TPS62750 www.ti.com ....................................................................................................................................................................................................... SLVS955 – JULY 2009 High Efficiency Step-Down Converter for USB Applications FEATURES 1 • • • • • • • • • • • DESCRIPTION Efficiency > 90% at Nominal Operating Conditions Programmable Average Input Current Limits for USB Applications – 50mA to 300mA for Low Current Limit Range – 300mA to 1.3A for High Current Limit Range – ±10% Current Accuracy Stable Output Voltage for Load Transients to Minimize Overshoot at Load Step Response Hot Plug and Reverse Current Protection Automatic PFM/PWM Mode transition VIN Range From 2.9V to 6V Adjustable VOUT From 0.8V to 0.85×VIN Softstart for Inrush Current Prevention 2.25 MHz Fixed Frequency Operation Short Cicruit and Thermal Shutdown Protection Available in a 2.5 × 2.5 10 pin SON Package The TPS62750 device is a highly efficient synchronous step down dc-dc converter optimized for USB powered portable applications. It can provide up to 1300mA average input current and is ideal for applications connected to a USB host. With an input voltage range of 2.9 V to 6.0V, the device supports batteries with extended voltage range and is ideal for powering USB applications where USB compliance is required. The TPS62750 operates at 2.25-MHz fixed switching frequency and enters Power Save Mode operation at light load currents to maintain high efficiency over the entire load current range. Output discharge allows the load to discharge in shutdown. The 10% accurate average input current limit can be programmed with an external resistor, allowing use in applications such as USB, where the current drawn from the bus must be limited to 500mA. The TPS62750 allows the use of small inductors and capacitors to achieve a small solution size. The TPS62750 is available in a 2,5mm × 2,5mm 10-pin SON package. APPLICATIONS • • • USB Wireless Modems Portable USB peripherals Handheld Computers TPS62750 VIN 5.0V VIN 2.2 µH L AV IN EN Ilim_U CIN Ilim_L R3 FB H/L GND PGND L1 VOUT 3.6V R1 R2 Cff CO CBULK R4 1 Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet. PRODUCTION DATA information is current as of publication date. Products conform to specifications per the terms of the Texas Instruments standard warranty. Production processing does not necessarily include testing of all parameters. Copyright © 2009, Texas Instruments Incorporated TPS62750 SLVS955 – JULY 2009 ....................................................................................................................................................................................................... www.ti.com These devices have limited built-in ESD protection. The leads should be shorted together or the device placed in conductive foam during storage or handling to prevent electrostatic damage to the MOS gates. ORDERING INFORMATION (1) TA PART NUMBER (2) OUTPUT VOLTAGE (3) PACKAGE PACKAGE DESIGNATOR ORDERING PACKAGE MARKING -40°C to 85°C TPS62750 Adjustable SON 2.5×2.5 -10 DSK TPS62750DSK NXJ (1) (2) (3) For the most current package and ordering information, see the Package Option Addendum at the end of this document, or see the TI website at www.ti.com The DSK (SON-10) package is available in tape on reel. Add R suffix to order quantities of 3000 parts per reel. Contact TI for other fixed output voltage options ABSOLUTE MAXIMUM RATINGS Over operating free-air temperature range (unless otherwise noted) (1) Input voltage range VIN, AVIN (2) Voltage range at EN, H/L, FB Voltage on L, ILim_U, ILim_L Peak output current VALUE UNIT –0.3 to 7.0 V –0.3 to VIN +0.3, ≤7.0 V –0.3 to 7.0 V Internally limited A HBM Human body model ESD rating (3) 4 CDM Charge device model kV 1.5 200 V Maximum operating junction temperature, TJ Machine model –40 to 125 °C Storage temperature range, Tstg –65 to 150 °C (1) (2) (3) Stresses beyond those listed under absolute maximum ratings may cause permanent damage to the device. These are stress ratings only and functional operation of the device at these or any other conditions beyond those indicated under recommended operating conditions is not implied. Exposure to absolute–maximum–rated conditions for extended periods may affect device reliability. All voltage values are with respect to network ground terminal. The human body model is a 100pF capacitor discharged through a 1.5 kΩ resistor into each pin. The machine model is a 200pF capacitor discharged directly into each pin. DISSIPATION RATINGS (1) (2) PACK AGE THERMAL RESISTANCE RθJA THERMAL RESISTANCE RθJP THERMAL RESISTANCE RθJC POWER RATING FOR TA ≤ 25°C DERATING FACTOR ABOVE TA = 25°C DSK 60.6°C/W 6.3°C/W 40°C/W 1650mW 17mW/°C (1) (2) Maximum power dissipation is a function of TJ(max), θJA and TA. The maximum allowable power dissipation at any allowable ambient temperature is PD = [TJ(max) - TA]/θJA This thermal data is measured with a high-K board (4 layer board according to JESD51-7 JEDEC standard). RECOMMENDED OPERATING CONDITIONS MIN NOM MAX UNIT Supply Voltage VIN 2.9 6 V Output voltage range for adjustable voltage 0.8 0.85 × VIN V Operating ambient temperature, TA –40 85 °C Operating virtual junction temperature, TJ –40 125 °C 2 Submit Documentation Feedback Copyright © 2009, Texas Instruments Incorporated Product Folder Link(s) :TPS62750 TPS62750 www.ti.com ....................................................................................................................................................................................................... SLVS955 – JULY 2009 ELECTRICAL CHARACTERISTICS Over full operating ambient