FP6791TSPTR

FP6791C 85T PWM Boost fitipower integrated technology lnc. DC-DC Controller Description Features The FP6791C is a CMOS step-up switching controller which incorporates a reference voltage circuit, an oscillator, an error amplifier, a PWM controller, an under voltage lockout circuit (UVLO) and a timer latch short-circuit protection circuit. ● Programmed Switching Frequency ● Programmed Maximum Duty Ratio ● Reference Voltage: 1.0V ±1.5% ● UVLO (Under-Voltage Lockout) Function: ▪ Detection Voltage 2.2V ▪ Hysteresis Width 0.3V ● Timer Latch Short-Circuit Protection Circuit: Delay Time Set by an External Capacitor. ● Internal Soft-Start Function ● External Compensation Network ● Small Package: 8-pin TSSOP ● RoHS Compliant The switching frequency can be controlled by the resistor connected to the ROSC pin, and the maximum duty ratio can be controlled by the resistor connected to the RDUTY pin. In addition, the FP6791C provides adjustable short-circuit protection delay time with an external capacitor which is connected to the CSP pin. If the maximum duty condition continues due to short-circuiting, the capacitor externally connected to the CSP pin will be charged, and oscillation will stop after a specific time. This condition will be cleared by re-application of power. This controller IC allows various settings and employs a small package, which make it easy to use. Applications ● LCD Panel ● Portable Equipment Pin Assignment Ordering Information TS Package (TSSOP-8) FP6791C□□□ TR: Tape/Reel CC FB CSP VIN 1 2 3 4 8 7 6 5 RDUTY ROSC G: Green VSS EXT Package Type TS: TSSOP-8 Figure 1. Pin Assignment of FP6791C FP6791C-1.1-FEB-2012 1 FP6791C 85T fitipower integrated technology lnc. Typical Application Circuit L1 VOUT D1 RDUTY VIN CIN M1 ROSC CF FP6791C EXT VIN ROSC RDUTY VSS CSP FB COUT RFB2 cc CSP RFB1 RZ CZ Figure 2. Typical Application Circuit of FP6791C External Parts List: Element Name Symbol Application1 : VIN=5V,VOUT=12V, Fequency~700kHz Application2 : VIN=3.3V, VOUT=10.5V Frequency~1.1MHz Inductor L1 4.7μH, TDK 10μH, TDK Diode D1 Schottky Diode Schottky Diode 40μF 10μF Power MOS Power MOS Output Capacitor COUT Transistor M1 Oscillation Frequency Setting Resistor ROSC 180kΩ±1% resistor 120kΩ±1% resistor Maximum Duty Ratio Setting Resistor RDUTY 220kΩ±1% resistor 110kΩ±1% resistor CSP 0.1μF ceramic capacitor 0.1μF ceramic capacitor Output Voltage Setting Resistor1 RFB1 8.2kΩ±1% resistor 6.8kΩ±1% resistor Output Voltage Setting Resistor2 RFB2 750Ω±1% resistor 715Ω±1% resistor FB Pin Capacitor CFB 2.2nF ceramic capacitor 1nF ceramic capacitor Phase Compensation Resistor RZ 56kΩ±1% resistor 100kΩ±1% resistor Phase Compensation Capacitor CZ 10nF ceramic capacitor 10nF ceramic capacitor Input Capacitor CIN 10μF ceramic capacitor 10μF ceramic capacitor Short-Circuit Capacitor Protection FP6791C-1.1-FEB-2012 Delay Setting 2 FP6791C 85T fitipower integrated technology lnc. Functional Pin Description Pin Name Pin Function CC Error amplifier circuit output and phase compensation pin FB Output voltage feedback pin CSP Short-circuit protection delay time setting pin VIN Power supply input pin EXT External transistor connection pin VSS GND pin ROSC Oscillation frequency setting resistor connection pin RDUTY Maximum duty setting resistor connection pin Block Diagram RDUTY ROSC VIN UVLO Oscillator Maximum duty circuit - EXT PWM comparator Timer latch short-circuit protection circuit + Error amplifier FB + Reference voltage (1V) soft-start circuit VSS CSP CC Figure 3. Block Diagram of FP6791C FP6791C-1.1-FEB-2012 3 fitipower integrated technology lnc. Absolute Maximum Ratings FP6791C 85T ● Supply Voltage (VIN) ------------------------------------------------------------------------------------------- -0.3V to + 6.5V ● FB pin voltage (VFB) ------------------------------------------------------------------------------------------- -0.3V to + 6.5V ● EXT pin voltage (VEXT) ---------------------------------------------------------------------------------------- -0.3V to + 6.5V ● CSP pin voltage (VCSP) ---------------------------------------------------------------------------------------- -0.3V to + 6.5V ● CC pin voltage (VCC) ------------------------------------------------------------------------------------------- -0.3V to + 6.5V ● CC pin current (ICC) -------------------------------------------------------------------------------------------- ±10mA ● ROSC pin voltage (VROSC) ----------------------------------------------------------------------------------- -0.3V to +6.5V ● ROSC pin current (IROSC) ------------------------------------------------------------------------------------- ±10mA ● RDUTY pin voltage (VRDUTY) --------------------------------------------------------------------------------- -0.3V to +6.5V ● RDUTY pin current (IRDUTY) ---------------------------------------------------------------------------------- ±10mA ● Storage temperature (TSTG) ---------------------------------------------------------------------------------- -40°C to +125°C ● Power dissipation (TA=+25°C), TSSOP-8 ---------------------------------------------------------------- +560mW ● Package Thermal Resistance, TSSOP-8 (θJA) ---------------------------------------------------------- 180°C/W ● Junction Temperature ----------------------------------------------------------------------------------------- +150°C ● Storage Temperature Range -------------------------------------------------------------------------------- -65°C to +150°C ● Lead Temperature (Soldering, 10s) ----------------------------------------------------------------------- +260°C Note 1：Stresses beyond those listed under “Absolute Maximum Ratings" may cause permanent damage to the device. Recommended Operating Conditions ● Supply Voltage (VIN) ------------------------------------------------------------------------------------------- +2.6V to +6V ● Operation Temperature Range (TOPR) --------------------------------------------------------------------- -40°C to +85°C FP6791C-1.1-FEB-2012 4 FP6791C 85T fitipower integrated technology lnc. Electrical Characteristics VIN=+5V, TA=25°C, unless otherwise specified. Parameter Symbol Conditions Min Typ Max Unit Operating Input Voltage VIN 2.6 5 6 V FB Voltage VFB 0.985 1 1.015 V Current Consumption (VIN=3.3V) Iss1 Fosc = 1.1MHz；VFB = 0.95V - 700 900 μA IEXT VEXT=VIN - 0.4V -100 -60 IEXT VEXT= 0.4V EXT Pin Output Current(VIN=3.3V) FB Voltage Temperature Coefficient Oscillation Frequency Oscillation Frequency Temperature Coefficient (Note5) Maximum Duty Cycle Soft-Start Time UVLO Detection Voltage UVLO Hysteresis Short-circuit protection delay time mA ∆VFB /∆Ta Ta = -40 ºC to +85 ºC FOSC ROSC=120kΩ (Note3) ∆FOSC /∆Ta Ta = -40 ºC to +85 ºC Fosc = 1.1MHz Duty RDUTY=100kΩ (Note4) 100 160 100 1.02 1.133 ppm/°C 1.246 500 ppm/°C 80.6 84.9 94 % tss 15 20 30 ms VUVLO 2.09 2.2 2.31 V VUVLOHYS 0.18 0.3 0.42 V 33 50 75 ms TPRO CSP=0.1μF ICCH VFB =2V 50 ICCL VFB =0V -50 μA CC Pin Output Current Timer Latch Reset Voltage MHz VRTLT 0.7 1 1.3 V Note 2：Specifications are production tested at TA=25°C. Specifications over the -40°C to 85°C operating temperature range are guaranteed by design. Note 3：The recommend ROSC value for setting oscillation frequency is ranging from 100kΩ to 300kΩ (FOSC = 500kHz to 1.3MHz). The oscillation frequency is in the range of typical values when an ideal ROSC is connected, so the fluctuation of the IC (±10%) must be considered. Note 4：The recommended RDUTY/ROSC ratio for setting the maximum duty is ranging from 0.5 to 3.2 (Max. Duty = 55% to 88.5%). The maximum duty is in the range of typical value when an ideal RDUTY is connected, so the fluctuation of the IC (±5%) must be considered. Note 5：Guarantee by design. FP6791C-1.1-FEB-2012 5 FP6791C 85T fitipower integrated technology lnc. Typical Performance Curves 10.7 100 