NX2837CUPTR

Evaluation board available SINGLE SUPPLY SYNCHRONOUS PWM CONTROLLER WITH FIXED 5V OUTPUT AND 3.3V/700mA LDO Pb Free Product DESCRIPTION The NX2837 controller IC is a single power supply synchronous Buck controller IC designed for step down DC to DC converter applications. NX2837 is optimized to convert bus voltages from 9V to 22V to fixed 5V output. This switching 5V output is the input supply of an internal 3.3V LDO which can provide output current up to 700mA. An internal regulator converts bus voltage to 5V, which provides voltage supply to internal logic and driver circuit. The NX2837 operates at 350kHz and employs fixed loss-less current limiting by sensing the Rdson of synchronous MOSFET followed by hiccup feature.Feedback under voltage triggers Hiccup. Other features of the device are: Internal schottky diode, 3.3V LDO power good indicator, Thermal shutdown, 5V gate drive, Adaptive deadband control, Internal digital soft start, Vcc undervoltage lock out and Shutdown capability via the comp pin. FEATURES Single supply voltage from 9V to 22V Internal 5V regulator Fixed 350kHz working frequency Internal Digital Soft Start Function Fixed 5V switching output Internal 700mA 3.3VLDO with Power Goood indicator Prebias Startup Less than 50 nS adaptive deadband Fixed current limit triggers hiccup by sensing Rdson of Synchronous MOSFET n Pb-free and RoHS compliant n n n n n n n n n APPLICATIONS LCD TV Graphic Card on board converters On board DC to DC application Hard Disk Drive Set Top Box n n n n n TYPICAL APPLICATION 220uF 6 VIN 5 10u BST 7 PGOOD 10k 10 10u 3 0.1u HDRV 2 5VREG NX2837 1u AO4800(half) 10uH SW 1 VOUT +5V@3A 1000uF LDRV 4 OUT5 LDO3 VIN +12V COMP AO4800(half) 9 4.7u 8 Patent Pending 28k GND(PAD) 33p 4.7n Figure1 - Typical application of 2837 ORDERING INFORMATION Device NX2837CUPTR Temperature 0 to 70oC Package MSOP-EP-10L Frequency 350kHz Pb-Free Yes Package Marking : NX2837XXX XXX is date code. For example, 735 means that this NX2837 is packaged in the 35th week of 2007 Rev 2.2 06/19/08 1 ABSOLUTE MAXIMUM RATINGS(NOTE1) 5VREG to GND & BST to SW voltage .............. 6.5V BST to GND Voltage ...................................... 30V VIN to GND Voltage ........................................ 25V SW to GND .................................................... -2V to 30V All other pins .................................................. -0.3V to 6.5V Storage Temperature Range ............................. -65oC to 150oC Operating Junction Temperature Range ............. -40oC to 125oC NOTE1: Stresses above those listed 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. PACKAGE INFORMATION 10-LEAD PLASTIC MSOP-EP θJA ≈ 46o C/W SW 1 10 LDO3 HDRV 2 BST 3 9 OUT5 GND (PAD) LDRV 4 5VREG 5 8 COMP 7 PGOOD 6 VIN ELECTRICAL SPECIFICATIONS Unless otherwise specified, these specifications apply over Vin = 12V, and T A =0 to 70oC. Followings are bypass capacitors:CVIN=1uF, C 5VREG=10uF, C LDO3=10uF, all X5R ceramic capacitors. Typical values refer to TA = 25oC. Low duty cycle pulse testing is used which keeps junction and case temperatures equal to the ambient temperature. PARAMETER OUT5 Voltage OUT5 Voltage SYM V5 OUT5 Voltage line regulation 5V REG 5VREG Output 5VREG UVLO 5VREG UVLO Hysteresis 5VREG Line Regulation Test Condition Input Voltage Current (Dynamic) Rev 2.2 06/19/08 TYP MAX Units 4.75 5 5.24 15 V VIN =9V to 22V 10 mV 5V REG rising 5 3.9 0.2 5.4 4.4 V V V VIN =9V to 30V 10 30 mV 4.8 5VREG Max Current Supply Voltage(Vin) Vin Voltage Range Input Voltage Current(Static) Min 20 Vin 50 9 No switching Switching with HDRV and LDRV open mA 30 3 3.9 5.3 3.5 4 6 V mA mA 2 PARAMET ER Vin UVLO V in-Threshold SYM Test Condition Min TYP MAX Units 6 6.5 7.5 V V in_UVLO VCC Rising V in-Hysteresis SS V in_Hyst VCC Falling Soft Start time Oscillator (Rt) Frequency Tss 2.4 2.9 3.4 mS FS 290 1.4 78 350 410 1.9 90 kHz Ramp-Amplitude Voltage Max Duty Cycle Min Controlable On Time V RAMP Output Impedance , Sinking Rise Time Fall Tim e Deadband Time Low Side Driver (C L=2200pF) Output Impedance, Sourcing Current Output Impedance, Sinking Current Rise Time Fall Tim e Deadband Time Rev 2.2 06/19/08 V % nS 1500 2000 0.3 2500 umho V 2.4 3 3.6 V Rsource(Hdrv) I=200mA 1.9 ohm R sink(Hdrv) I=200mA 1.7 ohm 14 17 30 ns ns ns THdrv(Rise) THdrv(Fall) Tdead(L to H) Ldrv going Low to Hdrv going High, 10%-10% Rsource (Ldrv) I=200mA 1.9 ohm R sink (Ldrv) I=200mA 1 ohm 13 12 10 ns ns ns TLdrv(Rise) TLdrv(Fall) Tdead(H to SW going Low to Ldrv L) going High, 10% to 10% LDO Output Voltage Line regulation Load regulation current lim it OCP OCP threshold 3.3V Power Good T hreshold Voltage as % of Vref Hysteresis Over temperature T hreshold Hysteresis Internal Schottky Diode Forward voltage drop 1.5 83 V 150 Error Amplifiers T ransconductance Comp SD Threshold OUT5 UVLO OUT5 UVLO threshold High Side Driver(C L=2200pF) Output Impedance , Sourcing 0.6 3.23 3.3 5 900 FB ramping up 3.37 10 2 V mV % mA 420 480 625 mV 85 90 5 95 % % 150 20 forward current=20mA 350 o o 500 C C mV 3 PIN DESCRIPTIONS PIN # PIN SYMBOL PIN DESCRIPTION An internal 5V regulator provides supply voltage for the low side fet driver, BST and internal logic circuit. A high frequency 10uF ceramic capacitor must be connected from this pin to the GND pin as close as possible 5 5VREG 6 VIN Voltage supply for the internal 5V regulator. A high freuqncy 1uF ceramic capacitor must be connected from this pin to GND. 9 OUT5 This pin is used to sense the output voltage of converter and regulates the output voltage to 5V. This pin is connected to the output UVLO comparator. When this pin falls below 3V, both HDRV and LDRV outputs are in hiccup.This pin also is the input of internal 3.3V LDO. 8 COMP This pin is the output of the error amplifier and is used to compensate the voltage control feedback loop. This pin is also used as a shut down pin. When this pin is pulled below 0.3V, both drivers are turned off and internal soft start is reset. 3 BST 10 LDO3 1 SW 2 HDRV PAD GND Ground pin. 4 LDRV Low side MOSFET gate driver. 7 PGOOD Rev 2.2 06/19/08 This pin supplies voltage to the high side driver. A high frequency ceramic capacitor of 0.1 to 1 uF must be connected from this pin to SW pin. This pin is the output of internal 3.3V LDO. A minimum of 10uF/X5R capacitor must be connected from this pin to ground to ensure stability. This pin is connected to the source of the high side MOSFET and provides return path for the high side driver. High side MOSFET gate driver. An open drain output that requires a pull up resistor to LDO3 or Vcc. When LDO3 reaches 90% of 3.3V, PGOOD transitions from LO to HI state. 4 BLOCK DIAGRAM VIN 5V Regulator BST 5VREG UVLO HDRV SW COMP 0.3V Control Logic PWM COMP FB OUT5 5VREG PWM generator Thermal Shutdown LDRV Hiccup Logic 0.48V + FB GND LDO3 360mV LDO_3.3V PGOOD logic PGOOD Figure 2 - Simplified block diagram of the NX2837 Rev 2.2 06/19/08 5 Demoboard Design sdfd 12V BUS C1 220u/16V C2 0.1u 5 BST 0.1u 3 VCC C4 0.1u C5 10u HDRV 5 6 VIN 6 C3 R6 2 4 SW LDO3 10 LDO3 VOUT PGOOD N X 2 8 3 7 /M S O P -E P 1 0 10k OUT DO3316P-103 C7 1000u,6.3V,30mohm 7 8 PGOOD 7 L1 SW 1 LDRV LDRV 2 4 M1A AO4800 C8 470p R2 10 1 LDO3 AO4800 3 U1 R1 M3B 0 GND OUT5 700mA power line 9 C9 4.7u LDO3 C6 10u 11 GNDPAD COMP 8 R5 28k C11 4.7n C10 33p Figure 3 - demoboard schematic of NX2837 Rev 2.2 06/19/08 6 Bill of Materials Item 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Rev 2.2 06/19/08 Quantity 1 3 2 1 1 1 1 1 1 1 1 1 1 1 1 C1 C2,C3,C4 C5,C6 C7 C8 C9 C10 C11 L1 M2 R1 R2 R5 R6 U1 Reference Part 220u/16V/ELEC 0.1u 10u,6.3V,X5R 1000u,6.3V,30mohm 470p 4.7u,6.3V,X5R 33p 4.7n DO3316P-103 AO4800 10k 10 28k 0 NX2837/MSOP-EP10 7 Demoboard Waveforms Fig.4 Output ripple(5V@2A,3,3V@650mA) Fig.6 Shutdown Fig.8 step dynamic response(3.3V@no load) Rev 2.2 06/19/08 Fig.5 Startup Fig.7 5V step response(5V@2A step, 3.3V@600mA DC) Fig.9 3.3V dynamic response (3.3V@500mA step, 5V@1A DC) 8 Fig.10 Output efficiency(VIN=12V, VOUT=5V) Rev 2.2 06/19/08 9 APPLICATION INFORMATION Symbol Used In Application Information: VIN - Input voltage VOUT - Output voltage IOUT - Output current = DVRIPPLE - Output voltage ripple FS VIN -VOUT VOUT 1 × × LOUT VIN FS ∆IRIPPLE = ...(2) 12V-5V 5V 1 × × = 0.833A 10uH 12V 350kHz Output Capacitor Selection - Working frequency Output capacitor is basically decided by the DIRIPPLE - Inductor current ripple amount of the output voltage ripple allowed during steady state(DC) load condition as well as specification for the load transient. The optimum design may require a couple Design Example The following is typical application for NX2837, the schematic is figure 1. VIN = 12V condition is determined by equation(3). VOUT=5V FS=350kHz ∆VRIPPLE = ESR × ∆IRIPPLE + IOUT=3A DVRIPPLE