LP3907 Dual High-Current Step-Down DC/DC and Dual Linear Regulator with I2C Compatible Interface General Description Features The LP3907 is a multi-function, programmable Power Management Unit, optimized for low power FPGAs, microprocessors and DSPs. This device integrates two highly efficient 1A/ 600mA step-down DC/DC converters with dynamic voltage management (DVM), two 300mA linear regulators and a 400kHz I2C compatible interface to allow a host controller access to the internal control registers of the LP3907. The LP3907 additionally features programmable power-on sequencing and a tiny 4 x 4 x 0.8mm 24–pin LLP pin package. ■ Compatible with advanced applications processors and Key Specifications Step-Down DC/DC Converter (Buck) ■ 1A/600mA output current ■ Programmable VOUT from: — Buck1 : 0.8V–2.0V @ 1A — Buck2 : 1.0V–3.5V @ 600mA ■ Up to 96% efficiency ■ 2.1MHz PWM switching frequency ■ PWM - PFM automatic mode change under low loads ■ ±3% output voltage accuracy ■ Automatic soft start FPGAs ■ 2 LDOs for powering Internal processor functions and I/Os ■ High speed serial interface for independent control of device functions and settings Precision internal reference Thermal overload protection Current overload protection 24-lead 4 × 4 × 0.8mm LLP package Software Programmable Regulators External Power-on-reset function for Buck1 and Buck2 (i.e., Power Good with delay function) ■ Undervoltage lock out detector to monitor input supply voltage ■ ■ ■ ■ ■ ■ Applications ■ FPGA, DSP core power ■ Applications processors ■ Peripheral I/O power Linear Regulators (LDO) ■ Programmable VOUT of 1.0V–3.5V ■ ±3% output voltage accuracy ■ 300mA output current ■ 30mV (typ) dropout © 2007 National Semiconductor Corporation 300178 www.national.com LP3907 Dual High-Current Step-Down DC/DC and Dual Linear Regulator with I2C Compatible Interface August 2007 LP3907 Typical Application Circuit 30017801 FIGURE 1. Application Circuit www.national.com 2 LP3907 30017802 FIGURE 2. Application Circuit 3 www.national.com LP3907 Connection Diagram 30017803 FIGURE 3. 24-Lead LLP Package (Top View) Note: The physical placement of the package marking will vary from part to part. (*) UZXYTT format: ‘U’ – wafer fab code; ‘Z’ – assembly code; ’XY’ 2 digit date code; ‘TT” – die run code. See http://www.national.com/quality/ marking_conventions.html for more information on marking information. (**) Package received will have XXXX replaced with the specific part version ordered. Ordering Information Voltage Option Order Number Voltage “JXQX” LP3907SQ-JXQX 24-lead LLP SQA024AE Voltage “JXQX” LP3907SQX-JXQX 24-lead LLP SQA024AE Voltage “JXQX” LP3907SQ-JXQX** 24-lead LLP SQA024AE 24-lead LLP SQA024AE 07PJXQX Voltage “JXQX” LP3907SQX-JXQX** Package Type NSC Package Drawing Package Marking Ordering Spec Supplied As 07-JXQX NOPB 1000 tape & reel 07-JXQX NOPB 4500 tape & reel 07PJXQX S7001874 1000 tape & reel S7001997 4500 tape & reel ** For Forced PWM Buck Regulators. Default Voltage Options www.national.com Regulator Version “JXQX” Default Voltages (V) SW1 1.2 SW2 3.3 LDO1 2.6 LDO2 3.3 4 LP3907 Pin Descriptions Pin Pin Name I/O Type 1 VINLDO12 I PWR Functional Description Analog Power for Internal Functions (VREF, BIAS, I2C, Logic) 2 EN_T I D Enable for preset power on sequence. (see page 24) 3 NPOR O D nPOR Power on reset pin for both Buck1 and Buck 2. Open drain logic output 100K pullup resistor. nPOR is pulled to ground when the voltages on these supplies are not good. See nPOR section for more info. 4 GND_SW1 G G Buck1 NMOS Power Ground 5 SW1 O PWR Buck1 switcher output pin 6 VIN1 I PWR Power in from either DC source or Battery to Buck1 7 ENSW1 I D Enable Pin for Buck1 switcher, a logic HIGH enables Buck1 8 FB1 I A Buck1 input feedback terminal 9 GND_C G G Non switching core ground pin 10 AVDD I PWR 11 FB2 I A Buck2 input feedback terminal 12 ENSW2 I D Enable Pin for Buck2 switcher, a logic HIGH enables Buck2 13 VIN2 I PWR Power in from either DC source or Battery to Buck2 14 SW2 O PWR Buck2 switcher output pin 15 GND_SW2 G G Buck2 NMOS Power ground 16 SDA I/O D I2C Data (bidirectional) 17 SCL I D I2C Clock 18 GND_L G G LDO ground 19 VINLDO1 I PWR Power in from either DC source or battery to input terminal to LDO1 20 LDO1 O PWR LDO1 Output 21 ENLDO1 I D LDO1 enable pin, a logic HIGH enables the LDO1 22 ENLDO2 I D LDO2 enable pin, a logic HIGH enables the LDO2 23 LDO2 O PWR LDO2 Output 24 VINLDO2 I PWR Power in from either DC source or battery to input terminal to LDO2 Analog Power for Buck converters A: Analog Pin D: Digital Pin G: Ground Pin PWR: Power Pin I: Input Pin I/O: Input/Output Pin O: Output Pin 5 www.national.com LP3907 Operating Ratings: Bucks Absolute Maximum Ratings (Notes 1, 2) If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. (Notes 1, 2, 7, 18) VIN VEN Junction Temperature (TJ) Range 2.8V to 5.5V 0 to (VIN + 0.3V) −40°C to +125° C Ambient Temperature (TA) Range (Note 6) −40°C to +85°C VIN, SDA, SCL −0.3V to +6V GND to GND SLUG ±0.3V Power Dissipation (PD_MAX) (TA=85°C, TMAX=125°C, )(Note 5) 1.43W Junction Temperature (TJ-MAX) 150°C Storage Temperature Range −65°C to +150°C Maximum Lead Temperature (Soldering) 260°C ESD Ratings Human Body Model (Note 4) Thermal Properties (Notes 3, 5, 6) Junction-to-Ambient Thermal Resistance (θJA) SQA024AE 28°C/W 2kV General Electrical Characteristics (Notes 1, 2, 7, 13, 17) Unless otherwise noted, VIN = 3.6V. Typical values and limits appearing in normal type apply for TJ = 25°C. Limits appearing in boldface type apply over the entire junction temperature range for operation, −40°C to +125°C. Symbol IQ VPOR Parameter Conditions VINLDO12 Shutdown Current VIN = 3.6V Power-On Reset Threshold VDD Falling Edge(Note 17) TSD Thermal Shutdown Threshold TSDH Themal Shutdown Hysteresis UVLO Under Voltage Lock Out Min Typ Max 3 Units µA 1.9 V 160 °C 20 °C Rising 2.9 Falling 2.7 V I2C Compatible Interface Electrical Specifications (Note 13) Unless otherwise noted, VIN = 3.6V. Typical values and limits appearing in normal type apply for TJ = 25°C. Limits appearing in boldface type apply over the entire junction temperature range for operation, −40°C to +125°C Symbol Parameter Conditions Min Typ Max Units 400 kHz FCLK Clock Frequency tBF Bus-Free Time Between Start and Stop (Note 13) 1.3 µs tHOLD Hold Time Repeated Start Condition (Note 13) 0.6 µs tCLKLP CLK Low Period (Note 13) 1.3 µs tCLKHP CLK High Period (Note 13) 0.6 µs tSU Set Up Time Repeated Start Condition (Note 13) 0.6 µs tDATAHLD Data Hold time (Note 13) 0 µs tDATASU Data Set Up Time (Note 13) 100 ns TSU Set Up Time for Start Condition (Note 13) 0.6 µs TTRANS Maximum Pulse Width of Spikes that (Note 13) Must be Suppressed by the Input Filter of Both DATA & CLK Signals. www.national.com 6 50 ns Unless otherwise noted, VIN = 3.6, CIN = 1.0µF, COUT = 0.47µF. Typical values and limits appearing in normal type apply for TJ = 25°C. Limits appearing in boldface type apply over the entire junction temperature range for operation, −40°C to +125°C. (Notes 2, 7, 8, 9, 10, 11, 12) Symbol VIN Parameter Operational Voltage Range Conditions Min VINLDO1 and VINLDO2 PMOS pins (Note 15) VOUT Accuracy Output Voltage Accuracy (Default VOUT) Load current = 1 mA Typ Max Units 1.74 5.5 V −3 3 % Line Regulation VIN = (VOUT + 0.3V) to 5.0V, (Note 12), Load Current = mA 0.15 %/V Load Regulation VIN = 3.6V, Load Current = 1mA to IMAX 0.011 %/mA ISC Short Circuit Current Limit LDO1-2, VOUT = 0V 500 VIN – VOUT Dropout Voltage Load Current = 50mA (Note 10) 30 PSRR Power Supply Ripple Rejection F = 10kHz, Load Current = IMAX 45 dB θn Supply Output Noise 10Hz < F < 100KHz 80 µVrms IQ (Notes 11, 14) Quiescent Current “On” IOUT = 0mA 40 µA Quiescent Current “On” IOUT = IMAX 60 µA ΔVOUT mA 200 