EL7581 ® Data Sheet March 9, 2006 3-Channel DC/DC Converter Features The EL7581 is a 3-channel DC/DC converter IC which is designed primarily for use in TFT/LCD applications. It features a PWM boost converter with 2.7V to 14V input capability and 5V to 17V output, which powers the column drivers and provides up to 720mA @12V, 570mA @ 15V from 5V input. A pair of charge pump control circuits provide regulated outputs of VON and VOFF supplies at 8V to 40V and -5V to -40V, respectively, each at up to 60mA. • TFT/LCD display supply - Boost regulator - VON charge pump - VOFF charge pump FN7100.5 • 2.7V to 14V VIN supply • 5V < VBOOST < 17V • 5V < VON < 40V The EL7581 features adjustable switching frequency, adjustable soft start, and a separate output VON enable control to allow selection of supply start-up sequence. An over-temperature feature is provided to allow the IC to be automatically protected from excessive power dissipation. • VBOOST = 12V @ 720mA The EL7581 is available in a 20 Ld HTSSOP package and is specified for operation over the full -40°C to +85°C temperature range. • Over 90% efficient DC/DC boost converter capability • VBOOST = 15V @ 570mA • High frequency, small inductor DC/DC boost circuit • Adjustable frequency • Adjustable soft-start Ordering Information PART NUMBER • -40V < VOFF < 0V PART TAPE & MARKING REEL PACKAGE PKG. DWG. # EL7581IRE 7581IRE - 20 Ld HTSSOP MDP0048 EL7581IRE-T7 7581IRE 7” 20 Ld HTSSOP MDP0048 EL7581IRE-T13 7581IRE 13” 20 Ld HTSSOP MDP0048 EL7581IREZ (Note) 7581IREZ - 20 Ld HTSSOP MDP0048 (Pb-Free) EL7581IREZ-T7 (Note) 7581IREZ 7” 20 Ld HTSSOP MDP0048 (Pb-Free) EL7581IREZ-T13 7581IREZ (Note) 13” 20 Ld HTSSOP MDP0048 (Pb-Free) NOTE: Intersil Pb-free plus anneal products employ special Pb-free material sets; molding compounds/die attach materials and 100% matte tin plate termination finish, which are RoHS compliant and compatible with both SnPb and Pb-free soldering operations. Intersil Pb-free products are MSL classified at Pb-free peak reflow temperatures that meet or exceed the Pb-free requirements of IPC/JEDEC J STD-020. • Adjustable outputs • Small parts count • Pb-free plus anneal available (RoHS compliant) Applications • TFT-LCD panels • PDAs Pinout EL7581 (20 LD HTSSOP) TOP VIEW VSSB 1 20 ROSC SS 2 19 ENP FBB 3 18 ENBN VDDB 4 17 VREF LX 5 LX 6 THERMAL PAD* 16 PGND 15 PGND LX 7 14 DRVP DRVN 8 13 VDDP VDDN 9 12 FBP FBN 10 11 VSSP *Refer to PCB layout guideline. 1 CAUTION: These devices are sensitive to electrostatic discharge; follow proper IC Handling Procedures. 1-888-INTERSIL or 1-888-468-3774 | Intersil (and design) is a registered trademark of Intersil Americas Inc. Copyright © Intersil Americas Inc. 2004, 2006. All Rights Reserved. All other trademarks mentioned are the property of their respective owners. EL7581 Absolute Maximum Ratings (TA = 25°C) Storage Temperature . . . . . . . . . . . . . . . . . . . . . . . .-65°C to +150°C Die Junction Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125°C Power Dissipation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . See Curves Operating Ambient Temperature . . . . . . . . . . . . . . . .