90 Freq=1.1MHz L=10uH 10.6 80 70 10.4 VOUT Efficiency 10.5 60 10.3 50 10.2 VIN=5V 40 VOUT=10.5V 10.1 30 10 50 100 Output current ( mA ) 200 250 300 Figure 5. Output Voltage vs. Output Current 1.20 1.18 1.18 1.17 1.16 Frequency (MHz) 1.16 Frequency (MHz) 150 Output Current (mA) Figure 4. Efficiency vs. Output Current 1.14 1.12 1.10 1.08 1.15 1.14 1.13 1.12 1.11 1.06 2.5 3.0 3.5 4.0 4.5 1.10 -40 5.0 -20 VIN (V) 0 20 40 60 80 o Junciton Temperature ( C) Figure 6. Frequency vs. Input Voltage Figure 7. Frequency vs. Junction Temperature 2.26 2.55 2.25 2.54 2.24 2.53 2.23 UVLO_H(V) UVLO_L (V) 100 2.22 2.21 2.52 2.51 2.50 2.20 2.49 2.19 2.18 -40 -20 0 20 40 60 80 o Junction Temperature ( C) Figure 8. UVLO Low Level vs. Junction Temperature FP6791C-1.1-FEB-2012 2.48 -40 -20 0 20 40 60 80 o Junction Temperature ( C) Figure 9. UVLO High Level vs. Junction Temperature 6 fitipower integrated technology lnc. Typical Performance Curves (Continued) FP6791C 85T 1.020 1.015 VIN=5V, VOUT=10.5V, L=10uH Freq=1.1MHz 1.010 V FB (V) 1.005 1.000 0.995 0.990 0.985 0.980 -40 -20 0 20 40 60 80 o Junction Temperature ( C) CH1: Output Voltage, AC-Coupled CH2: Switch Point CH4: Loading Current VIN=5V, VOUT=10.5V, ILOAD form 1mA to 100mA, L=10μH, FREQ=1.1MHz, COUT=4.7μF*4+0.1μF*2 Figure 10. VFB vs. Junction Temperature CH1: Output Voltage, AC-Coupled CH2: Switch Point CH4: Loading Current VIN=5V, VOUT=10.5V, ILOAD form 1mA to 200mA, L=10μH, FREQ=1.1MHz, COUT=4.7μF*4+0.1μF*2 Figure 12. Load transient Response FP6791C-1.1-FEB-2012 Figure 11. Load transient Response CH1: Output Voltage, AC-Coupled CH2: Switch Point CH4: Loading Current VIN=5V, VOUT=10.5V, ILOAD form 1mA to 300mA, L=10μH, FREQ=1.1MHz, COUT=4.7μF*4+0.1μF*2 Figure 13. Load transient Response 7 fitipower integrated technology lnc. Typical Performance Curves (Continued) CH1: Output Voltage CH2: Switch Point CH3: VIN CH4: Inductor Current VIN=5V, VOUT=10.5V, L=10μH, ILOAD =0mA, FREQ=1.1MHz, COUT=4.7μF*4+0.1μF*2 Figure 14. Light Load Start-up Waveform FP6791C-1.1-FEB-2012 FP6791C 85T CH1: Output Voltage CH2: Switch Point CH3: VIN CH4: Inductor Current VIN=5V, VOUT=10.5V, L=10μH, FREQ=1.1MHz ILOAD =300mA, COUT=4.7μF*4+0.1μF*2 Figure 15. Heavy Load Start-up Waveform 8 fitipower integrated technology lnc. Applications Information FP6791C 85T PWM Voltage Mode Converter Under Voltage Lockout The FP6791C is a CMOS step-up converter using a pulse width modulation method (PWM). The maximum duty ratio of FP6791C can be controlled by the resistor connected to the RDUTY pin. The converter can operate in both discontinuous conduction mode (DCM) and continuous conduction mode (CCM). The FP6791C operation can be best understood by referring to the block diagram in Figure 3. The error amplifier monitors the output voltage via the feedback resistor divider by comparing the feedback voltage with the reference voltage. When the feedback voltage is lower than the reference voltage, the error amplifier output will increase. The error amplifier output is then compared with the oscillator ramp voltage at the PWM controller. When the error amplifier output voltage is higher than ramp, the EXT pin turns on the external transistor, the output voltage will increase, and vice versa. As the feedback voltage is higher than the reference voltage, the error amplifier output will decrease. When the error amplifier output voltage is lower than ramp, the EXT pin turns off the external transistor, the output voltage will decrease. The under voltage lockout (UVLO) comparator has two voltage references, the start and stop thresholds. During power up, the UVLO comparator stop EXT pin switching and the external FET is held in the off status until the VIN reaches UVLO detection voltage. During VIN power down, the UVLO comparator allows the EXT pin switching until the UVLO stop threshold is reached. The UVLO function can prevent the IC form malfunction due to a transient