FA7700V, FA7701V CMOS IC For Switching Power Supply Control FA7700V, FA7701V ■ Description ■ Dimensions, mm 6.4 ±0.3 1.30 max 10 to 0 ˚ 4.4 ±0.2 TSSOP-8 0.1 ±0.05 FA7700V/FA7701V are the PWM type DC to DC converter control ICs with 1ch output that can directly drive power MOSFETs. CMOS devices with high breakdown voltage are used in these ICs and low power consumption is achieved. These ICs have not only the functions equivalent to those of FA76XX series but also the functions of directly driving Nch/Pch MOSFETs, lower power consumption, higher frequency operation, and less external components. 0.575 typ 3.1 • Wide range of supply voltage: VCC=2.5 to 20V • FA7700V: For boost, flyback converter (Maximum output duty cycle is 80%) • FA7701V: For buck converter (Maximum output duty cycle is 100%) • Output stage consist of CMOS push-pull circuit, and achieves a high speed switching of external MOSFETs. (FA7700V: For Nch-MOSFET driving, FA7701V: For Pch-MOSFET driving) • High accuracy reference voltage (Error amplifier): 0.88V±2% • Soft start function • Adjustable built-in timer latch for short-circuit protection • Output ON/OFF control function • Less external discrete components needed (2 components less than conventional version of the equivalent products) • Low power consumption Stand-by current: 40µA typ. Operating current: 1.2mA typ. (Including error amplifier output current and oscillator current) • High frequency operation: 50kHz to 1MHz • Package: TSSOP-8, thin and small ±0.3 0.15 ±0.1 ■ Features 0.65 0.22 0.5 ±0.1 ±0.2 ■ Block diagram FA7701V FA7700V RT 1 8 UVLO VREF REF 2 0.3V 5.5V OSC 1.5V S.C.DET 1.5V + – Power Good Signal 3 1 S.C.P + – 7 VCC REF 2 0.3V OSC S.C.P 1.5V S.C.DET BIAS 1.5V + – Power Good Signal 6 OUT IN– 3 CS + + – + ON/OFF + – 7 VCC 2.2V OFF 6 OUT 5 GND 5.5V PWM ER.AMP 5 4 0.88V – PWM 8 ON/OFF – + VREF 2.2V 2.2V OFF + – + + ER.AMP UVLO VREF ON/OFF ON/OFF 0.88V + – FB RT – + VREF 2.2V BIAS IN– CS GND FB 4 Pin No. Pin symbol Description 1 RT Oscillator timing resistor 2 REF Internal bias voltage 3 IN (–) Error amplifier inverting input 4 FB Error amplifier output 5 GND Ground 6 OUT Output for driving switching device 7 VCC Power supply 8 CS ON/OFF, soft start, timer latched short circuit protection 1 FA7700V, FA7701V ■ Absolute maximum ratings Item CS terminal voltage Symbol Vcc IREF ISO peak ISO cont ISI peak ISI cont VRT, VREF VIN–, VFB VCS CS terminal sink current Power dissipation Operating ambient temperature Operating junction temperature Storage temperature ICS Pd Ta Tj Tstg Power supply voltage REF terminal output current OUT terminal source current OUT terminal sink current RT, REF, IN–, FB terminal voltage Rating 20 2 –400 (peak) –50 (continuos) +150 (peak) +50 (continuos) +2.5 (max.) –0.3 (min.) Self limitingⱌ5.5 (max.) –0.3 (min.) 200 250 (Ta⬉25˚C) –30 to +85 +125 –40 to +150 Unit V mA mA mA V V µA mW ˚C ˚C ˚C Maximum power dissipation curve Max. power dissipation [mW] 300 250 200 150 100 50 0 –30 0 60 30 90 125 150 Ambient temperature [˚C] ■ Recommended operating condition Item Symbol Min. Typ. Max. Unit Supply voltage VCC 2.5 6 18 V DC feedback resistor of error amplifier RNF 100 kΩ VCC terminal capacitance CVCC 0.1 µF REF terminal capacitance CREF 0.047 CS terminal capacitance CS CS terminal sink current Icsin Oscillation frequency fosc * Lower limit of ICSIN does not include leak current “IL” for capacitor Cs. Set a resistor “RCS [MΩ]” connected between VCC terminal and CS terminal to satisfy the equation. 