LP3972SQ-A413

LP3972 Power Management Unit for Advanced Application Processors January 11, 2008 LP3972 Power Management Unit for Advanced Application Processors General Description The LP3972 is a multi-function, programmable Power Management Unit, designed especially for advanced application processors. The LP3972 is optimized for low power handheld applications and provides 6 low dropout, low noise linear regulators, three DC/DC magnetic buck regulators, a back-up battery charger and two GPIO’s. A high speed serial interface is included to program individual regulator output voltages as well as on/off control. ■ 100 mV (typ) dropout Features ■ Compatible with advanced applications processors requiring DVM (Dynamic Voltage Management) functions or I/O's ■ Three buck regulators for powering high current processor ■ 6 LDO's for powering RTC, peripherals, and I/O's ■ Backup battery charger with automatic switch for lithium■ ■ ■ ■ ■ ■ manganese coin cell batteries and Super capacitors I2C compatible high speed serial interface Software control of regulator functions and settings Precision internal reference Thermal overload protection Current overload protection Tiny 40-pin 5x5 mm LLP package Key Specifications Buck Regulators ■ Programmable VOUT from 0.725 to 3.3V ■ Up to 95% efficiency ■ Up to 1.6A output current ■ ±3% output voltage accuracy LDO’s ■ Programmable VOUT of 1.0V–3.3V ■ ±3% output voltage accuracy ■ 150/300/400 mA output currents — LDO RTC 30 mA — LDO 1 300 mA — LDO 2 150 mA — LDO 3 150 mA — LDO 4 150 mA — LDO 5 400 mA Applications ■ ■ ■ ■ ■ PDA phones Smart phones Personal Media Players Digital cameras Application processors — Marvell PXA — Freescale — Samsung © 2008 National Semiconductor Corporation 202076 www.national.com LP3972 Simplified Application Circuit 20207601 www.national.com 2 LP3972 20207628 — The I2C lines are pulled up via a I/O source — VINLDO4, 5 can either be powered from main battery source, or by a buck regulator or VIN. 3 www.national.com LP3972 Connection Diagrams and Package Mark Information 40-Pin Leadless Leadframe Package NS Package Number SQF40A 20207602 Note: Circle marks pin 1 position. Package Mark 20207604 Top View Note: The actual physical placement of the package marking will vary from part to part. (*) UZTTYY format: 'U' — wafer fab code; 'Z' — assembly code; 'XY' 2 digit date code; 'TT' — die run code. See http://www.national.com/quality/marking_convertion.html for more information on marking information. www.national.com 4 LP3972 Ordering Information Voltage Option Voltage A514 Voltage A514 Voltage A413 Voltage A413 Voltage E514 Voltage E514 Voltage I514 Voltage I514 Order Number LP3972SQ-A514 LP3972SQXA514 LP3972SQ-A413 LP3972SQXA413 LP3972SQ-E514 LP3972SQXE514 LP3972SQ-I514 LP3972SQX-I514 Package Type 40 lead LLP 40 lead LLP 40 lead LLP 40 lead LLP 40 lead LLP 40 lead LLP 40 lead LLP 40 lead LLP SQF040A SQF040A SQF040A SQF040A 72-E514 72-I514 72-I514 1000 tape & reel 4500 tape & reel SQF040A SQF040A 72-A413 72-E514 1000 tape & reel 4500 tape & reel NSC Package Drawing SQF040A SQF040A 72-A514 72-A413 1000 tape & reel 4500 tape & reel Package Marking 72-A514 Supplied As 1000 tape & reel 4500 tape & reel 20207605 Default VOUT Coding Z 0 1 2 3 4 5 6 7 8 9 Default VOUT 1.3 1.8 2.5 2.8 3.0 3.3 1.0 1.4 1.2 1.25 5 www.national.com LP3972 Pin Descriptions Pin # 1 Name PWR_ON I/O I Type D Description This is an active HI push button input which can be used to signal PWR_ON and PWR_OFF events to the CPU by controlling the ext_wakup [pin4] and select contents of register 8H'88 This is an active LOW input signal used for detecting an external HW event. The response is seen in the ext_wakup [pin4] and select contents of register 8H'88 This is an input signal used for detecting a external HW event. The response is seen in the ext_wakup [pin4] and select contents of register 8H'88. The polarity on this pin is assignable This pin generates a single 10mS pulse output to CPU in response to input from pin[s] 1, 2, and 3. Flags CPU to interrogate register 8H'88 Buck1 input feedback terminal Battery Input (Internal circuitry and LDO1-3 power input) LDO1 output LDO2 output Active low Reset pin. Signal used to reset the IC (by default is pulled high internally). Typically a push button reset. Ground Bypass Cap. for the high internal impedance reference. LDO3 output LDO4 output Power input to LDO4, this can be connected to either from a 1.8V supply to main Battery supply. Back Up Battery input supply. LDO_RTC output supply to the RTC of the application processor. Main Battery fault output, indicates the main battery is low (discharged) or the dc source has been removed from the system. This gives the processor an indicator that the power will shut down. During this time the processor will operate from the back up coin cell. 18 19 20 21 22 23 24 25 26 27 28 29 PGND2 SW2 VIN Buck2 SDA SCL FB2 nRSTO VOUT LDO5 VIN LDO5 VDDA FB3 GPIO1 / nCHG_EN G O I I/O I I O O I I I I/O G PWR PWR D D A D PWR PWR PWR A D Buck2 NMOS Power Ground Buck2 switcher output Battery input power to Buck2 I2C Data (Bidirectional) I2C Clock Buck2 input feedback terminal Reset output from the PMIC to the processor LDO5 output Power input to LDO5, this can be connected to VIN or to a separate 1.8V supply. Analog Power for VREF, BIAS Buck3 Feedback General Purpose I/O / Ext. backup battery charger enable pin. This pin enables the main battery / DC source power to charge the backup battery. This pin toggled via the application processor. By grounding this pin the DC source continuously charges the backup battery General Purpose I/O Battery input power to Buck3 Buck3 switcher output Buck3 NMOS Power Ground 2 nTEST_JIG I D 3 SPARE I D 4 5 6 7 8 9 10 11 12 13 14 15 16 17 EXT_WAKEUP FB1 VIN VOUT LDO1 VOUT LDO2 nRSTI GND1 VREF VOUT LDO3 VOUT LDO4 VIN LDO4 VIN BUBATT VOUT LDO_RTC nBATT_FLT O I I O O I G O O O I I O O D A PWR PWR PWR D G A PWR PWR PWR PWR PWR D 30 31 32 33 GPIO2 VIN Buck3 SW3 PGND3 I/O I O G D PWR PWR G www.national.com 6 LP3972 Pin # 34 35 Name BGND1,2,3 SYNC I/O G I Type G D Description Bucks 1, 2 and 3 analog Ground Frequency Synchronization: Connection to an external clock signal PLL to synchronize the PMIC internal oscillator. Input Digital enable pin for the high voltage power domain supplies. Output from the Monahans processor. Digital enable pin for the Low Voltage domain supplies. Output signal from the Monahans processor Buck1 NMOS Power Ground Buck1 Switcher output Battery input power to Buck1 36 37 38 39 40 SYS_EN PWR_EN PGND1 SW1 VIN Buck1 I I G O I D D G PWR PWR A: Analog Pin D: Digital Pin G: Ground Pin P: Power Pin I: Input Pin I/O: Input/Output Pin O: Output Pin Note: In this document active low logic items are prefixed with a lowercase “n” 7 www.national.com