LT3582

FEATURES n LT3582/LT3582-5/LT3582-12 I2C Programmable Boost and Single Inductor Inverting DC/DC Converters with OTP DESCRIPTION The LT®3582/LT3582-5/LT3582-12 are dual DC/DC converters featuring positive and negative outputs and integrated feedback resistors. The LT3582, with its built in One Time Programming (OTP), has configurable output settings via the I2C interface, including output voltage settings, power up sequencing, power down discharge, and output voltage ramp rates. LT3582 settings can be changed adaptively in the final product, or set during manufacturing and made permanent using the built in non-volatile OTP memory. The positive output voltage can be set between 3.2V and 12.775V in 25mV steps. The negative output voltage can be set between –1.2V and –13.95V in –50mV steps. The LT3582-5 and LT3582-12 are pre-configured at the factory for ±5V and ±12V outputs respectively. The LT3582 series includes two monolithic converters, one Boost and one Inverting. The Boost converter has an integrated power switch and output disconnect switch. The Inverting converter uses a single inductor topology and includes an integrated power switch. Both Boost and Inverting converters use a novel** control scheme resulting in low output voltage ripple while allowing for high conversion efficiency over a wide load current range. The LT3582 series is available in a 16-pin 3mm x 3mm QFN. L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. * Input thresholds are reduced to allow communication with low voltage digital ICs. (See Electrical Characteristics). **Patent Pending n n n n n n n n n Output Voltages: 3.2V to 12.775V and –1.2V to –13.95V (LT3582) 5V and –5V (LT3582-5) 12V and –12V (LT3582-12) Digitally Re-Programmable (LT3582) Via I2C for: Output Voltages Power Sequencing Output Voltage Ramp Rates Power-up Defaults Settable with Non-volatile OTP (LT3582) I2C Compatible Interface (Standard Mode*) All Power Switches Integrated 350mA Current Limit (Boost) 600mA Current Limit (Inverting) All Feedback Resistors Integrated Input Voltage Range: 2.55V to 5.5V Low Quiescent Current 325μA in Active Mode 0.01μA in Shutdown Mode Integrated Output Disconnect Tiny 16-pin 3mm × 3mm QFN Package APPLICATIONS n n n AMOLED Power CCD Power General Purpose DC/DC Conversion TYPICAL APPLICATION ±12V Supplies from a Single 5V Input SWN 6.8μH SWN SHDN VIN SWP GND LT3582 1μF 4.7μF 6.8μH EFFICIENCY (%) 75 65 150 55 45 35 0.1 1 10 LOAD CURRENT (mA) 100 50 0 100 3582512 TA01b 3582512 TA01a Efficiency and Power Loss 95 INPUT 4.5V TO 5.5V VOUTP VOUTN 350 300 250 200 POWER LOSS (mW) 85 VNEG –12V 85mA I2C INTERFACE 10μF VOUTN SDA SCL CA CAPP CAPP VOUTP VPP RAMPP RAMPN 10nF 4.7μF VPOS 12V 80mA ( OPTIONAL ON LT3582-5/LT3582-12 ) 10nF 3582512f 1 LT3582/LT3582-5/LT3582-12 ABSOLUTE MAXIMUM RATINGS (Note 1) PIN CONFIGURATION TOP VIEW GND 12 SWP 17 GND 11 CAPP 10 CAPP 9 5 VIN 6 RAMPN 7 RAMPP 8 SHDN VOUTP SDA SCL VPP VIN Voltage ..................................................................6V SWP Voltage .............................................................15V SWN Voltage ........................................................–16.5V CAPP Voltage ............................................................15V CAPP-VOUTP Voltage .................................... –0.8V to 8V ICAPP-VOUTP ........................................................±300mA VOUTP Voltage ...........................................................15V VOUTN Voltage ......................................................–16.5V RAMPP Voltage...........................................................3V RAMPN Voltage ..........................................................3V SHDN Voltage .................................................–0.5 to 6V VPP Voltage ...................................................–0.2 to 16V SDA, CA, SCL Voltage .....................................–0.5 to 6V Operating Junction Temperature Range (Notes 3, 5) LT3582E ............................................. –40°C to 125°C Storage Temperature Range .............. –65°C to 150°C 16 15 14 13 CA 1 VOUTN 2 SWN 3 SWN 4 UD PACKAGE 16-PIN (3mm × 3mm) PLASTIC QFN TJMAX = 125°C, θJA = 68°C/W EXPOSED PAD (PIN #17) IS GND, MUST BE SOLDERED TO PCB ORDER INFORMATION LEAD FREE FINISH LT3582EUD#PBF LT3582EUD-5#PBF LT3582EUD-12#PBF TAPE AND REEL LT3582EUD#TRPBF LT3582EUD-5#TRPBF LT3582EUD-12#TRPBF PART MARKING LDDB LDVG LDVH PACKAGE DESCRIPTION 16-Pin (3mm × 3mm) Plastic QFN 16-Pin (3mm × 3mm) Plastic QFN 16-Pin (3mm × 3mm) Plastic QFN TEMPERATURE RANGE –40°C to 125°C –40°C to 125°C –40°C to 125°C Consult LTC Marketing for parts specified with wider operating temperature ranges. Consult LTC Marketing for information on non-standard lead based finish parts. For more information on lead free part marking, go to: http://www.linear.com/leadfree/ For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/ ELECTRICAL CHARACTERISTICS Switching Regulator Characteristics SYMBOL VIN_MIN VIN_MAX IVIN IVIN_SHDN ICAPP_SHDN TOFF_MINP TOFF_MINN TON_MAX ILIMIT_P PARAMETER Minimum Operating Voltage Maximum Operating Voltage VIN Quiescent Current VIN Quiescent Current in Shutdown Minimum Switch Off Time Minimum Switch Off Time Maximum Switch On Time Boost Switch Current Limit The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VIN = 3.6V, VSHDN = VIN unless otherwise noted. (Note 3) CONDITIONS l l MIN 2.4 5.5 TYP 2.475 325 0.01 0 100 125 10 MAX 2.55 450 0.5 0.5 UNITS V V μA μA μA ns ns μs Ramp Current Configured to 1μA, SWOFF Bit Active VSHDN = 0 Boost Switch Inverting Switch Inverting and Boost Switches l CAPP Quiescent Current in Shutdown VSHDN = 0, VCAPP = 5.0V, VOUTP = 0V 285 350 430 mA 3582512f 2 LT3582/LT3582-5/LT3582-12 ELECTRICAL CHARACTERISTICS Switching Regulator Characteristics SYMBOL ILIMIT_N RON_P RON_N IOFF_P IOFF_N RON_DIS ILIMIT_DIS IVOUTP_PDS ICAPP_PDS IVOUTN_PDS TSTARTUP PARAMETER Inverting Switch Current Limit Boost Switch On Resistance Inverting Switch On Resistance Boost Switch Leakage Current into SWP pin ISWP = 200mA ISWN = – 400mA VSWP = 5V CONDITIONS l The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VIN = 3.6V, VSHDN = VIN unless otherwise noted. (Note 3) MIN 490 TYP 600 500 560 0.01 0.01 1.4 l MAX 720 UNITS mA mΩ mΩ 0.5 1 μA μA Ω Inverting Switch Leakage Current out VIN = 5.0, VSWN = 0.0 of SWN pin Output Disconnect Switch On Resistance Output Disconnect Current Limit VOUTP Power-Down Discharge Current CAPP Power-Down Discharge Current VOUTN Power-Down Discharge Current Configuration Startup Delay VOUTP = 8V CAPP = 8V VOUTN = – 8V VIN> VIN_MIN & SHDN > VSHDN_VIH to I2C Enabled and Power-up Sequencing Start l VCAPP = 10V, RAMPP > 1.4V 124 2.4 1.2 –1.4 155 4.8 2.4 –2.8 64 186 8.8 4.4 –4.2 128 mA mA mA mA μs Programmable Output Characteristics6 SYMBOL V VOUTP N_VOUTP V VOUTP_LSB V VOUTP_FS V VOUTP_MIN V VOUTP_LR V VOUTN N_VOUTN V VOUTN_LSB V VOUTN_FS V VOUTN_MIN V VOUTN_LR INL_VOUTP DNL_VOUTP INL_VOUTN DNL_VOUTN IRAMP00 IRAMP01 PARAMETER Positive Output Voltage Positive VOUTP Resolution2 VOUTP LSB2 VOUTP Full Scale Voltage2 Code = BFh, VPLUS = 1 Code = 00h, VPLUS = 0 Code = BFh, 2.575 < VIN < 5.5 LT3582-5 LT3582-12 l l l l CONDITIONS LT3582-5 LT3582-12 l l