F72820 F72820 Synchronous Buck PWM DC-DC Controller Release Date: July, 2007 Version: V0.24P Jul 2007 V0.24P F72820 F72820 Datasheet Revision History Version Date Page Revision History 0.21P Mar/2005 0.22P Jun/2005 14 Update application circuit 0.23P Mar/2006 15 Correct application circuit 0.24P Jul 2007 13 Update company address Preliminary version Please note that all data and specifications are subject to change without notice. All the trade marks of products and companies mentioned in this data sheet belong to their respective owners. LIFE SUPPORT APPLICATIONS These products are not designed for use in life support appliances, devices, or systems where malfunction of these products can reasonably be expected to result in personal injury. Customers using or selling these products for use in such applications do so at their own risk and agree to fully indemnify Fintek for any damages resulting from such improper use or sales. Jul 2007 V0.24P F72820 Table of Content 1. General Description ..................................................................................................................... 1 2. Feature List .................................................................................................................................. 1 3. Pin Configuration ......................................................................................................................... 2 4. Block Diagram.............................................................................................................................. 2 5. Pin Description ............................................................................................................................. 3 6. Function Description .................................................................................................................... 4 6.1 Bootstrap Operation ................................................................................................................. 4 6.2 Dual Power Operation.............................................................................................................. 4 6.3 Soft-Start .................................................................................................................................. 5 6.4 Over-current Protection............................................................................................................ 5 6.5 Under-voltage Protection ......................................................................................................... 6 6.6 Output Voltage Selection.......................................................................................................... 7 6.7 Converter Shut Down............................................................................................................... 7 6.8 PWM Controller Feedback Compensation............................................................................... 7 6.9 Typical Characteristic ............................................................................................................... 9 7. Electrical Characteristic.............................................................................................................. 11 8. Ordering Information .................................................................................................................. 12 9. Package Dimensions (8-SOP/150 mil)....................................................................................... 13 10. Application Circuit ...................................................................................................................... 14 Jul 2007 V0.24P F72820 1. General Description The F72820 is a single PWM DC-DC converter controller for application requiring high current such as motherboard, graphic card etc. The F72820 uses voltage mode PWM controller with fast transient response (driving two external N-channel MOSFETs in a synchronous rectified buck converter topology) and integrates some functions such as soft-start, over current and short circuit protections etc. Over current protection is achieved by monitoring the voltage drops across the high side MOSFET without the need for a current sensing resistor and short circuit condition is detected through FB pin. If fault conditions occur, the F72820 will initiate the soft start cycle. After three cycles and the fault conditions persist, the controller will go into shut down status. In shut down status, both gate drive signals will be low. To restart the controller, either recycling the Vcc supply or momentarily pulling OCSET pin below 1.25V. The F72820 is available in 8-SOP package. 