LP3972 Absolute Maximum Ratings (Note 1) If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. All Inputs GND to GND SLUG Junction Temperature (TJ-MAX) Storage Temperature Power Dissipation (TA = 70°C) (Note 3) Junction-to-Ambient Thermal Resistance θJA (Note 3) −0.3V to +6.5V ±0.3V 150°C −65°C to +150°C 3.2W 25°C/W Maximum Lead Temp (Soldering) ESD Rating (Note 5) Human Body Model Machine Model 260°C 2 kV 200V Operating Ratings VIN LDO 4,5 VEN Junction Temperature (TJ) Operating Temperature (TA) Maximum Power Dissipation (TA = 70°C) (Notes 3, 4) 2.7V to 5.5V 1.74 to (VIN −40°C to +125°C −40°C to +85°C 2.2W General Electrical Characteristics Symbol VIN, VDDA, VIN Buck1, 2 and 3 VINLDO4, VINLDO5 TSD 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, 6) Parameter Battery Voltage Power Supply for LDO 4 and 5 Thermal Shutdown (Note 14) Temperature Hysteresis **No input supply should be higher then VDDA Conditions Min 2.7 1.74 Typ 3.6 3.6 160 20 Max 5.5 5.5 Units V V °C Supply Specifications Supply (Notes 2, 5) VOUT (Volts) Range (V) Resolution (mV) N/A 25 100 100 50-600 25 25 50-600 50-600 IMAX Maximum Current Current (mA) 30 mA dc source 10 mA backup source 300 150 150 150 400 1600 1600 1600 LDO_RTC LDO1 (VCC_MVT) LDO2 LDO3 LDO4 LDO5 (VCC_SRAM) BUCK 1 (VCC_APPS) BUCK 2 BUCK 3 2.8V 1.7 to 2.0 1.8 to 3.3 1.8 to 3.3 1.0 to 3.3 0.850 to 1.5 0.725 to 1.5 0.8 to 3.3 0.8 to 3.3 www.national.com 8 LP3972 Default Voltage Option Version Enable LDO_RTC LDO1 LDO2 LDO3 LDO4 LDO5 BUCK1 BUCK2 BUCK3 Version Enable LDO_RTC LDO1 LDO2 LDO3 LDO4 LDO5 BUCK1 BUCK2 BUCK3 — — (Notes 2, 5) LP3972SQ-A514 LP3972SQ-A413 Version A 2.8 1.8 1.8D 3D 3D 1.4 1.4 3.3 1.8 — SYS_EN SYS_EN SYS_EN SYS_EN PWR_EN PWR_EN SYS_EN SYS_EN LP3972SQ-I514 Version I 2.8 1.8 1.8E 3D 3D 1.4 1.4 3.3 1.8 — SYS_EN SYS_EN SYS_EN SYS_EN PWR_EN PWR_EN SYS_EN SYS_EN 2.8 1.8 1.8E 3E 3E 1.4 1.4 3.3 1.8 2.8 1.8 1.8D 3D 2.8D 1.4 1.4 3 1.8 Version A SYS_EN SYS_EN SYS_EN SYS_EN PWR_EN PWR_EN SYS_EN SYS_EN LP3972SQ-E514 Version E SYS_EN SYS_EN SYS_EN SYS_EN PWR_EN PWR_EN SYS_EN SYS_EN Note : E = Regulator is ENABLED during startup D = Regulator is DISABLED during startup 9 www.national.com LP3972 LDO RTC Unless otherwise noted, VIN = 3.6V, CIN = 1.0 μF, COUT = 0.47 µF, COUT (VRTC) = 1.0 μF 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, 6, 7) and (Note 10) Symbol VOUT Accuracy ΔVOUT Parameter Output Voltage Accuracy Line Regulation Load Regulation Conditions VIN Connected, Load Current = 1 mA VIN = (VOUT nom + 1.0V) to 5.5V (Note 11) Load Current = 1 mA From Main Battery Load Current = 1 mA to 30 mA From Backup Battery VIN = 3.0V Load Current = 1 mA to 10 mA ISC Short Circuit Current Limit From Main Battery VIN = VOUT +0.3V to 5.5V From Backup Battery VIN - VOUT Dropout Voltage IQ_Max TP1 TP2 CO Maximum Quiescent Current Load Current = 10 mA IOUT = 0 mA 30 2.9 3.0 0.7 5 1.0 500 100 mA 30 375 mV μA V V μF mΩ Min 2.632 Typ 2.8 Max 2.968 0.15 0.05 0.5 %/mA Units V %/V RTC LDO Input Switched from Main VIN Falling Battery to Backup Battery RTC LDO Input Switched from Backup Battery to Main Battery Output Capacitor VIN Rising Capacitance for Stability ESR www.national.com 10 LP3972 LDO 1 to 5 Unless otherwise noted, VIN = 3.6V, CIN = 1.0 μF, COUT = 0.47 µF, COUT (VRTC) = 1.0 μF 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, 6, 7, 10, 11, 15) and (Note 16). Symbol VOUT Accuracy ΔVOUT Parameter Output Voltage Accuracy (Default VOUT) Line Regulation Load Regulation ISC Short Circuit Current Limit Conditions Load Current = 1 mA VIN =3.1V to 5.0V, (Note 11) Load Current = 1 mA VIN = 3.6V, Load Current = 1 mA to IMAX LDO1–4, VOUT = 0V LDO5, VOUT = 0V VIN - VOUT Dropout Voltage PSRR IQ Power Supply Ripple Rejection Quiescent Current “On” Quiescent Current “On” Quiescent Current “Off” TON COUT Turn On Time Output Capacitor Load Current = 50 mA (Note 7) f = 10 kHz, Load Current = IMAX IOUT = 0 mA IOUT = IMAX EN is de-asserted Start up from Shut-down Capacitance for Stability 0°C ≤ TJ ≤ 125°C −40°C ≤ TJ ≤ 125°C ESR 0.68 5 1.0 500 mΩ 0.33 45 40 60 0.03 300 0.47 µF μsec µA 400 500 150 Min −3 Typ Max 3 0.15 0.011 Units % %/V %/mA mA mV dB LDO Dropout Voltage vs. Load Current Collect Data For All LDO’s Dropout Voltage vs. Load Current Change in Output Voltage vs. Load Current 20207629 20207630 11 www.national.com LP3972 LDO1 Line Regulation VOUT = 1.8 volts VIN 3 to 4 volts Load = 100 mA LDO1 Load Transient VIN = 4.1 volts VOUT = 1.8 volts no-load-100 mA 20207631 20207632 Enable Start-up time (LDO1) LDO1 channel 2 LDO4 Channel 1 Sys_enable from 0 volts Load = 100mA 20207633 www.national.com 12 LP3972 Buck Converters SW1, SW2, SW3 Unless otherwise noted, VIN = 3.6V, 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, 6, 12) and (Note 13). Symbol VOUT Eff ISHDN Efficiency Shutdown Supply Current Sync Mode Clock Frequency fOSC IPEAK IQ RDSON (P) RDSON (N) TON CIN CO Internal Oscillator Frequency Peak Switching Current Limit Quiescent Current “On” Pin-Pin Resistance PFET Pin-Pin Resistance NFET Turn On Time Input Capacitor Output Capacitor Start up from Shut-down Capacitance for Stability Capacitance for Stability 8 8 No Load PFM Mode No Load PWM Mode Parameter Output Voltage Accuracy Conditions Default VOUT Load Current = 500 mA EN is de-asserted Synchronized from 13 MHz System Clock 10.4 Min −3 95 0.1 13 2.0 2.1 21 200 240 200 500 2.4 15.6 Typ Max +3 Units % % μA MHz MHz A μA mΩ mΩ μsec µF µF Buck 1 Output Efficiency vs. Load Current Varied from 1mA to 1.5 Amps VIN = 3, 3.5 volts VOUT = 1.4 volts Forced PWM VIN = 4.0-4.5 volts VOUT = 1.4 volts Forced PWM 20207634 20207635 13 www.national.com LP3972 VIN = 3, 3.5 volts VOUT = 1.4 volts Forced PWM Line Transient Response VIN = 3 – 3.6 V, VOUT = 1.2 V, 250 mA load 20207637 20207636 Load Transient 3.6 VIN, 3.3 VOUT, 0 – 100 mA load Mode Change Load transients 20 mA to 560 mA VOUT = 1.4 volts [PFM to PWM] VIN = 4.1 volts 20207638 20207639 Startup Startup into PWM Mode 980 mA [channel 2] VOUT = 1.4 volts VIN = 4.1 volts 20207638 www.national.com 14 LP3972 Back-Up Charger Electrical Characteristics Unless otherwise noted, VIN = VBATT = 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. (Notes 2, 6) and (Note 8). Symbol VIN IOUT Parameter Operational Voltage Range Backup Battery Charging Current Conditions Voltage at VIN VIN = 3.6V, Backup_Bat = 2.5V, Backup Battery Charger Enabled (Note 8) VIN = 5.0V Backup Battery Charger Enabled. Programmable 2.91 Min 3.3 190 Typ Max 5.5 Units V μA VOUT Charger Termination Voltage 3.1 9 15 V mA dB Backup Battery Charger Short Circuit Backup_Bat = 0V, Backup Battery Current Charger Enabled PSRR Power Supply Ripple Rejection Ratio IOUT ≤ 50 μA, VOUT = 3.15V VOUT + 0.4 ≤ VBATT = VIN ≤ 5.0V f < 10 kHz IOUT < 50 μA 0 μA ≤ IOUT ≤ 100 μA 5 IQ COUT Quiescent