MIN 4.95 11.88 9 TYP 5 12 25 MAX 5.05 12.1 UNITS V V Bits mV 12.56 3.152 –5.075 –12.1 8 12.775 3.20 –0.02 –5 –12 –50 12.94 3.248 –4.925 –11.868 V V %/V V V Bits mV VOUTP Minimum Voltage2 VOUTP Line Regulation Negative Output Voltage Negative VOUTN Resolution2 VOUTN LSB2 VOUTN VOUTN Full Scale Voltage2 Minimum Voltage2 Code = FFh Code = 00h Code = FFh, 2.575 < VIN < 5.5 l l l l l l l l –14.2 –1.23 –13.95 –1.205 –0.01 –13.7 –1.18 ±0.6 ±0.6 ±0.85 ±0.85 V V %/V LSB LSB LSB LSB μA μA VOUTN Line Regulation VOUTP Integral Nonlinearity 2, 4 VOUTP Differential Nonlinearity 2, 4 VOUTN VOUTN Integral Nonlinearity 2 Differential Nonlinearity 2 RAMPP/RAMPN Pull Up Current IRMP Code = 00 RAMPP/RAMPN Pull Up Current 2 IRMP Code = 01 VRAMPP = 0.0V VRAMPN = 0.0V VRAMPP = 0.0V VRAMPN = 0.0V 0.7 1.4 1.0 2.0 1.3 2.6 3582512f 3 LT3582/LT3582-5/LT3582-12 ELECTRICAL CHARACTERISTICS Programmable Output Characteristics SYMBOL IRAMP10 IRAMP11 V VPLUS PARAMETER RAMPP/RAMPN Pull Up Current 2 IRMP Code = 10 RAMPP/RAMPN Pull Up Current 2 IRMP Code = 11 VOUTP Voltage Increase When VPLUS Bit is Set from 0 to 12 CONDITIONS VRAMPP = 0.0V VRAMPN = 0.0V VRAMPP = 0.0V VRAMPN = 0.0V l l The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VIN = 3.6V, VSHDN = VIN unless otherwise noted. (Note 3) MIN 2.8 5.6 TYP 4.0 8.0 25 MAX 5.2 10.4 UNITS μA μA mV Input/Output Pin Characteristics SYMBOL VSHDN_VIH VSHDN_VIL VHYST_SHDN I SHDN_BIAS VCA_VIH VCA_VIL VSDA_VIH VSDA_VIL VSCL_VIH VSCL_VIL VHYST ILEAK_CA ILEAK_SCL ILEAK_SDA CIN VSDA_OL VPP_RANGE VPPUVLO PARAMETER SHDN Input Voltage High SHDN Input Voltage Low SHDN Input Hysteresis SHDN Pin Bias Current CA Input Voltage High CA Input Voltage Low SDA Input Voltage High SDA Input Voltage Low SCL Input Voltage High SCL Input Voltage Low Input Hysteresis CA Input Leakage Current SCL Input Leakage Current SDA Input Leakage Current Input Capacitance SDA Output Low Voltage VPP Voltage Range for OTP Write2 Under-voltage Lockout for VPP Pin2 l CONDITIONS l l MIN 1.1 TYP MAX 0.3 UNITS V V mV μA V V V V V V mV μA μA μA pF V V V 50 VSHDN = 1V l l l l l l 2.5 0.7 × VIN 4.5 6.5 0.3 × VIN 1.25 0.85 1.25 0.85 80 ±1 ±1 ±1 3 0.4 13 12.05 12.45 15 12.85 SDA, SCL Pins CA = 0V & 5.5V SCL = 0V & 5.5V SDA = 0V & 5.5V SDA, SCL Pins 3mA into SDA Pin l l l l I2C Timing Characteristics SYMBOL fSCL tLOW tHIGH tBUF tHD,STA tSU,STA tSU,STO tHD,DATXMIT PARAMETER Serial Clock Frequency Serial Clock Low Period Serial Clock High Period Bus Free Time Between Stop and Start Start Condition Hold Time Start Condition Setup Time Stop Condition Setup Time Data Hold Time Transmitting LT3582 Sending Data to Host CONDITIONS l l l l l l l l MIN 4.7 4.0 4.7 4.0 4.7 4.0 300 TYP MAX 100 UNITS kHz μs μs μs μs μs μs ns 3582512f 4 LT3582/LT3582-5/LT3582-12 ELECTRICAL CHARACTERISTICS I2C Timing Characteristics SYMBOL tHD,DATRCV tSU,DAT tF PARAMETER Data Hold Time Receiving Data Setup Time SDA Fall Time 400pF load, VIN ≥ 2.5V CONDITIONS LT3582 Receiving Data from Host l l l The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VIN = 3.6V, VSHDN = VIN unless otherwise noted. (Note 3) MIN 0 250 250 TYP MAX UNITS ns ns ns Note 1: Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. Exposure to any Absolute Maximum Rating condition for extended periods may affect device reliability and lifetime. Note 2: LT3582 only. Note 3: The LT3582E is guaranteed to meet performance specifications from 0°C to 125°C junction temperature. Specifications over the –40°C to 125°C operating junction temperature range are assured by design, characterization and correlations with statistical process controls. Note 4: These specifications apply to the VP trim bits in REG0 using a 50mV LSB and do not include the additional VPLUS trim bit. See Registers and OTP in the Applications Information section. Note 5: This IC includes over-temperature protection that is intended to protect the device during momentary overload conditions. Junction temperature will exceed the maximum operating junction temperature when over-temperature protection is active. Continuous operation above the specified maximum operating junction temperature may impair device reliability. Note 6: Output voltage is measured under non-switching test conditions approximating a moderate load current from the output. 3582512f 5 LT3582/LT3582-5/LT3582-12 TYPICAL PERFORMANCE CHARACTERISTICS Switching Frequencies (Figure 13) 10000 1.00 0.75 VOUTP FREQUENCY (kHz) ΔVOUT/VOUT (%) 1000 VOUTN 100 0.50 ΔVOUT/VOUT (%) 0.25 0 –0.25 –0.50 –0.75 10 0 20 40 60 80 LOAD CURRENT (mA) 100 3582512 G01 TA = 25°C unless otherwise noted. Load Regulation (Figure 13) 0.45 0.30 0.15 0 –0.15 –0.30 Output Voltage (Figure 13) VOUTN VOUTP VOUTP VOUTN –1.00 0 20 40 60 80 LOAD CURRENT (mA) 100 3582512 G02 –0.45 –50 –25 0 25 50 75 TEMPERATURE (°C) 100 125 3582512 G03 Quiescent Current – Not Switching 390 370 QUIESCENT CURRENT (μA) 350 330 310 290 270 250 2.5 3 3.5 4 VIN (V) 3582512 G04 Switch Resistance O.7 SWITCH CURRENT LIMIT (mA) 0.6 SWITCH RESISTANCE (Ω) 0.5 VOUTP 0.4 0.3 0.2 0.1 0 2.5 3 3.5 4 4.5 INPUT VOLTAGE (V) 5 5.5 VOUTN 700 Switch Current Limit SWN 600 500 400 SWP 300 4.5 5 5.5 200 –50 –25 0 25 50 75 TEMPERATURE (°C) 100 125 3582512 G05 3582512 G06 VOUTP and VOUTN Pin Current During Normal Operation 80 60 40 PIN CURRENT (μA) 20 0 –20 –40 –60 –80 –100 0 CURRENT OUT OF VOUTN PIN 2.5 5 7.5 10 |VOUT| (V) 12.5 15 VN CODE SET TO –5V VN CODE SET TO –12V VP CODE SET TO 5V CURRENT INTO VOUTP PIN PMOS CURRENT LIMIT (mA) VP CODE SET TO 12V 200 Output Disconnect PMOS Current Limit During Normal Operation 2.5 Output Disconnect PMOS On-Resistance 180 ON-RESISTANCE (Ω) –25 0 25 50 75 TEMPERATURE (°C) 100 125 2 160 1.5 140 1 120 0.5 100 –50 0 2 4 6 8 VCAPP (V) 10 12 3582512 G09 3582512 G07 3582512 G08 3582512f 6 LT3582/LT3582-5/LT3582-12 TYPICAL PERFORMANCE CHARACTERISTICS to Figure 13. Switching Waveform at 1mA Load (Boost) Note: All waveforms on this page apply Switching Waveform at 100mA Load (Boost) Switching Waveform at 10mA Load (Boost) VSWP 5V/DIV VSWP 5V/DIV VSWP 5V/DIV VVOUTP 10mV/DIV AC COUPLED VVOUTP 10mV/DIV AC COUPLED VVOUTP 10mV/DIV AC COUPLED IL2 0.2A/DIV 5μs/DIV 3582512 G10 IL2 0.2A/DIV 2μs/DIV 3582512 G11 IL2 0.2A/DIV 200ns/DIV 3582512 G12 Switching Waveform at 1mA Load (Inverting) VSWN 10V/DIV VVOUTN 20mV/DIV AC COUPLED VSWN 10V/DIV Switching Waveform at 10mA Load (Inverting) VVOUTN 0.1V/DIV AC COUPLED Load Transient, VOUTN, 30mA to 60mA to 30mA Steps VVOUTN 50mV/DIV AC COUPLED LOAD CURRENT –20mA/DIV IL1 0.2A/DIV 5μs/DIV 3582512 G13 IL1 0.2A/DIV 5μs/DIV 3582512 G14 IL1 0.2A/DIV 50μs/DIV 3582512 G15 Load Transient, VOUTP, 30mA to 60mA to 30mA Steps VOUTP 0.2V/DIV AC COUPLED LOAD CURRENT 20mA/DIV Power-Up Sequencing Waveforms (PUSEQ = 11) VRAMPN 1V/DIV VRAMPP 1V/DIV Power-Down Discharge Waveforms (PUSEQ = 11, PDDIS = 1) VRAMPN 1V/DIV VRAMPP 1V/DIV VVOUTP 5V/DIV VVOUTP 5V/DIV IL2 0.2A/DIV VVOUTN 5V/DIV VVOUTN 5V/DIV 50μs/DIV 3582512 G16 5ms/DIV 3582512 G17 5ms/DIV 3582512 G18 3582512f 7 LT3582/LT3582-5/LT3582-12 PIN FUNCTIONS CA (Pin 1): I2C Address Select Pin. Tie this pin to VIN to set the 7-bit address to 0110 001. Tie to GND for 1000 101. VOUTN (Pin 2): Negative Output Voltage Pin. When the converter is