temperature range, typical values are at TA = 25°C. Unless otherwise noted, specifications apply for condition VIN = EN = 5.0V. External components CIN = 10µF 0603, CO = 10µF 0603, CBULK = 1.5mF, L = 2.2µH, refer to parameter measurement information. PARAMETER TEST CONDITIONS MIN TYP MAX UNIT 6.0 V 745 960 µA 0.2 3.0 µA SUPPLY VIN Input Voltage Range IQ Operating Quiescent Current IOUT = 0 mA, device not switching (1) ISD Shutdown Current EN = GND VUVLO 2.9 Falling Undervoltage Lockout Threshold 2.4 V Rising 2.9 V ENABLE, H/L VIH High Level Input Voltage 2.9 V ≤ VIN ≤ 6.0V VIL Low Level Input Voltage 2.9 V ≤ VIN ≤ 6.0 V IIN Input bias Current Pin tied to GND or VIN High side MOSFET On-Resistance (H/L=HI) 1.0 V 0.4 V 0.01 1.0 µA VIN = 5.0 V, VGS = 6.5 V 130 290 mΩ High side MOSFET On-Resistance (H/L=LO) VIN = 5.0 V, VGS = 6.5 V 282 550 mΩ 58 125 mΩ 1500 1800 mA POWER SWITCH RDS(ON) Low Side MOSFET On-Resistance VIN = VGS = 5.0 V ILIMF Forward Current Limit High-Side and Low side VIN = VGS = 5.0 V IIN(MAX) Programmable Input current Range ILIM_U selected, H/L = High 300 1300 ILIM_L selected, H/L = Low 50 300 –10 10 ILIM_U selected, Current limit accuracy TSD 1200 mA % Thermal shutdown Increasing junction temperature 150 °C Thermal shudown hysteresis Decreasing junction temperature 20 °C OSCILLATOR fSW Oscillator Frequency 2.9 V ≤ VIN ≤ 6.0 V 2.0 2.25 2.5 MHz OUTPUT VOUT Adjustable Output Voltage Range Vref Reference Voltage VFB(PWM) Feedback Voltage PWM operation, 2.9 V ≤ VIN ≤ 6.0V (2) R(DIS_CH) Internal discharge resistor Activated with EN = GND (1) 0.8 0.85 × VIN 600 –1.5% 85 V mV 1.5% 235 300 Ω In PFM mode, the internal reference voltage is set to typ. 1.01 × Vref. See the parameter measurement information. Submit Documentation Feedback Copyright © 2009, Texas Instruments Incorporated Product Folder Link(s) :TPS62750 3 TPS62750 SLVS955 – JULY 2009 ....................................................................................................................................................................................................... www.ti.com DEVICE INFORMATION PIN ASSIGNMENTS DSK PACKAGE (TOP VIEW) 10 AD 1 9 4 Po 3 we r P 2 5 8 7 6 PIN FUNCTIONS PIN I/O DESCRIPTION NAME NO. PGND 1 L 2 OUT H/L 3 IN H/L pin = high enables the upper current limit threshold set by RSET_H. H/L pin = low enables the lower current limit threshold set by RSET_L. This pin must be terminated. EN 4 IN This is the enable pin of the device. Pulling this pin to low forces the device into shutdown mode. Pulling this pin to high enables the device. This pin must be terminated. FB 5 IN Feedback Pin for the internal regulation loop. Connect the external resistor divider to this pin. In case of fixed output voltage option, connect this pin directly to the output capacitor AGND 6 ISET_L 7 IN Sets the lower average input current limit by external resistor. ISET_U 8 IN Sets the upper average input current limit by external resistor. PVIN 9 IN VIN power supply pin for the Output stage AVIN 10 IN VIN low noise analog supply for the internal analog circuitry. This pin must be connected to PVIN 4 Power GND Pin for the N-MOSFET This is the switch pin and is connected to the internal MOSFET switches. Connect the external inductor between this terminal and the output capacitor. Analog GND Pin for the internal analog circuitry. Submit Documentation Feedback Copyright © 2009, Texas Instruments Incorporated Product Folder Link(s) :TPS62750 TPS62750 www.ti.com ....................................................................................................................................................................................................... SLVS955 – JULY 2009 FUNCTIONAL BLOCK DIAGRAM ILIM_L SOFTSTART ILIM_U AVIN Current Limit Comparator Undervoltage Lockout 1.8V Thermal Shutdown PVIN Limit High Side EN FB PFM Comparator VREF H/L Control Logic L Gate Driver Anti Shoot-Through Control Stage Error Amp. VREF Integrator FB Zero-Pole AMP. Reference 0.6V VREF VREF Sawtooth Generator PWM Comp. Limit Low Side Current Limit Comparator 3MHz Clock SHUTDOWN DRIVER AGND RDischarge PGND Submit Documentation Feedback Copyright © 2009, Texas Instruments Incorporated Product Folder Link(s) :TPS62750 5 TPS62750 SLVS955 – JULY 2009 ....................................................................................................................................................................................................... www.ti.com PARAMETER MEASUREMENT INFORMATION TPS62750 VIN 5.0V VIN 2.2 µH L L1 AV IN EN FB H/L GND PGND Ilim_U CIN Ilim_L R3 VOUT 3.6V R1 R2 Cff CO CBULK R4 List of Components COMPONENT REFERENCE PART NUMBER MANUFACTURER VALUE 10µF CIN GRM188R60J106M Murata COUT GRM188R60J106M Murata 10µF Cff C1608C0G1H471J TDK 470pF 6TPG150M Sanyo POSCAP 10 × 150µF 592D158X06R3X2T25H Vishay 1.5mF LPS3015-222ML Coilcraft 2.2µH CBULK L1 6 R1, R2 Depending on output voltage required. Equation 1 can be used to calculate the output voltage with different R1 and R2 values. R3, R4 Depending on the upper and lower current limits required. Equations 7 and 8 can be used for these calculations. Submit Documentation Feedback Copyright © 2009, Texas Instruments Incorporated Product Folder Link(s) :TPS62750 TPS62750 www.ti.com ....................................................................................................................................................................................................... SLVS955 – JULY 2009 TYPICAL CHARACTERISTICS TABLE OF GRAPHS Figure Maximum Output Current vs Input voltage Figure 1 Efficiency vs Output Current, Vin = [4.0V; 4.5V; 5.0V; 5.5V], Vout = 3.6V, H/L = High Figure 2 vs Output Current, Vin = [4.0V; 4.5V; 5.0V; 5.5V], Vout = 3.6V, H/L = Low Figure 3 vs Output Current, Vin = [4.0V; 4.5V; 5.0V; 5.5V], Vout = 2.5V, H/L = High Figure 4 vs Output Current, Vin = [4.0V; 4.5V; 5.0V; 5.5V], Vout = 2.5V, H/L = Low Figure 5 vs Input Voltage, Vout = 3.6V, Iout = [200mA, 400mA, 500mA, 700mA, 1000mA] Figure 6 Input Current vs Output Current, Vout =3.6V, Vin = [4.0V; 4.5V; 5.0V; 5.5V] Figure 7 Output Voltage vs Output Current, Vout = 3.6V, Vin = [4.5V; 5.0V; 5.5V], H/L = High Figure 8 Waveforms vs Output Current, Vout = 3.6V, Vin = [4.5V; 5.0V; 5.5V], H/L = Low Figure 9 vs Input Voltage, Iload = 300mA, Vout = 3.6V H/L=high Figure 10 vs Input Voltage, Iload = 500mA, Vout = 3.6V H/L=high Figure 11 vs Input Voltage, Iload = 100µA, Vout = 3.6V H/L=low Figure 12 vs Input Voltage, Iload = 80mA, Vout = 3.6V H/L=low Figure 13 Output Voltage Ripple, PFM Mode Iout = 50mA Figure 14 Output Voltage Ripple, PWM Mode Iout = 500mA Figure 15 Load Transient Vin = 5.0V, Vout = 3.6V, H/L = High, 50mA - 2A & 2A - 50mA, Pulse Load period = 4.6ms, duty cycle 12.5% Figure 16 Load Transient Vin = 5.0V, Vout = 3.6V, H/L = High, 50mA - 2A & 2A - 50mA, Pulse Load period = 4.6ms, duty cycle 25% Figure 17 Line Transient, Vin = 4.5V - 5.0V, Iout = 80mA, H/L = Low Figure 18 Line Transient, Vin = 4.5V - 5.0V, Iout = 200mA, H/L = Low Figure 19 Line Transient, Vin = 4.5V - 5.0V, Iout = 500mA, H/L = High Figure 20 Average Input current Limit vs RLIM_L Figure 21 Average Input current Limit vs RLIM_U Figure 22 Startup after Enable, Vin = 5.0V, Vout = 3.6V, Load = 80mA, H/L=Low Figure 23 Startup after Enable, Vin = 5.0V, Vout = 3.6V, Load = 500mA, H/L=High Figure 24 Output Discharge, Vin = 5.0V, Vout = 3.6V, No Load Figure 25 100 1000 950 900 VO = 3.6 V, H/L = High Imax = 25°C 800 750 VI = 4 V VI = 4.5 V 70 Imax = 85°C 700 650 600 550 500 60 50 40 450 30 400 350 20 300 250 200 2.9 VI = 5.5 V 80 Efficiency - % IO - Output Current - mA 850 VI = 5 V 90 Imax = -40°C VO = 3.6 V, H/L = High 10 3.3 3.7 4.1 4.5 4.9 5.3 VI - Output Voltage - V 5.7 0 0.2 Figure 1. Maximum Output Current 0.4 0.6 0.8 1 1.2 IO - Output Current - A 1.4 Figure 2. Efficiency vs Output Current Submit Documentation Feedback Copyright © 2009, Texas Instruments Incorporated Product Folder Link(s) :TPS62750 1.6 7 TPS62750 SLVS955 – JULY 2009 ....................................................................................................................................................................................................... www.ti.com 100 100 70 VI = 4 V 70 VI = 5.5 V 50 40 VI = 4.5 V 50 40 30 20 20 10 10 0.01 0.1 0.001 IO - Output Current - A VI = 3.5 V 60 30 0 0.0001 VI = 5 V 80 VI = 5 V 60 VI = 5.5 V 90 VI = 4.5 V 80 Efficiency - % VI = 4 V Efficiency - % 90 VO = 3.6 V, H/L Pin = Low VO = 2.5 V, H/L Pin = High 0 0.2 1 0.4 Figure 3. Efficiency vs Output Current VI = 3.5 V 60 50 90 VI = 4 V 80 VI = 4.5 V 70 VI = 5 V Efficiency - % 70 Efficiency - % 1.6 100 VO = 2.5 V, H/L Pin = Low 80 VI = 5.5 V 40 1A 400 mA 40 20 20 10 10 1 700 mA 500 mA 50 30 0.001 0.01 0.1 IO - Output Current - A 200 mA 60 30 0 0.0001 0 2.9 Figure 5. Efficiency vs Output Current 8 1.4 Figure 4. Efficiency vs Output Current 100 90 0.6 0.8 1 1.2 IO - Output Current - A Submit Documentation Feedback VO = 3.6 V, H/L Pin = High 3.4 3.9 4.4 4.9 VI - Input Voltage - V 5.4 5.9 Figure 6. Efficiency vs Input Voltage Copyright © 2009, Texas Instruments Incorporated Product Folder Link(s) :TPS62750 TPS62750 www.ti.com ....................................................................................................................................................................................................... SLVS955 – JULY 2009 3.7 0.6 VO = 3.6 V, H/L Pin = High VO = 3.6 V, H/L Pin = High 0.5 VO - Output Voltage DC - V II - input Current - A VI = 4 V VI = 4.5 V 0.4 VI = 5 V VI = 5.5 V 0.3 0.2 3.6 VI = 4.5 V VI = 5 V 3.5 VI = 5.5 V 0.1 0 0.2 0.4 0.6 0.8 1 1.2 IO - Output Current - A 1.4 3.4 0.2 1.6 Figure 7. Input Current vs Output Current 3.7 0.4 0.5 0.6 IO - Output Current - A 0.7 0.8 Figure 8. Output Voltage vs Output Current 3.744 VO = 3.6 V, H/L Pin = Low 3.708 VO = 3.6 V, Iload = 300 mA, H/L Pin = High Limit +3% 3.672 3.6 VO - Output Voltage - V VO - Output Voltage DC - V 0.3 3.636 VI = 5 V VI = 5.5 V 3.5 VI = 4.5 V 3.6 25°C 85°C 3.564 - 40°C 3.528 Limit -3% 3.492 3.4 0.0001 3.456 3.6 3.8 0.1001 IO - Output Current - A Figure 9. Output Voltage vs Output Current 4 4.2 4.4 4.6 4.8 5 5.2 5.4 5.6 5.8 VI - Input Voltage - V 6 Figure 10. Output Voltage vs Input Voltage Submit Documentation Feedback Copyright © 2009, Texas Instruments Incorporated Product Folder Link(s) :TPS62750 9 TPS62750 SLVS955 – JULY 2009 ....................................................................................................................................................................................................... www.ti.com 3.744 3.744 Limit +3% Limit +3% 3.708 3.708 3.636 3.6 3.564 3.672 VO = 3.6 V, Iload = 500 mA, H/L Pin = High VO - Output Voltage - V VO - Output Voltage - V 3.672 Iload = 100 mA, H/L Pin = High 3.636 25°C - 40°C 3.6 25°C 3.564 85°C 3.528 VO = 3.6 V, - 40°C 3.528 85°C Limit -3% Limit -3% 3.492 3.492 3.456 3.6 3.8 4 4.2 4.4 4.6 4.8 5 5.2 5.4 5.6 5.8 VI - Input Voltage - V 6 Figure 11. Output Voltage vs Input Voltage 3.456 3.6 3.8 4 4.2 4.4 4.6 4.8 5 5.2 5.4 5.6 5.8 VI - Input Voltage - V 6 Figure 12. Output Voltage vs Input Voltage 3.744 VIN = 5 V, VOUT = 3.6 V, IOUT = 50 mA Limit +3% 3.708 VO - Output Voltage - V 3.672 VO = 3.6 V, Iload = 80 mA, H/L Pin = Low 3.636 3.6 VOUT = 10 mV/div - 40°C 3.564 25°C 85°C 3.528 Limit -3% 3.492 ICOIL = 100 mA/div 3.456 3.6 3.8 4 4.2 4.4 4.6 4.8 5 5.2 5.4 5.6 5.8 