2. Feature List Provides one synchronous rectified buck DC-DC PWM controller Fast transient response (high bandwidth error amplifier; full 0~100% duty cycle) Fixed operation frequency : 300KHz Single loop voltage-mode control Few external components Output range adjustable down to 0.8V Operation is under 5V input Drives external N-channel MOSFETs Over current monitor is used by MOSFET RDS(ON) 0.8V internal reference voltage F72820 ±2% accuracy over line, load and temperature Internal soft-start (typically 3 ms) Internal loop compensation Under voltage fault monitoring and protection Over voltage protection 8-SOP package (150 mil) -1- Jul 2007 V0.24P F72820 3. Pin Configuration BOOT UGATE 1 2 GND 3 LGATE 4 F72820 8 7 PHASE OCSET 6 FB 5 VCC 4. Block Diagram Regulator VCC Reference Voltage Bias & SS BOOT Power On Reset 40uA 1.1V OVP OCSET OCP 0.5V Control Logic UVP PHASE 0.8V UGATE Error Amp Comp FB VCC GND LGATE 300KHz Tri-OSC Figure 1: Block Diagram F72820 -2- Jul 2007 V0.24P F72820 VIN BOOT 5V Q1 PWM CONTROLLER VOUT Q2 Figure 2: Simplified power system diagram 5. Pin Description AIN - Input pin(Analog) AOUT - Output pin(Analog) P - Power Pin No Pin Name TYPE 1 BOOT P PWR Description Provide ground reference voltage for high side MOSFET by bootstrap circuit or ATX 12V. 2 UGATE AOUT BOOT Higher gate drive output. Connect this pin to gate of the high side MOSFET 3 GND P 4 LGATE AOUT Power ground pin for the chip VCC Lower gate drive output. Connect this pin to gate of the low side MOSFET 5 VCC P 6 FB AIN IC supply voltage. This voltage is monitored for power-on-reset purpose. VCC Inverting input of the error amplifier used to compensate the feedback loop of the PWM controller. 7 OCSET/SD AOUT/AIN VCC This is multi-function pin. Connecting a resistor from this pin to drain of high side MOSFET and an internal 40uA current source to ground. OCSET voltage is reference for over current detect. When OCSET voltage is under 1.25V, shut down function will be enabled. 8 PHASE AIN VCC Connect to high side MOSFET source and monitor its voltage drop for over current protection. F72820 -3- Jul 2007 V0.24P F72820 6. Function Description The F72820 is a single PWM DC-DC converter controller for application requiring high current such as motherboard, graphic card etc. The F72820 uses voltage mode PWM controller with fast transient response (driving two external N-channel MOSFETs in a synchronous rectified buck converter topology) and integrates some functions such as soft-start, over current and short circuit protections etc. Over current protection is achieved by monitoring the voltage drop across the high side MOSFET, eliminating the need for a current sensing resistor and short circuit condition is detected through the FB pin. If fault conditions occur, the F72820 would initiate the soft start cycle. After three cycles and the fault condition persist, the controller will go into shut down status. In shut down, both gate drive signals will be low. To restart the controller, either recycle the Vcc supply or momentarily pull the OCSET pin below 1.25V. 6.1 Bootstrap Operation In single power supply system, the UGATE is powered by an external bootstrap circuit as Fig 3. The Boot capacitor, CBOOT is charged and generated a floating reference voltage at phase pin. Typically a 0.1uF CBOOT is enough for the most of applications. The CBOOT capacitor is refreshed and charged to a voltage of “VCC – Diode Drop” while low side power MOS turning on. 5V BOOT VCC UGATE Q1 VOUT PHASE LGATE Q2 Fig 3. Single 5V Power Supply Operation. 