operating, this pin is regulated to the programmed negative output voltage. Place a ceramic capacitor from this pin to GND. SWN (Pins 3 & 4): Negative switching node for the Inverting converter. This is the drain of the internal PMOS power switch. Connect one end of the Inverting inductor to these pins. Keep the trace area on these pins as small as possible. VIN (Pin 5): Input supply pin and source of the PMOS power switch. This pin must be bypassed locally with a ceramic capacitor. The operating voltage range of this pin is 2.55V to 5.5V. R AMPN (Pin 6): Soft start ramp pin for the Inverting converter. Place a capacitor from this pin to GND. A programmable current of 1μA - 8μA (LT3582) or 1μA (LT3582-5/LT3582-12) charges this pin during startup, limiting the ramp rate of VOUTN. This pin is discharged to GND during shutdown. RAMPP (Pin 7): Soft start ramp pin for the Boost converter. Place a capacitor from this pin to GND. A programmable current of 1μA - 8μA (LT3582) or 1μA (LT3582-5/LT3582-12) charges this pin during startup, limiting the ramp rate of VOUTP . This pin is discharged to GND in shutdown. SHDN (Pin 8): Shutdown Pin. Drive this pin to 1.1V or higher to enable the part. Drive to 0.3V or lower to shut down. Includes an integrated 222k pulldown resistor. VOUTP (Pin 9): Output of the Boost converter output disconnect circuit. A ceramic capacitor should be placed from this node to GND. During shutdown, this pin is disconnected from the Boost network which allows this pin to discharge to GND, assuming a load is present to discharge the capacitance. CAPP (Pins 10 & 11): Connect the Boost output capacitor from these pins to GND. During shutdown, the voltage on these pins will remain close to the input voltage due to the path through the Boost inductor and Schottky. During normal operation, CAPP will be boosted slightly higher than the programmed output voltage. SWP (Pin 12): Positive switching node for the Boost converter. This is the drain of the internal NMOS power switch. Connect one end of the Boost inductor to this pin. Keep the trace area on this pin as small as possible. GND (Pin 13): Ground Pin. Tie to a local ground plane. Proper PCB layout is required to achieve advertised performance; see Applications Information section for more information. VPP (Pin 14): Programming Voltage Pin. Drive this pin to 13-15V when programming the OTP memory. Float otherwise. A bypass capacitor should be placed from this node to GND if VPP is used for programming. If VPP falls below 13V during OTP programming, an internal FAULT bit, which can be read through the I2C interface, can be set high. SDA (Pin 15): I2C Bidirectional Data Pin. Tie to GND or VIN if unused. SCL (Pin 16): I2C Clock Pin. Tie to GND or VIN if unused. Exposed Pad (Pin 17): Ground Pin. Tie to a local ground plane. Proper PCB layout is required to achieve advertised performance; see Applications Information section for more information. 3582512f 8 LT3582/LT3582-5/LT3582-12 BLOCK DIAGRAM VIN SWP CAPP CAPP VOUTP Q Q S R VARIABLE DELAY VARIABLE DELAY S R Q Q SWN DISCONNECT CONTROL SWN + – IPEAK TOFF CONTROL IPEAK TOFF CONTROL + – OTP GND + + – – VOUTN FBN OTP + VCN VCP – – + + FBP 0.80V CHIP ENABLE 222k SHDN VIN 0.80V VPP 2V OTP ADJUST RAMPN 2V OTP ADJUST RAMPP + + – SCL VIN CAPP VOUTP SERIAL INTERFACE, LOGIC AND OTP SDA OUTPUT SEQUENCING BY OTP + – + – 0.75V FBP FBN 50mV OUTPUT SEQUENCING VOUTN CA 3582512 BD 3582512f 9 LT3582/LT3582-5/LT3582-12 OPERATION The LT3582 series are dual DC/DC converters, each containing both a Boost and an Inverting converter. Operation can be best understood by referring to the Block Diagram. The Boost and Inverting converters each use a novel control technique, which simultaneously varies both peak inductor current and switch off time. This results in high efficiency over a large load range and low output voltage ripple. In addition, this technique further minimizes output ripple when the switching frequency is in the audio band. Boost Converter: The Boost converter uses a grounded source NMOS power transistor as the main switching element. The current in the NMOS is constantly monitored and controlled, along with the off time of the switch to achieve regulation of VOUTP . The VOUTP voltage is divided by the internal programmable (LT3582 only) resistor divider to create FBP. The voltage on FBP is compared to an internal reference and amplified, creating an error signal on the VCP node which commands the appropriate peak inductor current and off time for the subsequent switching cycle. Inverting Converter: The Inverting converter uses a power PMOS transistor with the source connected to VIN. This topology requires only one external inductor, instead of the normally required two inductors plus flying capacitor. Regulation is achieved in a similar manner as the Boost. Output Power-up Sequencing: After an initial startup delay (TSTARTUP = 64μS typical), the outputs VOUTP and VOUTN rise (in magnitude) simultaneously with the LT3582-5/ LT3582-12 or in one of four selectable sequences with the LT3582. Using the I2C interface, the LT3582 outputs can be configured such that (1) they both rise simultaneously, (2) VOUTP rises to regulation before VOUTN rises, (3) VOUTN rises to regulation before VOUTP rises, or (4) neither output rises. The outputs of the LT3582-5 and LT3582-12 are pre-configured to rise simultaneously. The ramp rates of the outputs are proportional to the ramp rates of their respective RAMP pins. A capacitor is placed between each RAMP pin and ground. The RAMP pins are discharged during shutdown. Once enabled, configurable (LT3582) or pre-configured (LT3582-5/LT3582-12) currents charge each RAMP pin in the desired sequence causing the outputs to rise. Output Power-Down Discharge: The power-down discharge feature is permanently enabled on the LT3582-5 and LT3582-12 and can be enabled or disabled through I2C on the LT3582. Upon SHDN falling, and when powerdown discharge is enabled, internal transistors will activate to assist in discharging the outputs toward ground. When power-down discharge is disabled, the chip powers down immediately after SHDN falls and the outputs will discharge on their own depending on their external load capacitances and currents. OTP Memory (LT3582 Only): The LT3582 includes 22 bits of user programmable output settings and 1 programming lockout bit. Parameters such as positive & negative output voltages and power sequencing settings can be changed in real time with the integrated I2C interface. Settings can then be made permanent by programming to the on-chip non-volatile OTP (One Time Programmable) memory. 