Current Output Capacitance Output Capacitor ESR 25 0.1 500 μA μF mΩ LP3972 Battery Switch Operation The LP3972 has provisions for two battery connections, the main battery Vbat and Backup Battery The function of the battery switch is to connect power to the RTC LDO from the appropriate battery, depending on conditions described below: • If only the backup battery is applied, the switch will automatically connect the RTC LDO power to this battery. • If only the main battery is applied, the switch will automatically connect the RTC LDO power to this battery • If both batteries are applied, and the main battery is sufficiently charged (Vbat > 3.1V), the switch will automatically connect the RTC LDO power to the main battery. • As the main battery is discharged a separate circuit called nBATT_FLT will warn the system. Then if no action is taken to restore the charge on the main battery, and discharging is continued the battery switch will disconnect the input of the RTC_LDO from the main battery and connect to the backup battery. • The main battery voltage at which the RTC LDO is switched over from main to backup battery is 2.8V typically. • There is a hysteric voltage in this switch operation so; the RTC LDO will not be reconnected to main battery until main battery voltage is greater than 3.1V typically. • The system designer may wish to disable the battery switch when only a main battery is used. This is accomplished by setting the “no back up battery bit” in the control register 8h’0B bit 7 NBUB. With this bit set to “1”, the above described switching will not occur, that is the RTC LDO will remain connected to the main battery even as it is discharged below the 2.9V threshold. The Backup battery input should also be connected to main battery. 15 www.national.com LP3972 Logic Inputs and Outputs DC Operating Conditions Symbol VIL VIH ILEAK Parameter Low Level Input Voltage High Level Input Voltage Input Leakage Current Conditions (Note 2) Min VRTC −0.5V −1 +1 Max 0.5 Units V V µA Logic Inputs (SYS_EN, PWR_EN, SYNC, nRSTI, PWR_ON, nTEST_JIG, SPARE and GPI's) Logic Outputs (nRSTO, EXT_WAKEUP and GPO's) Symbol VOL VOH ILEAK Parameter Output Low Level Output High Level Output Leakage Current Conditions Load = +0.2 mA = IOL Max Load = −0.1 mA = IOL Max VON = VIN VRTC −0.5V +5 Min Max 0.5 Units V V µA Logic Output (nBATT_FLT) Symbol Parameter nBATT_FLT Threshold Voltage VOL VOH ILEAK Output Low Level Output High Level Input Leakage Current Conditions Programmable via Serial Interface Default = 2.8V Load = +0.4 mA = IOL Max Load = −0.2 mA = IOH Max VRTC −0.5V +5 Min 2.4 Typ 2.8 Max 3.4 0.5 Units V V V μA www.national.com 16 LP3972 I2C Compatible Serial Interface Electrical Specifications (SDA and SCL) 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. (Notes 2, 6) and (Note 9) Symbol VIL VIH VOL IOL FCLK tBF tHOLD tCLKLP tCLKHP tSU tDATAHLD tCLKSU TSU TTRANS Parameter Low Level Input Voltage High Level Input Voltage Low Level Output Voltage Low Level Output Current Clock Frequency Bus-Free Time Between Start and Stop Hold Time Repeated Start Condition CLK Low Period CLK High Period Set Up Time Repeated Start Condition Data Hold Time Data Set Up Time Set Up Time for Start Condition (Note 14) (Note 14) (Note 14) VOL = 0.4V (Note 14) (Note 14) (Note 14) (Note 14) (Note 14) (Note 14) (Note 14) (Note 14) (Note 14) (Note 14) 1.3 0.6 1.3 0.6 0.6 0 100 0.6 50 Conditions Min −0.5 0.7 VRTC 0 3.0 400 Typ Max 0.3 VRTC VRTC 0.2 VTRC mA kHz μs μs μs μs μs μs ns μs ns Units V Maximum Pulse Width of Spikes that Must (Note 14) be Suppressed by the Input Filter of Both DATA & CLK Signals Note 1: Absolute Maximum Ratings are limits beyond which damage to the device 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 tables. Note 2: All voltages are with respect to the potential at the GND pin. Note 3: 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 x PD-MAX). Note 4: Junction-to-ambient thermal resistance (θJA) is taken from a thermal modeling result, performed under the conditions and guidelines set forth in the JEDEC standard JESD51–7. The test board is a 4-layer FR-4 board measuring 102 mm x 76 mm x 1.6 mm with a 2x1 array of thermal vias. The ground plane on the board is 50 mm x 50 mm. Thickness of copper layers are 36 µm/1.8 µm/18 µm/36 µm (1.5 oz/1 oz/1 oz/1.5 oz). Ambient temperature in simulation is 22° C, still air. Power dissipation is 1W. 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. The value of θJA of this product can vary significantly, depending on PCB material, layout, and environmental conditions. In applications where high maximum power dissipation exists (high VIN, high IOUT), special care must be paid to thermal dissipation issues. For more information on these topics, please refer to Application Note 1187: Leadless Leadframe Package (LLP) and the Power Efficiency and Power Dissipation section of this datasheet. Note 5: The Human body model is a 100 pF capacitor discharged through a 1.5 k ??? resistor into each pin. (MIL-STD-883 3015.7) The machine model is a 200 pF capacitor discharged directly into each pin. (EAIJ) Note 6: All limits guaranteed at room temperature (standard typeface) and at temperature extremes (bold typeface). All room temperature limits are production tested, guaranteed through statistical analysis or guaranteed by design. All limits at temperature extremes are guaranteed via correlation using standard Statistical Quality Control (SQC) methods. All limits are used to calculate Average Outgoing Quality Level (AOQL). Note 7: Dropout voltage is the input-to-output voltage difference at which the output voltage is 100 mV below its nominal value. Note 8: Back-up battery charge current is programmable via the I2C compatible interface. Refer to the Application Section for more information. Note 9: The I2C signals behave like open-drain outputs and require an external pull-up resistor on the system module in the 2 kΩ to 20 kΩ range. Note 10: LDO_RTC voltage can track LDO3 voltage. LP3972 has a tracking function (nIO_TRACK). When enabled, LDO_RTC voltage will track LDO3 voltage within 200mV down to 2.8V when LDO3 is enabled Note 11: VIN minimum for line regulation values is 2.7V for LDOs 1–3 and 1.8V for LDOs 4 and 5. Condition does not apply to input voltages below the minimum input operating voltage. Note 12: The input voltage range recommended for ideal applications performance for the specified output voltages is given below: VIN = 2.7V to 5.5V for 0.80V < VOUT < 1.8V VIN = (VOUT+ 1V) to 5.5V for 1.8V ≤ VOUT ≤ 3.3V Note 13: Test condition: for VOUT less than 2.7V, VIN = 3.6V; for VOUT greater than or equal to 2.7V, VIN = VOUT+ 1V. Note 14: This electrical specification is guaranteed by design. Note 15: An increase in the load current results in a slight decrease in the output voltage and vice versa. Note 16: Dropout voltage is the input-to-output voltage difference at which the output voltage is 100 mV below its nominal value. This specification does not apply for input voltages below 2.7V for LDOs 1–3 and 1.8V for LDOs 4 and 5. 