2 1 µF 0.01 10 µF 1* 50 µA 50 1000 kHz VCC – 1.5 50µA + IL 0.1 ⬍ RCS [MΩ] ⬍ VCC – 1.5 1µA + IL FA7700V, FA7701V ■ Electrical characteristics (Ta=25˚C, VCC=6V, RT=22kΩ) Internal bias section (REF terminal voltage) Item Symbol Test condition Min. Typ. Max. Unit Output voltage VREF REF terminal source current 2.16 2.23 2.30 V mV IREF=0mA Line regulation VLINE Vcc=2.5 to 20V, IREF=0mA ±2 ±14 Load regulation VLOAD IREF=0 to 2mA ±2 ±12 Variation with temperature VTC1 Ta=–30 to 25°C ±0.3 % VTC2 Ta=25 to 85°C ±0.3 % mV Oscillator section (Frequency set by RT terminal) Item Symbol Test condition Min. Typ. Max. Unit Oscillation frequency fosc RT=22kΩ 155 185 215 kHz Line regulation fLINE Vcc=2.5 to 20V ±0.1 % Variation with temperature fTC1 Ta=–30 to 25°C, 50k to 1MHz ±2 % fTC2 Ta=25 to 85°C, 50k to 1MHz ±3 % Error amplifier section (IN- terminal, FB terminal) Item Symbol Test condition Min. Typ. Max. Unit Reference voltage VB IN- terminal, FB terminal: 0.863 0.880 0.897 V +500 nA ±5 mV Shorted (voltage follower) Input current IIN– VB line regulation VBLINE Vcc=2.5 to 20V ±1 VBTC1 Ta=–30 to 25°C ±0.3 % VBTC2 Ta=25 to 85°C ±0.3 % VB variation with temperature Open loop gain -500 AVO 70 dB Unity gain bandwidth fT Output current Source IOHE FB terminal=VREF– 0.5V –220 –160 1.5 –100 µA MHz Sink IOLE FB terminal=0.5V 3 6 12 mA Pulse width modulation (PWM) section (FB terminal voltage and duty cycle) Item Symbol Test condition Min. Typ. Max. Unit FB 0% threshold VFB0 Duty cycle = 0% 0.560 0.660 0.760 V FB 50% threshold Maximum duty cycle FA7700 FA7701 VFB50 Duty cycle = 50% DMAX1 RT=100kΩ, f=50kHz 85 90 95 % DMAX2 RT=22kΩ, fⱌ185kHz 83 88 93 % DMAX3 RT=3kΩ, fⱌ1MHz 80 86 92 DMAX 0.880 V 100 % % Undervoltage lock-out section (VCC terminal voltage) Item Symbol ON threshold VCCON OFF threshold VCCOF Hysteresis voltage VCCHY Variation with temperature VCCHY Test condition Min. 1.60 0.04 Typ. Max. Unit 2.07 2.30 V 1.93 0.14 V 0.24 V Ta= –30 to 25°C +0.2 mV/°C Ta= 25 to 85°C –0.2 mV/°C 3 FA7700V, FA7701V ON/OFF section (CS terminal voltage) Item Symbol ON/OFF threshold VONOF Test condition Min. Typ. Max. Unit 0.150 0.300 0.450 V Threshold variation with temperature VONTC Ta = –30 to 85°C Item Symbol Test condition Min. Typ. Max. Unit Threshold voltage 1 VCS0 Duty cycle=0% 0.560 0.660 0.760 V Threshold voltage 2 VCS50 Duty cycle=50% +0.5 mV/°C Soft start section (CS terminal voltage) 0.880 V Timer latched short circuit protection section (FB terminal, CS terminal) Item Symbol Test condition Min. Typ. Max. Unit Short detection threshold voltage VFBTH FB terminal voltage 1.350 1.500 1.650 V Latched mode threshold voltage VCSTH CS terminal voltage 2.050 2.200 2.350 V Latched mode reset voltage VCSRE CS terminal voltage 1.700 2.030 2.300 V Latched mode hysteresis VCSHY CS terminal voltage 50 170 350 mV CS terminal clamped voltage VCSCL1 FB terminal<1.35V, CS sink current= +1µA 1.400 1.500 1.600 V VCSCL2 FB terminal>1.65V, CS sink current= +150µA 4.500 5.500 6.500 V Output stage section (OUT terminal) Item Symbol Test condition Typ. Max. Unit High side on resistance RONH VCC=6V, source current= –50mA 10 20 Ω RONH VCC=2.5V, source current= –50mA 18 36 Ω Low side on resistance RONL VCC=6V, sink current= +50mA 5 10 Ω RONL VCC=2.5V, sink current= +50mA 5 10 Ω tr 330pF load to GND terminal 20 ns 330pF load to VCC terminal 25 ns 330pF load to GND terminal 45 ns 330pF load to VCC terminal 40 ns Rise time FA7700 FA7701 Fall time FA7700 tf FA7701 Min. Overall section (Supply current to VCC terminal) Item Symbol Test condition OFF mode supply current ICCST1 CS terminal=0V Operating