6.2 Dual Power Operation The F72820 Power-on-reset monitors VCC supply voltage and input voltage at the OCSET pin. POR level is 3.8V with 0.5V hysteresis at VCC voltage and 1.25V at OCSET voltage, The POR function initiates soft-start operation and reset control logic after these supply voltages exceed their POR threshold voltages. F72820 -4- Jul 2007 V0.24P F72820 VCC BOOT Regulator 12V 5V UGATE Q1 VOUT PHASE LGATE Q2 Figure 4 6.3 Soft-Start The POR function initiates the digital soft-start sequence; the soft start function is used to prevent surge current from power supply input during power on. When soft start event, PWM error amplifier reference inputs are forced to track a voltage level proportional to the soft-start voltage. As the soft-start voltage slews up, the PWM comparator regulates the output relative to the tracked soft-start voltage, slowly charging the output capacitor(s), the soft start duration is 3mS in typical case. 6V VCC 3V VOUT 0V 3mS TIME Figure 5 6.4 Over-current Protection The over current protection function of the F72820 is trigger when the voltage across the RDS (ON) of upper side MOSFET the developed by drain current exceeds over-current tripping level. An external resistor (ROCSET) programs the over-current tripping level of the PWM converter. As show on Figure 6, the internal 40uA current sink develops a voltage across ROCSET that is reference to VIN. The over current comparator detect over current event when UGATE is high and PHASE voltage is under OCSET voltage. When OC be detected, over current protect function will soft start three times and check over current again. If over current event is true, the F72820 will be shut down. F72820 -5- Jul 2007 V0.24P F72820 OVER-CURRENT TRIP: VDS > VSET I D x R DS(ON) > I OCSET x R OCSET V PHASE = VIN V OCSET = VIN - VDS VSET OCSET R OCSET I OCSET BOOT 40uA VIN = 5V iD VSET UGATE VDS Q1 OC PHASE VOUT LGATE Q2 Figure 6 6.5 Under-voltage Protection Pins FB are monitored during converter operation by under-voltage (UV) comparators. If the FB voltage drops below 0.5V, a fault signal is generated. The internal fault logic shut down regulator simultaneously when the fault signal triggers a restart. At time t0, VOUT has dropped below 0.5V of the nominal output voltage. Output is quickly shut down and the internal soft-start function begins producing soft-start ramps. The delay interval, t0 to 3*tss, seen by the output is equivalent to three soft-start cycles. After a short delay interval of 10.5ms, the fourth internal soft-start cycle initiates a normal soft-start ramp of the output, at time 3*tss. Both outputs are brought back into regulation by time 4*tss, as long as the UV event has cleared. When the cause of the UV still been present after the delay interval. A fault signal could then be generated and the outputs once again shutdown. 3V 1.5V 0V VOUT t0 tss 2tss 3tss 4tss TIME Delay interval Figure 7 F72820 -6- Jul 2007 V0.24P F72820 6.6 Output Voltage Selection The output voltage of the PWM converter can be programmed to any level between VIN (i.e. 5+V) and the internal reference, 0.8V. An external resistor divider is used to scale the output voltage relative to the reference voltage and feed it back to the inverting input of the error amplifier, see Figure 8. Depending on the value chosen for R1 (the resistor connected between VOUT1 and FB), R4 (the resistor connected from FB to GND) can be calculated based on the following equation: R4 = R1× 0.8V VOUT − 0.8V (EQ1) If the desired output voltage is 0.8V, simply route VOUT back to FB through R1, but do not populate R4. 5V BOOT VCC UGATE Q1 PHASE LGATE FB VOUT Q2 R1 R4 Figure 8: Output voltage selection 6.7 Converter Shut Down Pulling low the OCSET pin by a small signal transistor can shutdown the F72820 PWM controller as show is typical application circuit. 