3582512f 10 LT3582/LT3582-5/LT3582-12 APPLICATIONS INFORMATION I2C Interface The LT3582 series contains an I2C compatible interface with reduced input threshold voltages to allow for direct communication with low voltage digital ICs (see Electrical Characteristics). I2C communication is disabled when SHDN is low. After SHDN rises, I2C communication is re-enabled after a delay of 64μs (typical). The chip is a read-write slave device which allows the user to read the current settings and, for the LT3582, write new ones. Most settings can be made permanent via the One-Time-Programmable memory. The chip will always enable using the data stored in OTP and the LT3582 can be reconfigured after power-up. START and STOP Conditions When the bus is idle, both SCL and SDA are high. A bus master signals the beginning of a transmission with a START condition by transitioning SDA from high to low while SCL is high, as shown in Figure 1. When the master has finished communicating with the slave, it issues a STOP condition by transitioning SDA from low to high while SCL is high. The bus is then free for another transmission. ACKnowledge The acknowledge signal (ACK) is used in handshaking between transmitter and receiver to indicate that the most recent byte of data was received. The transmitter always releases the SDA line during the acknowledge clock pulse. When the slave is the receiver, it pulls down the SDA line so that it remains LOW during this pulse to acknowledge receipt of the data. If the slave fails to acknowledge by leaving SDA high, then the master may abort the transmission by generating a STOP condition. When the master is receiving data from the slave, the master pulls down the SDA line during the clock pulse to indicate receipt of the data. After the last byte has been received the master leaves the SDA line HIGH (not acknowledge) and issues a stop condition to terminate the transmission. Device Addressing The LT3582 series supports two 7-bit chip addresses depending on the logic state of the CA pin. The addresses are 0110 001 (CA=1) and 1000 101 (CA=0). Also, there are seven internal data byte locations as shown in Table 1. OTP0-OTP2 are the OTP memory bytes. REG0-REG2 are the corresponding volatile registers used for storing alternate settings. Finally, the Command Register (CMDR) is used for additional control of the chip. All data bytes can be read from their assigned register addresses. Since they share the same register addresses, reads of the OTP and REG data bytes are differentiated by their corresponding RSEL (Register Select) bits in the SDA A6 - A0 B7 - B0 B7 - B0 SCL S 1-7 8 9 1-7 8 9 1-7 8 9 P START CONDITION CHIP ADDRESS R/W ACK DATA ACK DATA ACK STOP CONDITION 3582512 F01 Figure 1. Data Transfer over I2C Bus 3582512f 11 LT3582/LT3582-5/LT3582-12 APPLICATIONS INFORMATION CMDR register. All data written to register addresses 0-2 is stored in REGO-REG2. Regardless of the RSEL bits, OTP bytes cannot be written directly. See the OTP Programming section for more information. Data Transfer Protocol The LT3582 series supports 8-bit data transfers in the transaction formats shown in Figures 2 and 3 below. Multiple data bytes can only be transferred by issuing multiple transactions. Figure 2 shows the required format for writing a byte of data to the LT3582 series. Again, the chip address depends on the CA pin logic state. S CHIP ADDR 0110 001 OR 1000 101 W 0 A 0 REG ADDR 00000b2:b0 A 0 DATA b7:b0 A 0 P LT3582 Chip Configuration Settings such as output voltages and sequencing are digitally programmable. The chip uses settings from either the REG or OTP bytes, depending on the states of the corresponding RSEL bits (0 for OTP and 1 for REG). During shutdown the RSEL bits are reset low. As a result, the initial configuration comes from the OTP data bytes. After power-up, the configuration can be changed by writing new settings to the appropriate REG data byte(s) then setting the corresponding RSEL bit(s). Finally, data in the REG bytes can be permanently programmed to OTP by applying voltage to the VPP pin and setting the WOTP bit in the Command Register. See the OTP Programming section for more information. LT3582-5/LT3582-12 Chip Configuration The LT3582-5/LT3582-12 are shipped from the factory with the OTP memory pre-programmed and LOCKed which prohibits subsequent changes to the configuration. The configuration can still be read through the I2C bus and the RST & SWOFF bits of the CMDR register (described later) are functional. The following sections describe the various configurable features of the LT3582. The LT3582-5 and LT3582-12 are pre-configured as follows: VP and VN are programmed for ±5V or ±12V respectively, LOCK = 1, IRMP = 00, PDDIS = 1, PUSEQ = 11 and VPLUS may be 1 or 0. Since LOCK = 1, subsequent configuration changes are prohibited. See Configuration Lockout (LOCK Bit) for more information. Registers and OTP FROM MASTER TO SLAVE FROM SLAVE TO MASTER A: ACKNOWLEDGE (LOW) A: NOT ACKNOWLEDGE (HIGH) R: READ BIT (HIGH) W WRITE BIT (LOW) S: START CONDITION P: STOP CONDITION Figure 2: I2C Byte Write Transaction A byte of data is read from the LT3582 series using the format shown in Figure 3. This transaction requires four I2C bytes to read one byte of chip data and must be repeated for each subsequent byte of data that is read. S CHIP ADDR 0110 001 OR 1000 101 S W 0 A 0 REG ADDR 00000b2:b0 A 0 CHIP ADDR 0110 001 OR 1000 101 R 1 A 0 DATA b7:b0 A 1 P Figure 3: I2C Byte Read Transaction The registers and OTP bytes for the LT3582 series are organized as shown in Table 1. The CMDR is reset to 00h upon power up, during shutdown and during under-voltage and thermal lockouts. REG0-REG2 are never reset and must always be loaded with valid data before use. The LT3582’s OTP memory is shipped with all 0’s, and as a result, the PUSEQ bits are configured to disable the outputs. The PUSEQ bits must be reconfigured to enable the outputs. 3582512f 12 LT3582/LT3582-5/LT3582-12 APPLICATIONS INFORMATION CMDR: The Command Register is used to control various functions of the chip. During shutdown and power-up the CMDR is initialized to 00h. The RSEL (Register Select) bits are functional only for the LT3582. The LT3582-5 and LT3582-12 function as if the RSEL bits are always “0”. These bits perform three functions: • Each RSEL bit instructs the chip whether to use the configuration data from the corresponding OTP byte (RSELx=0) or the REG byte (RSELx=1). Changing an RSELx bit immediately updates the chip configuration. • Each RSEL bit determines if I2C reads return data from the corresponding OTP byte (RSELx=0) or the REG byte (RSELx=1). • OTP programming only programs data to the bytes with corresponding RSEL bits set high. Setting the SWOFF bit immediately disables the Boost and Inverting power switches and opens the output disconnect PMOS switch. It is recommended to set this bit before writing new configuration data. This can prevent unexpected chip behavior while modifying the configuration and also forces a soft-start after SWOFF is cleared (see Soft-Start and Power-up Sequencing). Writing “1” to the RST bit resets the internal I2C logic and the CMDR register. Reading bit 6 of the CMDR returns the FAULT bit indicating if an OTP programming attempt may have failed. FAULT is cleared during reset, power-up, or by writing a “1” to the CF (Clear Fault) bit. Conditions that set the FAULT bit are (1) OTP programming in which the VPP voltage is too low or (2) attempted OTP programming when the LOCK bit is set. OTP write attempts that set the FAULT bit due to low VPP voltage should be considered failures and the device should be discarded. Attempts to re-program the OTP memory after the FAULT bit has been set are not recommended. Finally, setting the WOTP