202. 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 C2 VCC BOOT D1 5V 1µF UGATE 0.1µF + PHASE VCC LGATE RT9202 Fig.1 Single 5V power Supply Operation Dual Power Operation The RT9202 was 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 RT9202 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 Fig.2. DS9202-02 August 2002 VCC 6.0V Regulator R1 BOOT C1 10 12V 5V 1µF + UGATE VCC C2 1µF LGATE RT9202 Fig.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 A built-in soft-start is used to prevent surge current from power supply input during power on. The softstart 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 RT9202 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 Fig.1, the internal 40µA 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 over-current www.richtek.com 9 RT9202 Internal SS The OC trip point varies with MOSFET’s RDS(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 RSD(ON) at the highest junction temperature 2. The minimum IOCSET from the characteristics 3. Determine IPEAK for IPEAK > IOUT(MAX) + (∆I)/2 COUNT = 1 COUNT = 2 4V INDUCTOR CURRENT comparator trips to set the over-current latch. Both VSET and VDS are referenced to VIN and a small capacitor across ROCSET helps VOCSET tracking the variations of VIN due to MOSFET switching. The overcurrent function will be tripped at a peak inductor current (IPEAK) determined by: 0V COUNT = 3 2V OVERLOAD APPLIED 0A T0T1 T2 TIME T3 Fig. 4 Shutdown Pulling low the OCSET pin by a small single transistor can shutdown the RT9202 PWM controller as shown in typical application circuit. where ∆I is the output inductor ripple current. OVER-CURRENT TRIP: VDS > VSET iD ×R DS(ON) > IOCSET × ROCSET VIN = +5V OCSET ROCSET IOCSET 40µA VSET+ VDS+ + DRIVE VCC UGATE iD OC _ PHASE GATE PWM VPHASE = VIN - VDS CONTROL VOCSET = VIN - VSET Fig.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 OVthreshold is 1.0V. Both UV/OV detection have 30µS triggered delay. When OC or UV trigged, a hiccup restart sequence will be initialized, as shown in Fig.4. Only 3 times of trigger are allowed to latch off. Hiccup is disabled during soft-start interval. www.richtek.com 10 DS9202-02 August 2002 RT9202 Applications Information Inductor Selection The RT9202 was designed for VIN = 5V, step-down application mainly. Fig.5 shows the typical topology and waveforms of step-down converter. L Q VL D VI The ripple current of inductor can be calculated as follows: ILRIPPLE = (5V - VOUT)/L × TON C R VO C.C.M. TS Because operation frequency is fixed at 300kHz, TON = 3.33 × VOUT/5V The VOUT ripple is VOUT RIPPLE = ILRIPPLE × ESR TON TOFF VI - VO VL ESR is output capacitor equivalent series resistor - VO Table 1 shows the ripple voltage of VOUT: VIN = 5V iL µQ IL = IO µIL iQ IQ iD ID Fig.5 Table 1 VOUT 3.3V 2.5V 1.5V Inductor 2µH 5µH 2µH 5µH 2µH 5µH 1000µF (ESR=53mΩ) 100mV 40mV 110mV 44mV 93mV 37mV 1500µF (ESR=33mΩ) 62mV 25mV 68mV 28mV 58mV 23mV 3000µF (ESR=21mΩ) 40mV 16mV 43mV 18mV 37mV 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 DS9202-02 August 2002 www.richtek.com 11 RT9202 Reference Voltage Because RT9202 use a low 35dB gain error amplifier, shown in Fig. 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 voltage can be calculated as Fig. 8. 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. I3 56K EA + PWM _ _ 5 0.8 × 1.6 VOUT 1 LC filter pole PO = × π × LC 2 1K + The output amplitude of ramp oscillator is 1.6V, the loop gain and loop pole/zero are calculated as follows: I2 REP 0.8V RAMP 1.75V Fig. 7 Another concern is high ESR induced ripple may trigger UV or OV protections. 0.82 VIN = 5V 0.81 FB (V) PWM Loop Stability The RT9202 is a voltage mode buck controller designed for 5V step-down applications. The gain of error amplifier is fixed at 35dB for simplified design. + FB _ 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 manufacturer of the load on specific decoupling requirements. 