17 www.national.com LP3972 Buck Converter Operation DEVICE INFORMATION The LP3972 includes three high efficiency step down DC-DC switching buck converters. Using a voltage mode architecture with synchronous rectification, the buck converters have the ability to deliver up to 1600 mA depending on the input voltage, output voltage, ambient temperature and the inductor chosen. There are three modes of operation depending on the current required - PWM, PFM, and shutdown. The device operates in PWM mode at load currents of approximately 100 mA or higher, having voltage tolerance of ±3% with 95% efficiency or better. Lighter load currents cause the device to automatically switch into PFM for reduced current consumption. Shutdown mode turns off the device, offering the lowest current consumption (IQ, SHUTDOWN = 0.01 µA typ). Additional features include soft-start, under voltage protection, current overload protection, and thermal shutdown protection. The part uses an internal reference voltage of 0.5V. It is recommended to keep the part in shutdown until the input voltage is 2.7V or higher. CIRCUIT OPERATION The buck converter operates as follows. 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 (VIN– VOUT)/L, by storing energy in a magnetic field. During the second portion of each cycle, the controller 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 –VOUT/L. The output filter stores charge when the inductor current is high, and releases it when inductor current is low, smoothing the voltage across the load. The output voltage is regulated by modulating the PFET switch on time to control the average current sent to the load. The effect is identical to sending a duty-cycle modulated rectangular wave formed by the switch and synchronous rectifier at the SW pin to a low-pass filter formed by the inductor and output filter capacitor. The output voltage is equal to the average voltage at the SW pin. PWM OPERATION During PWM operation the converter operates as a voltage mode controller with input voltage feed forward. This allows the converter to achieve good load and line regulation. The DC gain of the power stage is proportional to the input voltage. To eliminate this dependence, feed forward inversely proportional to the input voltage is introduced. While in PWM (Pulse Width Modulation) mode, the output voltage is regulated by switching at a constant frequency and then modulating the energy per cycle to control power to the load. At the beginning of each clock cycle the PFET switch is turned on and the inductor current ramps up until the comparator trips and the control logic turns off the switch. The current limit comparator can also turn off the switch in case the current limit of the PFET is exceeded. Then the NFET switch is turned on and the inductor current ramps down. The next cycle is initiated by the clock turning off the NFET and turning on the PFET. 20207611 FIGURE 1. Typical PWM Operation Internal Synchronous Rectification While in PWM mode, the converters 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. Current Limiting A current limit feature allows the converters to protect itself and external components during overload conditions. PWM mode implements current limiting using an internal comparator that trips at 2.0 A (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. B: The peak PMOS switch current drops below the IMODE level, (Typically IMODE < 30 mA + VIN/42Ω). www.national.com 18 LP3972 20207612 FIGURE 2. Typical PFM Operation 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 90% Default value Buck 3 Supply Output Voltage Status 0 - (Buck 3) output voltage < 90% Default value 1 - (Buck 3) output voltage > 90% Default value Buck 2 Supply Output Voltage Status 0 - (Buck 2) output voltage < 90% Default value 1 - (Buck 2) output voltage > 90% Default value LDO_1 Output Voltage Status 0 - (VCC_LDO1) output voltage < 90% of selected value 1 - (VCC_LDO1) output voltage > 90% of selected value Reserved 6 R B3_OK 5 R B2_OK 4 R LDO1_OK 3 — — 39 www.national.com LP3972 Bit 2:0 Access R Name BCT Description Binary coded thermal management flag status register Temperature   Ascending °C Data Code 40 000 60 001 80 010 100 011 120 100 140 101 160 110 Reserved 111 www.national.com 40 LP3972 LOGIC OUTPUT ENABLE REGISTER (LOER) 8H’84 Bit Designation Reset Value 7 Reserved 0 6* B3ENC 1 5* B2ENC 1 4* B1ENC 0 3* L5EC 0 2* L4EC 1 1* L3EC 1 0* L2EC 1 Note: ** denotes one time factory programmable EPROM registers for default values LOGIC OUTPUT ENABLE REGISTER (LOER) DEFINITIONS 8H’84 Bit 7 6 Access — R/W Name — B3ENC Reserved Connects Buck 3 enable to SYS_EN or PWR_EN Logic Control pin 0 - Buck 3 enable connected to PWR_EN 1 - Buck 3 enable connected to SYS_EN, Default Connects Buck 2 enable to SYS_EN or PWR_EN Logic Control pin 0 - Buck 2 enable connected to PWR_EN 1 - Buck 2 enable connected to SYS_EN, Default Connects Buck 1 enable to SYS_EN or PWR_EN Logic Control pin 0 - Buck 1 enable connected to PWR_EN, Default 1 - Buck 1 enable connected to SYS_EN Connects LDO5 enable to SYS_EN or PWR_EN Logic Control pin 0 - LDO 5 enable connected to PWR_EN, Default 1 - LDO 5 enable connected to SYS_EN Connects LDO4 enable to SYS_EN or PWR_EN Logic Control pin 0 - LDO 4 enable connected to PWR_EN 1 - LDO 4 enable connected to SYS_EN, Default Connects LDO3 enable to SYS_EN or PWR_EN Logic Control pin 0 - LDO 3 enable connected to PWR_EN 1 - LDO 3 enable connected to SYS_EN, Default Connects LDO2 enable to SYS_EN or PWR_EN Logic Control pin 0 - LDO 2 enable connected to PWR_EN 1 - LDO 2 enable connected to SYS_EN, Default Description 5 R/W B2ENC 4 R/W B1ENC 3 R/W L5EC 2 R/W L4EC 1 R/W L3EC 0 R/W L2EC 41 www.national.com LP3972 VCC_BUCK 2 TARGET VOLTAGE REGISTER (B2TV) 8H’85 Bit Designation Reset Value 0 7 6 Reserved 0 0 1 5 4** 3** 1 2** 0 1** 0 0** 1 Buck 2 Output Voltage (B2OV) Note: ** denotes one time factory programmable EPROM registers for default values VCC_BUCK 2 TARGET VOLTAGE REGISTER (B2TV) 8H’85 DEFINITIONS Bit 7:5 4:0 Access — R/W B2OV Name Reserved Output Voltage Data Code 5h’01 5h’02 5h’03 5h’04 5h’05 5h’06 5h’07 5h’08 5h’09 5h’0A 5h’0B 5h’0C (V) 0.80 0.85 0.90 0.95 1.00 1.05 1.10 1.15 1.20 1.25 1.30 1.35 Data Code 5h’0D 5h’0E 5h’0F 5h’10 5h’11 5h’12 5h’13 5h’14 5h’15 5h’16 5h’17 5h’18 5h’19 (V) 1.40 1.45 1.50 1.55 1.60 1.65 1.70 1.80 1.90 2.50 2.80 3.00 3.30 Description BUCK 3 TARGET VOLTAGE REGISTER (B3TV) 8H’86 Bit Designation Reset Value 0 7 6 Reserved 0 0 1 5 4** 3** 0 