-40°C to +85°C VIN Input Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14V VDDB, VDDP, VDDN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18V LX Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18V Maximum Continuous Output Current . . . . . . . . . . . . . . . . . . . . . .1A CAUTION: Stresses above those listed in “Absolute Maximum Ratings” may cause permanent damage to the device. This is a stress only rating and operation of the device at these or any other conditions above those indicated in the operational sections of this specification is not implied. IMPORTANT NOTE: All parameters having Min/Max specifications are guaranteed. Typ values are for information purposes only. Unless otherwise noted, all tests are at the specified temperature and are pulsed tests, therefore: TJ = TC = TA Electrical Specifications PARAMETER VIN = 3.3V, VBOOST = 12V, ROSC = 100kΩ, TA = 25°C Unless Otherwise Specified. DESCRIPTION CONDITIONS MIN TYP MAX UNIT DC/DC BOOST CONVERTER IQ1_B Quiescent Current - Shut-down ENBN = ENP = 0V 0.8 10 µA IQ2_B Quiescent Current - Switching ENBN = VDDB 4.8 8 mA V(FBB) Feedback Voltage 1.275 1.300 1.325 V VREF Reference Voltage 1.260 1.310 1.360 V VROSC Oscillator Set Voltage 1.260 1.325 1.390 V I(FBB) Feedback Input Bias Current VDDB Boost Converter Supply Range 2.7 DMAX Maximum Duty Cycle 85 I(LX)MAX Peak Internal FET Current RDS-ON Switch On Resistance at VBOOST = 10V, I(LX) total = 500mA ILEAK-SWITCH Switch Leakage Current I(LX) total VBOOST Output Range VBOOST > VIN + VDIODE ∆VBOOST/∆VIN Line Regulation 2.7V < VIN < 13.2V, VBOOST = 15V 0.1 % ∆VBOOST/∆IO1 Load Regulation 50mA < IO1 < 300mA 0.5 % FOSC-RANGE Frequency Range ROSC range = 240kΩ to 60kΩ 200 FOSC1 Switching Frequency ROSC = 100kΩ 620 0.1 µA 17 V 92 % 2.75 A 0.15 Ω 5 680 2 µA 17 V 1000 kHz 750 kHz POSITIVE REGULATED CHARGE PUMP (VON) Most positive VON output depends on the magnitude of the VDDP input voltage (normally connected to VBOOST) and the external component configuration (doubler or tripler) VDDP Supply Input for Positive Charge Pump Usually connected to VBOOST output IQ1(VDDP) Quiescent Current - Shut-down ENP = 0V IQ2(VDDP) Quiescent Current - Switching ENBN = ENP = VDDB V(FBP) Feedback Reference Voltage I(FBP) Feedback Input Bias Current I(DRVP) RMS DRVP Output Current 1.245 VDDP = 12V VDDP = 6V ILR_VON Load Regulation 5mA < IL < 15mA FPUMP Charge Pump Frequency Frequency set by ROSC - see boost section 2 5 17 V 11.5 20 µA 2.3 5 mA 1.310 1.375 V 0.1 µA 60 mA 15 -0.5 mA 0.03 0.5*FOSC 0.5 %/mA EL7581 Electrical Specifications PARAMETER VIN = 3.3V, VBOOST = 12V, ROSC = 100kΩ, TA = 25°C Unless Otherwise Specified. (Continued) DESCRIPTION CONDITIONS MIN TYP MAX UNIT NEGATIVE REGULATED CHARGE PUMP (VOFF) Most negative VOFF output depends on the magnitude of the VDDN input voltage (normally connected to VBOOST) and the external component configuration (doubler or tripler) VDDN Supply Input for Negative Charge Pump Usually connected to VBOOST output IQ1(VDDN) Quiescent Current - Shut-down ENBN = 0V IQ2(VDDN) Quiescent Current - Switching ENBN = VDDB V(FBN) Feedback Reference Voltage I(FBN) Feedback Input Bias Current Magnitude of input bias 0.1 µA I(DRVN) RMS DRVN Output Current VDDN = 12V 60 mA 5 -80 VDDN = 6V ILR_VOFF Load Regulation -15mA < IL < -5mA FPUMP Charge Pump Frequency Frequency set by ROSC - see boost section 17 V 1.2 10 µA 2.3 5 mA 0 +80 mV 15 -0.5 mA 0.03 0.5 %/mA 0.5*FOSC ENABLE CONTROL LOGIC VHI-ENX Enable Input High Threshold X = “BN”, “P” VLO-ENX Enable Input Low Threshold X = “BN”, “P” IL(EN”X”) Logic Low Bias Current X = “BN”, “P” = 0V 0.1 IL(ENBN) Logic High Bias Current ENBN = 