mode supply current ICC0 Duty cycle=0%, OUT:Open, IN–=0V, FB:Open ICC1 Duty cycle=50%, OUT:Open, IN–, FB:Shorted ICCLAT CS terminal >2.35V, IN–=0V, FB:Open Latched mode supply current 4 Min. Typ. Max. Unit 40 100 µA 0.9 1.5 mA 1.2 2.0 mA 0.9 1.5 mA FA7700V, FA7701V ■ Characteristic curves Oscillation frequency (fOSC) vs. timing resistor resistance (RT) Oscillation frequency (fOSC) vs. ambient temperature 10000 5 Oscillation frequency variation [%] Oscillation frequency [kHz] 4 1000 100 3 fosc=1MHz 2 1 0 fosc=185kHz –1 fosc=50kHz –2 –3 –4 10 1 10 –5 –40 100 100 100 90 90 80 80 70 70 fosc=1MHz 50 40 80 100 50 40 30 20 fosc=185kHz 10 10 0.7 0.9 1.1 0 0.5 1.3 0.7 0.9 1.1 1.3 CS terminal voltage [V] FB terminal voltage [V] Duty cycle vs. FB terminal voltage FA7701 Duty cycle vs. CS terminal voltage FA7701 100 100 90 90 80 80 70 Duty cycle [%] 70 Duty cycle [%] 60 fosc=1MHz fosc=185kHz 20 fosc=1MHz 60 50 40 fosc=1MHz 60 50 40 30 30 20 20 fosc=185kHz fosc=185kHz 10 0 0.5 40 20 60 30 0 0.5 0 Duty cycle vs. CS terminal voltage FA7700 Duty cycle [%] Duty cycle [%] Duty cycle vs. FB terminal voltage FA7700 60 –20 Ambient temperature Ta [˚C] Timing resisitor RT [kΩ] 0.7 0.9 10 1.1 FB terminal voltage [V] 1.3 0 0.5 0.7 0.9 1.1 1.3 CS terminal voltage [V] 5 FA7700V, FA7701V Maximum duty cycle vs. ambient temperature FA7700 Error amp. reference voltage vs. ambient temperature 94 0.90 fosc=50kHz 92 0.89 88 Reference voltage [V] Max. duty cycle [%] 90 fosc=185kHz 86 fosc=1MHz 84 0.88 0.87 82 80 –40 –20 0 20 40 60 80 0.86 –40 100 –20 0 20 60 40 80 100 Ambient temperature Ta [˚C] Ambient temperature Ta [˚C] Internal bias voltage vs. ambient temperature Undervoltage lock-out vs. ambient temperarure 2.28 2.20 2.15 Vcc terminal ON/OFF threshold Internal bias voltage [V] 2.26 2.24 2.22 2.20 Vcc ON 2.10 2.05 2.00 Vcc OFF 1.95 1.90 1.85 2.18 –40 –20 0 20 40 60 80 1.80 –40 100 –20 Ambient temperature Ta [˚C] CS terminal ON/OFF threshold vs. ambient temperature 0.35 CS terminal sink current [ A] CS terminal ON/OFF threshold 40 60 80 100 200 180 0.30 0.25 0.20 –20 0 20 40 60 Ambient temperature Ta [˚C] 80 100 Ta=25˚C –30˚C 85˚C 160 Ta=25˚C Ta=–30˚C 140 Ta=85˚C 120 100 80 FB>1.65V 60 40 FB<1.35V 20 6 20 CS terminal voltage vs. CS terminal sink current 0.40 0.15 –40 0 Ambient temperature Ta [˚C] 0 0 1 2 3 4 5 CS terminal voltage [V] 6 7 FA7700V, FA7701V Operating mode supply current vs. VCC Operating mode supply current vs. VCC 3 Duty=50% IN(–)–FB:shorted Operating mode supply current [mA] Operating mode supply current [mA] 2 fosc=1MHz 1.5 1 fosc=185kHz 0.5 0 0 0.5 2 1.5 1 2.5 fosc=1MHz 2 1.5 fosc=185kHz 1 0.5 0 3 2.5 Duty=50% IN(–)–FB:shorted 4 6 12 10 8 Vcc [V] 16 14 OFF mode supply current vs. temperature 1.5 RT=22kΩ Operating mode supply current [mA] OFF mode supply current [ A] CS=0V 55 50 Vcc=20V 45 40 Vcc=6V 35 –20 20 0 40 80 60 1.4 1.3 Vcc=20V (Duty=50%) 1.2 1 0.9 0.8 –20 0 40 20 80 60 100 Temperature Ta [˚C] Latched mode supply current vs. temperature Oscillation frequency vs. operating mode supply current 3 Vcc=6V RT=22kΩ CS > 2.35V 0.95 0.9 0.85 0.8 0.75 –20 0 20 40 60 Temperature Ta [˚C] 80 100 Operating mode supply current [mA] 1 Operating mode supply current [mA] Vcc=6V (Duty=0%) 0.7 0.6 –40 100 Vcc=6V (Duty=50%) 1.1 Temperature Ta [˚C] 0.7 –40 20 Operating mode supply current vs. temperature 60 30 –40 18 Vcc [V] Vcc=6V Duty=50% 2.5 2 1.5 1 0.5 0 10 100 1000 Oscillation frequency [kHz] 7 FA7700V, FA7701V OUT terminal source current vs. OUT terminal voltage OUT terminal sink current vs. OUT terminal