bit starts the OTP programming. Table 1: LT3582 Series Register Map REGISTER ADDRESS 00h 01h REGISTER NAME REG0/ OTP0 REG1/ OTP1 BIT BIT DESCRIPTION NAME VP VN LOCK VPLUS IRMP VOUTP Output Voltage (00h=3.2V, BFh = 12.75V) VOUTN Output Voltage (00h=1.2V, FFh = 13.95V) Reserved, Write to 0 Lockout Bit: See “OTP Programming Lockout” Section. VOUTP Output Voltage Bit: Increase VOUTP by ~25mV RAMPP & RAMPN Pullup Current: IRAMP = (2) IRMP μA 7:0 7:0 7 6 02h REG2/ OTP2 5 4:3 2 1:0 PDDIS Power-Down Discharge Enable. PUSEQ Must be 11 if Set. PUSEQ Power-Up Sequencing: 00 = Outputs Disabled, 01 = VOUTN Ramp 1st, 10 = VOUTP Ramp 1st, 11 = Both Ramp Together WOTP Write OTP Memory CF/ Clear Fault/OTP Programming FAULT Fault RST Reset Reserved, Write to 0 SWOFF Switches-Off RSEL2 Register Select 2 (0=OTP2, 1=REG2) RSEL1 Register Select 1 (0=OTP1, 1=REG1) RSEL0 Register Select 0 (0=OTP0, 1=REG0) 7 6 5 4 04h CMDR 3 2 1 0 OTP0/REG0 & OTP1/REG1: Data in addresses 00h & 01h is used to set the output voltages of the Boost and Inverting converters respectively. See Setting the Output Voltages for more information. 3582512f 13 LT3582/LT3582-5/LT3582-12 APPLICATIONS INFORMATION OTP2/REG2: Data in address 02h configures the output voltage sequencing, sets a fine voltage adjust for VOUTP , and determines if further OTP programming is permitted or not. Proper uses of the bits in address 02h are discussed in the following sections. Setting the Output Voltages (VP , VPLUS and VN bits) The LT3582 series contains two resistor dividers which are programmable in the LT3582, to set the output voltages. The positive output voltage VOUTP is adjustable in 25mV steps by setting the VP bits in REG0/OTP0 in addition to the VPLUS bit in REG2/OTP2. VOUTP = 3.2V + (VP • 50mV) + (VPLUS • 25mV) where: VP = an integer value from 0 to 191 VPLUS = 0 or 1 The VOUTN voltage is adjustable in –50mV steps by setting the VN bits in REG1/OTP1. VOUTN = –1.2V – (VN • 50mV) where: VN = an integer value from 0 to 255 Dynamically Changing the Output Voltage (LT3582 Only): After output regulation has been reached, it’s possible to change the output voltages by writing new values to the VN or VP bits. When reducing the magnitude of an output voltage, it will decay at a rate dependent on the load current and capacitance. Configuring a large increase in magnitude of an output voltage can cause a large increase in switch current to charge the output capacitor. Before reconfiguring the outputs, consider forcing a soft-start by asserting the SWOFF bit before writing the new VP or VN codes. Subsequently clearing SWOFF initiates the new soft-start sequence. Soft-Start/Output Voltage Ramping (IRMP bits) The LT3582 series contains soft-start circuitry to control the output voltage ramp rates, therefore limiting peak switch currents during start-up. High switch currents are inherent in switching regulators during startup since the feedback loop is saturated due to VOUT being far from its final value. The regulator tries to charge the output capacitor as quickly as possible which results in large currents. Capacitors must be connected from RAMPP & RAMPN to ground for soft-start. During shutdown or when the SWOFF bit is set, the RAMP capacitors are discharged to ground. After SHDN rises or SWOFF is cleared, the capacitors are charged by programmable (LT3582 only) currents, thus creating linear voltage ramps. The VOUT voltages ramp in proportion to their respective RAMP voltages according to: VOUT _RAMP _RATE = Proportionality Constant RAMP pin ramp rate (V/Sec) where: IRAMP = RAMP pin charging current set by IRMP bits (1μA, 2μA, 4μA or 8μA for LT3582, 1μA for LT3582-5/LT3582-12) CRAMP = External RAMP pin capacitor (Farads) VOUT = Output voltage during regulation For example, selecting IRAMP = 1μA, CRAMP = 10nF and VOUTP = 12V results in a power-up ramp rate of 1.5Volt/ms (see Figure 6). Ramp rates less than 1-10V/ms generally result in good startup characteristics. The outputs should linearly follow the RAMPx voltages with no distortions. Figure 7 shows an excessive startup ramp rate of ~120V/ms in which several startup issues have occurred: A) the expected VOUTP ramp up path is not followed B) inductor current ringing occurs C) the VOUTP ramp rate is limited due to the output VOUT I • RAMP Volts / Sec 0.8 V CRAMP 3582512f 14 LT3582/LT3582-5/LT3582-12 APPLICATIONS INFORMATION disconnect current limit being reached D) additional ringing occurs when the CAPP pin starts charging E) output voltage overshoot occurs because the inductor currents are maximized during the output ramp up. In some cases it may be desirable to use only one RAMP pin capacitor. In cases where PUSEQ = 11 (see Power-Up Sequencing section) the RAMPP & RAMPN pins can be connected together and to a single capacitor. In this case the capacitor will charge with twice the current configured by the IRMP bits. Ramping VOUTP from Ground: The LT3582 series has the unique ability to generate a smooth VOUTP voltage ramp starting from ground and continuing all the way up to regulation (see Figure 6). This ability is not possible with typical Boost converters in which the output is taken from the cathode of the Schottky diode (CAPP node in Figure 5). The LT3582 series incorporates an output disconnect PMOS allowing VOUTP to be grounded during shutdown. L1 SWP D1 C1 C2 VIN C3 DISCONNECT CONTROL LOAD A 3582512 F05 Once enabled, the Disconnect Control circuit actively drives the PMOS gate allowing VOUTP to ramp up linearly as shown in Figure 6. Once VOUTP reaches regulation, the PMOS is fully turned “on” to reduce resistance and improve efficiency. Power-Up Sequencing (PUSEQ bits) Once enabled, the part requires a delay of TSTARTUP (64μs typ) to properly configure itself. Once configured, the order in which VOUTP and VOUTN ramp to regulation is controlled by the PUSEQ bits. The combinations available for the LT3582 are shown in Table 2. The LT3582-5/LT3582-12 are pre-configured with the 11 combination. Table 2. Power-Up Sequences PUSEQ[1:0] Power-Up Sequence 00 01 10 11 Outputs are disabled, neither output ramps up VOUTN ramps up 1st, followed by VOUTP VOUTP ramps up 1st, followed by VOUTN Both VOUTP & VOUTN r amp up starting at the same time. CAPP LT3582 SERIES VOUTP Selecting the 01 or 10 combinations cause one of the outputs to start ramping shortly after SHDN rises. The ramp rate of VOUT is controlled by the RAMP pin as discussed in the Soft-Start section. After VOUT nears its target regulation voltage, the remaining output is activated and ramps VRAMPP 0.5V/DIV CAPP 3V/DIV VOUTP 3V/DIV C IL2 0.2A/DIV B D E Figure 5: Boost Converter Topology CAPP 2V/DIV VOUTP 2V/DIV VRAMPP 0.2V/DIV IL2 0.2A/DIV 50μs/DIV 3582512 F07 Figure 7: VOUTP Soft-Start with Excessive Ramp Rate 5μs/DIV 3582512 F06 Figure 6: VOUTP Soft-Start Ramping from Ground 3582512f 15 LT3582/LT3582-5/LT3582-12 APPLICATIONS INFORMATION under control of its respective RAMP pin (see Figure 8 below). The power-up sequencing concludes when both outputs have reached regulation. Evaluating PUSEQ Settings (LT3582 Only): After SHDN rises, the LT3582 uses the PUSEQ configuration found in OTP. The effects of differing PUSEQ settings can be observed without writing to OTP by taking the following actions: 1. Write the SWOFF bit high, stopping both converters and discharging the RAMP pins. 2. Write the desired settings to the PUSEQ bits in REG2. 