mV Quiescent Current “Off” EN is de-asserted(Note 16) 0.03 µA TON Turn On Time Start up from shut-down 300 µs COUT Output Capacitor Capacitance for stability 0°C ≤ TJ ≤ 125°C 0.33 0.47 µF −40°C ≤ TJ ≤ 125°C 0.68 1.0 µF ESR 5 500 mΩ Buck Converters SW1, SW2 Unless otherwise noted, VIN = 3.6, CIN = 10 µF, COUT = 10 µF, LOUT = 2.2 µH ceramic. Typical values and limits appearing in normal type apply for TJ = 25°C. Limits appearing in boldface type apply over the entire junction temperature range for operation, −40° C to +125°C. (Notes 2, 7, 8, 9, 11, 18) Symbol VOUT Parameter Conditions Min Typ −3 Max Units +3 % Output Voltage Accuracy Default VOUT Line Regulation 2.8< VIN < 5.5 IO =10mA 0.089 %/V Load Regulation 100mA < IO < IMAX 0.0013 %/mA Eff Efficiency Load Current = 250mA ISHDN Shutdown Supply Current EN is de-asserted fOSC Internal Oscillator Frequency IPEAK Buck1 Peak Switching Current Limit Buck2 Peak Switching Current Limit 1.0 1.7 No load PFM Mode 96 % 0.01 µA 2.1 MHz 1.5 A IQ (Note 14) Quiescent Current “On” RDSON (P) Pin-Pin Resistance PFET RDSON (N) Pin-Pin Resistance NFET TON Turn On Time Start up from shut-down CIN Input Capacitor Capacitance for stability 10 µF CO Output Capacitor Capacitance for stability 10 µF 7 33 µA 200 mΩ 180 mΩ 500 µs www.national.com LP3907 Low Drop Out Regulators, LDO1 and LDO2 LP3907 I/O Electrical Characteristics Unless otherwise noted: Typical values and limits appearing in normal type apply for TJ = 25°C. Limits appearing in boldface type apply over the entire junction temperature range for operation, TJ = 0°C to +125°C. (Note 13) Symbol Parameter VIL Input Low Level VIH Input High Level Conditions Limit Min Max Units 0.4 V V 1.2 Power On Reset Threshold/Function (POR) Symbol Parameter Conditions Min Typ nPOR nPOR = Power on reset forBuck1 and Buck2 Default 50 nPOR threshold Percentage of Target voltage Buck1 or Buck2 VBUCK1 AND VBUCK2 rising 94 VBUCK1 OR VBUCK2 falling 85 Max Units ms % Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the component may occur. Operating Ratings are conditions under which operation of the device is guaranteed. Operating Ratings do not imply guaranteed performance limits. For guaranteed performance limits and associated test conditions, see the Electrical Characteristics. Note 2: All voltages are with respect to the potential at the GND pin. Note 3: Internal thermal shutdown circuitry protects the device from permanent damage. Thermal shutdown engages at TJ = 160°C (typ.) and disengages at TJ = 140°C (typ.) Note 4: The Human body model is a 100pF capacitor discharged through a 1.5kΩ resistor into each pin. (MILSTD - 883 3015.7) Note 5: In applications where high power dissipation and/or poor package thermal resistance is present, the maximum ambient temperature may have to be derated. Maximum ambient temperature (TA-MAX) is dependent on the maximum operating junction temperature (TJ-MAX-OP = 125°C), the maximum power dissipation of the device in the application (PD-MAX), and the junction-to-ambient thermal resistance of the part/package in the application (θJA), as given by the following equation: TA-MAX = TJ-MAX-OP − (θJA × PD-MAX). See Applications section. Note 6: Junction-to-ambient thermal resistance is highly application and board-layout dependent. In applications where high maximum power dissipation exists, special care must be paid to thermal dissipation issues in board design. Note 7: Min and Max limits are guaranteed by design, test, or statistical analysis. Typical numbers are not guaranteed, but do represent the most likely norm. Note 8: CIN, COUT: Low-ESR Surface-Mount Ceramic Capacitors (MLCCs) used in setting electrical characteristics. Note 9: The device maintains a stable, regulated output voltage without a load. Note 10: Dropout voltage is the voltage difference between the input and the output at which the output voltage drops to 100mV below its nominal value. Note 11: Quiescent current is defined here as the difference in current between the input voltage source and the load at VOUT. Note 12: VIN minimum for line regulation values is 1.8V. Note 13: This specification is guaranteed by design. Note 14: The IQ can be defined as the standing current of the LP3907 when the I2C bus is active and all other power blocks have been disabled via the I2C bus, or it can be defined as the I2C bus active, and the other power blocks are active under no load condition. These two values can be used by the system designer when the LP3907 is powered using a battery. Note 15: Pins 24, 19 can operate from VIN min of 1.74 to a VIN max of 5.5V. This rating is only for the series pass PMOS power FET. It allows the system design to use a lower voltage rating if the input voltage comes from a buck output. Note 16: The IQ exhibits a higher current draw when the EN pin is de-asserted because the I22 buffer pins draw an additional 2µA. Note 17: VPOR is voltage at which the EPROM resets. This is different from the UVLO on VINLDO12, which is the voltage at which the regulators shut off; and is also different from the nPOR function, which signals if the regulators are in a specified range. Note 18: Buck VIN ≥ VOUT + 1V. www.national.com 8 Output Voltage Change vs Temperature (LDO1) VIN = 3.6V, VOUT = 2.6V, 100mA load LP3907 Typical Performance Characteristics — LDO TA = 25°C unless otherwise noted Output Voltage Change vs Temperature (LDO2) VIN = 3.6V, VOUT = 3.3V, 100mA load 30017835 30017836 Load Transient (LDO1) 3.6 VIN, 2.6VOUT, 0 – 150 mA load Load Transient (LDO2) 3.6 VIN, 3.3 VOUT, 0 – 150mA load 30017837 30017838 Line Transient (LDO1) 3.6 - 4.2 VIN, 2.6 VOUT, 300mA load Line Transient (LDO2) 3 – 4.2 VIN, 3.3VOUT, 300 mA load 30017839 30017840 9 www.national.com LP3907 Enable Start-up time (LDO1) ) 0-3.6 VIN, 2.6 VOUT, 1mA load Enable Start-up time (LDO2) 0 – 3.6 VIN, 3.3 VOUT, 1 mA load 30017841 30017842 LDO Maximum Load VIN = 1.74V 30017867 www.national.com 10 LP3907 Typical Performance Characteristics — Bucks VIN= 2.8V to 5.5V, TA = 25°C Shutdown Current vs. Temp Output Voltage vs. Supply Voltage (VOUT = 1.0 V) 30017843 30017844 Output Voltage vs. Supply Voltage (VOUT = 1.8V) Output Voltage vs. Supply Voltage (VOUT = 3.5V) 30017845 30017846 11 www.national.com LP3907 Typical Performance Characteristics — Buck1 VIN= 2.8V to 5.5V, TA = 25°C, VOUT = 1.2V, 2.0V Efficiency vs Output Current (VOUT =2.0V, L= 2.2µH — Forced PWM mode) Efficiency vs Output Current (VOUT =1.2V, L= 2.2µH —(Forced PWM mode) 30017847 30017848 Efficiency vs Output Current (VOUT =1.2V, L= 2.2µH — PWM mode to PFM mode) Efficiency vs Output Current (VOUT =2.0V, L= 2.2µH — PWM mode to PFM mode) 30017850 30017849 www.national.com 12 LP3907 Typical Performance Characteristics — Buck2 VIN= 4.5V to 5.5V, TA = 25°C, VOUT = 1.8V, 3.3V Efficiency vs Output Current (VOUT =3.3V, L= 2.2µH — Forced PWM mode) Efficiency vs Output Current ( VOUT =1.8V, L= 2.2µH —Forced PWM mode) 30017851 30017852 Typical Performance Characteristics — Buck2 VIN= 4.3V to 5.5V, TA = 25°C, VOUT = 1.8V, 3.3V Efficiency vs Output Current (VOUT =1.2V, L= 2.2µH — PWM mode to PFM mode) Efficiency vs Output Current (VOUT =2.0V, L= 2.2µH — PWM mode to PFM mode) 30017853 30017854 13 www.national.com LP3907 Typical Performance Characteristics — Bucks VIN= 3.6V, TA = 25°C, VOUT = 1.2V unless otherwise noted Mode Change by Load Transient VOUT = 1.2V, ILOAD = 50–150mA (PFM to PWM Mode) Load Transient Response VOUT = 1.2V, ILOAD = 300–500mA (PWM Mode) 30017856 30017857 Line Transient Response VIN = 3.6 – 4.2V, VOUT = 1.2V, 250mA load Line Transient Response VIN = 3.6 – 4.2V, VOUT = 3.3V, 250 mA load 30017859 30017858 Start up into PWM Mode VOUT = 1.2V, 1.0A load Start up into PWM Mode VOUT = 3.3 V, 600mA load 30017860 www.national.com 