voltage 450 200 OUT terminal source current [mA] OUT terminal source current [mA] 400 350 Vcc=20V 300 250 Vcc=12V 200 Vcc=6V 150 100 Vcc=2.5V 150 100 50 50 0 0 0 5 10 20 15 25 Error amplifier gain and phase vs. frequency 80 180 160 140 60 120 100 40 Phase 80 60 20 1MΩ 40 390Ω 0 + + – 20 0 –20 3 0 6 3 1k 6 3 10k 6 3 100k Frequency [Hz] 8 6 3 1M 6 10M Phase [deg] Gain [dB] Gain 0 0.5 1 OUT terminal voltage [V] OUT terminal voltage [V] 1.5 FA7700V, FA7701V ■ Description of each circuit OSC 1. Reference voltage circuit This circuit consists of the reference voltage circuit using band gap reference, and also serves as the power supply of the internal circuit. The precision of output is 2.23V±3%. It is stabilized under the supply voltage of 2.5V or over. The precision of reference voltage of error amplifier circuit is 0.88V±2%, and the reference voltage circuit is connected to the non-inverting input of the error amplifier circuit. 2. Oscillator The oscillator generates a triangular waveform by charging and discharging the built-in capacitor. A desired oscillation frequency can be determined by the value of the resistor “RT” connected to the RT terminal (Fig. 1). The built-in capacitor voltage oscillates between approximately 0.66V and 1.1V with almost the same charging and discharging gradients. You can set the desired oscillation frequency by changing the gradients using the resistor connected to the RT terminal. (Large RT: Low frequency, small RT: High frequency) The oscillator waveform cannot be observed from the outside because a terminal for this purpose is not provided. The oscillator output is connected to the PWM comparator. RT Fig. 1 RT value: small 1.1V 0.66V Fig. 2 Vout 3. Error amplifier circuit The IN(–) terminal (Pin 3) is an inverting input terminal. The non-inverting input is internally connected to the reference voltage (0.88V±2%; 25˚C). The FB terminal (Pin 4) is the output of the error amplifier. Gain setting and phase compensation setting is done by connecting a capacitance and a resistor between the FB terminal and the IN(–) terminal. Vout which is the output voltage of DC to DC converter can be calculated by: R1 + R2 Vout = VB ⫻ R2 Gain AV between the Vout and the FB terminal can be calculated by: RNF AV = – R1 4. PWM comparator The PWM comparator has 4 input terminals. (Fig. 4) The oscillator output is compared with the CS terminal voltage , and the error amplifier voltage , then, the lower voltage between and is preferred. While the preferred voltage is lower than the oscillator output, the PWM comparator output is Low. While the preferred voltage is higher than the oscillator output, the PWM comparator output is High (Fig. 5). When the IC starts, the capacitor connected to the CS terminal is charged through the resistor connected to the power supply, and then the output pulses begin to widen gradually as the operation of soft start. In steady operation, the pulse width is determined based on the voltage of the error amplifier , and then the output voltage is stabilized. The Dead Time control voltage ( DT voltage) of FA7700 and FA7701 has different characteristics to adjust the ICs to various types of power supply circuits being controlled and also to reduce external discrete components as many as possible. FA7700 is developed for fly-back circuits, and boost circuits, and the DT voltage is set in the IC so that the maximum output duty cycle is fixed to 80% min.. (Maximum output duty cycle changes according to operation frequencies. ––See page 6 “Maximum output duty