2** 1 1** 0 0** 0 Buck 3 Output Voltage (B3OV) Note: ** denotes one time factory programmable EPROM registers for default values BUCK 3 TARGET VOLTAGE REGISTER (B3TV) 8H’86 DEFINITIONS Bit 7:5 4:0 Access — R/W B3OV Name Reserved Output Voltage Data Code 5h’01 5h’02 5h’03 5h’04 5h’05 5h’06 5h’07 5h’08 5h’09 5h’0A 5h’0B 5h’0C (V) 0.80 0.85 0.90 0.95 1.00 1.05 1.10 1.15 1.20 1.25 1.30 1.35 Data Code 5h’0D 5h’0E 5h’0F 5h’11 5h’12 5h’13 5h’14 5h’15 5h’16 5h’17 5h’18 5h’19 (V) 1.40 1.45 1.50 1.60 1.65 1.70 1.80 1.90 2.50 2.80 3.00 3.30 Description               Default www.national.com 42 LP3972 VCC_BUCK 3:2 VOLTAGE RAMP CONTROL REGISTER (B32RC) VCC_Buck 3:2 Voltage Ramp Control Register (B32RC) 8h’87 Bit Designation Reset Value 1 7 6 0 5 1 4 0 3 1 2 0 1 1 0 0 Ramp Rate (B3RR) Ramp Rate (B2RR) Buck 3:2 Voltage Ramp Control Register (B3RC) 8h’87 Definitions Bit 7:4 Access R/W Name B3RR Data Code 4h’0 4h’1 4h’2 4h’3 4h’4 4h’5 4h’6 4h’7 4h’8 4h’9 4h’A Data Code 4h’0 4h’1 4h’2 4h’3 4h’4 4h’5 4h’6 4h’7 4h’8 4h’9 4h’A Description Ramp Rate mV/µS Instant 1 2 3 4 5 6 7 8 9 10 Ramp Rate mV/µS Instant 1 2 3 4 5 6 7 8 9 10 3:0 R/W B2RR 43 www.national.com LP3972 INTERRUPT STATUS REGISTER ISRA This register specifies the status bits for the interrupts generated by the PMIC. Thermal warning of the IC, GPIO1, GPIO2, PWR_ON pin, TEST_JIG factory programmable on signal, and the SPARE pin. Interrupt Status Register ISRA 8h’88 Bit Designation Reset Value 7 Reserved 0 6 T125 0 5 GPI2 0 4 GPI1 0 3 WUP3 0 2 WUP2 0 1 WUPT 0 0 WUPS 0 Interrupt Status Register ISRA 8h’88 Definitions Bit 7 6 Access — R Name — T125 Reserved Status bit for thermal warning PMIC T>125C 0 = PMIC Temp. < 125°C 1 = PMIC Temp. > 125°C Status bit for the input read in from GPIO 2 when set as Input 0 = GPI2 Logic Low 1 = GPI2 Logic High Status bit for the input read in from GPIO 1 when set as Input 0 = GPI1 Logic Low 1 = GPI1 Logic High PWR_ON Pin long pulse Wake Up Status 0 = No wake up event 1 = Long pulse wake up event PWR_ON Pin Short pulse Wake Up Status 0 = No wake up event 1 = Short pulse wake up event TEST_JIG Pin Wake Up Status 0 = No wake up event 1 = Wake up event SPARE Pin Wake Up Status 0 = No wake up event 1 = Wake up event Description 5 R GPI2 4 R GPI1 3 R WUP3 2 R WUP2 1 R WUPT 0 R WUPS www.national.com 44 LP3972 BACKUP BATTERY CHARGER CONTROL REGISTER (BCCR) This register specifies the status of the main battery supply. NBUB bit Backup Battery Charger Control Register (BCCR) 8h’89 Bit Designation Reset Value 7** NBUB 0 6 CNBFL 0 0 5** 4** nBFLT 1 0 3** 2 BUCEN 0 0 1 IBUC 1 0 Note: ** denotes one time factory programmable EPROM registers for default values Backup Battery Charger Control Register (BCCR) 8h’89 Definitions Bit 7 Access R/W Name NBUB Description No back-up battery default setting. Logic will not allow switch over to back-up battery. 0 = Back up Battery Enabled, Default 1 = Back up Battery Disabled Control for nBATT_FLT output signal 0 = nBATT_FLT Enabled 1 = nBATT_FLT Disabled nBATT_FLT monitors the battery voltage and can be set to the Assert voltages listed below. Data Code 3h’01 3h’02 3h’03 3h’04 3h’05 Asserted 2.6 2.8 3.0 3.2 3.4 De-Asserted 2.8 3.0 3.2 3.4 3.6 Note: 6 R/W CNBFL 5:3 R/W BFLT   Default 2 R/W BUCEN Enables backup battery charger 0 = Back up Battery Charger Disabled 1 = Back up Battery Charger Enabled Charger current setting for back-up battery Data Code 2h’00 2h’01 2h’02 2h’03 BU Charger I (µA) 260 190 325 390 Note: 1:0 R/W IBUC   Default 45 www.national.com LP3972 MARVELL PXA INTERNAL 1 REVISION REGISTER (II1RR) 8H’8E Bit Designation Reset Value 0 0 0 0 7 6 5 4 II1RR 0 0 0 0 3 2 1 0 MARVELL PXA INTERNAL 1 REVISION REGISTER (II1RR) 8H’8E DEFINITIONS Bit 7:0 Access R Name II1RR Description Intel internal usage register for revision information. MARVELL PXA INTERNAL 2 REVISION REGISTER (II2RR) 8H’8F Bit Designation Reset Value 0 0 0 0 7 6 5 4 II2RR 0 0 0 0 3 2 1 0 MARVELL PXA INTERNAL 2 REVISION REGISTER (II2RR) 8H’8F DEFINITIONS Bit 7:0 Access R Name II2RR Description Intel internal usage register for revision information. REGISTER PROGRAMMING EXAMPLES Example 1) Start of Day Sequence PMIC Register Address 8h’23 8h’29 8h’10 PMIC Register Name ADTVI SDTV1 OVER1 Register Data 00011011 00011011 00000111 Description Sets the SOD VCC_APPS voltage Sets the SOD VCC_SRAM voltage Enables VCC_SRAM and VCC_APPS to their programmed values. SODl Multi-byte random register transfer is outlined below: 20207644 www.national.com 46 LP3972 Device Address, Register A Address, Ach, Register A Data, Ach Register M Address, Ach, Register M Data, Ach Register X Address, Ach, Register X Data, Ach Register Z Address, Ach, Register Z Data, Ach, Stop Example 2) Voltage change Sequence PMIC Register Address 8h’24 8h’2A 8h’20 PMIC Register Name ADTV2 SDTV2 VCC1 Register Data 00010111 00001111 00110011 Description Sets the VCC_APPS target voltage 2 to 1.3 V Sets the VCC_SRAM target voltage 2 to 1.1 V Enable VCC_SRAM and VCC_APPS to change to their programmed target values. I2C DATA EXCHANGE BETWEEN MASTER AND SLAVE DEVICE 20207645 47 www.national.com LP3972 LP3972 Controls DIGITAL INTERFACE CONTROL SIGNALS Signal SYS_EN PWR_EN SCL SDA nRSTI nRSTO nBATT_FLT PWR_ON nTEST_JIG SPARE EXT_WAKEUP GPIO1 / nCHG_EN GPIO2 High Voltage Power Enable Low Voltage Power Enable Serial Bus Clock Line Serial Bus Data Line Forces an unconditional hardware reset Forces an unconditional hardware reset Main Battery removed or discharged indicator Wakeup Input to CPU Wakeup Input to CPU Wakeup Input to CPU Wake-Up Output for application processor General Purpose I/O /External Back-up Battery Charger enable General Purpose I/O Low Low Low High Low High/Low High — — Definition Active State High High Clock Signal Direction Input Input Input Bidirectional Input Output Output Input Input Input Output Bidirectional /Input Bidirectional POWER DOMAIN ENABLES PMU Output HW Enable LDO_RTC LDO 1 (VCC_MVT) LDO2 LDO3 — SYS_EN SYS_EN SYS_EN SW Enable — LDO1_EN LDO2_EN LDO3_EN PMU Output LDO5 (VCC_SRAM) Buck1 (VCC_APPS) BUCK2 BUCK3 HW Enable PWR_EN PWR_EN SYS_EN SYS_EN SW Enable S_EN A_EN B2_EN B3_EN LDO4 SYS_EN LDO4_EN POWER DOMAINS SEQUENCING (DELAY) By default SYS_EN must be on to have PWR_EN enable but this feature can be switched off by register bit BP_SYS. By default SYS_EN enables LDO1 always first and after a typical of 1 ms delay others. Also when SYS_EN is set off the LDO1 will go off last. This function can be switched off or delay can be changed by DELAY bits via serial interface as seen on table below. 