5V 7.5 15 µA IL(ENP) Logic High Bias Current ENP = 5V 3.3 7.5 µA 1.4 V 0.6 V µA OVER-TEMPERATURE PROTECTION TOT Over-temperature Threshold 130 °C THYS Over-temperature Hysteresis 40 °C 3 EL7581 Pin Descriptions I = Input, O = Output, S = Supply PIN NUMBER PIN NAME PIN TYPE 1 VSSB S Ground for DC/DC boost and reference circuits; chip substrate 2 SS I Soft-start input; the capacitor connected to this pin sets the current limited start time 3 FBB I Voltage feedback input for boost circuit; determines boost output voltage, VBOOST 4 VDDB S Positive supply input for DC/DC boost circuits 5 LX O Boost regulator inductor drive connected to drain of internal NFET 6 LX O Boost regulator inductor drive connected to drain of internal NFET 7 LX O Boost regulator inductor drive connected to drain of internal NFET 8 DRVN O Driver output for the external generation of negative charge pump voltage, VOFF 9 VDDN S Positive supply for input for VOFF generator 10 FBN I Voltage feedback input to determine negative charge pump output, VOFF 11 VSSP S Negative supply pin for both the positive and negative charge pumps 12 FBP I Voltage feedback to determine positive charge pump output, VON 13 VDDP S Positive supply input for VON generator 14 DRVP O Voltage driver output for the external generation of positive charge pump, VON 15 PGND O Power ground, connected to source of internal NFET 16 PGND O Power ground, connected to source of internal NFET 17 VREF I Voltage reference for charge pump circuits; decouple to ground 18 ENBN I Enable pin for boost (VBOOST generation) and negative charge pump (VOFF generation); active high 19 ENP I Enable for DRVP (VON generation); active high 20 ROSC I Connected to an external resistor to ground; sets the switching frequency of the DC/DC boost 4 PIN FUNCTION EL7581 Typical Performance Curves 95 95 9V 90 85 15V 12V EFFICIENCY (%) EFFICIENCY (%) 90 80 75 70 65 60 200 400 600 800 85 9V 15V 80 1K 12V 75 70 65 VIN = 3.3V FS = 700kHz 60 0 200 VIN = 5V FS = 1MHz 0 5V IOUT (mA) 400 600 800 1K IOUT (mA) FIGURE 1. EFFICIENCY vs IOUT FIGURE 2. EFFICIENCY vs IOUT 95 95 9V 90 15V 85 5V 12V EFFICIENCY (%) EFFICIENCY (%) 90 80 75 70 65 V = 5V IN FS = 700kHz 60 0 200 85 9V 80 15V 75 70 65 VIN = 3.3V FS = 1MHz 60 400 600 800 0 1K 200 800 1K 3 2 VIN = 3.3V FS = 1MHz 1 0.5 0 15V 5V 9V -1 12V -1.5 250 VIN = 5V FS = 1MHz 2.5 LOAD REGULATION (%) 1.5 LOAD REGULATION (%) 600 FIGURE 4. EFFICIENCY vs IOUT FIGURE 3. EFFICIENCY vs IOUT -2 50 400 IOUT (mA) IOUT (mA) -0.5 12V 2 1.5 1 0.5 0 -0.5 9V -1 450 650 850 IOUT (mA) FIGURE 5. LOAD REGULATION 5 1050 -1.5 50 15V 250 450 12V 650 850 IOUT (mA) FIGURE 6. LOAD REGULATION 1050 EL7581 Typical Performance Curves (Continued) 3 VIN = 3.3V FS = 700kHz 3 2 1 0 5V -1 9V 15V -2 50 250 VIN=5V FS = 700kHz 2.5 LOAD REGULATION (%) LOAD REGULATION (%) 4 12V 2 1.5 1 0.5 0 -0.5 -1 450 650 850 -2 50 1050 250 450 IOUT (mA) 850 1050 FIGURE 8. LOAD REGULATION 6.5 20 19 VDDN = 15V 6 VDDP = 15V VDDN = 12V 5.5 18 VDDP = 12V VOFF (-V) VON (V) 650 9V IOUT (mA) FIGURE 7. LOAD REGULATION 17 16 5 4.5 4 15 3.5 14 0 10 20 30 40 50 60 70 0 80 10 20 30 40 50 60 70 80 ILOAD (mA) ILOAD (mA) FIGURE 10. VOFF vs IOFF FIGURE 9. VON vs ION SWITCHING PERIOD (µs) = 0.0118 ROSC + 0.378 f(MHz) = 1/(0.0118 ROSC + 0.378) 1400 6 1200 5 SWITCHING PERIOD (µs) FREQUENCY (kHz) 12V 15V -1.5 1000 800 600 400 200 4 3 2 1 0 0 0 50 100 150 200 250 300 ROSC (kΩ) FIGURE 11. FS