30017861 14 LP3907 Start up into PFM Mode VOUT = 1.2V, 30mA load Start up into PFM Mode VOUT = 3.3V, 30mA load 30017880 30017862 15 www.national.com LP3907 DC/DC Converters OVERVIEW The LP3907 supplies the various power needs of the application by means of two Linear Low Drop Regulators (LDO1 and LDO2) and two Buck converters (SW1 and SW2). The table hereunder lists the output characteristics of the various regulators. Supply Specification Output VOUT Range(V) Resolution (mV) IMAX Maximum Output Current (mA) analog 1.0 to 3.5 100 300 analog 1.0 to 3.5 100 300 SW1 digital 0.8 to 2.0 50 1000 SW2 digital 1.0 to 3.5 100 600 Supply Load LDO1 LDO2 *For default values of the regulators, please consult page 3 of this datasheet. LINEAR LOW DROPOUT REGULATORS (LDOS) LDO1 and LDO2 are identical linear regulators targeting analog loads characterized by low noise requirements. LDO1 and LDO2 are enabled through the ENLDO pin or through the corresponding LDO1 or LDO2 control register. The output voltages of both LDOs are register programmable. The default output voltages are factory programmed during Final Test, which can be tailored to the specific needs of the system designer. NO-LOAD STABILITY The LDOs will remain stable and in regulation with no external load. This is an important consideration in some circuits, for example, CMOS RAM keep-alive applications. grammable in steps of 100mV from 1.0V to 3.5V by programming bits D4-0 in the LDO Control registers. Both LDO1 and LDO2 are enabled by applying a logic 1 to the ENLDO1 and ENLDO2 pin. Enable/disable control is also provided through enable bit of the LDO1 and LDO2 control registers. The value of the enable LDO bit in the register is logic 1 by default. The output voltage can be altered while the LDO is enabled. 30017822 LDO1 AND LDO2 CONTROL REGISTERS LDO1 and LDO2 can be configured by means of the LDO1 and LDO2 control registers. The output voltage is pro- www.national.com 16 FUNCTIONAL DESCRIPTION The LP3907 incorporates two high-efficiency synchronous switching buck regulators, SW1 and SW2, that deliver a constant voltage from a single Li-Ion battery to the portable system processors. Using a voltage mode architecture with synchronous rectification, both bucks have the ability to deliver up to 1000mA and 600mA, respectively, depending on the input voltage and output voltage (voltage head room), and the inductor chosen (maximum current capability). There are three modes of operation depending on the current required - PWM, PFM, and shutdown. PWM mode handles current loads of approximately 70mA or higher, delivering voltage precision of +/-3% with 90% efficiency or better. Lighter output current loads cause the device to automatically switch into PFM for reduced current consumption (IQ = 15µA typ.) and a longer battery life. The Standby operating mode turns off the device, offering the lowest current consumption. PWM or PFM mode is selected automatically or PWM mode can be forced through the setting of the buck control register. Both SW1 and SW2 can operate up to a 100% duty cycle (PMOS switch always on) for low drop out control of the output voltage. In this way the output voltage will be controlled down to the lowest possible input voltage. Additional features include soft-start, under-voltage lock-out, current overload protection, and thermal overload protection. CURRENT LIMITING A current limit feature allows the converter to protect itself and external components during overload conditions. PWM mode implements current limiting using an internal comparator that trips at 1.5A for Buck1 and at 1.0A for Buck2 (typ). If the output is shorted to ground the device enters a timed current limit mode where the NFET is turned on for a longer duration until the inductor current falls below a low threshold, ensuring inductor current has more time to decay, thereby preventing runaway. PFM OPERATION At very light loads, the converter enters PFM mode and operates with reduced switching frequency and supply current to maintain high efficiency. The part will automatically transition into PFM mode when either of two conditions occurs for a duration of 32 or more clock cycles: A. The inductor current becomes discontinuous or B. The peak PMOS switch current drops below the IMODE level CIRCUIT OPERATION DESCRIPTION A buck converter contains a control block, a switching PFET connected between input and output, a synchronous rectifying NFET connected between the output and ground (BCKGND pin) and a feedback path. During the first portion of each switching cycle, the control block turns on the internal PFET switch. This allows current to flow from the input through the inductor to the output filter capacitor and load. The inductor limits the current to a ramp with a slope of During PFM operation, the converter positions the output voltage slightly higher than the nominal output voltage during PWM operation, allowing additional headroom for voltage drop during a load transient from light to heavy load. The PFM comparators sense the output voltage via the feedback pin and control the switching of the output FETs such that the output voltage ramps between 0.8% and 1.6% (typical) above the nominal PWM output voltage. If the output voltage is below the ‘high’ PFM comparator threshold, the PMOS power switch is turned on. It remains on until the output voltage exceeds the ‘high’ PFM threshold or the peak current exceeds the I PFM level set for PFM mode. The typical peak current in PFM mode is: by storing energy in a magnetic field. During the second portion of each cycle, the control block turns the PFET switch off, blocking current flow from the input, and then turns the NFET synchronous rectifier on. The inductor draws current from ground through the NFET to the output filter capacitor and load, which ramps the inductor current down with a slope of Once the PMOS power switch is turned off, the NMOS power switch is turned on until the inductor current ramps to zero. When the NMOS zero-current condition is detected, the NMOS power switch is turned off. If the output voltage is below the ‘high’ PFM comparator threshold (see figure below), the PMOS switch is again turned on and the cycle is repeated until the output reaches the desired level. Once the output reaches the ‘high’ PFM threshold, the NMOS switch is turned on briefly to ramp the inductor current to zero and then both output switches are turned off and the part enters an extremely low power mode. Quiescent supply current during this ‘sleep’ mode is less than 30µA, which allows the part to achieve high efficiencies under extremely light load condi- The output filter stores charge when the inductor current is high, and releases it when low, smoothing the voltage across the load. PWM OPERATION During PWM operation the converter operates as a voltagemode controller with input voltage feed forward. This allows the converter to achieve excellent load and line regulation. The DC gain of the power stage is proportional to the input voltage. To eliminate this dependence, feed forward voltage inversely proportional to the input voltage is introduced. 