VI - Input Voltage - V Figure 13. Output Voltage vs Input Voltage 10 t - Time - 400 ns/div 6 Figure 14. Output Voltage Ripple – PFM Mode Submit Documentation Feedback Copyright © 2009, Texas Instruments Incorporated Product Folder Link(s) :TPS62750 TPS62750 www.ti.com ....................................................................................................................................................................................................... SLVS955 – JULY 2009 VIN = 5 V, VOUT = 3.6 V, IOUT = 500 mA VOUT = 200 mV/div IIN = 500 mA/div VOUT = 10 mV/div ICOIL = 200 mA/div VIN = 5 V, VOUT = 3.6 V, IOUT = 50 mA - 2A ICOIL = 100 mA/div t - Time - 1 ms/div Figure 16. Load Transient t - Time - 400 ns/div Figure 15. Output Voltage Ripple – PWM Mode VOUT = 200 mV/div IIN = 500 mA/div IIN = 200 mV/div VOUT = 10 mV/div ICOIL = 200 mA/div VIN = 5 V, VOUT = 3.6 V, IOUT = 50 mA - 2 A VIN = 4.5 V - 5 V, VOUT = 3.6 V, IOUT = 80 mA t - Time - 1 ms/div t - Time - 1 ms/div Figure 18. Line Transient Figure 17. Load Transient VIN =200 mV/div VIN = 200 mV/div VOUT = 10 mV/div VOUT = 10 mV/div VIN = 4.5 V - 5 V, VOUT = 3.6 V, IOUT = 200 mA VIN = 4.5 V - 5 V, VOUT = 3.6 V, IOUT = 500 mA t - Time - 1 ms/div Figure 20. Line Transient t - Time - 1 ms/div Figure 19. Line Transient Submit Documentation Feedback Copyright © 2009, Texas Instruments Incorporated Product Folder Link(s) :TPS62750 11 TPS62750 SLVS955 – JULY 2009 ....................................................................................................................................................................................................... www.ti.com 1.4 Average Input Current Limit - A Average Input Current Limit - A 0.3 0.25 0.2 0.15 0.1 0.05 0 0 1.2 1 0.8 0.6 0.4 0.2 0 60 80 40 100 120 140 RLIM_L - Lower Limit Resistance - kW 20 0 Figure 21. Average Input Current Limit 20 40 60 80 100 RLIM_U - Upper Limit Resistance - kW Figure 22. Average Input Current Limit EN = 200 mV/div EN = 5 V/div VOUT = 1 mV/div VOUT = 1 mV/div VIN = 5 V, VOUT = 3.6 V, IOUT = 80 mA ICOIL = 100 mA/div ICOIL = 200 mA/div IIN = 50 mA/div IIN = 100 mA/div VIN = 5 V, VOUT = 3.6 V, IOUT = 500 mA t - Time - 10 ms/div Figure 24. Startup After Enable t - Time - 10 ms/div Figure 23. Startup After Enable EN = 5 V/div VIN = 5 V, VOUT = 3.6 V, IOUT = no load VOUT = 1 mV/div ICOIL = 200 mA/div t - Time - 200 ms/div Figure 25. Output Discharge 12 Submit Documentation Feedback Copyright © 2009, Texas Instruments Incorporated Product Folder Link(s) :TPS62750 TPS62750 www.ti.com ....................................................................................................................................................................................................... SLVS955 – JULY 2009 DETAILED DESCRIPTION OPERATION The TPS62750 step down converter operates with typically 2.25MHz fixed frequency pulse width modulation (PWM) at moderate to heavy load currents. At light load currents the converter can automatically enter Power Save Mode and operates then in PFM (Pulse Frequency Mode) mode. During PWM operation, the converter uses a unique fast response voltage mode controller scheme with input voltage feed-forward to achieve good line and load regulation allowing the use of small ceramic input and output capacitors. At the beginning of each clock cycle initiated by the clock signal, the High Side MOSFET switch is turned on. The current flows from the input capacitor via the High Side MOSFET switch through the inductor to the output capacitor and load. During this phase, the current ramps up until the PWM comparator trips and the control logic will turn off the switch. The current limit comparator will also turn off the switch in case the current limit of the High Side MOSFET switch is exceeded. After a dead time preventing shoot through current, the Low Side MOSFET rectifier is turned on and the inductor current will ramp down. The current flows now from the inductor to the output capacitor and to the load. It returns back to the inductor through the Low Side MOSFET rectifier. The next cycle will be initiated by the clock signal again turning off the Low Side MOSFET rectifier and turning on the on the High Side MOSFET switch. POWER SAVE MODE If the load current decreases, the converter will enter Power Save Mode operation automatically. During Power Save Mode the converter skips switching and operates with reduced frequency in PFM mode with a minimum quiescent current to maintain high efficiency. The transition from PWM mode to PFM mode occurs once the inductor current in the Low Side MOSFET switch becomes zero, which indicates discontinuous conduction mode. During the Power Save Mode the output voltage is monitored with a PFM comparator. As the output voltage falls below the PFM comparator threshold of VOUT nominal +1%, the device starts a PFM current pulse. For this the High Side MOSFET switch will turn on and the inductor current ramps up. After the On-time expires the switch will be turned off and the Low Side MOSFET switch will be turned on until the inductor current becomes zero. The converter effectively delivers a current to the output capacitor and the load. If the load is below the delivered current the output voltage will rise. If the output voltage is equal or higher than the PFM comparator threshold, the device stops switching and enters a sleep mode. In case the output voltage is still below the PFM comparator threshold, further PFM current pulses will be generated until the PFM comparator threshold is reached. The converter starts switching again once the output voltage drops below the PFM comparator threshold. With a fast single threshold comparator, the