FP6711 FITIPOWER | Alldatasheet

Document overview

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Technical content

Features

  • Synchronous Rectification: 94% Efficiency
  • Very Low Start-up Voltage at 0.85V
  • Automatically Switch to PFM Mode for Improving Efficiency at Light Load
  • Built-in True Shutdown: Isolation of Load from Battery during Shutdown
  • Internal Anti-Ringing Switch across Inductor
  • Low Battery Warning Display
  • Fixed Frequency Operation at 500kHz
  • Very Low Shutdown Current at 1μA
  • Small 10-Pin MSOP Package
  • RoHS Compliant

Applications

  • Handheld Instrument
  • Cordless Phone
  • Wireless Handset
  • GPS Receiver
  • MP3 P: Green G: Green TR: Tape/Reel FP6711□□□ Package Type MS: MSOP-10

fitipower integrated technology lnc. Figure 2. Typical Application Circuit of FP6711 EN Chip-enable input. Pull the pin high to enable IC. Pull the pin low to shutdown IC. adjusted from 1.8V to 4V. The feedback voltage is typical at 0.5V. high. It will be disabled when this pin is connected to logic low. used. Don’t leave this pin floating. threshold voltage of 500mV. An external pull-up resistor has to be connected between LBO and VOUT.

fitipower integrated technology lnc. Figure 3. Block Diagram of FP6711 Note 1：Stresses beyond those listed under “Absolute Maximum Ratings" may cause permanent damage to the device.

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Electrical Characteristics

(VIN=1.2V, EN=VIN, TA=25C, unless otherwise specified) Parameter Symbol Conditions Min Typ Max Unit Start-up Voltage VST IOUT =1mA 0.85 V Output Voltage Range VOUT IOUT =1mA 1.8 4 V Quiescent Current (No Switching) IQ VFB>0.7V 25 40 µA Switch Current Limit (Note2) ILIM VOUT =3.3V 1 A Feedback Voltage VFB 490 500 510 mV Oscillation Frequency fOSC 420 500 780 kHz Maximum Duty Cycle DMAX 85 % NMOS Switch ON Resistance (Note2) RDS(ON) VOUT =3.3V 0.35 Ω PMOS Switch ON Resistance (Note2) RDS(ON) VOUT =3.3V 0.45 Ω Line Regulation VLINE VIN =2V to 2.4V Io =100mA 0.3 % Load Regulation VLOAD VIN =2V IOUT =50 to 100mA 0.1 % Auto-Discharge Switch Resistance (Note2) 300 400 Ω Residual Output Voltage after Discharge ADEB =VIN EN =GND 0.4 V LBI Voltage Threshold VLBI VLBI voltage decreasing 480 500 520 mV LBI Input Hysteresis 10 mV LBI Input Current 0.1 1 µA LBO Output Low Voltage VLBO VLBI =0V, VOUT =3.3V 0.2 V LBO Output Leakage Current VLBI =650mV, VLBO =VO 0.1 1 µA FB Input Bias Current I(FB) 0.1 1 µA EN/ADEN Input Low Voltage VIL 0.8V<VIN<5V VIN0.1 V EN/ADEN Input High Voltage VIH 0.8V<VIN<5V VIN0.9 V EN/ADEN Input Current EN/ADEN =GND or VIN 0.1 1 µA Shutdown Current from Power Source IOFF EN =0V, ADEN= VIN 1 5 µA Over-Temperature Protection (Note2) TSD 150 C Δ TSD Hysteresis 20 C Note 2：The specification is guaranteed by design, not production tested.

fitipower integrated technology lnc. Figure 22. Load Transient Response Figure 23. Converter Start-up Time after Enable