17 www.national.com LP3907 INTERNAL SYNCHRONOUS RECTIFICATION While in PWM mode, the buck uses an internal NFET as a synchronous rectifier to reduce rectifier forward voltage drop and associated power loss. Synchronous rectification provides a significant improvement in efficiency whenever the output voltage is relatively low compared to the voltage drop across an ordinary rectifier diode. SW1, SW2: Synchronous StepDown Magnetic DC/DC Converters LP3907 tions. When the output drops below the ‘low’ PFM threshold, the cycle repeats to restore the output voltage to ~1.6% above the nominal PWM output voltage. If the load current should increase during PFM mode (see figure below) causing the output voltage to fall below the ‘low2’ PFM threshold, the part will automatically transition into fixed-frequency PWM mode. Power On Sequence). The SW1 and SW2 output voltages revert to default values when the power on sequence has been completed. The default output voltage for each buck converter is factory programmable. (See Application Notes). SW1, SW2 CONTROL REGISTERS SW1, SW2 can be enabled/disabled through the corresponding control register. The Modulation mode PWM/PFM is by default automatic and depends on the load as described above in the functional description. The modulation mode can be overridden by setting I2C bit to a logic 1 in the corresponding buck control register, forcing the buck to operate in PWM mode regardless of the load condition. SW1, SW2 OPERATION SW1 and SW2 have selectable output voltages ranging from 0.8V to 3.5V (typ.). Both SW1 and SW2 in the LP3907 are I2C register controlled and are enabled by default through the internal state machine of the LP3907 following a Power-On event that moves the operating mode to the Active state. (see 30017814 SHUTDOWN MODE During shutdown the PFET switch, reference, control and bias circuitry of the converters are turned off. The NFET switch will be on in shutdown to discharge the output. When the converter is enabled, soft start is activated. It is recommended to disable the converter during the system power up and under voltage conditions when the supply is less than 2.8V. down to the lowest possible input voltage. When the device operates near 100% duty cycle, output voltage ripple is approximately 25mV. The minimum input voltage needed to support the output voltage is VIN, MIN = ILOAD * (RDSON, PFET + RINDUCTOR) + VOUT SOFT START The soft-start feature allows the power converter to gradually reach the initial steady state operating point, thus reducing start-up stresses and surges. The two LP3907 buck converters have a soft-start circuit that limits in-rush current during start-up. During start-up the switch current limit is increased in steps. Soft start is activated only if EN goes from logic low to logic high after VIN reaches 2.8V. Soft start is implemented by increasing switch current limit in steps of 180mA, 300mA, and 720mA for Buck1; 161mA, 300mA and 536mA for Buck2 (typ. Switch current limit). The start-up time thereby depends on the output capacitor and load current demanded at startup. — RINDUCTOR — ILOAD — RDSON, PFET LOW DROPOUT OPERATION The LP3907 can operate at 100% duty cycle (no switching; PMOS switch completely on) for low drop out support of the output voltage. In this way the output voltage will be controlled www.national.com 18 Load current Drain to source resistance of PFET switch in the triode region Inductor resistance POWER ON EN_T assertion causes the LP3907 to emerge from Standby mode to Full Operation mode at a preset timing sequence. By default, the enables for the LDOs and Bucks (ENLDO1, ENLDO2, EN_T, ENSW1, ENSW2) are 500K internally pulled down, which causes the part to stay OFF until enabled. If the 30017809 19 www.national.com LP3907 user wishes to have a preset timing sequence to power on the regulators, the external regulator enables must be tied LOW. Otherwise, simply tie the enables of each specific regulator HIGH to turn on automatically. EN_T is edge triggered with rising edge signaling the chip to power on. The EN_T input is deglitched and the default is set at 1ms. As shown in the next 2 diagrams, a rising EN_T edge will start a power on sequence, while a falling EN_T edge will start a shutdown sequence. If EN_T is high, toggling the external enables of the regulators will have no effect on the chip. The regulators can also be programmed through I2C to turn on and off. By default, I2C enables for the regulators on ON. The regulators are on following the pattern below: Regulators on = (I2C enable) AND (External pin enable OR EN_T high). FLEXIBLE POWER SEQUENCING OF MULTIPLE POWER SUPPLIES The LP3907 provides several options for power on sequencing. The two bucks can be individually controlled with ENSW1 and ENSW2. The two LDOs can also be individually controlled with ENLDO1 and ENLDO2. If the user desires a set power on sequence, he can program the chip through I2C and raise EN_T from LOW to HIGH to activate the power on sequencing. LP3907 LP3907 Default Power-Up Sequence 30017810 Power-On Timing Specification Symbol Description Min Typ Max Units t1 Programmable Delay from EN_T assertion to VCC_Buck1 On 1.5 ms t2 Programmable Delay from EN_T assertion to VCC_Buck2 On 2 ms t3 Programmable Delay from EN_T assertion to VCC_LDO1 On 3 ms t4 Programmable Delay from EN_T assertion to VCC_LDO2 On 6 ms Note: The LP3907 default Power on delays can be reprogrammed at final test or I2C to 1, 1.5, 2, 3, 6, or 11ms. www.national.com 20 LP3907 LP3907 Default Power-Off Sequence 30017811 Symbol Description Min Typ Max Units t1 Programmable Delay from EN_T deassertion to VCC_Buck1 Off 1.5 ms t2 Programmable Delay from EN_T deassertion to VCC_Buck2 Off 2 ms t3 Programmable Delay from EN_T deassertion to VCC_LDO1 Off 3 ms t4 Programmable Delay from EN_T deassertion to VCC_LDO2 Off 6 ms Note: The LP3907 default Power on delays can be reprogrammed at final test to 0, .5, 1, 2, 5, or 10ms. Default setting is the same as the on sequence. 21 www.national.com LP3907 is logic LOW when either of the buck outputs are below 91% of the rising value , or when one or both outputs fall below 82% of the desired value. The time delay between output voltage level and nPOR is enabled is (50µs, 50ms, 100ms, 200ms) 50ms by default. The system designer can choose the external pull-up resistor (i.e. 100kΩ) for the nPOR pin. Flexible Power-On Reset (i.e., Power Good with delay) The LP3907 is equipped with an internal Power-On-Reset (“POR”) circuit which monitors the output voltage levels on bucks 1 and 2. The nPOR is an open drain logic output which NPOR With Counter Delay 30017821 The above diagram shows the simplest application of the Power On Reset, where both switcher enables are tied together. In Case 1, RDY1 causes NPOR to transition LOW and triggers the NPOR delay counter. If the power supply for Buck2 does not come on within that period, NPOR will stay LOW, indicating a power fail mode. Case 2 indicates the vice www.national.com versa scenario if Buck1 supply did not come on. In both cases the NPOR remains LOW. Case 3 shows a typical application of the Power On Reset, where both switcher enables are tied together. Even if RDY1 ramps up slightly faster than RDY2 (or vice versa), the NPOR signal will trigger a programmable delay before going HIGH, as explained below. 22 LP3907 Faults Occurring in Counter Delay After Startup 30017881 The above timing diagram details the Power good with delay with respect to the enable signals EN1, and EN2. The RDY1, RDY2 are internal signals derived from the output of two comparators. Each comparator has been trimmed as follows: Comparator Level If EN1 and RDY1 signals are High at time t1, then the RDY1 signal rising edge triggers the programmable delay counter (50μs, 50ms, 100ms, 200ms). This delay forces NPOR LOW between time interval t1 and t2. NPOR is then pulled high after the programmable delay is completed. Now if EN2 and RDY2 are initiated during this interval the NPOR signal ignores this event. If either RDY1or RDY2 were to go LOW at t3 then the programmable delay is triggered again. Buck Supply Level HIGH Greater than 94% LOW Less than 85% The circuits for EN1 and RDY1 is symmetrical to EN2 and RDY2, so each reference to EN1 and RDY1 will also work for EN2 and RDY2 and vice versa. 