3. Set the RSEL2 bit high which selects the REG2 configuration settings. 4. Write SWOFF low which restarts both converters. This will initiate the desired power-up sequence that can be observed with an oscilloscope. Power-Down Discharge (PDDIS bit) The PDDIS bit is used to enable power down discharge. This bit is pre-configured to a “1” for the LT3582-5 and LT3582-12, thus enabling power-down discharge.Setting PDDIS = 0 disables the power-down discharge causing the chip to shut down immediately after SHDN falls. The PDDIS bit must only be set in conjunction with PUSEQ being set to 11. Driving SHDN low, with power-down discharge enabled (PDDIS = 1) causes the chip to power-down after first discharging the output voltages. Specifically, driving SHDN low causes the following sequence of events to happen: 1. Both converters are turned off. 2. Discharge currents are enabled to discharge the output capacitors • See Electrical Charateristics for IVOUTP-PDS and ICAPP-PDS which help discharge VOUTP and CAPP • See Electrical Charateristics for IVOUTN-PDS which helps discharge VOUTN 3. The chip waits until the output voltages have discharged to within ~0.5V to ~1.5V of ground. 4. Discharge currents are disabled and the LT3582 powers down. RAMPP VRAMPP 0.5V/DIV VRAMPN 0.5V/DIV VVOUTP 5V/DIV VVOUTN 5V/DIV RAMPN 5ms/DIV 3582512 F08 Figure 8: Power-up Sequencing (PUSEQ=10) 3582512f 16 LT3582/LT3582-5/LT3582-12 APPLICATIONS INFORMATION Since the LT3582 series won’t power-down until both outputs are discharged (when power-down sequencing is enabled), make sure VOUTP & VOUTN can be grounded. This is not a problem in most topologies. However, read the section Output Disconnect Operating Limits for additional information. Configuration Lockout (LOCK bit) After a desired configuration is programmed into OTP, the LOCK bit can be set to prohibit subsequent changes to the configuration. The LT3582-5 and LT3582-12 are preconfigured with the LOCK bit set to a logic “1” which: • Forces the chip to use the OTP configuration only. • Forces all I2C reads from addresses 0-2 to return OTP data. • Prohibits any further programming of the OTP memory. Any further attempts to program OTP leaves the OTP memory unchanged and sets the FAULT bit in the CMDR. The LOCK OTP bit is set by programming a logic “1” into bit 6 of OTP2. Regardless of the RSEL2 setting, I2C reads of the LOCK bit always indicate the LOCKed or unlocked state of the OTP memory. OTP Programming (LT3582 only) The LT3582 contains One Time Programmable non-volatile memory to permanently store the chip configuration. Before programming, it’s recommended to set the SWOFF bit to disable switching activity and prevent unexpected chip behavior while the configuration is being changed. Programming involves the transfer of information from the REG bytes to the OTP bytes. Therefore, valid data must first be written to the desired REG bytes. After the REG bytes are written, they are selected by setting the corresponding RSEL bits in the CMDR. This forces the chip into the desired configuration and selects those bytes for programming to OTP. After 15V has been applied to VPP, the WOTP bit is set in the CMDR to start the programming. Finally, the WOTP bit is cleared to finish the programming. An example programming algorithm is given below. OTP programming draws about 3-6mA per bit from the VPP pin. It is possible to program all 23 bits simultaneously (up to ~138mA), but it is recommended that one byte is programmed at a time to reduce noise on VPP caused by the sudden change in current. A 1-10μF VPP bypass capacitor is also recommended to prevent voltage droop after programming begins. Also, avoid hot-plugging VPP which results in very fast voltage ramp rates and can lead to excessive voltage on the VPP pin. Example OTP Programming Algorithm: 1. Apply 15V to the VPP pin. This can be done at any time before step 5. 2. Write 50h to the CMDR. This disables the power switches during programming by setting the SWOFF bit in the CMDR. This also clears the FAULT bit. 3. Write desired data to REG0-REG2. 4. Write 11h to the CMDR. This selects REG0 for programming while keeping the switches off. 5. Write 91h to the CMDR. This programs the REG0 data to OTP0. 6. Write 11h to the CMDR. This command can be sent immediately after step 5. This stops the programming. 7. Read the CMDR and verify that the FAULT bit is not set. 8. Repeat steps 4-7 for the remaining bytes that need programming. 9. Write 10h to the CMDR. This selects the OTP data for read verification. 3582512f 17 LT3582/LT3582-5/LT3582-12 APPLICATIONS INFORMATION 10. Read the OTP data and verify the contents. 11. Write 00h to CMDR. This enables the power switches and the chip will operate from the OTP configuration. 12. Float the VPP pin. This can be done at any time after step 8. Choosing Inductors Several series of inductors that work well with the LT3582 series are listed in Table 3. This table is not complete, and there are many other manufacturers and parts that can be used. Consult each manufacturer for more detailed information and for their entire selection of related parts, as many different sizes and shapes are available. Table 3: Inductor Manufacturers Coilcraft Murata Sumida TDK Würth Elektronik LPS3008-LPS4018 Series, www.coilcraft.com XPL2010 Series LQH32C, LQH43C Series www.murata.com CDRH26D09, CDRH26D11, www.sumida.com CDRH3D14 Series VLF and VLCF Series www.tdk.com WE-TPC Series Type T, TH, www.we-online.com XS and S inductor current without saturating. To minimize radiated noise, use a toroidal or shielded inductor (note that the inductance of shielded types will drop more as current increases, and will saturate more easily). Peak Current Rating: Real inductors can experience a drop in inductance as current and temperature increase. The inductors should have saturation current ratings higher than the peak inductor currents. The peak inductor currents can be calculated as: IPK ≅ ILIMIT + where: IPK ILIMIT L VLSWON TOS = Peak inductor current = Typically 350mA for Boost and 600mA for Inverting = Inductance in μH = Maximum inductor voltage when the power switch is “on”. Typically max VIN for the Boost and Inverting converters. = 100 for Boost and 125 for Inverting VLSWON • TOS mA L Inductances of 2.2μH-10μH typically result in a good tradeoff between inductor size and system performance. More inductance typically yields an increase in efficiency at the expense of increased output ripple. Less inductance may be used in a given application depending on required efficiency and output current. For higher efficiency, choose inductors with high frequency core material, such as ferrite, to reduce core losses. Also to improve efficiency, choose inductors with more volume for a given inductance. The inductor should have low DCR (copper-wire resistance) to reduce I2R losses, and must be able to handle the peak Maximum Load Currents: Use one of the following equations to estimate the maximum output load current for the