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Application Information

The device is based on a current-mode control topology and uses a constant frequency pulse-width modulator to regulate the output voltage. The controller limits the current through the power switch on a pulse by pulse basis. The current sensing circuit is integrated in the device; therefore, no additional components are required. Due to the nature of the boost converter topology used here, the peak switch current is the same as the peak inductor current, which will be limited by the integrated current limiting circuits unde r normal operating conditions. The control loop must be externally compensated with an R-C network connected to the COMP pin. Synchronous Rectifier The device integrates an N-channel and a P - channel MOSFET transistor to realize a synchronous rectifier. There is no additional Schottky diode required. Because the device uses a integrated low RDS(ON) PMOS switch for rectification, the power conversion efficiency reaches 94%. A special circuit is applied to disconnect the load from the input during shutdown of the converter. In conventional synchronous rectifier circuits, the backgate diode of the high -side PMOS is forward biased in shutdown and allows current flowing from the battery to the output. This device, however, uses a special circuit to disconnect the backgate diode of the high -side PMOS and so, disconnects the output circuitry from the source when the regulator is not enabled (EN = low). PFM Mode The FP6711 is designed for high efficiency o ver a wide output current range. Even at light load, the efficiency stays high because the switching losses of the converter are minimized by effectively reducing the switching frequency. The controller will enter a power saving mode if certain condition s are met. In this mode, the co ntroller only switches on the transistor if the output voltage trips below a set threshold voltage. It ramps up the output voltage with one or several pulses, and goes again into PFM mode once the output voltage exceeds a set threshold voltage. Device Enable The device will be shut down when EN is set to GND. In this mode, the regulator stops switching, all internal control circuitry including the low -battery comparator will be switched off, and the load is disconnected from the input (as described in above synchronous rectifier section). This also means that the output voltage may drop below the input voltage during shutdown. The device is put into operation when EN is set high. During start -up of the converter, the duty cycle is limited in order to avoid high peak currents drawn from the battery. The limit is set internally by the current limit circuit and is pro portional to the voltage on the COMP pin. Under-Voltage Lockout Under-voltage lockout function prevents the device from starting up if the supply voltage on VBAT is lower than approximately 0.7V. This under-voltage lockout function is implemented in order to prevent the malfunctioning of the converter. When the battery is being discharged, the device will automatically enter the shutdown mode if the voltage on VBAT drops below approximately 0.7V.

10 FP6711-1.4-DEC-2011 FP6711 85T fitipower integrated technology lnc. Application Information (Continued) Auto-Discharge The auto -discharge function is useful for applications where the supply voltage of a µC, µP , or memory has to be removed during shutdown in order to ensure a defined state of the system. The auto -discharge function will be enabled when the ADEN is set high ; and it will be disabled when the ADE N is set to GND. When the auto-discharge function is enabled, the output capacitor will be discharged after the device is shut down by setting EN to GND. The capacitors connected to the output are discharged by an integrated switch of 300Ω, hence the dis charge time depends on the total output capacitance. The residual voltage on VOUT is less than 0.4V after auto-discharge. The resistive divider scales down the battery voltage to a voltage level of 500mV, which is then compared to the LBI threshold volta ge. The LBI pin has a built -in hysteresis of 10mV. See the application section for more details about the programming of the LBI threshold. If the low -battery detection circuit is not used, the LBI pin should be connected to GND (or to VBAT) and the LBO pin can be left unconnected. Do not let the LBI pin float. Low-Battery Detector Circuit (LBI and LBO) The low-battery detector circuit is typically used to supervise the battery voltage and generate an error flag when the battery voltage drops below user -set threshold voltage. The function is active only when the device is enabled. When the device is disabled, the LBO pin will be high impedance. The LBO pin goes active low when the voltage on the LBI pin decreases below the set threshold voltage of 500 mV ±15 mV, which is equal to the internal reference voltage. The battery voltage, at the detection circuit switches, can be programmed with a resistive divider connected to the LBI pin. Anti-Ringing Switch The device integrates a circuit which removes the ringing that typically appears on the SW node when the converter enters the discontinuous current mode. In this case, the current through the inductor ramps to zero and the integrated PMOS switch turns off to prevent a reverse current from the output capacitors back to the battery. Due to remaining energy that is stored in parasitic components of the semiconductors and the inductor, a ringing on the SW pin is induced. The integrated anti -ringing switch clamps this voltage internally to VBAT; therefore, dampens this ringing. Adjustable Output Voltage The accuracy of the output voltage is determined by the accuracy of the internal voltage reference, the controller topology, and the accuracy of the external resistor. The reference voltage has an accuracy of ± 4%. The controller switches between fixed frequency and PFM mode, depending on load current. The tolerance of the resistors in the feedback divider determine s the total system accuracy. Design Procedure The FP6711 boost converter family is intended for systems that are powered by a single -cell NiCd or NiMH battery with a typic al terminal voltage between 0.9V to 1.6 V. It can also be used in systems that are powered by two-cell NiCd or NiMH batteries with a ty pical stack voltage between 1.8V to 3.2V. Additionally, single or dual-cell, primary and secondary alkaline battery cells can be the power source in systems where the FP6711 is used. (1) Programming the Output Voltage The output voltage of the FP6711 can be adjusted with an external resistor divider. The typical value of the voltage on the FB pin is 500mV in fixed frequency operation . The maximum allowed value for the output voltage is 3.3V. The current through the resistive divider should be about 100 times greater than the current into the FB pin. The typical current into the FB pin is 0.01µA, and the voltage across R4 is typically 500mV. Based on those two values, the recommended value for R4 is in the range of 500kΩ in order to set the divider current at 1µA. From that, the value of resistor R3, depending on the needed output voltage (V O), can be calculated using Equation 1. 1) - mV 500 V (500k) 1- V V (R4R3 O FB