23 www.national.com LP3907 NPOR Mask Window 30017813 If the EN1 and RDY1 are initiated in normal operation, then NPOR is asserted and deasserted as explained above. In Case 1, we see that case where EN2 and RDY2 are initiated after triggered programmable delay. To prevent the NPOR being asserted again, a masked window ( 5ms ) counter delay is triggered off the EN2 rising edge. NPOR is still held HIGH for the duration of the mask, whereupon the NPOR status afterwards will depend on the status of both RDY1 and RDY2 lines. www.national.com In Case 2, we see the case where EN2 is initiated after the RDY1 triggered programmable delay, but RDY2 never goes HIGH (Buck2 never turns on). Normal operation operation of NPOR occurs wilth respect to EN1 and RDY1, and the NPOR signal is held HIGH for the duration of the mask window. We see that NPOR goes LOW after the masking window has timed out because it is now dependent on RDY1 and RDY2, where RDY2 is LOW. 24 LP3907 Design Implementation of the Flexible Power-On Reset 30017812 An internal Power-on reset of the IC is used with EN1, and EN2 to produce a reset signal (LOW) to the delay timer NPOR. EN1 and RDY1 or EN2 and RDY2 are used to generate the set signal (HIGH) to the delay timer. S=R=1 never occurs. The mask timers are triggered off EN1 and EN2 which are gated with RDY1, and RDY2 to generate outputs to the final AND gate to generate the NPOR. four voltage regulators whenever this supply voltage is less than 2.8VDC. The circuit incorporates a bandgap based circuit that establishes the reference used to determine the 2.8VDC trip point for a VIN OK – Not OK detector. This VIN OK signal is then used to gate the enable signals to the four regulators of the LP3907. When VINLDO12 is greater than 2.8VDC the four enables control the four regulators, when VINLDO12 is less than 2.8VDC the four regulators are disabled by the VIN detector being in the “Not OK” state. The circuit has built in hysteresis to prevent chattering occurring. Under Voltage Lock Out The LP3907 features an “under voltage lock out circuit”. The function of this circuit is to continuously monitor the raw input supply voltage (VINLDO12) and automatically disables the 25 www.national.com LP3907 Signal timing specifications are according to the I2C bus specification. The maximum bit rate is 400kbit/s. See I2C specification from Philips for further details. I2C Compatible Serial Interface I2C SIGNALS The LP3907 features an I2C compatible serial interface, using two dedicated pins: SCL and SDA for I2C clock and data respectively. Both signals need a pull-up resistor according to the I2C specification. The LP3907 interface is an I2C slave that is clocked by the incoming SCL clock. I2C DATA VALIDITY The data on the SDA line must be stable during the HIGH period of the clock signal (SCL), e.g.- the state of the data line can only be changed when CLK is LOW. 30017816 I2C Signals: Data Validity to HIGH while the SCL is HIGH. The 2C master always genI2C START AND STOP CONDITIONS erates START and STOP bits. The I2C bus is considered to START and STOP bits classify the beginning and the end of be busy after START condition and free after STOP condition. the I2C session. START condition is defined as the SDA signal During data transmission, I2C master can generate repeated transitioning from HIGH to LOW while the SCL line is HIGH. START conditions. First START and repeated START condiSTOP condition is defined as the SDA transitioning from LOW tions are equivalent, function-wise. 30017817 START and STOP Conditions www.national.com 26 30017818 I2C Chip Address 30017819 w = write (SDA = “0”) r = read )SDA = “1”) acl = aclmpw;edge )SDA pulled down by either master or slave) rs = repeated start id = LP3907 chip address: 0x60 I2C Write Cycle When a READ function is to be accomplished, a WRITE function must precede the READ function, as shown in the Read Cycle waveform. 30017824 I2C Read Cycle 27 www.national.com LP3907 bit which is a data direction bit (R/W). Please note that according to industry 2C standards for 7-bit addresses, the MSB of an 8-bit address is removed, and communication actually starts with the 7th most significant bit. For the eighth bit (LSB), a “0” indicates a WRITE and a “1” indicates a READ. The second byte selects the register to which the data will be written. The third byte contains data to write to the selected register. LP3907 has a chip address of 60’h, which is factory programmed. TRANSFERRING DATA Every byte put on the SDA line must be eight bits long, with the most significant bit (MSB) being transferred first. Each byte of data has to be followed by an acknowledge bit. The acknowledged related clock pulse is generated by the master. The transmitter releases the SDA line (HIGH) during the acknowledge clock pulse. The receiver must pull down the SDA line during the 9th clock pulse, signifying acknowledgement. A receiver which has been addressed must generate an acknowledgement (“ACK”) after each byte has been received. After the START condition, the 2C master sends a chip address. This address is seven bits long followed by an eighth LP3907 LP3907 Control Registers Register Address Register Name Read/ Write Register Description 0x02 ICRA R Interrupt Status Register A 0x07 SCR1 R/W System Control 1 Register 0x10 BKLDOEN R/W Buck and LDO Output Voltage Enable Register 0x11 BKLDOSR R Buck and LDO Output Voltage Status Register 0x20 VCCR R/W Voltage Change Control Register 1 0x23 B1TV1 R/W Buck1 Target Voltage 1 Register 0x24 B1TV2 R/W Buck1 Target Voltage 2 Register 0x25 B1RC R/W Buck1 Ramp Control 0x29 B2TV1 R/W Buck2 Target Voltage 1 Register 0x2A B2TV2 R/W Buck2 Target Voltage 2 Register 0x2B B2RC R/W Buck2 Ramp Control 0x38 BFCR R/W Buck Function Register 0x39 LDO1VCR R/W LDO1 Voltage control Registers 0x3A LDO2VCR R/W LDO2 Voltage control Registers INTERRUPT STATUS REGISTER (ISRA) 0X02 This register informs the System Engineer of the temperature status of the chip. D7-2 D1 D0 Name — Temp 125°C — Access — R — Data Reserved Status bit for thermal warning PMIC T>125°C 0 – PMIC Temp. < 125°C 1 – PMIC Temp. > 125°C Reserved Reset 0 0 0 CONTROL 1 REGISTER (SCR1) 0X07 This register allows the user to select the preset delay sequence for power-on timing, to switch between PFM and PWM mode for the bucks, and also to select between an internal and external clock for the bucks. D7 D6-4 D3 D2 D1 D0 — EN_DLY — FPWM2 FPWM1 ECEN Access — R/W — R/W R/W R/W Data Reserved Selects the preset Reserved delay sequence from EN_T assertion (shown below) Buck2 PWM /PFM Mode select 0 – Auto Switch PFM PWM operation 1 – PWM Mode Only Buck 1 PWM /PFM Reserved Mode select 0 – Auto Switch PFM PWM operation 1 – PWM Mode Only Reset 0 010 0 0 Name www.national.com 1 28 0 LP3907 EN_DLY PRESET DELAY SEQUENCE AFTER EN_T ASSERTION Delay (ms) EN_DLY<2:0> Buck1 Buck2 LDO1 LDO2 1 1 1 1 001 1 1.5 2 2 010 1.5 2 3 6 011 1.5 2 1 1 100 1.5 2 3 6 101 1.5 1.5 2 2 110 3 2 1 1.5 111 2 3 6 11 000 BUCK AND LDO OUTPUT VOLTAGE ENABLE REGISTER (BKLDOEN) – 0X10 This register controls the enables for the Bucks and LDOs. D7 D6 D5 D4 D3 D2 D1 D0 Name — LDO2EN — LDO1EN — BK2EN — BK1EN Access — R/W — R/W — R/W — R/W Data Reserved 0 – Disable 1 – Enable Reserved 0 – Disable 1 – Enable Reserved 0 – Disable 1 – Enable Reserved 0 – Disable 1 – Enable Reset 0 1 1 1 0 1 0 1 BUCK AND LDO STATUS REGISTER (BKLDOSR) – 0X11 This register monitors whether the Bucks and LDOs meet the voltage output specifications. D7 D6 D5 D4 D3 D2 D1 D0 Name BKS_OK LDOS_OK LDO2_OK LDO1_OK — BK2_OK — BK1_OK Access R R R R — R — R Data 0 – Buck 1-2 Not Valid 1 – Bucks Valid 0 – LDO 1-2 0 – LDO2 Not 0 – LDO1 Not Reserve Not Valid Valid Valid d 1 – LDOs Valid 1 – LDO2 Valid 1 – LDO1 Valid 0 – Buck2 Not Reserve Valid d 1 – Buck2 Valid 0 – Buck1 Not Valid 1 – Buck1 Valid