8h’80 Bit 5:4 DELAY bits Delay, ms ‘00’ 0 ‘01’ 0.5 ‘10’ 1.0 ‘11’ 1.5 LDO_RTC TRACKING (nIO_TRACK) LP3972 has a tracking function (nIO_TRACK). When enabled, LDO_RTC voltage will track LDO3 voltage within 200 mV down to 2.8V when LDO3 is enabled. This function can be switched on/off by nIO_TRACK register bit BPTR. POWER SUPPLY ENABLE SYS_EN and PWR_EN can be changed by programmable register bits. www.national.com 48 LP3972 WAKE-UP FUNCTIONALITY (PWR_ON, nTEST_JIG, SPARE AND EXT_WAKEUP) Three input pins can be used to assert wakeup output for 10 ms for application processor notification to wakeup. SPARE Input can be programmed through I2C compatible interface to be active low or high (SPARE bit, Default is active low ‘1’). A reason for wakeup event can be read through I2C compatible interface also. Additionally wakeup inputs have 30 ms debounce filtering. Furthermore PWR_ON have distinguishing between short and long (∼1s) pulses (push button input). LP3972 also has an internal Thermal Shutdown early warning that generates a wakeup to the system also. This is generated usually at 125°C. WAKEUP register bits WUP0 WUP1 WUP2 WUP3 TSD_EW Reason for WAKEUP SPARE TEST_JIG PWR_ON short pulse PWR_ON long pulse TSD Early Warning INTERNAL THERMAL SHUTDOWN PROCEDURE Thermal shutdown is build to generate early warning (typ. 125°C) which triggers the EXT_WAKEUP for the processor acknowledge. When a thermal shutdown triggers (typ. 160° C) the PMU will reset the system until the device cools down. BATTERY SWITCH AND BACK UP BATTERY CHARGER When Back-Up battery is connected but the main battery has been removed or its supply voltage too low, LP3972 uses Back-Up Battery for generating LDO_RTC voltage. When Main Battery is available the battery fet switches over to the main battery for LDO_RTC voltage. When Main battery voltage is too low or removed nBATT_FLT is asserted. If no back up battery exists, the battery switch to back up can be switched off by nBU_BAT_EN bit. User can set the battery fault determination voltage and battery charger current via I2C compatible interface. Enabling of back up battery charger can be done via serial interface (nBAT_CHG_EN) or external charger enable pin (nCHG_EN). Pin 29 is set as external charger enable input by default. 20207619 49 www.national.com LP3972 GENERAL PURPOSE I/O FUNCTIONALITY (GPIO1 AND GPIO2) LP3972 has 2 general purpose I/Os for system control. I2C compatible interface will be used for setting any of the pins to Controls GPIO X X 1 X 0 1 0 1 GPIO X X 0 X 0 0 1 1 Nextchgen_sel 1 1 1 X 0 0 0 0 bucen 0 0 X 1 X X X X input, output or hi-Z mode. Inputs value can be read via serial interface (GPI1,2 bits). The pin 29 functionality needs to be set to GPIO by serial interface register bit nEXTCHGEN. (GPIO/CHG) Port Function GPIO1 Input = 0 Input = 1 X X HiZ Input (dig)-> Output = 0 Output = 1 Input 0 0 Reg Gpin 1 0 0 0 Enabled batmonchg Function Enabled Not Enabled   GPIO 0 1 0 1 GPIO 0 0 1 1 Factory fm disabled GPIO_tstiob 1 1 1 1 GPIO2 HiZ Input (dig)-> Output = 0 Output = 1 gpin2 0 input 0 0 The LP3972 has provision for two battery connections, the main battery Vbat and Backup Battery (See Applications Schematic Diagrams 1 & 2 of the LP3972 Data Sheet). The function of the battery switch is to connect power to the RTC LDO from the appropriate battery, depending on conditions described below: • If only the backup battery is applied, the switch will automatically connect the RTC LDO power to this battery. • If only the main battery is applied, the switch will automatically connect the RTC LDO power to this battery. • If both batteries are applied, and the main battery is sufficiently charged (VBAT > 3.1V), the switch will automatically connect the RTC LDO power to the main battery. • As the main battery is discharged by use, the user will be warned by a separate circuit called nBATT_FLT. Then if no action is taken to restore the charge on the main battery, and discharging is continued the battery switch will protect the RTC LDO by disconnecting from the main battery and connecting to the backup battery. • — The main battery voltage at which the RTC LDO is switched from main to backup battery is 2.9V typically. — There is a hysterisis voltage in this switch operation so, the RTC LDO will not be reconnected to main battery until main battery voltage is greater than 3.1V typically. Additionally, the user may wish to disable the battery switch, such as, in the case when only a main battery is used. This is accomplished by setting the “no back up battery bit” in the control register 8h’89 bit 7 NBUB. With this bit set to “1”, the above described switching will not occur, that is the RTC LDO will remain connected to the main battery even as it is discharged below the 2.9 Volt threshold. REGULATED VOLTAGES OK All the power domains have own register bit (X_OK) that processor can read via serial interface to be sure that enabled powers are OK (regulating). Note that these read only bits are only valid when regulators are settled (avoid reading these bits during voltage change or power up). www.national.com 50 LP3972 THERMAL MANAGEMENT Application: There is a mode wherein all 6 comparators (flags) can be turned on via the “enallflags” control register bit. This mode allows the user to interrogate the device or system temperature under the set operating conditions. Thus, the rate of temperature change can also be estimated. The system may then negotiate for speed and power trade off, or deploy cooling maneuvers to optimize system performance. The “enallflags” bit needs enabled only when the “bct bits are read to conserve power. Note: The thermal management flags have been verified functional. Presently these registers are accessible by factory only. If there is a demand for this function, the relevant register controls may be shifted into the user programmable bank; the temperature range and resolution of these flags, might also be refined/redefined. THERMAL WARNING 2 of 6 low power comparators, each consumes less than 1 µA, are always enabled to operate the “T=125°C warning flag with hysteresis. This allows continuous monitoring of a thermal-warning flag feature with very low power consumption. LP3972 THERMAL FLAGS FUNCTIONAL DIAGRAM, DATA FROM INITIAL SILICON The following functions are extra features from the thermal shutdown circuit: 20207646 51 www.national.com LP3972 Application Note - LP3972 Reset Sequence INITIAL COLD START POWER ON SEQUENCE 1. The Back up battery is connected to the PMU, power is applied to the back-up battery pin, the RTC_LDO turns on and supplies a stable output voltage to the VCC_BATT pin of the Applications processor (initiating the power-on reset event) with nRSTO asserted from the LP3972 to the processor. 2. nRSTO de-asserts after a minimum of 50 mS. 3. The Applications processor waits for the de-assertion of nBATT_FLT to indicate system power (VIN) is available. 