output voltage ripple during PFM mode operation can be kept very small. The PFM Pulse is timing controlled, which allows to modify the charge transferred to the output capacitor by the value of the inductor. The resulting PFM output voltage ripple depends in first order on the size of the output capacitor and the inductor value. Increasing output capacitor values and/or inductor values will minimize the output ripple. The PFM mode is left and PWM mode entered in case the output current can not longer be supported in PFM mode. ENABLE The device is enabled setting EN pin to high. During the start up time tstart-up the internal circuits are settled. Afterwards the device activates the soft start circuit. The EN input can be used to control power sequencing in a system with various DC/DC converters. The EN pin can be connected to the output of another converter, to drive the EN pin high and getting a sequencing of supply rails. With EN = GND, the device enters shutdown mode. In this mode, all circuits are disabled. In fixed output voltage versions, the internal resistor divider network is disconnected from FB pin. Submit Documentation Feedback Copyright © 2009, Texas Instruments Incorporated Product Folder Link(s) :TPS62750 13 TPS62750 SLVS955 – JULY 2009 ....................................................................................................................................................................................................... www.ti.com OUTPUT CAPACITOR DISCHARGE With EN = GND, the device enters shutdown mode and all internal circuits are disabled. The SW pin is connected to PGND via an internal resistor (typically 235Ω) to discharge the output capacitor. SOFT START The TPS62750 has an internal soft start circuit that controls the ramp up of the output voltage. The output voltage ramps up from 5% to 95% of its nominal value in a controlled manner. This limits the inrush of current in the converter during start-up and prevents possible voltage drops when a battery or high impedance power source is used. During soft start, the target average input current limit is reduced to 1/3 of its nominal value (ILIM_L or ILIM_U) until the output voltage reaches 1/3 of its nominal value. Once the output voltage trips this threshold, the device operates with its set target average input current limit. The Soft-Start circuit is enabled after the start-up time tstart-up has expired. HOT-PLUG PROTECTION In many applications it may be necessary to remove modules or pc boards while the main unit is still operating. These are considered hot-plug applications. Such implementations require the control of current surges seen by the main power supply and the card being inserted. The most effective way to control these surges is to limit and slowly ramp the current and voltage being applied to the card, similar to the way in which a power supply normally turns on. Due to the controlled rise times and fall times and input over-voltage clamping of the TPS62750, these devices can be used to provide a softer start-up to devices being hot-plugged into a powered system. The UVLO feature of the TPS62750 also ensures that the switch is off after the card has been removed, and that the switch is off during the next insertion. The UVLO feature insures a soft start with a controlled rise time for every insertion of the card or module. REVERSE CURRENT PROTECTION The USB specification does not allow an output device to source current back into the USB port. However, the TPS62750 is designed to safely power non-compliant devices. When disabled, each output is switched to a high-impedance state, blocking reverse current flow from the output back to the input. SHORT-CIRCUIT PROTECTION During normal operation the High Side and Low Side MOSFET switches are protected by its current limits ILIMF. Once the High Side MOSFET switch reaches its current limit, it is turned off and the Low Side MOSFET switch is turned on. The High Side MOSFET switch can only turn on again, once the current in the Low Side MOSFET switch decreases below its current limit. The device is capable to provide peak inductor currents up to its internal current limit ILIMF. As soon as the output voltage falls below 1/3 of the nominal output voltage due to overload or short circuit condition, the converter current limit is reduced to 1/3 of the nominal value ILIMF. Due to the short-circuit protection is enabled during start-up, the device does not deliver more than 1/3 of its nominal current limit ILIMF until the output voltage exceeds 1/3 of the nominal output voltage. This needs to be considered when a load is connected to the output of the converter, which acts as a current sink. THERMAL SHUTDOWN As soon as the junction temperature, TJ, exceeds 150°C (typical) the device goes into thermal shutdown. In this mode, the High Side and Low Side MOSFETs are turned-off. The device continues its operation when the junction temperature falls below the thermal shutdown hysteresis. 