Reset 0 0 0 0 0 0 0 0 BUCK VOLTAGE CHANGE CONTROL REGISTER 1 (VCCR) – 0X20 This register selects and controls the output target voltages for the buck regulators. D7-6 D5 D4 D3-2 D1 D0 Name — B2VS B2GO — B1VS B1GO Access — R/W R/W — R/W R/W Data Reserved Buck2 Target Voltage Select 0 – B2VT1 1 – B2VT2 Buck2 Voltage Ramp Reserved CTRL 0 – Hold 1 – Ramp to B2VS selection Buck1 Target Voltage Select 0 – B1VT1 1 – B1VT2 Buck1 Voltage Ramp CTRL 0 – Hold 1 – Ramp to B1VS selection Reset 00 0 0 0 0 00 29 www.national.com LP3907 BUCK1 TARGET VOLTAGE 2 REGISTER (B1TV2) – 0X24 This register allows the user to program the output target voltage of Buck1. BUCK1 TARGET VOLTAGE 1 REGISTER (B1TV1) – 0X23 This register allows the user to program the output target voltage of Buck1. Name Access Data D7-5 D4-0 — BK1_VOUT1 Name — R/W Access Reserved Buck1 Output Voltage (V) www.national.com 000 D4-0 — BK1_VOUT2 — R/W Reserved Buck1 Output Voltage (V) 5’h00 Ext Ctrl 5’h00 Ext Ctrl 5’h01 0.80 5’h01 0.80 5’h02 0.85 5’h02 0.85 5’h03 0.90 5’h03 0.90 5’h04 0.95 5’h04 0.95 5’h05 1.00 5’h05 1.00 5’h06 1.05 5’h06 1.05 5’h07 1.10 5’h07 1.10 5’h08 1.15 5’h08 1.15 5’h09 1.20 5’h09 1.20 5’h0A 1.25 5’h0A 1.25 5’h0B 1.30 5’h0B 1.30 5’h0C 1.35 5’h0C 1.35 5’h0D 1.40 5’h0D 1.40 5’h0E 1.45 5’h0E 1.45 5’h0F 1.50 5’h0F 1.50 5’h10 1.55 5’h10 1.55 5’h11 1.60 5’h11 1.60 5’h12 1.65 5’h12 1.65 5’h13 1.70 5’h13 1.70 5’h14 1.75 5’h14 1.75 5’h15 1.80 5’h15 1.80 5’h16 1.85 5’h16 1.85 5’h17 1.90 5’h17 1.90 5’h18 1.95 5’h18 1.95 5’h19 2.00 5’h19 2.00 5’h1A–5’h1F Reset Data D7-5 2.00 5’h1A–5’h1F 01001 Reset 30 000 01001 2.00 LP3907 BUCK1 RAMP CONTROL REGISTER (B1RC) - 0x25 This register allows the user to program the rate of change between the target voltages of Buck1. Name Access Data D7 D6-4 D3-0 ---- ---- B1RS ---- ---- Reserved Reserved R/W Data Code Ramp Rate mV/us 4h'0 Instant 4h'1 1 4h'2 2 4h'3 3 4h'4 4 4h'5 5 4h'6 6 4h'7 7 4h'8 8 4h'9 9 4h'A 10 4h'B - 4h'F Reset 0 010 10 1000 31 www.national.com LP3907 BUCK2 TARGET VOLTAGE 2 REGISTER (B2TV2) – 0X2A This register allows the user to program the output target voltage of Buck2. BUCK2 TARGET VOLTAGE 1 REGISTER (B2TV1) – 0X29 This register allows the user to program the output target voltage of Buck2. Name Access Data D7-5 D4-0 — BK2_VOUT1 Name — R/W Access Reserved Buck2 Output Voltage (V) www.national.com 000 D4-0 — BK2_VOUT2 — R/W Reserved Buck2 Output Voltage (V) 5’h00 Ext Ctrl 5’h00 Ext Ctrl 5’h01 1.0 5’h01 1.0 5’h02 1.1 5’h02 1.1 5’h03 1.2 5’h03 1.2 5’h04 1.3 5’h04 1.3 5’h05 1.4 5’h05 1.4 5’h06 1.5 5’h06 1.5 5’h07 1.6 5’h07 1.6 5’h08 1.7 5’h08 1.7 5’h09 1.8 5’h09 1.8 5’h0A 1.9 5’h0A 1.9 5’h0B 2.0 5’h0B 2.0 5’h0C 2.1 5’h0C 2.1 5’h0D 2.2 5’h0D 2.2 5’h0E 2.4 5’h0E 2.4 5’h0F 2.5 5’h0F 2.5 5’h10 2.6 5’h10 2.6 5’h11 2.7 5’h11 2.7 5’h12 2.8 5’h12 2.8 5’h13 2.9 5’h13 2.9 5’h14 3.0 5’h14 3.0 5’h15 3.1 5’h15 3.1 5’h16 3.2 5’h16 3.2 5’h17 3.3 5’h17 3.3 5’h18 3.4 5’h18 3.4 5’h19 3.5 5’h19 3.5 5’h1A–5’h1F Reset Data D7-5 3.5 5’h1A–5’h1F 01001 Reset 32 000 01001 3.5 LP3907 BUCK2 RAMP CONTROL REGISTER (B2RC) - 0x2B This register allows the user to program the rate of change between the target voltages of Buck2 Name Access Data D7 D6-4 D3-0 ---- ---- B2RS ---- ---- Reserved Reserved R/W Data Code Ramp Rate mV/us 4h'0 Instant 4h'1 1 4h'2 2 4h'3 3 4h'4 4 4h'5 5 4h'6 6 4h'7 7 4h'8 8 4h'9 9 4h'A 10 4h'B - 4h'F Reset 0 010 10 1000 33 www.national.com LP3907 netic Interference (EMI). The spread spectrum modulation frequency refers to the rate at which the frequency ramps up and down, centered at 2MHz. BUCK FUNCTION REGISTER (BFCR) – 0x38 This register allows the Buck switcher clock frequency to be spread across a wider range, allowing for less Electro-mag- 30017825 This register also allows dynamic scaling of the NPOR Delay Timing. The LP3907 is equipped with an internal Power-OnReset (“POR”) circuit which monitors the output voltage levels on the buck regulators, allowing the user to more actively monitor the power status of the chip. The Under Voltage Lock-Out feature continuously monitor the raw input supply voltage (VINLDO12) and automatically disables the four voltage regulators whenever this supply voltage D7-2 D4 is less than 2.8VDC. This prevents the user from damaging the power source (i.e. battery), but can be disabled if the user wishes. Note that if the supply to VDD_M is close to 2.8V with a heavy load current on the regulators, the chip is in danger of powering down due to UVLO. If the user wishes to keep the chip active under those conditions, enable the “Bypass UVLO” feature. D3 D1 D0 Name — BP_UVLO TPOR BK_SLOMOD BK_SSEN Access — R/W R/w R/W R/W Bypass UVLO monitoring 0 - Allow UVLO 1 - Disable UVLO NPOR Delay Timing 00 - 50µs 01 - 50ms 10 - 100ms 11 - 200ms Buck Spread Spectrum Modulation 0 – 10 kHz triangular wave 1 – 2 kHz triangular wave Spread Spectrum Function Output 0 – Disabled 1 – Enabled 01 1 Data Reserved Reset 000 www.national.com 0 34 0 Name Access Data D7-5 D4-0 — LDO1_OUT Name — R/W Access Reserved LDO1 Output voltage (V) 000 D4-0 — LDO2_OUT — R/W Reserved LDO2 Output voltage (V) 5’h00 1.0 5’h00 1.0 5’h01 1.1 5’h01 1.1 5’h02 1.2 5’h02 1.2 5’h03 1.3 5’h03 1.3 5’h04 1.4 5’h04 1.4 5’h05 1.5 5’h05 1.5 5’h06 1.6 5’h06 1.6 5’h07 1.7 5’h07 1.7 5’h08 1.8 5’h08 1.8 5’h09 1.9 5’h09 1.9 5’h0A 2.0 5’h0A 2.0 5’h0B 2.1 5’h0B 2.1 5’h0C 2.2 5’h0C 2.2 5’h0D 2.3 5’h0D 2.3 5’h0E 2.4 5’h0E 2.4 5’h0F 2.5 5’h0F 2.5 5’h10 2.6 5’h10 2.6 5’h11 2.7 5’h11 2.7 5’h12 2.8 5’h12 2.8 5’h13 2.9 5’h13 2.9 5’h14 3.0 5’h14 3.0 5’h15 3.1 5’h15 3.1 5’h16 3.2 5’h16 3.2 5’h17 3.3 5’h17 3.3 5’h18 3.4 5’h18 3.4 5’h19 3.5 5’h19 3.5 5’h1A–5’h1F Reset Data D7-5 3.5 5’h1A–5’h1F 01111 Reset 35 000 3.5 10111 www.national.com LP3907 LDO2 CONTROL REGISTER (LDO2VCR) – 0X3A This register allows the user to program the output target voltage of LDO 2. LDO1 CONTROL REGISTER (LDO1VCR) – 0X39 This register allows the user to program the output target voltage of LDO 1. LP3907 External Capacitors The regulators on the LP3907 require external capacitors for regulator stability. These are specifically designed for portable applications requiring minimum board space and smallest components. These capacitors must be correctly selected for good performance. Application Notes ANALOG POWER SIGNAL ROUTING All power inputs should be tied to the main VDD source (i.e. battery), unless the user wishes to power it from another source. (i.e. external LDO output). The analog VDD inputs power the internal bias and error amplifiers, so they should be tied to the main VDD. The analog VDD inputs must have an input voltage between 2.8 and 5.5V, as specified in the Electrical Characteristics Section in the front of the datasheet. The other VINs (VINLDO1, VINLDO2, VIN1, VIN2) can actually have inputs lower than 2.8V, as long as it's higher than the programmed output (+0.3V, to be safe). The analog and digital grounds should be tied together outside of the chip to reduce noise coupling. LDO CAPACITOR SELECTION Input Capacitor An input capacitor is required for stability. It is recommended that a 1.0μF capacitor be connected between the LDO input pin and ground (this capacitance value may be increased without limit). This capacitor must be located a distance of not more than 1cm from the input pin and returned to a clean analog ground. Any good quality ceramic, tantalum, or film capacitor may be used at the input. Important: Tantalum capacitors can suffer catastrophic failures due to surge currents when connected to a low impedance source of power (like a battery or a very large capacitor). If a tantalum capacitor is used at the input, it must be guaranteed by the manufacturer to have a surge current rating sufficient for the application. There are no requirements for the ESR (Equivalent Series