vs. temperature”.) It prevents magnetic saturation of the transformer or the like when a short-circuit in the output circuit occurs. FA7701 is developed for buck circuits, and it is designed for the maximum output duty cycle of 100%. The timing chart of PWM comparator is described in Fig. 5. RT value: large RNF Er. AMP R1 3 4 IN(–) R2 FB VB PWM (0.88V) Fig. 3 Oscillation output CS terminal voltage Error amplifier output DT voltage – + + + PMW output Fig. 4 Error amplifier output Oscillation output CS terminal voltage DT voltage PWM output pulse Fig. 5 9 FA7700V, FA7701V 5. Soft start function As described in Fig. 6, RCS is connected between CS terminal and VCC terminal, and Cs is connected between CS terminal and GND. The voltage of CS terminal rises when starting the power supply, because Cs is charged by Vcc through Rcs. The soft start function starts by charging a capacitor Cs connected to PWM comparator. To estimate the soft start period, the time (ts) between the start and the moment when the width of output pulse reaches 50% is calculated by: (V ts [ms] ⱌ Cs ⫻ RCS ⫻ 1n VCC – 0.88 CC RCC Rcs REF OFF + C3 0.3 V CS ON/OFF Output off 8 + 1.5V 5.5V C1 S.C.P Cs FB ) 2.2V C2 + Cs : Capacity of Cs [µF] Rcs : Resistance of Rcs [kΩ] Vcc : Supply voltage [V] S.C.DET 1.5V Fig. 6 The maximum current flowing in Rcs should be within the recommended value (50µA max.). Vcc – 1.5 Vcc – 1.5 ⬍ Rcs [MΩ] ⬍ 1µA + IL 50µA + IL Vcc (IL: leak current of capacitor Cs) CS Note: This IC operates ON/OFF function by the CS terminal (CS < 0.3V typ. : OFF), then it turns off the internal bias voltage VREF (off mode). Therefore, you can not connect the resistor “Rcs” between CS terminal and REF terminal, and can connect the resistor only to VCC terminal. 7. Timer latch short-circuit protection circuit The short-circuit protection circuit consists of two comparators C1, C2 (Fig. 6). In steady operation, the output of S.C.DET comparator C2 is set to High, and the CS terminal is clamped by the 1.5V Zener diode, because the output of error amplifier is about 1V. If the converter output voltage drops due to a short-circuit, when the output voltage of error amplifier rises excesses 1.5V, the output of S.C.DET comparator C2 is set to low, and then the clamp of Zener diode is turned off. As a result, the voltage of CS terminal rises up to the lower value of either 5.5 V or the voltage of VCC terminal. If the voltage of CS terminal excesses 2.2V, the output of S.C.P comparator C1 is set to high, and the circuit shuts down the output circuit of the IC. When it occurs, the current consumption of the IC is 0.9mA (typ.) because the IC is set to OFF latch mode. The period (tp) between the occurrence of a short-circuit in the converter output and the triggering of the short-circuit protection function can be calculated by the following expression: tp [ms] ⱌ Cs ⫻ RCS ⫻ 1n – 1.5 ( Vcc Vcc – 2.2 ) Cs : Capacitance of Cs [µF] Rcs : Resistance of Rcs [kΩ] Vcc : Supply voltage [V] Note: When the IC is used in a product with low VCC voltage, the period (tp) of the triggering of the short-circuit protection described above fluctuates significantly. Therefore, sufficient care should be taken in such cases. Example When Rcs=750kΩ, Cs=0.1µF: Vcc=2.5V: tp ⱌ 90ms Vcc=3.6V: tp ⱌ 30ms 10 Cs Fig. 7 6 Lower value of either 5.5V or Vcc terminal voltage 5 CS terminal voltage [V] 6. ON/OFF circuit The ON/OFF function can be controlled by external signal to the CS terminal, the IC becomes off mode. When the CS terminal voltage is below 0.30V(typ.), the output of