status when power is applied or a momentary drop of the power supply voltage. Soft Start Compensation The FP6791C includes internal 20mS (Typ.) soft start function. The soft start function can minimize the inrush current. When power is on, a constant current will charge an internal capacitor. When power is off, the internal capacitor will be discharge for next soft start time. The compensation circuit is designed to guarantee stability over the full input/output voltage and fill output load range. The compensation circuit can prevent excessive output ripple and unstable operation from deteriorating the efficiency. The compensation is implemented by connecting RZ and CZ series network between VSS pin and CC pin. RZ sets the high frequency gain for a high speed transient response. CZ sets the pole and zero of the error amplifier and keeps the system stable. Adjust RZ and CZ, taking into consideration conditions such as the inductor, output, and load current, so that optimum transient characteristics can be obtained. Output Voltage Setting With the FP6791C, the output voltage can be set value by external divider network. An external resistor divider is required to divide the output voltage down to the nominal reference voltage. As shown in Figure 2, the resistor divider output feeds to the FB pin, which connects to the inverting input of the error amplifier. The non-inverting input of the error amplifier is connected to a 1V (Typ.) reference voltage. The following equation can be used to calculate the RFB1 and RFB2 value. V UT FP6791C-1.1-FEB-2012 1 F 1 F 2 Short Circuit Protection The short circuit protection function will stop switching when output voltage drops due to output short. The capacitor which connected to the CSP pin is used to set delay time of short circuit protection. If the maximum duty condition continues because of short circuit, the capacitor externally connected to the CSP pin will be charged, and EXT pin will stop switching after CSP pin voltage rises above the reference voltage. Than FP6791C latches off until input voltage is re-started. VF 9 FP6791C 85T fitipower integrated technology lnc. Applications Information (Continued) Oscillation Frequency Setting Inductor selection The oscillation of FP6791C can be set in a range of 500kHz to 1.3MHz (ROSC=100kΩ to 300kΩ) by using external resistor which connects to ROSC pin. Select the resistor by Figure 16. The inductor selection depends on the switching frequency and current ripple by the following formula: V f 1400 Frequency (kHz) ∆ S V V UT Where fOSC is switching frequency of the FP6791C 1200 *The switching frequency of the FP6791C ranges between 500kHz and 1.3MHz. The switching frequency can be set value by external resistor. 1000 800 600 400 50 100 150 200 250 300 350 Rosc (kohm) Figure 16. Rosc vs. Frequency Maximum Duty Ratio Setting The maximum duty of FP6791C can be set in a range of 55% to 88.5% by an external resistor which connects to RDUTY pin. The ratio of RDUTY/ROSC must range from 0.5 to 3.2 and ROSC conform to range between 100kΩ to 300kΩ. Select the resistor by referring to Figure 17. 90 85 Rosc=100kohm 80 Max. Duty (%) 1 75 Although small physical size and high efficiency are major concerns, the inductor should have low core losses and series resistance (DCR, copper wire resistance). The minimum inductor value, peak current rating and series resistance will affect the converter efficiency, maximum output load capability, transient response time and output voltage ripple. The inductor selection depends on input voltage, output voltage and maximum output current. Very high inductor minimize the current ripple and therefore reduce the peak current, which decreases core losses in the inductor and conduct losses in the entire power path. However, large inductor values also require more energy storage and more turns of wire. The size of inductor will become bigger and increase conduct