Resistance) on the input capacitor, but tolerance and temperature coefficient must be considered when selecting the capacitor to ensure the capacitance will remain approximately 1.0μF over the entire operating temperature range. COMPONENT SELECTION Inductors for SW1 and SW2 There are two main considerations when choosing an inductor; the inductor should not saturate and the inductor current ripple is small enough to achieve the desired output voltage ripple. Care should be taken when reviewing the different saturation current ratings that are specified by different manufacturers. Saturation current ratings are typically specified at 25ºC, so ratings at maximum ambient temperature of the application should be requested from the manufacturer. There are two methods to choose the inductor saturation current rating: Output Capacitor The LDOs on the LP3907 are designed specifically to work with very small ceramic output capacitors. A 0.47µF ceramic capacitor (temperature types Z5U, Y5V or X7R) with ESR between 5 mΩ to 500 mΩ, is suitable in the application circuit. It is also possible to use tantalum or film capacitors at the device output, COUT (or VOUT), but these are not as attractive for reasons of size and cost. The output capacitor must meet the requirement for the minimum value of capacitance and also have an ESR value that is within the range 5 mΩ to 500 mΩ for stability. Method 1: The saturation current is greater than the sum of the maximum load current and the worst case average to peak inductor current. This can be written as follows: IRIPPLE: IOUTMAX: VIN: L: f: VOUT: Capacitor Characteristics The LDOs are designed to work with ceramic capacitors on the output to take advantage of the benefits they offer. For capacitance values in the range of 0.47µF to 4.7µF, ceramic capacitors are the smallest, least expensive and have the lowest ESR values, thus making them best for eliminating high frequency noise. The ESR of a typical 1.0µF ceramic capacitor is in the range of 20mΩ to 40mΩ, which easily meets the ESR requirement for stability for the LDOs. For both input and output capacitors, careful interpretation of the capacitor specification is required to ensure correct device operation. The capacitor value can change greatly, depending on the operating conditions and capacitor type. In particular, the output capacitor selection should take account of all the capacitor parameters, to ensure that the specification is met within the application. The capacitance can vary with DC bias conditions as well as temperature and frequency of operation. Capacitor values will also show some decrease over time due to aging. The capacitor parameters are also dependent on the particular case size, with smaller sizes giving poorer performance figures in general. As an example, below is typical graph comparing different capacitor case sizes in a Capacitance vs. DC Bias plot. Average to peak inductor current Maximum load current Maximum input voltage to the buck Min inductor value including worse case tolerances (30% drop can be considered for method 1) Minimum switching frequency (1.6 MHz) Buck Output voltage Method 2: A more conservative and recommended approach is to choose an inductor that has saturation current rating greater than the maximum current limit of 1250mA for Buck1 and 1750mA for Buck2. Given a peak-to-peak current ripple (IPP) the inductor needs to be at least Inductor LSW1,2 www.national.com Value Unit Description 2.2 µH SW1,2 inductor Notes D.C.R. 70mΩ 36 The worse case is when VIN = 2VOUT. 30017828 Graph Showing a Typical Variation in Capacitance vs. DC Bias Output Capacitor Selection for SW1, SW2 A 10μF, 6.3V ceramic capacitor should be used on the output of the sw1 and sw2 magnetic dc/dc converters. The output capacitor needs to be mounted as close as possible to the output of the device. A large value may be used for improved input voltage filtering. The recommended capacitor types are X7R or X5R. Y5V type capacitors should not be used. DC bias characteristics of ceramic capacitors must be considered when selecting case sizes like 0805 and 0603. DC bias characteristics vary from manufacturer to manufacturer and DC bias curves should be requested from them and analyzed as part of the capacitor selection process. The output filter capacitor of the magnetic dc/dc converter smooths out current flow from the inductor to the load, helps maintain a steady output voltage during transient load changes and reduces output voltage ripple. These capacitors must be selected with sufficient capacitance and sufficiently low ESD to perform these functions. The output voltage ripple is caused by the charging and discharging of the output capacitor and also due to its ESR and can be calculated as follows: As shown in the graph, increasing the DC Bias condition can result in the capacitance value that falls below the minimum value given in the recommended capacitor specifications table. Note that the graph shows the capacitance out of spec for the 0402 case size capacitor at higher bias voltages. It is therefore recommended that the capacitor manufacturers' specifications for the nominal value capacitor are consulted for all conditions, as some capacitor sizes (e.g. 0402) may not be suitable in the actual application. The ceramic capacitor’s capacitance can vary with temperature. The capacitor type X7R, which operates over a temperature range of −55°C to +125°C, will only vary the capacitance to within ±15%. The capacitor type X5R has a similar tolerance over a reduced temperature range of −55°C to +85°C. Many large value ceramic capacitors, larger than 1µF are manufactured with Z5U or Y5V temperature characteristics. Their capacitance can drop by more than 50% as the temperature varies from 25°C to 85°C. Therefore X7R is recommended over Z5U and Y5V in applications where the ambient temperature will change significantly above or below 25°C. Tantalum capacitors are less desirable than ceramic for use as output capacitors because they are more expensive when comparing equivalent capacitance and voltage ratings in the 0.47µF to 4.7µF range. Another important consideration is that tantalum capacitors have higher ESR values than equivalent size ceramics. This means that while it may be possible to find a tantalum capacitor with an ESR value within the stable range, it would have to be larger in capacitance (which means bigger and more costly) than a ceramic capacitor with the same ESR value. It should also be noted that the ESR of a typical tantalum will increase about 2:1 as the temperature goes from 25°C down to −40°C, so some guard band must be allowed. Voltage peak-to-peak ripple due to ESR can be expressed as follows: VPP–ESR = 2 × IRIPPLE × RESR Because the VPP-C and VPP-ESR are out of phase, the rms value can be used to get an approximate value of the peak-topeak ripple: Input Capacitor Selection for SW1 and SW2 A ceramic input capacitor of 10µF, 6.3V is sufficient for the magnetic dc/dc converters. Place the input capacitor as close as possible to the input of the device. A large value may be used for improved input voltage filtering. The recommended capacitor types are X7R or X5R. Y5V type capacitors should not be used. DC bias characteristics of ceramic capacitors must be considered when selecting case sizes like 0805 and 0603. The input filter capacitor supplies current to the PFET Note that the output voltage ripple is dependent on the inductor current ripple and the equivalent series resistance of the output capacitor (RESR). The RESR is frequency dependent as well as temperature dependent. The RESR should be calculated with the applicable switching frequency and ambient temperature. 