6.8 PWM Controller Feedback Compensation The F72820 is a voltage mode step down PWM controller. The gain of error amp is fixed at 34dB for simplified design and saving external components. The amplitude of internal Tri-wave OSC is 1.75V. The loop gain and loop Zero/Pole are calculated as follow equations. F72820 -7- Jul 2007 V0.24P F72820 5 0.8 × 1.8 Vout 1 DC_Loop_Ga in = 34dB × Pole_of_LC _Filter = 2π LC Pole_of_EA = 130kHz Zero_of_Ou tput_Cap_E SR = 1 2π × ESR × C VIN UGATE VREF Error Amp L comp VOUT LGATE 1.75V ESR C The F72820 Bode plot as shown Figure 9 Gain ( dB ) 40 Cout=1000u ( ESR=30m ) Lout=4.7u Vout=1.6V Pole of LC Filter Zero of Cout ESR 30 20 10 Pole of EA 0.1k F72820 1k 10k 100k f ( Hz ) 1M -8- Jul 2007 V0.24P F72820 6.9 Typical Characteristic Dead time Dead time UGATE UGATE LGATE LGATE Power up Power off UGATE UGATE OCSET OCSET FB VOUT FB VOUT Load transient response Load transient response UGATE UGATE LGATE UGATE VOUT VOUT F72820 -9- Jul 2007 V0.24P F72820 Bootstrap Wave Form Over-Current Protect UGATE UGATE LGATE LGATE BOOT OCSET PHASE VOUT Reference VS Temperature Iocset VS. Temperature 42.5 794.6 Iocset (uA) Reference (mV) 794.8 794.4 794.2 794 42 41.5 41 40.5 793.8 40 25℃ 35℃ 45℃ 55℃ 65℃ 75℃ 85℃ 25℃ 35℃ 45℃ 55℃ 65℃ 75℃ 85℃ Temperature (℃) Temperature (℃) Frequency (kHz) Oscillator Frequency VS. Temperature 316 314 312 310 308 306 304 302 25℃ 35℃ 45℃ 55℃ 65℃ 75℃ 85℃ Temperature (℃) F72820 -10- Jul 2007 V0.24P F72820 7. Electrical Characteristic Absolute Maximum Ratings PARAMETER SYMBOL RATINGS UNIT VCC 7 V 12VCC 15 V IC supply voltage Gate drivers supply voltage PWM controller outputs UGATE, LGATE Feedback voltages of both regulators FB, FB2, COMP GND - 0.3-17 V HBM 2 kV Tj 150 °C TSTO -65 ~ 150 °C 260 °C ESD classification Maximum junction temperature (plastic package) Maximum storage temperature V Maximum lead temperature (soldering 10s) Note: If ICs are stressed beyond the limits listed in the “absolute maximum ratings”, they may be permanently destroyed. These are stress ratings only and functional operation of the device at these or any other condition beyond those indicated under “recommended operating conditions” is not implied. Exposure to absolute maximum rated conditions for extended periods may affect device reliability. Package thermal information PARAMETER SYMBOL SOIC UNIT Rth_ja 133 °C/W Thermal resistance junction-ambient DC and AC electrical characteristics PARAMETER SYMBOL TEST CONDITIONS MIN. TYP. MAX. UNIT 2 4 mA 5.5 6 V 3.8 4.0 V VCC SUPPLY CURRENT/Regulated Voltage Nominal supply current 5VCC ICC UGATE, LGATE and DRIVE2 open Regulated Voltage from BOOT VCC VBOOT = 12V 5.0 POWER-ON RESET Rising VCC threshold VOCSET = 4.5V Falling VCC threshold VOCSET1 = 4.5V Rising VOCSET Threshold 3.1 3.3 V 0.8 1.25 2.0 V 250 300 350 kHz OSCILLATOR AND Protection Free running frequency Ramp Amplitude FB Over Voltage Trip F72820 FOSC VCC=5V △VOSC 1.75 FB Rising -11- 1.0 1.1 * VP-P 1.2 V Jul 2007 V0.24P F72820 PARAMETER SYMBOL MIN. TYP. MAX. UNIT FB Falling 0.4 0.5 0.6 V VOCSET = 4.5V 35 40 45 uA TSS 1 3 6 ms VREF 0.784 0.8 0.816 V FB Under Voltage Trip OCSET Current Source Soft-start interval IOCSET TEST CONDITIONS REFERENCE VOLTAGE Reference voltage PWM CONTROLLER GATE DRIVERS Upper Drive Source RUGATE BOOT = 12V ; BOOT – VUGATE = 1V 8 12 Ω Upper Drive Sink RUGATE VUGATE = 1V 4 6 Ω Lower Drive Source RLGATE VCC – VLGATE = 1V 3 4.5 Ω Lower Drive Sink RLGATE VLGATE = 1V 2 3 Ω Error Amplifier DC Gain 34 * dB Note: Design Guarantee 8. Ordering Information F72820 Part Number Package Type Production Flow F72820 SG 8-SOP (Green Package) Commercial, 0°C to +70°C -12- Jul 2007 V0.24P F72820 9. Package Dimensions (8-SOP/150 mil) 8 5 c E HE L 4 1 0.25 D O A Y e SEATING PLANE GAUGE PLANE A1 b Control demensions are in milmeters . SYMBOL A A1 b c E D e HE Y L θ DIMENSION IN MM MIN. MAX. 1.35 1.75 0.10 0.25 0.33 0.51 0.19 0.25 3.80 4.00 4.80 5.00 1.27 BSC 6.20 5.80 0.10 0.40 1.27 0 10 DIMENSION IN INCH MIN. MAX. 0.053 0.069 0.010 0.004 0.013 0.020 0.008 0.010 0.150 0.157 0.188 0.196 0.050 BSC 0.228 0.016 0 0.244 0.004 0.050 10 Feature Integration Technology Inc. Headquarters Taipei Office 3F-7, No 36, Tai Yuan St., Bldg. K4, 7F, No.700, Chung Cheng Rd., Chupei City, Hsinchu, Taiwan 302, R.O.C. Chungho City, Taipei, Taiwan 235, R.O.C. TEL : 886-3-5600168 TEL : 866-2-8227-8027 FAX : 886-3-5600166 FAX : 866-2-8227-8037 www: http://www.fintek.com.tw Please note that all datasheet and specifications are subject to change without notice. All the trade marks of products and companies mentioned in this datasheet belong to their respective F72820 -13- Jul 2007 V0.24P F72820 10. Application Circuit 14 F72820 15