vs ROSC 6 350 400 450 0 50 100 150 200 250 300 350 400 ROSC (kΩ) FIGURE 12. SWITCHING PERIOD vs ROSC 450 EL7581 Typical Performance Curves (Continued) ROSC = 61.9kΩ 1.27 970 1.265 968 VOLTAGE (V) FREQUENCY (kHz) 969 967 966 965 1.26 1.255 964 963 962 3 3.5 4 4.5 5 5.5 6 1.25 -50 0 50 100 TEMPERATURE (°C) VDDB (V) FIGURE 14. VREF vs TEMPERATURE FIGURE 13. FS vs VDDB IO = 5mA, VON = 18V, CON = 2.2µF VIN = 5V, VBOOST = 13V, IO = 100mA, CBOOST = 22µF VLX (10V/DIV) 50mV/DIV ∆VBOOST (20mV/DIV) 0.5µs/DIV 2µs/DIV FIGURE 15. BOOST STAGE FIGURE 16. VON RIPPLE IO = 5mA, VOFF = -6V, COFF = 3.3µF IO = 18mA, VON = 18V, CON = 2.2µF 20mV/DIV 50mV/DIV 2µs/DIV FIGURE 17. VON RIPPLE 7 10µs/DIV FIGURE 18. VOFF RIPPLE 150 EL7581 Typical Performance Curves (Continued) IO = 15mA, VOFF = -6V, COFF = 3.3µF VBOOST = 13V, IO = 100mA to 420mA, CBOOST = IO 20mV/DIV ∆VO (100mV/DIV) 2µs/DIV 20µs/DIV FIGURE 19. VOFF RIPPLE FIGURE 20. BOOST CONVERTER TRANSIENT RESPONSE CSS = 0.1µF CSS = 0.033µF VIN 2V/DIV VIN 2V/DIV IIN 0.5A/DIV IIN 0.5A/DIV 1mA/DIV 1ms/DIV FIGURE 21. START-UP VOLTAGE AND CURRENT FIGURE 22. START-UP VOLTAGE AND CURRENT CSS = 0.1µF CSS = 0.1µF VBOOST VBOOST 100mA 5V/DIV 5V/DIV 10V/DIV 2V/DIV VON 10V/DIV VOFF 2V/DIV 1ms/DIV FIGURE 23. POWER-UP, NO DELAY RC NETWORK ON ENABLE PINS 8 VON VOFF 200ms/DIV FIGURE 24. POWER-DOWN, NO DELAY RC NETWORK ON ENABLE PINS EL7581 Typical Performance Curves (Continued) CSS = 0.1µF CSS = 0.1µF VBOOST VBOOST 5V/div 5V/DIV 10V/DIV VON VON 10V/DIV VOFF 2V/DIV VOFF 2V/DIV 1ms/DIV 200ms/DIV FIGURE 26. POWER-UP, 100K AND 0.1µF DELAY NETWORK ON ENP FIGURE 25. POWER-DOWN, 100K AND 0.1µF DELAY NETWORK ON ENP VIN = 3.3V VOUT = 11.3V IOUT = 50mA VIN = 3.3V VOUT = 11.3V IOUT = 250mA FIGURE 28. LX WAVEFORM - CONTINUOUS MODE FIGURE 27. LX WAVEFORM - DISCONTINUOUS MODE JEDEC JESD51-7 HIGH EFFECTIVE THERMAL CONDUCTIVITY TEST BOARD HTSSOP EXPOSED DIEPAD SOLDERED TO PCB PER JESD51-5 3.5 50 CONDITION: θJA (°C/W) POWER DISSIPATION (W) 20-PIN HTSSOP THERMAL PAD SOLDERED TO 2-LAYER PCB WITH 0.039" THICKNESS AND 1-oz COPPER ON BOTH SIDES 45 40 35 30 2.857W 3 2.5 θ HT S JA = 2 35 1.5 SO P2 0 °C /W 1 0.5 0 25 1 2 3 4 5 6 7 8 9 PCB AREA (in2) FIGURE 29. 20-PIN HTSSOP THERMAL RESISTANCE vs PCB AREA, NO AIR FLOW 9 0 25 50 75 85 100 125 150 AMBIENT TEMPERATURE (°C) FIGURE 30. PACKAGE POWER DISSIPATION vs AMBIENT TEMPERATURE EL7581 Typical Performance Curves (Continued) JEDEC JESD51-3 LOW EFFECTIVE THERMAL CONDUCTIVITY TEST BOARD 1 POWER DISSIPATION (W) 0.9 800mW 0.8 0.7 θ HT JA = 0.6 0.5 SS O 12 5 0.4 °C / P2 0 W 0.3 0.2 0.1 0 0 25 50 75 85 125 100 150 AMBIENT TEMPERATURE (°C) FIGURE 31. PACKAGE POWER DISSIPATION vs AMBIENT TEMPERATURE Block Diagram VOUT 10µH R2 R1 13kΩ VIN 110kΩ 49Ω 10µF 10µF 0.1µF FBB LX VDDB MAX_DUTY ROSC REFERENCE GENERATOR R3 62kΩ VREF VRAMP PWM COMPARATOR PWM LOGIC 0.15Ω ENBN 12µA START-UP OSCILLATOR + ILOUT VSSB 7.2K 80mΩ SS 0.1µF 10 PGND EL7581 Applications Information Steady-State Operation The EL7581 is high efficiency multiple output power solution designed specifically for thin-film transistor (TFT) liquid crystal display (LCD) applications. The device contains one high current boost converter and two low power charge pumps (VON and VOFF). When the output reaches the preset voltage, the regulator operates at steady state. Depending on the input/output condition and component, the inductor operates at either continuous-conduction