0.80 0.79 0.78 0.5 1 1.5 2 2.5 3 3.5 4 4.5 VOUT (V) DC loop gain GA = 35dB × Fig. 8 Error Amp pole PA = 300kHz ESR zero ZO = 1 × π × ESR × C 2 The RT9202 Bode plot as shown Fig.6 is stable in most of application conditions. VOUT = 3.3V COUT = 1500µF(33mΩ) L=2µH 40 VOUT = 1.5V PO = 2.9kHz VOUT = 2.5V 30 Feedback Divider The reference of RT9202 is 0.8V. The output voltage can be set using a resistor based divider as shown in Fig.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. ZO = 3.2kHz VOUT = 3.3V 20 Loop Gain 10 100 1k 10k 100k 1M Fig. 6 www.richtek.com 12 DS9202-02 August 2002 RT9202 especially the high-frequency ceramic decoupling capacitors, close to the power switches. Place the output inductor and output capacitors between the MOSFETs and the load. Also locate the PWM controller near by MOSFETs. VIN L VOUT + C OUT C1 RT9202 R1 FB R2 < 1K Fig. 9 PWM Layout Considerations MOSFETs switch very fast and efficiently. The speed with which the current transitions from one device to another causes voltage spikes across the interconnecting impedances and parasitic circuit elements. The voltage spikes can degrade efficiency and radiate noise, that results in ocer-voltage stress on devices. Careful component placement layout and printed circuit design can minimize the voltage spikes induced in the converter. Consider, as an example, the turn-off transition of the upper MOSFET prior to turn-off, the upper MOSFET was carrying the full load current. During turn-off, current stops flowing in the upper MOSFET and is picked up by the low side MOSFET or Schottky diode. Any inductance in the switched current path generates a large voltage spike during the switching interval. Careful component selections, layout of the critical components, and use shorter and wider PCB traces help in minimizing the magnitude of voltage spikes. A multi-layer printed circuit board is recommended. Fig.10 shows the connections of the critical components in the converter. Note that the capacitors CIN and COUT each of them represents numerous physical capacitors. Use a dedicated grounding plane and use vias to ground all critical components to this layer. Apply another solid layer as a power plane and cut this plane into smaller islands of common voltage levels. The power plane should support the input power and output power nodes. Use copper filled polygons on the top and bottom circuit layers for the PHASE node, but it is not necessary to oversize this particular island. Since the PHASE node is subjected to very high dV/dt voltages, the stray capacitance formed between these island and the surrounding circuitry will tend to couple switching noise. Use the remaining printed circuit layers for small signal routing. The PCB traces between the PWM controller and the gate of MOSFET and also the traces connecting source of MOSFETs should be sized to carry 2A peak currents. VOUT 5V + There are two sets of critical components in a DC-DC converter using the RT9202. The switching power components are most critical because they switch large amounts of energy, and as such, they tend to generate equally large amounts of noise. The critical small signal components are those connected to sensitive nodes or those supplying critical bypass current. IL IQ1 Q1 + IQ2 + LOAD Q2 GND LGATE VCC UGATE GND RT9202 FB Fig. 10 The power components and the PWM controller should be placed firstly. Place the input capacitors, DS9202-02 August 2002 www.richtek.com 13 RT9202 Package Information H A M J B F C D I Dimensions In Millimeters Symbol www.richtek.com 14 Dimensions In Inches Min Max Min Max A 4.801 5.004 0.189 0.197 B 3.810 3.988 0.150 0.157 C 1.346 1.753 0.053 0.069 D 0.330 0.508 0.013 0.020 F 1.194 1.346 0.047 0.053 H 0.178 0.254 0.007 0.010 I 0.102 0.254 0.004 0.010 J 5.791 6.198 0.228 0.244 M 0.406 1.270 0.016 0.050 DS9202-02 August 2002 RT9202 DS9202-02 August 2002 www.richtek.com 15 RT9202 RICHTEK TECHNOLOGY CORP. RICHTEK TECHNOLOGY CORP. Headquarter Taipei Office (Marketing) 5F, No. 20, Taiyuen Street, Chupei City 8F-1, No. 137, Lane 235, Paochiao Road, Hsintien City Hsinchu, Taiwan, R.O.C. Taipei County, Taiwan, R.O.C. Tel: (8863)5526789 Fax: (8863)5526611 Tel: (8862)89191466 Fax: (8862)89191465 Email: [email protected] www.richtek.com 16 DS9202-02 August 2002