4. After system power (VIN) is applied, the LP3972 deasserts nBATT_FLT. Note that BOTH nRSTO and nBATT_FLT need to be de-asserted before SYS_EN is enabled. The sequence of the two signals is independent of each other. 5. The Applications processor asserts SYS_EN, the LP3972 enables the system high-voltage power supplies. The Applications processor starts its countdown timer set to 125 mS. 6. The LP3972 enables the high-voltage power supplies. — LDO1 power for VCC_MVT (Power for internal logic and I/O Blocks), BG (Bandgap reference voltage), OSC13M (13 MHz oscillator voltage) and PLL enabled first, followed by others if delay is on. 7. Countdown timer expires; the Applications processor asserts PWR_EN to enable the low-voltage power supplies. The processor starts the countdown timer set to 125 mS period. 8. The Applications processor asserts PWR_EN (ext. pin or I2C), the LP3972 enables the low-voltage regulators. 9. Countdown timer expires; If enabled power domains are OK (I2C read) the power up sequence continues by enabling the processors 13 MHz oscillator and PLL’s. 10. The Applications processor begins the execution of code. 20207622 * Note that BOTH nRSTO and nBATT_FLT need to be de-asserted before SYS_EN is enabled. The sequence of the two signals is independent of each other and can occur is either order. www.national.com 52 LP3972 POWER-ON TIMING Symbol t1 t2 t3 t4 t5 Description Delay from VCC_RTC assertion to nRSTO de-assertion Delay from nBATT_FLT de-assertion to nRSTI assertion Delay from nRST de-assertion to SYS_EN assertion Delay from SYS_EN assertion to PWR_EN assertion Delay from PWR_EN assertion to nRSTO de-assertion Min 50 100 10 125 125 Typ Max Units mS µS mS mS mS HARDWARE RESET SEQUENCE Hardware reset initiates when the nRSTI signal is asserted (low). Upon assertion of nRST the processor enters hardware RESET SEQUENCE 1. nRSTI is asserted. 2. nRSTO is asserted and will de-asserts after a minimum of 50 mS 3. The Applications processor waits for the de-assertion of nBATT_FLT to indicate system power (VIN) is available. 4. After system power (VIN) is turned on, the LP3972 deasserts nBATT_FLT. 5. The Applications processor asserts SYS_EN, the LP3972 enables the system high-voltage power supplies. The Applications processor starts its countdown timer. reset state. The LP3972 holds the nRST low long enough (50 ms typ.) to allow the processor time to initiate the reset state. 6. The LP3972 enables the high-voltage power supplies. 7. Countdown timer expires; the Applications processor asserts PWR_EN to enable the low-voltage power supplies. The processor starts the countdown timer. 8. The Applications processor asserts PWR_EN, the LP3972 enables the low-voltage regulators. 9. Countdown timer expires; If enabled power domains are OK (I2C read) the power up sequence continues by enabling the processors 13 MHz oscillator and PLL’s. 10. The Applications processor begins the execution of code. 53 www.national.com LP3972 Application Hints LDO CONSIDERATIONS External Capacitors The LP3972’s regulators 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. Input Capacitor An input capacitor is required for stability. It is recommended that a 1.0 µF 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 1 cm from the input pin and returned to a clean analogue 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 current 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 1.0 µF over the entire operating temperature range. Output Capacitor The LDO’s are designed specifically to work with very small ceramic output capacitors. A 1.0 μF ceramic capacitor (temperature types Z5U, Y5V or X7R) with ESR between 5 mΩ to 500 mΩ, are suitable in the application circuit. For this device the output capacitor should be connected between the VOUT pin and ground. 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 (see the section Capacitor Characteristics). 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. No-Load Stability The LDO’s 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. Capacitor Characteristics The LDO’s 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 0.47 µF to 4.7 µF, 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 1.0 µF ceramic capacitor is in the range of 20 mΩ to 40 mΩ, which easily meets the ESR requirement for stability for the LDO’s. 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 www.national.com 54 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 dependant on the particular case size, with smaller sizes giving poorer performance figures in general. As an example, Figure 4 shows a typical graph comparing different capacitor case sizes in a Capacitance vs. DC Bias plot. As shown in the graph, increasing the DC Bias condition can result in the capacitance value falling 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. 20207623 FIGURE 4. Graph Showing a Typical Variation in Capacitance vs. DC Bias 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 1 µF 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 0.47 µF to 4.7 µF 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. LP3972 BUCK CONSIDERATIONS Inductor Selection 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. Different saturation current rating specs are followed by different manufacturers so attention must be given to details. Saturation current ratings are typically specified at 25°C so ratings at max ambient temperature of application should be requested from manufacturer. There are two methods to choose the inductor saturation current rating. 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 A 2.2 μH inductor with a saturation current rating of at least TBD mA is recommended for most applications. The inductor’s resistance should be less than 0.3Ω for a good efficiency. Table 1 lists suggested inductors and suppliers. For low-cost applications, an unshielded bobbin inductor could be considered. For noise critical applications, a toroidal or shielded bobbin inductor should be used. A good practice is to lay out the board with overlapping footprints of both types for design flexibility. This allows substitution of a low-noise shielded inductor, in the event that noise from low-cost bobbin models is unacceptable. Input Capacitor Selection A ceramic input capacitor of 10 μF, 6.3V is sufficient for most applications. Place the input capacitor as close as possible to the VIN pin of the device. A larger value may be used for improved input voltage filtering. Use X7R or X5R types, do not use Y5V. 