mode or discontinuous-conduction mode. The boost converter contains an integrated N-channel MOSFET to minimize the number of external components. The converter output voltage can be set from 5V to 18V with external resistors. The VON and VOFF charge pumps are independently regulated to positive and negative voltages using external resistors. Output voltages as high as 40V can be achieved with additional capacitors and diodes. In the continuous-conduction mode, the inductor current is a triangular waveform and LX voltage a pulse waveform. In the discontinuous-conduction mode, the inductor current is completely ‘dried-out’ before the MOSFET is turned on again. The input voltage source, the inductor, and the MOSFET and output diode parasitic capacitors forms a resonant circuit. Oscillation will occur in this period. This oscillation is normal and will not affect the regulation. Boost Converter The boost converter operates in constant frequency pulsewidth-modulation (PWM) mode. Quiescent current for the EL7581 is only 5mA when enabled, and since only the low side MOSFET is used, switch drive current is minimized. 90% efficiency is achieved in most common application operating conditions. A functional block diagram with typical circuit configuration is shown on the previous page. Regulation is performed by the PWM comparator which regulates the output voltage by comparing a divided output voltage with an internal reference voltage. The PWM comparator outputs its result to the PWM logic. The PWM logic switches the MOSFET on and off through the gate drive circuit. Its switching frequency is external adjustable with a resistor from timing control pin (ROSC) to ground. The boost converter has 200kHz to 1.2MHz operating frequency range. Start-Up After VDDB reaches a threshold of about 2V, the power MOSFET is controlled by the start-up oscillator, which generates fixed duty-ratio of 0.5 - 0.7 at a frequency of several hundred kilohertz. This will boost the output voltage, providing the initial output current load is not too great (<250mA). When VDDB reaches about 3.7V, the PWM comparator takes over the control. The duty ratio will be decided by the multiple-input direct summing comparator, Max_Duty signal (about 90% duty-ratio), and the Current Limit Comparator, whichever is the smallest. The soft-start is provided by the current limit comparator. As the internal 12µA current source charges the external softstart capacitor, the peak MOSFET current is limited by the voltage on the capacitor. This in turn controls the rising rate of output voltage. The regulator goes through the start-up sequence as well after the ENBN signal is pulled to HI. 11 At very low load, the MOSFET will skip pulse sometimes. This is normal. Current Limit The MOSFET current limit is nominal ILMT = 2.75A. This restricts the maximum output current IOMAX based on the following formula: V IN ∆L I OMAX = I LMT – ------- × -------- 2 VO where: • ∆IL is the inductor peak-to-peak current ripple and is decided by: V IN D ∆I L = --------- × ------L FS • D is the MOSFET turn-on radio and is decided by: V O - V IN D = ----------------------VO • FS is the switching frequency. The following table gives typical values: (Margins are considered in deriving IOMAX. They are 10%, 3%, 20%, 10%, and 20% on VIN, VO, L, FS, and ILMT, respectively.) TABLE 1. MAXIMUM CONTINUOUS OUTPUT CURRENT VIN (V) VO (V) L (µH) FS (kHz) IOMAX (mA) 3.3 5 10 1000 1200 3.3 9 10 1000 660 3.3 12 10 1000 490 3.3 15 10 1000 390 5 9 10 1000 980 5 12 10 1000 720 5 15 10 1000 570 12 15 10 1000 1300 12 18 10 1000 1100 EL7581 Component Considerations Input Capacitor It is recommended that CIN is larger than 10µF. Theoretically, the input capacitor has ripple current of ∆IL. Due to high-frequency noise in the circuit, the input current ripple may exceed the theoretical value. Larger capacitor will reduce the ripple further. Boost Inductor The inductor has peak and average current decided by: ∆I I LPK = I LAVG + --------L 2 Elantec demo board, MBRM120 is selected. Its forward voltage drop is 450mV at 1A forward current. Output Capacitor The EL7581 is specially compensated to be stable with capacitors which have a worst-case minimum value of 10µF at the particular VOUT being set. Output ripple voltage requirements also determine the minimum value and the type of capacitors. Output ripple voltage consists of two components - the voltage drop caused by the switching current though the ESR of the output capacitor and the charging and discharging of the output capacitor: I OUT V OUT - V IN V RIPPLE = I LPK × ESR + ------------------------------- × -----------------------------C × FS V OUT IO I LAVG = ------------1-D The inductor should be chosen to be able to handle this current. Furthermore, due to the fixed internal compensation, it is recommended that maximum inductance of 10µH and 15µH to be used in the 5V and 12V or higher output voltage, respectively. The output diode has average current of IO, and peak current the same as the inductor's peak current. Schottky diode is recommended and it should be able to handle those currents. Feedback Resistor Network An external resistor divider is required to divide the output voltage down to the nominal reference voltage. Current drawn by the resistor network should be limited to maintain the overall converter efficiency. The maximum value of the resistor network is limited by the feedback input bias current and the potential for noise being coupled into the feedback pin. A resistor network in the order of 200kΩ is recommended. The boost converter output voltage is determined by the following relationship: R1 + R2 V BOOST = --------------------- × V FBB R1 Where VFBB is 1.300V as specified. A 3.9nF compensation capacitor across the feedback resistor to ground is recommended to keep the converter in stable operation at low output current and high frequency conditions. Schottky Diode Speed, forward voltage drop, and reverse current are the three most critical specifications for selecting the Schottky diode. The entire output current flows through the diode, so the diode average current is the same as the average load current and the peak current is the same as the inductor peak current. When selecting the diode, one must consider the forward voltage drop at the peak diode current. On the 12 OUT For low ESR ceramic capacitors, the output ripple is dominated by the charging/discharging of the output capacitor. In addition to the voltage rating, the output capacitor should also be able to handle the RMS current is given by: I CORMS = 2 ∆I L 1 ( 1 - D ) × D + ------------------- × ------ × I LAVG 2 12 I LAVG Positive and Negative Charge Pump (VON and VOFF) The EL7581 contains two independent charge pumps (see charge pump block and connection