RT9209APS

RT9209/A Synchronous Buck PWM DC-DC with Enable & PGOOD General Description The RT9209/A 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 into a small 8-pin package. The RT9209/A uses an internal compensated 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 260kHz/ 400kHz oscillator reduce the component size for saving board area. The RT9209/A future a enable control pin to shutdown PWM switching and a 90% power good flag indicator. The FB pin under voltage detection function monitor the output short circuit which trigger a three time hiccup sequence to latch off the chip function. Features Operates at 5V 0.8V Internal Reference Drives Two N-MOSFET Voltage Mode PWM Control Fast Transient Response Fixed 260kHz/400kHz Oscillator Frequency Dynamic 0 to 100% Duty Cycle Internal PWM Loop Compensation Internal Soft-Start Adaptive Non-Overlapping Gate Driver Over-Voltage Protection Uses Lower MOSFET RoHS Compliant and 100% Lead (Pb)-Free Applications 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 Ordering Information RT9209/A P ackage Type S : SOP-8 Operating Temperature Range P : Pb Free with Commercial Standard G : Green (Halogen Free with Commercial Standard) 400kHz 260kHz Pin Configurations (TOP VIEW) FB 8 2 3 4 7 6 5 SS PGOOD BOOT UGATE 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. VCC LGATE GND SOP-8 DS9209/A-08 March 2007 www.richtek.com 1 RT9209/A Typical Application Circuit 5V R1 120 R2 250 R3 10K PGOOD 1 2 C3 1uF 3 4 FB VCC LGATE SS PGOOD BOOT 8 7 6 5 C2 0.1uF D1 MU CBOOT 0.1uF A ML L1 VOUT 5uH C4 1000uF C1 470uF GND UGATE RT9209/A Figure A. RT9209/A Booted from 5V 5V R1 120 R2 250 R4 10K PGOOD 1 2 C3 1uF 3 4 FB VCC LGATE SS PGOOD BOOT 8 7 6 5 C2 0.1uF A ML MU L1 VOUT 5uH C4 1000uF C1 470uF GND UGATE RT9209/A R3 12V 10 C5 1uF Figure B. RT9209/A Booted from 12V www.richtek.com 2 DS9209/A-08 March 2007 RT9209/A MU COUT 1000uF GND CVCC 1uF CBOOT VCC BOOT 0.1uF RT9209/A GND Return Diode D L 5uH G S + + CIN1 1uF CIN2 470uF Layout Placement Layout Notes 1. Put CIN1 & CIN2 to be near the MU drain and ML source nodes. 2. Put RT9209/A 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 + PGOOD Soft Start 0.72V 0.8 Reference 1V + OVP 6.5V Regulation BOOT PGOOD SS UGATE 0.5V +UVP 0.8V FB + SS Error Amplifier + +PWM - Control Logic VCC LGATE PWM Loop Compensation GND 260kHz/300kHz Oscillator DS9209/A-08 March 2007 www.richtek.com 3 RT9209/A Functional Pin Description FB (Pin1) 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. VCC (Pin 2) This is the main bias supply for the RT9209/A. 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 6.5V regulator output powered from BOOT pin when BOOT pin is directly powered from ATX 12V. LGATE (Pin 3) Connect LGATE to the PWM converter's lower MOSFET gate. This pin provides the gate drive for the lower MOSFET. GND (Pin 4) Signal and power ground for the IC. All voltage levels are measured with respect to this pin. UGATE (Pin 5) Connect UGATE pin to the PWM converter's upper MOSFET gate. This pin provides the gate drive for the upper MOSFET. BOOT (Pin 6) 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 situation, a internal 6.5V regulator will supply to VCC pin for internal voltage bias. PGOOD (Pin 7) PGOOD is an open collector output used to indicate the status of the PWM converter output voltage. This pin is pulled low when the FB is not over 90% of the reference voltage. SS (Pin 8) Connect a capacitor from this pin to ground. This capacitor, along with an internal 22μA current source, sets the softstart internal of the synchronous PWM converter. Absolute Maximum Ratings Supply Input Voltage, VCC ------------------------------------------------------------------------------------------- 7V BOOT & UGATE to GND --------------------------------------------------------------------------------------------- 19V Input, Output or I/O Voltage ----------------------------------------------------------------------------------------- GND-0.3V to 7V Power Dissipation, PD @ TA = 25°C SOP-8 -------------------------------------------------------------------------------------------------------------------- 0.625W Package Thermal Resistance SOP-8, θJA -------------------------------------------------------------------------------------------------------------- 160° C/W Ambient Temperature Range ---------------------------------------------------------------------------------------- 0°C to +70°C Junction Temperature Range ---------------------------------------------------------------------------------------- 0°C to +125°C Storage Temperature Range ---------------------------------------------------------------------------------------- −65°C to +150°C 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. www.richtek.com 4 DS9209/A-08 March 2007 RT9209/A Electrical Characteristics (VCC = 5V, TA = 25°C, Unless otherwise specified.) Parameter VCC Supply Current Nominal Supply Current Power-On Reset Rising VCC Threshold VCC Threshold Hysteresis 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 Protection FB Over-Voltage Trip FB Under-Voltage Trip Power Good Threshold Power Good Hysteresis Power Good Sink Capability SS Source Current RT9209 RT9209A Symbol Test Conditions Min Typ Max Units ICC UGATE, LGATE open -- 3 6 mA 3.7 0.3 4.1 0.5 4.5 0.7 V V 0.784 0.8 0.816 V 210 350 Δ VOSC -- 260 400 1.75 310 450 -- kHz VP-P 33 35 40 dB RUGATE RUGATE RLGATE RLGATE BOOT= 12V BOOT-VUGATE = 1V VUGATE = 1V VCC - VLGATE = 1V, VLGATE = 1V ----- 7 7 7 3 12 7.5 6 4 Ω Ω Ω Ω FB Rising FB Falling FB pin Rising --86 -- 1 0.6 90 2 --95 -0.4 V V % % V μA IPGOOD = 1mA -12 20 32 DS9209/A-08 March 2007 www.richtek.com 5 RT9209/A Typical Operating Characteristics Dead Time Booted from 5V UGATE UGATE LGATE Dead Time Booted from 5V LGATE IOUT = 0A IOUT = 0A Time (50ns/Div) Time (50ns/Div) Dead Time Booted from 12V UGATE Dead Time Booted from 12V UGATE LGATE LGATE IOUT = 0A IOUT = 0A Time (50ns/Div) Time (50ns/Div) Load Transient UGATE Load Transient UGATE VOUT VCC = 5V VOUT = 2.5V COUT = 1000uF IOUT = 10A to 0A VCC = 5V VOUT = 2.5V COUT = 1000uF IOUT = 0A to 10A VOUT IOUT IOUT Time (10us/Div) Time (10us/Div) www.richtek.com 6 DS9209/A-08 March 2007 RT9209/A Power On Booted from 5V IOUT = 10A CSS = 0.1uF Power Off Booted from 5V IOUT = 10A VCC VOUT VCC VOUT Time (2.5ms/Div) Time (10ms/Div) Power On Booted from 12V IOUT = 10A VCC Power Off Booted from 12V IOUT = 10A VCC VOUT VOUT Time (2.5ms/Div) Time (50ms/Div) Boostrap Waveform Booted from 5V Boostrap Waveform UGATE UGATE LGATE LGATE A node Booted from 12V, A node Time (1us/Div) Time (1us/Div) DS9209/A-08 March 2007 www.richtek.com 7 RT9209/A Short Hiccup Booted from 5V Booted from 12V Short Hiccup UGATE UGATE VOUT VOUT Time (500ms/Div) Time (25ms/Div) VCC vs. VSS IOUT = 10A CSS = 0.1uF PGOOD vs. VOUT VCC PGOOD VSS VOUT Time (5ms/Div) Time (25ms/Div) Reference vs. Temperature 0.808 0.806 0.804 400 410 Oscillator Frequency vs. Temperature Reference (V) 0.802 0.8 0.798 0.796 0.794 0.792 0.79 0.788 -35 -15 5 25 45 65 85 105 125 Frequency (kHz) 390 380 370 360 RT9209A 350 -35 -15 5 25 45 65 85 105 125 Temperature (°C) Temperature (°C) www.richtek.com 8 DS9209/A-08 March 2007 RT9209/A POR(Rising/Falling) vs. Temperature 4.2 4.1 4 Rising POR (V) 3.9 3.8 3.7 Falling 3.6 3.5 -35 -15 5 25 45 65 85 105 125 Temperature (°C) DS9209/A-08 March 2007 www.richtek.com 9 RT9209/A Application Information The RT9209/A operates at either single 5V power supply with a bootstrap UGATE driver or a 5V/12V dual-power supply form the ATX SMPS. The dual- power supply is recommended for high current applications, the RT9209/A can deliver higher gate driving current while operating with ATX SMPS based on a dual-power supply. The Bootstrap Operation In a single power supply system, the UGATE driver of RT9209/A is powered by an external bootstrap circuit, as shown in the Figure1. The boot capacitor, C BOOT , generates a floating reference. Typically a 0.1μF CBOOT is enough for most of MOSFETs used with the RT9209/A. The voltage drop between BOOT and A node is refreshed to a voltage of VCC − diode drop (VD) while the lower MOSFET turning on. C2 1uF LGATE 5V VCC 6.5V Regulator BOOT C1 1uF UGATE R1 10 + 12V 5V A VCC RT9209/A Figure 2. Dual Power Supply Operation Power On Reset The Power-On Reset (POR) monitors the supply voltage (normal +5V) at the VCC pin. The VCC POR level is set to 4.1V with 0.5V hysteresis. 