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 switch of the converter in the first half of each cycle and reduces voltage ripple imposed on the input power source. A ceramic capacitor’s low ESR provides the best noise filtering of the input voltage spikes due to this rapidly changing current. Select a capacitor with sufficient ripple current rating. The input current ripple can be calculated as: • IRIPPLE: Average to peak inductor current • IOUTMAX: Maximum load current (1500 mA) • VIN: Maximum input voltage in application • L: Min inductor value including worst case tolerances (30% drop can be considered for method 1) • f: Minimum switching frequency (1.6 MHz) • VOUT: Output voltage Method 2 A more conservative and recommended approach is to choose an inductor that has saturation current rating greater than the max current limit of TBD mA. The worst case is when VIN = 2 * VOUT TABLE 1. Suggested Inductors and Their Suppliers Model FDSE0312-2R2M DO1608C-222 Vendor Toko Coilcraft Dimensions LxWxH (mm) 3.0 x 3.0 x 1.2 6.6 x 4.5 x 1.8 D.C.R (Typ) 160 mΩ 80 mΩ Output Capacitor Selection Use a 10 μF, 6.3V ceramic capacitor. Use X7R or X5R types, do not use Y5V. 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 as part of the capacitor selection process. The output filter capacitor 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 ESR 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: Voltage peak-to-peak ripple due to ESR can be expressed as follows VPP-ESR = (2 * IRIPPLE) * RESR Because these two components are out of phase the rms value can be used to get an approximate value of peak-to-peak ripple. Voltage peak-to-peak ripple, root mean squared can be expressed as follows 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); make sure the value used for calculations is at the switching frequency of the part. 55 www.national.com LP3972 TABLE 2. Suggested Capacitor and Their Suppliers Model GRM21BR60J106K JMK212BJ106K C2012X5R0J106K Type Ceramic, X5R Ceramic, X5R Ceramic, X5R Vendor Murata Taiyo-Yuden TDK Voltage 6.3V 6.3V 6.3V Case Size Inch (mm) 0805 (2012) 0805 (2012) 0805 (2012) www.national.com 56 LP3972 Buck Output Ripple Management If VIN and ILOAD increase, the output ripple associated with the Buck Regulators also increases. The figure below shows the safe operating area. To ensure operation in the area of concern it is recommended that the system designer circumvents the output ripple issues to install schottky diodes on the Bucks (s) that are expected to perform under these extreme corner conditions. (Schottky diodes are recommended to reduce the output ripple, if system requirements include this shaded area of operation. VIN > 1.5V and ILOAD > 1.24) 20207647 57 www.national.com LP3972 Board Layout Considerations PC board layout is an important part of DC-DC converter design. Poor board layout can disrupt the performance of a DCDC converter and surrounding circuitry by contributing to EMI, ground bounce, and resistive voltage loss in the traces. These can send erroneous signals to the DC-DC converter IC, resulting in poor regulation or instability. Good layout for the converters can be implemented by following a few simple design rules. 1. Place the converters, inductor and filter capacitors close together and make the traces short. The traces between these components carry relatively high switching currents and act as antennas. Following this rule reduces radiated noise. Special care must be given to place the input filter capacitor very close to the VIN and GND pin. 2. Arrange the components so that the switching current loops curl in the same direction. During the first half of each cycle, current flows from the input filter capacitor through the converter and inductor to the output filter capacitor and back through ground, forming a current loop. In the second half of each cycle, current is pulled up from ground through the converter by the inductor to the output filter capacitor and then back through ground forming a second current loop. Routing these loops so the current curls in the same direction prevents magnetic field reversal between the two half-cycles and reduces radiated noise. 3. Connect the ground pins of the converter and filter capacitors together using generous component-side copper fill as a pseudo-ground plane. Then, connect this to the ground-plane (if one is used) with several vias. This reduces ground-plane noise by preventing the switching currents from circulating through the ground plane. It also reduces ground bounce at the converter by giving it a low-impedance ground connection. Use wide traces between the power components and for power connections to the DC-DC converter circuit. This reduces voltage errors caused by resistive losses across the traces. Route noise sensitive traces, such as the voltage feedback path, away from noisy traces between the power components. The voltage feedback trace must remain close to the converter circuit and should be direct but should be routed opposite to noisy components. This reduces EMI radiated onto the DC-DC converter’s own voltage feedback trace. A good approach is to route the feedback trace on another layer and to have a ground plane between the top layer and layer on which the feedback trace is routed. In the same manner for the adjustable part it is desired to have the feedback dividers on the bottom layer. Place noise sensitive circuitry, such as radio RF blocks, away from the DC-DC converter, CMOS digital blocks and other noisy circuitry. Interference with noisesensitive circuitry in the system can be reduced through distance. 4. 5. 6. www.national.com 58 LP3972 Physical Dimensions inches (millimeters) unless otherwise noted 40-Pin Leadless Leadframe Package NS Package Number SQF40A 59 www.national.com LP3972 Power Management Unit for Advanced Application Processors Notes For more National Semiconductor product information and proven design tools, visit the following Web sites at: Products Amplifiers Audio Clock Conditioners Data Converters Displays Ethernet Interface LVDS Power Management Switching Regulators LDOs LED Lighting PowerWise Serial Digital Interface (SDI) Temperature Sensors Wireless (PLL/VCO) www.national.com/amplifiers www.national.com/audio www.national.com/timing www.national.com/adc www.national.com/displays www.national.com/ethernet www.national.com/interface www.national.com/lvds www.national.com/power www.national.com/switchers www.national.com/ldo www.national.com/led www.national.com/powerwise www.national.com/sdi www.national.com/tempsensors www.national.com/wireless WEBENCH Analog University App Notes Distributors Green Compliance Packaging Design Support www.national.com/webench www.national.com/AU www.national.com/appnotes www.national.com/contacts www.national.com/quality/green www.national.com/packaging www.national.com/quality www.national.com/refdesigns www.national.com/feedback Quality and Reliability Reference Designs Feedback THE CONTENTS OF THIS DOCUMENT ARE PROVIDED IN CONNECTION WITH NATIONAL SEMICONDUCTOR CORPORATION (“NATIONAL”) PRODUCTS. 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