diagram.) The negative charge pump inverts the VDDN supply voltage and provides a regulated negative output voltage. The positive charge pump doubles the VDDP supply voltage and provides a regulated positive output voltage. The regulation of both the negative and positive charge pumps is generated by the internal comparator that senses the output voltage and compares it with and internal reference. The switching frequency of the charge pump is set to ½ the boost converter switching frequency. The pumps use pulse width modulation to adjust the pump period, depending on the load present. The pumps are shortcircuit protected to 180mA at 12V supply and can provide 15mA to 60mA for 6V to 12V supply. EL7581 VDDN 5V to 17V VDDP 5V to 17V 0.1µF RONP 0.1µF CCPP RONP DRVN OSC DRVP CCPN VOFF RONN COUT2 RONN 3.3µF R21 FBN 2.2µF FBP + + - V COUT1ON R12 VSSP VSSN + - VFBP R11 RON is 30 - 40Ω for VDD 6V to 17V R22 VREF (1.32V) Positive Charge Pump Design Considerations A single stage charge pump is shown above. The maximum VON output voltage is determined by the following equation: 1 1 V ON ( max ) ≤ 2 × V DDCPP - I OUT × 2 × ( R ONN + R ONP ) - 2 × V DIODE - I OUT × -------------------------------------------- - I OUT × -----------------------------------------------0.5 × F × C 0.5 × F × C S where: • RONN and RONP resistance values depend on the VDDP voltage levels. For 12V supply, RON is typically 33Ω. For 6V supply, RON is typically 45Ω. If additional stage is required, the LX switching signal is recommended to drive the additional charge pump diodes. The drive impedance at the LX switching is typically 150mΩ. The figure on the next page illustrates an implementation for two-stage positive charge pump circuit. 13 CPP S OUT1 EL7581 Two-Stage Positive Charge Pump Circuit VDDP VBOOST (5V-17V) RONP VLX CCPP DRNP VON CCPP RONN COUT1 COUT1 VSSP R12 + FBP 1.265V + - R11 The maximum VON output voltage for N+1 stage charge pump is: 1 V ON ( max ) ≤ 2 × V DDP - I OUT × 2 × ( R ONN + R ONP ) - 2 × V DIODE - I OUT × -------------------------------------------- - I OUT × 0.5 × F S × C CPP 1 1 1 ------------------------------------------------ + N × V LX ( max ) - N × 2 × V DIODE + I OUT × -------------------------------------------- + I OUT × ------------------------------------------------ 0.5 × F S × C OUT1 0.5 × F S × C CPP 0.5 × F S × C OUT1 R11 and R12 set the VON output voltage: R 11 + R 12 V ON = V FBP × --------------------------R 11 Where VFPB is nominal 1.310V. Negative Charge Pump Design Considerations The criteria for the negative charge pump is similar to the positive charge pump. For a single stage charge pump, the maximum VOFF output voltage is: 1 1 V OFF ( max ) ≥ I OUT × 2 × ( R ONN + R ONP ) + 2 × V DIODE - IOUT × -------------------------------------------- - I OUT × ------------------------------------------------ - V DDN 0.5 × F S × C CPN 0.5 × F S × C OUT2 Similar to positive charge pump, if additional stage is required, the LX switching signal is recommended to drive the additional charge pump diodes. The figure on the next page shows a two stage negative charge pump circuit. 