14 Submit Documentation Feedback Copyright © 2009, Texas Instruments Incorporated Product Folder Link(s) :TPS62750 TPS62750 www.ti.com ....................................................................................................................................................................................................... SLVS955 – JULY 2009 APPLICATION INFORMATION Wireless Module PA TPS62750 USB 5.0V ILIM_U ILIM_L C IN 10µF R LIM_U 3.7V R1 AV IN EN 2.2µH Wireless BB + PMIC VOUT VIN FB H/L GND PGND R2 Cff CO CBUFF RLIM_L PMU, DCDC, LDO Figure 26. TPS62750DSK in a typical USB Datacard application A growing variety of applications in notebooks, PC's and other mobile systems TDMA data communication techniques which require peak current (typically 2A) during the transmission of signals which can exceed the maximum current specified by the USB standard. Therefore the application must be designed to limit the input power and draw on card-based storage for most of the energy requirement during a typical transmission cycle. A typical GSM signal is transmitted over the carrier at a rate of 216 Hz (4.616ms pulse repetition interval). The transmission period is divided into eight time slots and depending on the power class being used, the duty cycle of this high current pulse can range anywhere between one-eighth of the cycle (577us) up to half of the transmission cycle (2.308ms). The TPS62750 external current limit programming resistors can be easily used to adjust the required input current limit, thereby allowing the user to stay well within the specification requirement stipulated by USB. The TPS62750 is a high efficiency buck converter with programmable input average current limit that provides the needed flexibility when designing a GSM/GPRS power supply solution. The high efficiency of the converter maximizes the average output power without overloading the bus. A bulk output capacitor is used to supply the energy and maintain the output voltage during the high current pulses OUTPUT VOLTAGE SETTING R ö æ VOUT = VREF ´ ç 1 + 1 ÷ with an internal reference voltage VREF typical 0.6V R2 ø è (1) To minimize the current through the feedback divider network, we recommend that the R2 resistor value be 180k. The sum of R1 and R2 should not exceed ~1.5MΩ, to keep the network robust against noise. An external feed forward capacitor Cff is required for optimum load transient response. The value of Cff should be a minimum of 470pF (see table below). Route the FB line away from noise sources, such as the inductor or the SW line. OUTPUT CAPACITOR FEEDFORWARD CAPACITOR 1 mF – 2.5 mF 470 pF > 2.5 mF 1 nF Submit Documentation Feedback Copyright © 2009, Texas Instruments Incorporated Product Folder Link(s) :TPS62750 15 TPS62750 SLVS955 – JULY 2009 ....................................................................................................................................................................................................... www.ti.com INDUCTOR SELECTION The inductor value has a direct effect on the ripple current. The selected inductor has to be rated for its dc resistance and saturation current. The inductor ripple current (ΔIL) decreases with higher inductance and increases with higher VIN or VOUT. The inductor selection has also impact on the output voltage ripple in PFM mode. Higher inductor values will lead to lower output voltage ripple and higher PFM frequency, lower inductor values will lead to a higher output voltage ripple but lower PFM frequency. Equation 2 calculates the maximum inductor current under static load conditions. The saturation current of the inductor should be rated higher than the maximum inductor current as calculated with Equation 3. This is recommended because during heavy load transient the inductor current will rise above the calculated value. Vout 1Vin D IL = Vout ´ L ´ ¦ (2) ILmax = Ioutmax + DIL 2 (3) With: f = Switching Frequency (2.25MHz typical) L = Inductor Value ΔIL= Peak to Peak inductor ripple current ILmax = Maximum Inductor current A more conservative approach is to select the inductor current rating just for the maximum switch current of the corresponding converter. Accepting larger values of ripple current allows the use of low inductance values, but results in higher output voltage ripple, greater core losses, and lower output current capability. The device has been optimized to operate with inductance values between 1.0µH and 4.7µH. It is recommended that inductance values of at least 1.0µH is used, even if Equations 2 and 3 yield something lower. The total losses of the coil have a strong impact on the efficiency of the DC/DC conversion and consist of both the losses in the dc resistance (R(DC)) and the following frequency-dependent components: • The losses in the core material (magnetic hysteresis loss, especially at high switching frequencies) • Additional losses in the conductor from the skin effect (current displacement at high frequencies) • Magnetic field losses of the neighboring windings (proximity effect) • Radiation losses Table 1. List of Inductors MANUFACTURER INDUCTOR TYPE DIMENSIONS [mm] Coilcraft LPS3015-222ML 3.0 x 3.0 x 1.5 TOKO 1127AS-2R2M 3.5 x 3.7 x 1.8 Murata LQH32PN1R0N0 3.2 x 2.5 x 1.7 TOKO DB3015 Series 3.2 x 3.2 x 1.5 INPUT CAPACITOR SELECTION Because of the nature of the buck converter having a pulsating input current, a low ESR input capacitor is required for best input voltage filtering and minimizing the interference with other circuits caused by high input voltage spikes. For most applications a 4.7µF to 10µF ceramic capacitor is recommended. The input capacitor can be increased without any limit for better input voltage filtering. Take care when using only small ceramic input capacitors. When a ceramic capacitor is used at the input and the power is being supplied through long wires, such as from a wall adapter, a load step at the output or VIN step on the input can induce ringing at the VIN pin. This ringing can couple to the output and be mistaken as loop instability or could even damage the part by exceeding the maximum ratings. 