11 FP6711-1.4-DEC-2011 FP6711 85T fitipower integrated technology lnc. Application Information (Continued) (2) Programming the Low Battery Comparator Threshold Voltage The current through the resistive divider should be about 100 times greater than the current into the LBI pin. The typical current into the LBI pin is 0.01µ A; the voltage across R2 is equal to the reference voltage that is generated on -chip, which has a value of 500 mV±15mV. The recommended value for R2 is therefore in the range of 500 kΩ. From that, the value of resistor R1, depending on the desired minimum battery voltage V BAT, can be calculated using Equation 2. 1) - mV 500 V (500k) 1- V V (R2R1 BAT RE F …..(2) For example, if the low -battery detection circuit should flag an error condition on the LBO output pin at a battery voltage of 1V, a resistor in the range of 500kΩ should be chosen for R1. The output of the low battery comparator is a simple open-drain output that goes active low if the battery voltage drops below the programmed threshold voltage on LBI. The output requires a pull-up resistor with a recommended value of 1MΩ, and should only be pulled up to the VO. If not used, the LBO pin ca n be left floating or tied to GND. (3) Inductor Selection A boost converter normally requires two main passive components for storing energy during the conversion. A boost inductor is required and a storage capacitor at the output. To select the boost inductor, it is recommended to keep the possible peak inductor current below the current limit threshold of the power switch in the chosen configuration. The second parameter for choosing the inductor is the desired current ripple in the inductor. Normally, it is advisable to work with a ripple of less than 20% of the average inductor current. A smaller ripple reduces the magnetic hysteresis losses in the inductor, as well as output voltage ripple and EMI. But in the same way, regulation time at load changes rises. In addition, a larger inductor increases the total system cost. With those parameters, it is possible to calculate the value for the inductor by using Equation 3. OUTL BATOUTBAT V××IΔ )V-(V×V=L f …..(3) Parameter f is the switching frequency and ΔI L is the ripple current in the inductor, i.e, 20% x IL. In this example, the desired inductor has the value of 12µH. With this calculated value and currents, it is possible to choose a suitable inductor. Care must be taken that load transients and losses in the circuit can le ad to higher currents . Also, the losses in the inductor caused by magnetic hysteresis losses and copper losses are a major parameter for total circuit efficiency. (4) Capacitor Selection The major parameter necessary to define the output capacitor is the maximum allowed output voltage ripple of the converter. This ripple is determined by two parameters of the capacitor, the capacitance and the ESR. It is possible to calculate the minimum capacitance needed for the defined ripple, supposing that the ESR is zero, by using Equation 4. OUT BATOUTOUT MIN V×VΔ× )V-(V×I=C f …..(4) Parameter f is the switching frequency and △V is the maximum allowed ripple. With a chosen ripple voltage of 15mV, a minimum capacitance of 10 µF is needed. The total ripple is larger due to the ESR of the output capacitor. This additional component of the ripple can be calculated using Equation 5. ESROUTESR R×I=VΔ …..(5) An additional ripple of 30mV is the result of using a tantalum capacitor with a low ESR of 300mΩ. The total ripple is the sum of the ripple caused by the capacitance and the ripple caused by the ESR of the capacitor. In this example, the total ripple is 45mV. It is possible to improve the design by enlarging the capacitor or using smaller capacitors in parallel to reduce the ESR or by using better capacitors with lower ESR, like ceramics. For example, a 10µF ceramic capacitor with an ESR of 50mΩ is used on the evaluation module (EVM). Tradeoffs must be made between performance and costs of the converter circuit. A 10µF input capacitor is recommended to improve transient behavior of the regulator. A ceramic or tantalum capacitor with a 100nF in parallel placed close to the IC is recommended.

13 FP6711-1.4-DEC-2011 FP6711 85T fitipower integrated technology lnc. Outline Information SYMBOLS UNIT DIMENSION IN MILLIMETER MIN MAX A 0.75 1.10 A1 0.00 0.15 A2 0.75 0.95 B 0.17 0.33 D 2.90 3.10 E 4.80 5.00 E1 2.90 3.10 e 0.40 0.60 L 0.40 0.80 Carrier dimensions Life Support Policy Fitipower’s products are not authorized for use as critical components in life support devices or other medical systems.