losses. Low inductor values decrease the size but increase the current ripple and the peak current. Choose the inductor values based on the application. In addition, it is important to ensure the inductor saturation current exceeds the peak value of inductor current in application to prevent core saturation. Calculating the ripple current at operation point and the peak current required for the inductor： V 70 ∆ (M V 65 60 (MAX) ( 1.0 1.5 2.0 2.5 3.0 RDUTY/ROSC (Rosc=100kohm) MAX) Figure 17. RDUTY/ROSC vs. Max. Duty UT(MAX) V FP6791C-1.1-FEB-2012 UT V 2 f S 3.5 ( UT .MAX) 55 0.5 V ) V (M UT ) f V (M ) S ∆ 2 1 V 2 f S V (M ) V UT 1 V (M ) V UT 10 FP6791C 85T fitipower integrated technology lnc. Applications Information (Continued) Where expected efficiency at that operating point. The value can be taken form an appropriate curve in the typical operating characteristics. ∆IL=inductor ripple current, IL(MAX) =inductor peak current. In addition, the following equation used here assumes a constant K, which is the ratio of the inductor peak-to-peak AC current to average DV inductor current. A good compromise between the size of the inductor versus loss and output ripple is to choose a K 0.3 to 0.5. The peak inductor current is given by： UT(MAX) ∆ V V (M UT 1 ) 2 Where K=ratio of the inductor peak-to-peak AC current to average DC inductor current, ∆IL=inductor ripple current. The inductor value is then given by: L 2 VIN (MIN )    D K  fOSC  VOUT  IOUT (MAX ) Where uty cycle V (M (MAX) ) VF V UT ds(on) VF V UT VF = Catch diode forward drop f = Switching frequency The inductor’s saturation current rating should exceed IL(MAX) and the inductor DC current rating should exceed IIN(DC,MAX). Rectifier diode selection The diode is the largest source of loss in DC-DC converters. A high speed diode is necessary due to the high switching frequency. The Schottky diodes are recommended because of their fast recovery time and low forward drop voltage for better efficiency. The forward drop voltage of the Schottky diode will result in the conduction losses in the diode, and the diode capacitance will cause the switching losses. Therefore, it is necessary to consider both forward voltage drop and diode capacitance for diode selection. In addition, the reverse voltage rating of this diode should 1.3 times of the maximum output voltage. The rectifier diode must meet the output and peak inductor current requirement. FP6791C-1.1-FEB-2012 Output Capacitor Selection The capacitor on the output side (COUT) is used for sustaining the output voltage when the external MOSFET or diode is switched on and smoothing the ripple voltage. Select an appropriate capacitance value based on the load condition. For lower output voltage ripple, the low ESR ceramic capacitor is recommended. The output voltage ripple consists of two components. One is the pulsating output ripple current through ESR, and the other is the capacitive ripple caused by charging and discharging. VO  VRIPPLE _ ESR  VRIPPLE _ C  IL  RESR  IL C OUT  VOUT  VIN  V  OUT  fOSC     Where ∆VO=output voltage ripple, ∆IL=inductor ripple current, IL(MAX) = inductor peak current. The optimal capacitor differs depending on the inductor value, wiring, and application (output load), so select the capacitor after performing sufficient evaluation under the actual usage condition. Input Capacitor Selection The capacitor on input side (CIN) can stabilize the input voltage and minimize peak current ripple form the power source for better efficiency. The value of the capacitor depends on the impedance of the input source used. For better input bypassing, low ESR ceramic capacitor is recommended for better performance. External Switch Transistor An enhancement N-channel MOSFET or a bipolar NPN transistor can be used as the external switch transistor. For high efficiency, it’s ideal to use a MOSFET with a low RDS-ON and small input capacitance. It is a more efficient switch than a bipolar NPN transistor. The RDS-ON and input capacitance generally share a trade-off relationship. The RDS-ON is efficient in a range which the output current is relatively great during low frequency switching, and the input capacitance is efficient in a rang which the output current is middling during high frequency switching. 