positive and negative output voltages: IOUTP = ⎛ VIN(MIN) ⎞ ⎛ TOFF _ MIN • (VOUTP + 0.5 – VIN(MIN) )⎞ ⎟ • 0.8η ⎜ ⎟ • ⎜IPK – 2•L ⎝ VOUTP ⎠ ⎝ ⎠ or IOUTN = ⎛ ⎞⎛ VIN(MIN) • (|VOUTN | +0.5)⎞ T ⎜ ⎟ • ⎜IPK – OFF _ MIN ⎟ • 0.8η ⎜V ⎟ 2•L ⎠ IN(MIN) + |VOUTN |⎠ ⎝ ⎝ 3582512f 18 LT3582/LT3582-5/LT3582-12 APPLICATIONS INFORMATION Where… = Regulation voltage VOUT VIN(MIN) = Minimum input voltage. = Peak inductor current. See prior section IPK Peak Current Rating. Use minimum ILimit rating for these calculations. η = Power conversion efficiency (about 88% for Boost or 78% for Inverting) TOFF_MIN = Minimum switch off time. Typically 100ns for Boost and 125ns for Inverting. IOUT = Output load current For example, if VOUTP = 10V, VOUTN = –10V, VIN = 5V, and L = 4.7μH then IOUTP = 117mA and IOUTN = 105mA. Note: The 155mA (Typ) current limit of the output disconnect PMOS (see Electrical Characteristics) may limit maximum IOUTP unless CAPP is shorted to VOUTP. See Improving Boost Converter Efficiency. Maximum Slew Rate: Lower inductance causes higher current slew rates which can lead to current limit overshoot. Choose an inductance higher than LMIN to limit the overshoot: LMIN = VIN(MAX) • 0.2µH where VIN(MAX) is the maximum input voltage. Using the previous example VIN = 3V, LMIN = 0.6μH. Capacitor Selection The small size and low ESR of ceramic capacitors makes them suitable for most LT3582 series applications. X5R and X7R types are recommended because they retain their capacitance over wider voltage and temperature ranges than other types such as Y5V or Z5U. A 4.7μF input capacitor and a 2.2μF-10μF output capacitor are sufficient for most LT3582 series applications. Always use a capacitor with a sufficient voltage rating. Many capacitors rated at 2.2μF to 10μF, particularly 0805 or 0603 case sizes, have greatly reduced capacitance at the desired output voltage. Generally a 1206 capacitor will be adequate. A 0.22μF to 1μF capacitor placed on the CAPP node is recommended to filter the inductor current while the larger 2.2μF to 10μF placed on the VOUTP & VOUTN nodes will give excellent transient response and stability. Avoid placing large value capacitors (generally > 6.8μF) on both CAPP and VOUTP. This configuration can be less stable since it creates two poles, one at the CAPP pin and the other at the VOUTP pin, which can be near each other in frequency. Table 4 shows a list of several capacitor manufacturers. Consult the manufacturers for more detailed information and for their entire selection of related parts. Table 4: Ceramic Capacitor Manufacturers MANUFACTURER Kemet Murata Taiyo Yuden TDK PHONE 408-986-0424 814-237-1431 408-573-4150 847-803-6100 URL www.kemet.com www.murata.com www.t-yuden.com www.tdk.com Diode Selection Schottky diodes, with their low forward voltage drops and fast switching speeds, are recommended for use with the LT3582 series. The Diodes Inc. B0540WS is a very good choice in a small SOD-323 package. This diode is rated to handle an average forward current of 500mA and performs well across a wide temperature range. Schottky diodes with very low forward voltage drops are also available. These diodes may improve efficiency at moderate and cold temperatures, but will likely reduce efficiency at higher temperatures due to excessive reverse leakage currents. 3582512f 19 LT3582/LT3582-5/LT3582-12 APPLICATIONS INFORMATION Output Disconnect Operating Limits The LT3582 series has a PMOS output disconnect switch connected between CAPP and VOUTP . During normal operation, the switch is closed and current is internally limited to about 155mA (see Figure 9). Make sure that the output load current doesn’t exceed the PMOS current limit. Exceeding the current limit causes a significant rise in PMOS power consumption which may damage the device. During shutdown, the PMOS switch is open and CAPP is isolated from VOUTP up to a voltage difference of 5-5.5V. In most cases this allows VOUTP to discharge to ground. However, when the Boost inductor input exceeds 5.5V, the CAPP-VOUTP voltage may exceed 5V allowing some current flow through the PMOS switch. In addition, applying CAPP-VOUTP voltages in excess of 5.7V(typical) may activate internal protection circuitry which turns the PMOS “on” (see Figure 10). If the current is not limited, this can lead to a sharp increase in the PMOS power consumption and may damage the device. If this situation cannot be avoided, limit PMOS power consumption to less than 1/3 Watt (about 50mA at 7V) to avoid damaging the device. Refer to the Absolute Maximum Ratings table for maximum limits on CAPP-VOUTP voltages and currents. Improving Boost Converter Efficiency The efficiency of the Boost converter can be improved by shorting the CAPP pin to the VOUTP pin (see Figure 11). The power loss in the PMOS disconnect circuit is then made negligible. In most applications, the associated CAPP pin capacitor can be removed and the larger VOUTP capacitor can adequately filter the output voltage. Note that the ripple voltage on VOUTP will typically increase in this configuration since the output disconnect PMOS, when not shorted, helps to create an RC filter at the output. Also, if the VOUTP pin is shorted to CAPP, the power-down discharge should not be enabled. VOUTP cannot be discharged to ground during shutdown due to the path from VIN to VOUTP through the external inductor ICAPP-VOUTP 20μA/DIV VCAPP-VOUTP 1V/DIV 180 160 140 PMOS CURRENT (mA) 120 100 80 60 40 20 0 0 100 200 300 CAPP-VOUTP (mV) 400 500 3582512 F10 3582512 F11 Figure 10: PMOS Current vs. Voltage During Shutdown 4 3 12 5 11 10 9 14 15 16 1 C1 ILOAD SWN SWN SWP VIN CAPP 13 GND LT3582 CAPP VOUTP 2 VOUTN VPP SDA SCL 8 SHDN Figure 9: PMOS Current vs. Voltage During Normal Operation RAMPP RAMPN 7 6 CA 3582512 F12 Figure 11: Improved Efficiency 3582512f 20 LT3582/LT3582-5/LT3582-12 APPLICATIONS INFORMATION and diode. Finally, due to the path from VIN to VOUTP, current will flow through the integrated feedback resistor whenever voltage is present on VIN. Inrush Current When the Boost inductor input voltage (usually VIN) is stepped from ground to the operating voltage, a high level of inrush current may flow through the inductor and Schottky diode into the CAPP capacitor. Conditions that increase inrush current include a larger more abrupt voltage step at the inductor input, larger CAPP capacitors and inductors with low inductances and/or low saturation currents. For circuits that use output capacitor values within the recommended range and have input voltages of less than 5V, inrush current remains low, posing no hazard to the devices. In cases where there are large input voltage steps (more than 5V) and/or a large CAPP capacitor is used, inrush current should be measured to ensure safe operation. Thermal Lockout If the die temperature reaches approximately 147°C, the part will go into thermal lockout. In this event, the chip is reset which turns off the power switches and starts to discharge the RAMP capacitors. The part will be re-enabled when the die temperature drops by about 3.5°C. Board Layout Considerations As with all switching regulators, careful attention must be paid to the PCB board layout and component placement. To maximize efficiency, switch rise and fall times are made as short as possible. To prevent electromagnetic interference (EMI) problems, proper layout of the high frequency switching path is essential. The voltage signals of the SWP and SWN pins have sharp rising and falling edges. Minimize the length and area of all traces connected to the SWP/SWN pins and always use a ground plane under the switching regulator to minimize interplane coupling. Suggested component placement is shown in Figure 12. Make sure to include the ground plane cuts as shown in Figure 12. The switching action of the regulators can cause large current steps in the ground plane. The cuts reduce noise by recombining the current steps into a continuous flow under the chip, thus reducing di/dt related ground noise in the ground plane. 