16 Submit Documentation Feedback Copyright © 2009, Texas Instruments Incorporated Product Folder Link(s) :TPS62750 TPS62750 www.ti.com ....................................................................................................................................................................................................... SLVS955 – JULY 2009 OUTPUT CAPACITOR SELECTION The TPS62750 has been specifically internally compensated to operate with large capacitance values. But to maintain loop stability of the device, it is recommended to use a small ceramic capacitor placed as close as possible to the VOUT and GND pins of the IC in parallel with the large holdup capacitor. To get an estimate of the small ceramic recommended minimum output capacitance, Equation 4 can be used. ( I × VOUT - VIN Cmin = OUT f × ΔV × VOUT ) (4) Parameter f is the switching frequency and ΔV is the maximum allowed ripple. With a chosen ripple voltage of 10 mV, a minimum effective capacitance of 2.7 µF is needed. The total ripple is larger due to the ESR of the output capacitor. This additional component of the ripple can be calculated using Δ VESR = IOUT x RESR. A capacitor with a value in the range of the calculated minimum should be used. This is required to maintain control loop stability. There are no additional requirements regarding minimum ESR. There is no upper limit for the output capacitance value. Larger capacitors cause lower output voltage ripple as well as lower output voltage drop during load transients. Note that ceramic capacitors have a DC Bias effect, which will have a strong influence on the final effective capacitance needed. Therefore the right capacitor value has to be chosen very carefully. Package size and voltage rating in combination with material are responsible for differences between the rated capacitor value and the effective capacitance. To calculate the value of the effective capacitance required to buffer a GSM transmission pulse, the following equations can be used: Capacitance = I× Dt DV (5) Assuming the DCDC supplies ~700mA, the rest of the energy to supply the GSM transmission pulse must come from the capacitor. ICAP = IGSM - IDCDC ICAP = 2A - 700mA = 1.3A Assuming a GSM transmission pulse width of 1.154ms and allowing a maximum voltage drop on the output of 350mV, the effective capacitance required is: Capacitance = 1.3A ×1.154ms = 4.2mF 350mV (6) List of Capacitors COMPONENT REFERENCE PART NUMBER CO GRM188R60J106M69D Murata 10µF 6TPG150M Sanyo POSCAP 150µF 592D158X06R3X2T25H Vishay 1.5mF 592D228X06R3X2T22H Vishay 2.2mF CBULK MANUFACTURER VALUE AVERAGE INPUT CURRENT LIMIT The average input current is set by selecting the correct external resistor value correlating to the required current limit. The current limit can be selected between a high current limit (ILIM_U) and a lower limit (ILIM_L) by toggling the H/L pin high or low. This has the added benefit that of allowing a device first plugged into the USB port to enumerate at 100mA before switching over to the high power mode (500mA). The equations below are a guideline for selecting the correct resistor value: Submit Documentation Feedback Copyright © 2009, Texas Instruments Incorporated Product Folder Link(s) :TPS62750 17 TPS62750 SLVS955 – JULY 2009 ....................................................................................................................................................................................................... www.ti.com æ 1.23 Upper range: RLIM_U = ç ç ILIM_U è ö ÷ ´ 20000 ÷ ø (7) æ 1.23 = ç ç ILIM_L è ö ÷ ´ 5400 ÷ ø (8) Lower range: RLIM_L Examples of different input current limit values selectable are given in the table below: AVERAGE INPUT CURRENT REQUIRED RESISTOR VALUE 50 mA 132.8 K 100 mA 66.5 K 400 mA 61.5 K 500 mA 49.2 K 600 mA 41 K 700 mA 35.1 K CHECKING LOOP STABILITY The first step of circuit and stability evaluation is to look from a steady-state perspective at the following signals: • Switching node, SW • Inductor current, IL • Output ripple voltage, VO(AC) These are the basic signals that need to be measured when evaluating a switching converter. When the switching waveform shows large duty cycle jitter or the output voltage or inductor current shows oscillations, the regulation loop may be unstable. This is often a result of board layout and/or L-C combination. As a next step in the evaluation of the regulation loop, the load transient response is tested. The time between the application of the load transient and the turn on of the P-channel MOSFET, the output capacitor must supply all of the current required by the load. VO immediately shifts by an amount equal to ΔI(LOAD) × ESR, where ESR is the effective series resistance of CO. ΔI(LOAD) begins to charge or discharge CO generating a feedback error signal used by the regulator to return VO to its steady-state value. The results are most easily interpreted when the device operates in PWM mode. During this recovery time, VO can be monitored for settling time, overshoot or ringing that helps judge the converter’s stability. Without any ringing, the loop has usually more than 45° of phase margin. Because the damping factor of the circuitry is directly related to several resistive parameters (e.g., MOSFET RDSon) that are temperature dependant, the loop stability analysis has to be done over the input voltage range, load current range, and temperature range. + + Ω 470pF Ω Ω Ω Ω Ω Figure 27. Checking Loop Stability 18 Submit Documentation Feedback Copyright © 2009, Texas Instruments Incorporated Product Folder Link(s) :TPS62750 TPS62750 www.ti.com ....................................................................................................................................................................................................... SLVS955 – JULY 2009 LAYOUT CONSIDERATIONS As for all switching power supplies, the layout is an important step in the design. Proper function of the device demands careful attention