11 fitipower integrated technology lnc. Applications Information (Continued) Select a MOSFET whose RDS-ON and input capacitance are optimal depending on the usage conditions. The input voltage is supplied for the gate voltage of the MOSFET, so select a MOSFET with a gate withstanding voltage that is equal to maximum usage value of the input voltage or higher and drain withstanding voltage that is equal to the output voltage and diode voltage or higher. An enhancement N-channel MOSFET can be selected by the following guidelines: FP6791C 85T Layout Recommendation For high frequency switching power supplies, the device’s performance including efficiency, output noise, transient response and control loop stability are dramatically affected by PCB layout. There are some general guidelines for layout: 2. Low gate threshold voltage. 1. Place the external power components (the input capacitors, output capacitors, inductor and diode, etc.) in close proximity to the device. The traces which connect to these components should be as short and wide as possible to minimize parasitic inductance and resistance. 3. Rated continuous drain current should be larger than the peak inductor current. 2. Place output capacitor next to Schottky diode as possible. 4. Low gate capacitance. 3. Place input capacitor close to the VIN pin. 1. Low RDS-ON. If a MOSFET with a threshold near the UVLO detection voltage is used, a large current may flow and stop the output voltage from rising and possibly generating heat in the worst case. Select a MOSFET with a threshold that is sufficiently lower than the UVLO detection voltage value. Feed-forward Capacitor Selection The feed-forward capacitor (CF) is used to improve the performance of internally compensated DC-DC converter. To optimize transient response, a feed-forward capacitor value is chosen such that the gain and phase of the feedback increases the bandwidth of the converter, while still maintaining an acceptable phase margin. In general, capacitor causes the loop gain to crossover too high in frequency and the feed-forward capacitor phase contribution is insufficient, resulting in unacceptable phase margin or instability. The following process outlines a step by step procedure for optimizing the feed-forward capacitor. 4. The input and output capacitors’ ground should be wide and short enough to connect to a ground plane. 5. The feedback network should sense the output voltage directly form the point of load, and be as far away from noisy loop as possible. 6. The compensation circuit should be away from the power loops and should be shielded with a ground trace to prevent noise coupling. 7. Place the resistor close to RDUTY and ROSC pin. 1. Determine the crossover frequency of converter. 2. Once the crossover frequency is known, the equation allows calculation of feed-forward capacitor value which prompts a good compromise between bandwidth improvement and acceptable phase margin. The feed-forward capacitor is selected by the following formula: CFB  1 2  fcrossover FP6791C-1.1-FEB-2012  1 R FB1  1 1     R FB1 R FB 2    12 FP6791C 85T fitipower integrated technology lnc. Outline Information TSSOP-8 Package (Unit: mm) SYMBOLS UNIT DIMENSION IN MILLIMETER MIN MAX A 0.80 1.20 A1 0.00 0.15 A2 0.80 1.05 b 0.19 0.30 D 2.90 3.10 E 6.20 6.60 E1 4.30 4.50 e 0.55 0.75 L 0.45 0.75 Note：Followed from JEDEC MO-153-F. Carrier dimensions Life Support Policy Fitipower’s products are not authorized for use as critical components in life support devices or other medical systems. FP6791C-1.1-FEB-2012 13