37 www.national.com LP3907 switch of the dc/dc converter in the first half of each cycle and reduces voltage ripple imposed on the input power source. A ceramic capacitor’s low ESR (Equivalent Series Resistance) provides the best noise filtering of the input voltage spikes due to fast current transients. A capacitor with sufficient ripple current rating should be selected. The Input current ripple can be calculated as: LP3907 Min Value Unit CLDO1 Capacitor 0.47 µF LDO1 output capacitor Description Ceramic, 6.3V, X5R Recommended Type CLDO2 0.47 µF LDO2 output capacitor Ceramic, 6.3V, X5R CSW1 10.0 µF SW1 output capacitor Ceramic, 6.3V, X5R CSW2 10.0 µF SW2 output capacitor Ceramic, 6.3V, X5R Buck regulators. (Read below: Factory programmable options). The I2C-less system must rely on the correct default output values of the LDO and Buck converters. I2C Pullup Resistor Both SDA and SCL terminals need to have pullup resistors connected to VINLDO12 or to the power supply of the I2C master. The values of the pull-up resistors (typ. ∼1.8kΩ) are determined by the capacitance of the bus. Too large of a resistor combined with a given bus capacitance will result in a rise time that would violate the max. rise time specification. A too small resistor will result in a contention with the pull-down transistor on either slave(s) or master. Factory Programmable Options The following options are EPROM programmed during final test of the LP3907. The system designer that needs specific options is advised to contact the local National Semiconductor sales office. Operation without I2C Interface Operation of the LP3907 without the I2C interface is possible if the system can operate with default values for the LDO and Factory programmable options Current value Enable delay for power on code 010 (see Control 1 register section) SW1 ramp speed 8 mV/µs SW2 ramp speed 8 mV/µs The I2C Chip ID address is offered as a metal mask option. The current value equals 0x60. Power dissipation of Buck1 PBuck1 = PIN – POUT = VoutBuck1* IoutBuck1 * (1 -η1) / η1 [V*A] HIGH VINHIGH-LOAD OPERATION Additional information is provided when the IC is operated at extremes of VIN and regulator loads. These are described in terms of the Junction temperature and, Buck output ripple management. η1 = efficiency of buck 1 Power dissipation of Buck2 PBuck2 = PIN – POUT = VoutBuck2 * IoutBuck2 * (1 - η2) / η2 [V*A] η2 = efficiency of Buck2 Where η is the efficiency for the specific condition taken from efficiency graphs. JUNCTION TEMPERATURE The maximum junction temperature TJ-MAX-OP of 125ºC of the IC package. The following equations demonstrate junction temperature determination, ambient temperature TA-MAX and Total chip power must be controlled to keep TJ below this maximum: TJ-MAX-OP = TA-MAX + (θJA) [ °C/ Watt] * (PD-MAX) [Watts] Total IC power dissipation PD-MAX is the sum of the individual power dissipation of the four regulators plus a minor amount for chip overhead. Chip overhead is Bias, TSD & LDO analog. PD-MAX = PLDO1 + PLD02 + PBUCK1 + PBUCK2 + (0.0001A * VIN) [Watts]. Power dissipation of LDO1 PLDO1 = (VINLDO1- VOUTLDO1) * IoutLDO1 [V*A] Power dissipation of LDO2 PLDO2 = (VINLDO2 - VoutLDO2) * IoutLDO2 [V*A] www.national.com 38 The LP3907 is a monolithic device with integrated power FETs. For that reason, it is important to pay special attention to the thermal impedance of the LLP package and to the PCB layout rules in order to maximize power dissipation of the LLP package. The LLP package is designed for enhanced thermal performance and features an exposed die attach pad at the bottom center of the package that creates a direct path to the PCB for maximum power dissipation. Compared to the traditional leaded packages where the die attach pad is embedded inside the molding compound, the LLP reduces one layer in the thermal path. The thermal advantage of the LLP package is fully realized only when the exposed die attach pad is soldered down to a thermal land on the PCB board with thermal vias planted un- 39 www.national.com LP3907 derneath the thermal land. Based on thermal analysis of the LLP package, the junction-to-ambient thermal resistance (θJA) can be improved by a factor of two when the die attach pad of the LLP package is soldered directly onto the PCB with thermal land and thermal vias, as opposed to an alternative with no direct soldering to a thermal land. Typical pitch and outer diameter for thermal vias are 1.27mm and 0.33mm respectively. Typical copper via barrel plating is 1oz, although thicker copper may be used to further improve thermal performance. The LP3907 die attach pad is connected to the substrate of the IC and therefore, the thermal land and vias on the PCB board need to be connected to ground (GND pin). For more information on board layout techniques, refer to Application Note AN–1187 “Leadless Lead frame Package (LLP).” on http://www.national.com This application note also discusses package handling, solder stencil and the assembly process. Thermal Performance of the LLP Package LP3907 Physical Dimensions inches (millimeters) unless otherwise noted 4 X 4 X 0.8 mm 24-Pin LLP Package NS Package SQA24A For ordering, refer to Ordering Information table www.national.com 40 LP3907 Notes 41 www.national.com LP3907 Dual High-Current Step-Down DC/DC and Dual Linear Regulator with I2C Compatible Interface Notes THE CONTENTS OF THIS DOCUMENT ARE PROVIDED IN CONNECTION WITH NATIONAL SEMICONDUCTOR CORPORATION (“NATIONAL”) PRODUCTS. NATIONAL MAKES NO REPRESENTATIONS OR WARRANTIES WITH RESPECT TO THE ACCURACY OR COMPLETENESS OF THE CONTENTS OF THIS PUBLICATION AND RESERVES THE RIGHT TO MAKE CHANGES TO SPECIFICATIONS AND PRODUCT DESCRIPTIONS AT ANY TIME WITHOUT NOTICE. NO LICENSE, WHETHER EXPRESS, IMPLIED, ARISING BY ESTOPPEL OR OTHERWISE, TO ANY INTELLECTUAL PROPERTY RIGHTS IS GRANTED BY THIS DOCUMENT. TESTING AND OTHER QUALITY CONTROLS ARE USED TO THE EXTENT NATIONAL DEEMS NECESSARY TO SUPPORT NATIONAL’S PRODUCT WARRANTY. EXCEPT WHERE MANDATED BY GOVERNMENT REQUIREMENTS, TESTING OF ALL PARAMETERS OF EACH PRODUCT IS NOT NECESSARILY PERFORMED. NATIONAL ASSUMES NO LIABILITY FOR APPLICATIONS ASSISTANCE OR BUYER PRODUCT DESIGN. BUYERS ARE RESPONSIBLE FOR THEIR PRODUCTS AND APPLICATIONS USING NATIONAL COMPONENTS. PRIOR TO USING OR DISTRIBUTING ANY PRODUCTS THAT INCLUDE NATIONAL COMPONENTS, BUYERS SHOULD PROVIDE ADEQUATE DESIGN, TESTING AND OPERATING SAFEGUARDS. EXCEPT AS PROVIDED IN NATIONAL’S TERMS AND CONDITIONS OF SALE FOR SUCH PRODUCTS, NATIONAL ASSUMES NO LIABILITY WHATSOEVER, AND NATIONAL DISCLAIMS ANY EXPRESS OR IMPLIED WARRANTY RELATING TO THE SALE AND/OR USE OF NATIONAL PRODUCTS INCLUDING LIABILITY OR WARRANTIES RELATING TO FITNESS FOR A PARTICULAR PURPOSE, MERCHANTABILITY, OR INFRINGEMENT OF ANY PATENT, COPYRIGHT OR OTHER INTELLECTUAL PROPERTY RIGHT. LIFE SUPPORT POLICY NATIONAL’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES OR SYSTEMS WITHOUT THE EXPRESS PRIOR WRITTEN APPROVAL OF THE CHIEF EXECUTIVE OFFICER AND GENERAL COUNSEL OF NATIONAL SEMICONDUCTOR CORPORATION. As used herein: Life support devices or systems are devices which (a) are intended for surgical implant into the body, or (b) support or sustain life and whose failure to perform when properly used in accordance with instructions for use provided in the labeling can be reasonably expected to result in a significant injury to the user. A critical component is any component in a life support device or system whose failure to perform can be reasonably expected to cause the failure of the life support device or system or to affect its safety or effectiveness. National Semiconductor and the National Semiconductor logo are registered trademarks of National Semiconductor Corporation. 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