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 soft-start voltage is controlled by an internal 22μA to change a capacitor slowly. It clamps the ramping of reference voltage at the input of error amplifier and the pulse-width of the output driver slowly. Under Voltage and Over Voltage Protection The voltage at FB pin is monitored and protected against OC (over current), and OV (over voltage). The UV threshold is 0.5V and OV-threshold is 1.0V. Both UV/OV detection have 30ms triggered delay. When OC or UV trigged, a hiccup re-start sequence will be initialized, as shown in Figure 3. Only 3 times of trigger are allowed to latch off. Hiccup is disabled during soft-start interval. Shutdown Pulling low the SS pin by a small single transistor can shutdown the RT9209/A PWM controller as shown in typical application circuit. C2 1uF VCC BOOT C1 UGATE 0.1uF + - D1 + 5V A VCC LGATE RT9209/A Figure 1. Single 5V power Supply Operation Dual Power Operation The RT9209/A is designed to supply a regulated 6.5V at VCC pin automatically when BOOT pin is powered by a 12V. In a system with ATX 5V/12V power supply, the RT9209/A is ideal for higher current applications due to the higher gate driving capability, VUGATE = 12V and VLGATE = 6.5V. A RC (10Ω/1μF) filter is also recommended at BOOT pin to prevent the ringing induced from fast poweron, as shown in Figure 2. www.richtek.com 10 DS9209/A-08 March 2007 RT9209/A COUNT = 1 Internal COUNT = 2 COUNT = 3 4V SS Q 2V 0V OVERLOAD L INDUCTOR CURRENT VI D C R VO APPLIED C.C.M. 0A T0 T1 T2 TIME T3 TS TON TOFF VI - VO Figure 3 Inductor Selection The RT9209/A was designed for VIN = 5V, step-down application mainly. Figure 4 shows the typical topology and waveforms of step-down converter. The ripple currents of inductor can be calculated as follows: ILRIPPLE = (5V - VOUT) L × TON iQ VL - VO iL uQ uIL IL = IO Because operation frequency is fixed at 260kHz/400kHz, TON = 3.85 × VOUT 5V , or 2.5 × VOUT 5V IQ The VOUT ripple is VOUT RIPPLE = ILRIPPLE × ESR iD ID ESR is output capacitor equivalent series resistor Figure 4 DS9209/A-08 March 2007 www.richtek.com 11 RT9209/A 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. 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 PWM Loop Stability The RT9209/A 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 1.6V, the loop gain and loop pole/zero are calculated as follows : DC loop gain GA = 35 dB × LC filter pole PO = 1 2 1 2 5 1.6 × π × LC × 0.8 VOUT Feedback Divider The reference of RT9209/A is 0.8V. The output voltage can be set using a resistor based divider as shown in Figure 8. Put the R1 and R2 as close as possible to FB pin and R2 should less than 1 kΩ to avoid noise coupling. VIN Reference Voltage Because RT9209/A use a low 35dB gain error amplifier, shown in Figure 6. 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 Figure 7. R2 FB + R1 1K REF 0.8V 56K EA + RAMP 1.75V + PWM - Figure 6 0.82 VIN = 5V 0.81 FB (V) 0.80 0.79 0.78 0.5 1 1.5 2 2.5 3 VOUT (V) 3.5 4 4.5 Figure 7 Error Amp pole PA = 300kHz ESR zero ZO = × π × ESR × C The RT9209/A Bode plot as shown Figure 5 is stable in most of application conditions. COUT = 1500uF(33mΩ) L = 2uH VOUT = 1.5V PO = 2.9kHz VOUT = 2.5V ZO = 3.2kHz VOUT = 3.3V VOUT = 3.3V A L VOUT + 40 30 20 COUT R1 RT9209/A FB Loop Gain 10 R2 100 1k 10k 100k 1M Figure 5 www.richtek.com 12 Figure 8 DS9209/A-08 March 2007 RT9209/A 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 over-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. There are two sets of critical components in a DC-DC converter using the RT9209/A. 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. The power components and the PWM controller should be placed firstly. Place the input capacitors, 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. A multi-layer printed circuit board is recommended. Figure 9 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 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. IQ1 5V Q1 IQ2 Q2 + IL A + VOUT + CIN GND COUT LOAD GND LGATE VCC RT9209/A UGATE FB Figure 9 DS9209/A-08 March 2007 www.richtek.com 13 RT9209/A Outline Dimension A H M J B F C I D Dimensions In Millimeters Symbol Min A B C D F H I J M 4.801 3.810 1.346 0.330 1.194 0.170 0.050 5.791 0.400 Max 5.004 3.988 1.753 0.508 1.346 0.254 0.254 6.200 1.270 Dimensions In Inches Min 0.189 0.150 0.053 0.013 0.047 0.007 0.002 0.228 0.016 Max 0.197 0.157 0.069 0.020 0.053 0.010 0.010 0.244 0.050 8-Lead SOP Plastic Package Richtek Technology Corporation Headquarter 5F, No. 20, Taiyuen Street, Chupei City Hsinchu, Taiwan, R.O.C. Tel: (8863)5526789 Fax: (8863)5526611 Richtek Technology Corporation Taipei Office (Marketing) 8F, No. 137, Lane 235, Paochiao Road, Hsintien City Taipei County, Taiwan, R.O.C. Tel: (8862)89191466 Fax: (8862)89191465 Email: marketing@richtek.com www.richtek.com 14 DS9209/A-08 March 2007