to PCB layout. Care must be taken in board layout to get the specified performance. If the layout is not carefully done, the regulator could show poor line and/or load regulation, stability issues as well as EMI problems. It is critical to provide a low inductance, impedance ground path. Therefore, use wide and short traces for the main current paths. The input capacitor should be placed as close as possible to the IC pins as well as the inductor and output capacitor. Connect the GND Pin of the device to the Power Pad of the PCB and use this Pad as a star point. Use a common Power GND node and a different node for the Signal GND to minimize the effects of ground noise. Connect these ground nodes together to the Power Pad (star point) underneath the IC. Keep the common path to the GND PIN, which returns the small signal components and the high current of the output capacitors as short as possible to avoid ground noise. The FB line should be connected right to the output capacitor and routed away from noisy components and traces (e.g., SW line). R2 R3 C3 R4 R1 VIN COUT CIN GND VOUT L1 Current select Enable Figure 28. Suggested Layout Submit Documentation Feedback Copyright © 2009, Texas Instruments Incorporated Product Folder Link(s) :TPS62750 19 TPS62750 SLVS955 – JULY 2009 ....................................................................................................................................................................................................... www.ti.com THERMAL INFORMATION Implementation of integrated circuits in low-profile and fine-pitch surface-mount packages typically requires special attention to power dissipation. Many system-dependant issues such as thermal coupling, airflow, added heat sinks, and convection surfaces, and the presence of other heat-generating components, affect the power-dissipation limits of a given component. Three basic approaches for enhancing thermal performance are listed below: • • • Improving the power dissipation capability of the PCB design Improving the thermal coupling of the component to the PCB Introducing airflow into the system For more details on how to use the thermal parameters in the dissipation ratings table please check the Thermal Characteristics Application Note (SZZA017) and the IC Package Thermal Metrics Application Note (SPRA953). 20 Submit Documentation Feedback Copyright © 2009, Texas Instruments Incorporated Product Folder Link(s) :TPS62750 PACKAGE OPTION ADDENDUM www.ti.com 30-Jul-2009 PACKAGING INFORMATION Orderable Device Status (1) Package Type Package Drawing Pins Package Eco Plan (2) Qty TPS62750DSKR ACTIVE SON DSK 10 3000 Green (RoHS & no Sb/Br) CU NIPDAU Level-1-260C-UNLIM TPS62750DSKT ACTIVE SON DSK 10 250 CU NIPDAU Level-1-260C-UNLIM Green (RoHS & no Sb/Br) Lead/Ball Finish MSL Peak Temp (3) (1) The marketing status values are defined as follows: ACTIVE: Product device recommended for new designs. LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect. NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design. PREVIEW: Device has been announced but is not in production. Samples may or may not be available. OBSOLETE: TI has discontinued the production of the device. (2) Eco Plan - The planned eco-friendly classification: Pb-Free (RoHS), Pb-Free (RoHS Exempt), or Green (RoHS & no Sb/Br) - please check http://www.ti.com/productcontent for the latest availability information and additional product content details. TBD: The Pb-Free/Green conversion plan has not been defined. Pb-Free (RoHS): TI's terms "Lead-Free" or "Pb-Free" mean semiconductor products that are compatible with the current RoHS requirements for all 6 substances, including the requirement that lead not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, TI Pb-Free products are suitable for use in specified lead-free processes. Pb-Free (RoHS Exempt): This component has a RoHS exemption for either 1) lead-based flip-chip solder bumps used between the die and package, or 2) lead-based die adhesive used between the die and leadframe. The component is otherwise considered Pb-Free (RoHS compatible) as defined above. Green (RoHS & no Sb/Br): TI defines "Green" to mean Pb-Free (RoHS compatible), and free of Bromine (Br) and Antimony (Sb) based flame retardants (Br or Sb do not exceed 0.1% by weight in homogeneous material) (3) MSL, Peak Temp. -- The Moisture Sensitivity Level rating according to the JEDEC industry standard classifications, and peak solder temperature. Important Information and Disclaimer:The information provided on this page represents TI's knowledge and belief as of the date that it is provided. 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Addendum-Page 1 PACKAGE MATERIALS INFORMATION www.ti.com 28-Jul-2009 TAPE AND REEL INFORMATION *All dimensions are nominal Device Package Package Pins Type Drawing SPQ Reel Reel A0 Diameter Width (mm) (mm) W1 (mm) B0 (mm) K0 (mm) P1 (mm) W Pin1 (mm) Quadrant TPS62750DSKR SON DSK 10 3000 179.0 8.4 2.73 2.73 0.8 4.0 8.0 Q2 TPS62750DSKT SON DSK 10 250 179.0 8.4 2.73 2.73 0.8 4.0 8.0 Q2 Pack Materials-Page 1 PACKAGE MATERIALS INFORMATION www.ti.com 28-Jul-2009 *All dimensions are nominal Device Package Type Package Drawing Pins SPQ Length (mm) Width (mm) Height (mm) TPS62750DSKR SON DSK 10 3000 195.0 200.0 45.0 TPS62750DSKT SON DSK 10 250 195.0 200.0 45.0 Pack Materials-Page 2 IMPORTANT NOTICE Texas Instruments Incorporated and its subsidiaries (TI) reserve the right to make corrections, modifications, enhancements, improvements, and other changes to its products and services at any time and to discontinue any product or service without notice. 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