3582512f 21 LT3582/LT3582-5/LT3582-12 APPLICATIONS INFORMATION CA SCL SDA VPP CVPP (OPT) 16 VOUTN COUTN 1 15 17 14 13 12 11 10 9 CCAPP L1 2 3 GND L2 CIN 4 5 6 7 8 COUTP VIN VIAS TO GROUND PLANE UNDER PIN 17 REQUIRED TO IMPROVE THERMAL PERFORMANCE SHDN VOUTP GROUND PLANE 3582512 G13 Figure 12: Suggested Component Placement (not to scale) 3582512f 22 LT3582/LT3582-5/LT3582-12 TYPICAL APPLICATION ±5V Outputs from a Single 2.7V to 3.8V Input SWN D1 L1 6.8μH SWN SHDN VIN SWP GND LT3582 VNEG –5V 100mA (VIN ≥ 2.7V) 125mA (VIN ≥ 3.3V) I2C INTERFACE C2 10μF VOUTN SDA SCL CA RAMPP RAMPN C6 22nF 3582512 TA02a INPUT 2.7V TO 3.8V L2 6.8μH D2 C4 1μF C1 4.7μF CAPP CAPP VOUTP VPP C3 10μF VPOS 5V 100mA (VIN ≥ 2.7V) 124mA (VIN ≥ 3.3V) ( OPTIONAL ON LT3582-5 ) C5 22nF REG0/OTP0 = 24h REG1/OTP1 = 4Ch REG2/OTP2 = 03h D1-D2: DIODES INC. B0540WS-7 L1-L2: COILCRAFT LPS4018-682ML C1: 4.7μF 6.3V, X5R, 0805 , C2-C3: 10μF 6.3V, X5R 0805 , C4: 1μF 6.3V, X5R, 0603 , C5-C6: 22nF 0603 , Efficiency and Power Loss, Load from VOUTP to GND 95 85 EFFICIENCY (%) 75 65 55 45 35 0.1 1 10 LOAD CURRENT (mA) VIN = 3.3V 100 90 80 Efficiency and Power Loss, Load from VOUTN to GND 95 85 140 VIN = 3.3V 180 160 60 50 40 30 20 10 0 100 3582512 TA02b EFFICIENCY (%) 70 Efficiency and Power Loss, Load from VOUTP to VOUTN 95 85 EFFICIENCY (%) 75 65 55 45 35 0.1 1 10 LOAD CURRENT (mA) VIN = 3.3V 300 250 POWER LOSS (mW) 200 150 100 50 0 100 3582512 TA02d POWER LOSS (mW) POWER LOSS (mW) 75 65 120 100 80 55 45 60 40 20 35 0.1 1 10 LOAD CURRENT (mA) 0 100 3582512 TA02c 3582512f 23 LT3582/LT3582-5/LT3582-12 TYPICAL APPLICATION ±5V Outputs from a Single 2.7V to 3.8V Input (Improved Efficiency) SWN D1 L1 6.8μH SWN SHDN VIN SWP GND LT3582 VNEG –5V 100mA (VIN ≥ 2.7V) 125mA (VIN ≥ 3.3V) IC INTERFACE 2 INPUT 2.7V TO 3.8V L2 6.8μH D2 C3 10μF C1 4.7μF C2 10μF VOUTN SDA SCL CA CAPP CAPP VOUTP VPP RAMPP RAMPN C6 22nF 3582512 TA03 VPOS 5V 110mA (VIN ≥ 2.7V) 150mA (VIN ≥ 3.3V) ( OPTIONAL ON LT3582-5 ) C5 22nF REG0/OTP0 = 24h REG1/OTP1 = 4Ch REG2/OTP2 = 03h D1-D2: DIODES INC. B0540WS-7 L1-L2: COILCRAFT LPS4018-682ML C1: 4.7μF 6.3V, X5R, 0805 , C2-C3: 10μF 6.3V, X5R, 0805 , C4: 1μF 6.3V, X5R, 0603 , C5-C6: 22nF 0603 , Efficiency and Power Loss, Load from VOUTP to GND 95 85 EFFICIENCY (%) 75 65 55 45 35 0.1 1 10 LOAD CURRENT (mA) VIN = 3.3V 80 70 60 POWER LOSS (mW) 3582512f 50 40 30 20 10 0 100 3582512 TA03a 24 LT3582/LT3582-5/LT3582-12 TYPICAL APPLICATION 12V and –5V Outputs from a Single 2.7V to 5.5V Input SWN D1 L1 6.8μH SWN SHDN VIN SWP GND LT3582 VNEG –5V 100mA I2C INTERFACE C2 10μF VOUTN SDA SCL CA RAMPP RAMPN C6 22nF 3582512 TA04a INPUT 2.7V TO 5.5V L2 6.8μH D2 C4 1μF C1 4.7μF CAPP CAPP VOUTP VPP C3 4.7μF VPOS 12V 38mA (VIN = 2.7) 58mA (VIN = 3.6) 95mA (VIN = 5.5) C5 22nF REG0/OTP0 = B0h REG1/OTP1 = 4Ch REG2/OTP2 = 0Bh D1-D2: DIODES INC. B0540WS-7 L1-L2: COILCRAFT LPS4018-682ML C1: 4.7μF 6.3V, X5R, 0805 , C2: 10μF 6.3V, X5R, 0805 , C3: 4.7μF 16V, X5R, 0805 , C4: 1μF 16V, X5R, 0603 , C5-C6: 22nF 0603 , Efficiency and Power Loss, Load from VOUTP to GND 95 85 EFFICIENCY (%) 75 65 55 45 35 0.1 1 10 LOAD CURRENT (mA) VIN = 3.6V 100 90 80 Efficiency and Power Loss, Load from VOUTN to GND 95 85 140 POWER LOSS (mW) VIN = 3.6V 180 160 60 50 40 30 20 10 0 100 3582512 TA04b EFFICIENCY (%) 70 Efficiency and Power Loss, Load from VOUTP to VOUTN 95 85 EFFICIENCY (%) 75 65 55 45 35 0.1 1 10 LOAD CURRENT (mA) VIN = 3.6V 200 180 160 140 120 100 80 60 40 20 0 100 3582512 TA04d POWER LOSS (mW) 75 65 120 100 80 55 45 60 40 20 35 0.1 1 10 LOAD CURRENT (mA) 0 100 3582512 TA04c POWER LOSS (mW) 3582512f 25 LT3582/LT3582-5/LT3582-12 TYPICAL APPLICATION SWN D1 L1 6.8μH SWN SHDN VIN SWP GND LT3582 VNEG –12V 85mA I2C INTERFACE C2 4.7μF VOUTN SDA SCL CA RAMPP RAMPN C6 10nF 3582512 TA05a INPUT 4.5V TO 5.5V L2 6.8μH D2 C4 1μF C1 4.7μF CAPP CAPP VOUTP VPP C3 VPOS 12V 80mA ( OPTIONAL ON LT3582-12 ) C5 10nF REG0/OTP0 = B0h REG1/OTP1 = D8h REG2/OTP2 = 03h D1-D2: DIODES INC. B0540WS-7 L1-L2: COILCRAFT XPL2010-682 C1: 4.7μF 6.3V, X5R, 0805 , C2: 4.7μF 16V, X5R, 0805 , C3: 1× 4.7μF OR 2× 4.7μF OR 10μF 16V, X5R, 0805 C4: 1μF 16V, X5R, 0603 , C5-C6: 10nF 0603 , Figure 13. ±12V Outputs from a Single 5V Input VOUTP Ripple 25 80 VOUTN Ripple and C2 Selection 20 OUTPUT RIPPLE (mV) OUTPUT RIPPLE (mV) 4.7μF 16V 0805 X5R 60 15 40 10μF 16V 0805 X5R 10 20 2× 4.7μF 16V 0805 X5R 5 0 0 0 20 40 60 LOAD CURRENT (mA) 80 3582512 TA05b 0 20 40 60 LOAD CURRENT (mA) 80 3582512 TA05c Also See Typical Characteristics and Front Page for Additional Data 3582512f 26 LT3582/LT3582-5/LT3582-12 PACKAGE DESCRIPTION UD Package 16-Lead Plastic QFN (3mm × 3mm) (Reference LTC DWG # 05-08-1691) 0.70 0.05 3.50 0.05 2.10 1.45 0.05 0.05 (4 SIDES) PACKAGE OUTLINE 0.25 0.05 0.50 BSC RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS 0.75 0.05 BOTTOM VIEW—EXPOSED PAD R = 0.115 TYP 15 16 0.40 1 1.45 0.10 (4-SIDES) 2 0.10 PIN 1 NOTCH R = 0.20 TYP OR 0.25 45 CHAMFER 3.00 0.10 (4 SIDES) PIN 1 TOP MARK (NOTE 6) (UD16) QFN 0904 0.200 REF 0.00 – 0.05 NOTE: 1. DRAWING CONFORMS TO JEDEC PACKAGE OUTLINE MO-220 VARIATION (WEED-2) 2. DRAWING NOT TO SCALE 3. ALL DIMENSIONS ARE IN MILLIMETERS 4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE 5. EXPOSED PAD SHALL BE SOLDER PLATED 6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION ON THE TOP AND BOTTOM OF PACKAGE 0.25 0.05 0.50 BSC 3582512f Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights. 27 LT3582/LT3582-5/LT3582-12 TYPICAL APPLICATION Tiny AMOLED Power Supply is 0.8mm (Max) Thin SWN D1 L1 1.5μH SWN SHDN VIN SWP GND LT3582 VNEG –5V 90mA IC INTERFACE 2 Efficiency and Power Loss, Load from VOUTP to VOUTN 90 VIN = 3.3V 350 300 250 C1 10μF EFFICIENCY (%) 70 200 60 150 50 40 30 0.1 1 10 LOAD CURRENT (mA) 100 50 0 100 3582512 TA06b 3582512 TA06a INPUT 2.7V TO 4.2V L2 1.5μH D2 C4 10μF 80 POWER LOSS (mW) C2 10μF VOUTN SDA SCL CA C5 10nF CAPP CAPP VOUTP VPP RAMPP RAMPN C6 10nF C3 10μF VPOS 4.6V 100mA REG0/OTP0 = 1Ch REG1/OTP1 = 4Ch REG2/OTP2 = 07h D1-D2: PANASONIC M21D3800L LOW VF SCHOTTKY L1-L2: TDK MLP3216S1R5L C1-C4: TAIYO YUDEN JMK212BJ106MK, 6.3V, X5R 0805 C5-C6: 0402 X5R RELATED PARTS PART LT1944/-1(Dual) LT1945(Dual) LT3463/A DESCRIPTION Dual Output 350mA ISW, Constant Off-Time, High Efficiency Step-Up DC/DC Converter Dual Output, Pos/Neg, 350mA ISW, Constant OffTime, High Efficiency Step-Up DC/DC Converter COMMENTS VIN: 1.2V to 15V, VOUT(MAX) = 34V, IQ = 20μA, ISD