14 EL7581 Two-Stage Negative Charge Pump Circuit VDDN 5V-17V VLX RONP CCPN DRVN RONN VOFF CCPN COUT2 COUT2 VSSN + - R21 FBN R22 VREF The maximum VOFF output voltage for N+1 stage charge pump is: 1 1 V OFF ( max ) ≥ I OUT × 2 × ( R ONN + R ONP ) + 2 × V DIODE - I OUT × -------------------------------------------- - I OUT × ------------------------------------------------ 0.5 × F × C 0.5 × F × C S CPN 1 1 V DDN - N × V LX ( max ) + N × 2 × V DIODE + I OUT × -------------------------------------------- + I OUT × ------------------------------------------------ 0.5 × F × C 0.5 × F × C S CPN S S OUT2 OUT2 R21 and R22 determine VOFF output voltage: R 21 V OFF = – V REF × ---------R 22 Where VREF is nominal 1.310V. Over-Temperature Protection An internal temperature sensor continuously monitors the die temperature. In the event that die temperature exceeds the thermal trip point, the device will shut down and disable itself. The upper and lower trip points are typically set to 130°C and 90°C respectively. PCB Layout Guidelines Careful layout is critical in the successful operation of the application. The following layout guidelines are recommended to achieve optimum performance. • VREF and VDDB bypass capacitors should be placed next to the pins. • Place the boost converter diode and inductor close to the LX pins. • Place the boost converter output capacitor close to the PGND pins. • Locate feedback dividers close to their respected feedback pins to avoid switching noise coupling into the high impedance node. • Place the charge pump feedback resistor network after the diode and output capacitor node to avoid switching noise. 15 • Thermal pad needs to be connected to PGND pins electrically, and it should be soldered to PCB with thermal vias connecting to ground plane for maximum heat dissipation. • All low-side feedback resistors should be connected directly to VSSB. VSSB should be connected to the power ground close at one point only. A demo board is available to illustrate the proper layout implementation. EL7581 Typical Application Circuit R2 R3 110K 1 VSSB ROSC 20 C7 C10 61.9K 2 SS ENP 19 0.1µF OPEN R1 13K R4 49.9 VBOOST (12V@ 500mA) C6 0.1µF C5 10µF + C3 C4 ENBN 18 4 VDDB VREF 17 5 LX PGND 16 6 LX PGND 15 7 LX DRVP 14 8 DRVN VDDP 13 9 VDDN FBP 12 L1 VIN VOFF (-6V@ 15mA) GND C1 10µF + C2 4.7µF 10µH C21 R21 154K C27 0.1µF C26 3.3µF 0.1µF 10 FBN VSSP 11 R6 0 C8 C50 0.1µF OPEN 1nF C12 0.1µF VON (18V@18mA) D11** C22 0.1µF 499K C9 D1* 22µF OPEN 3 FBB R5 C11 0.1µF C16 C17 R12 0.1µF 2.2µF 51K R11 3.9K D21** R22 33.2K * MBRM120LT3 ** BAT54S 16 EL7581 Package Outline Drawing NOTE: The package drawing shown here may not be the latest version. To check the latest revision, please refer to the Intersil website at http://www.intersil.com/design/packages/index.asp All Intersil U.S. products are manufactured, assembled and tested utilizing ISO9000 quality systems. Intersil Corporation’s quality certifications can be viewed at www.intersil.com/design/quality Intersil products are sold by description only. Intersil Corporation reserves the right to make changes in circuit design, software and/or specifications at any time without notice. Accordingly, the reader is cautioned to verify that data sheets are current before placing orders. Information furnished by Intersil is believed to be accurate and reliable. However, no responsibility is assumed by Intersil or its subsidiaries for its use; nor for any infringements of patents or other rights of third parties which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of Intersil or its subsidiaries. For information regarding Intersil Corporation and its products, see www.intersil.com 17