ON/OFF comparator C3 is set to LOW, and the internal power source VREF is shut off, then the IC is switched to the off mode. The power consumption in the off mode is 40µA(typ.). A sample circuit is given in Fig. 7. ON/OFF 4 Start-up 3 2.2V 2 1.5V tp Short circuit protection 1 0 Momentary short circuit Soft start Short circuit Time Fig. 8 FA7700V, FA7701V You can reset the off latch mode operation of the short-circuit protection by either of the following ways: lowering the CS voltage below 2.03V (typ.); lowering the Vcc voltage below the Off threshold voltage of undervoltage lock out; 1.93V (typ.); lowering the voltage of FB terminal below 1.5V (typ.) The off latch mode action cannot be triggered by externally applying voltage of over 2.2V forcibly to the CS terminal (1.5V, ZD clamped). Characteristics of the current and the voltage of CS terminal is shown in the characteristic curve (CS terminal voltage vs. CS terminal sink current) on page 6. Be sure to use the IC up to the recommended CS terminal current of 50µA. ■ Design advice 8. Output circuit The IC contains a push-pull output stage and can directly drive MOSFETs (FA7700: N ch, FA7701: P ch). The maximum peak current of the output stage is a sink current of +150mA, and a source current of –400mA. The IC can also drive NPN, and PNP transistors. The maximum peak current in such cases is ±50mA. Be sure to design the output current considering the rating of power dissipation. fOSC = 3000 ⫻ RT –0.9 9. Power good signal circuit/ Undervoltage lockout circuit The IC contains a protection circuit against undervoltage malfunctions to protect the circuit from the damage caused by malfunctions when the supply voltage drops. When the supply voltage rises from 0V, the circuit starts to operate at VCC of 2.07V (typ.) and outputs generate pulses. If a drop of the supply voltage occurs, it stops output at VCC of 1.93V (typ.). when it occurs, the CS terminal is turned to Low level and then it is reset. The power good signal circuit monitors the voltage of REF terminal, and stops output until the voltage of REF terminal excesses approximately 2V to prevent malfunctions. 1. Setting the oscillation frequency As described in item 2 “Oscillator” of “Description of each circuit”, a desired oscillation frequency can be determined by the value of the resistor connected to the RT terminal. When designing an oscillation frequency, you can set any frequency between 50kHz and 1MHz. You can roughly obtain the oscillation frequency from the characteristic curve “Oscillation frequency (fosc) vs. timing resistor resistance(RT)” or the value can be calculated by the following expression. RT = ( 3000 ) f 1.11 OSC fOSC: Oscillation frequency [kHz] RT: Timing resistor [kΩ] This expression, however, can be used for rough calculation, the value obtained is not guaranteed. The operation frequency varies due to the conditions such as tolerance of the characteristics of the ICs, influence of noises, or external discrete components. When determining the values, be sure to verify the effectiveness of the values of the components in an actual circuit. 2. Operation around the maximum or the minimum output duties As described in characteristic curves on page 5, “output duty cycle vs. FB terminal voltage (VFB)” and “output duty cycle vs. CS terminal voltage (Vcs)”, the linearity of the output duty of this IC drops around the minimum output duty and the maximum output duty (FA7701 only). This phenomena are conspicuous when operating in a high frequency (when the pulse width is narrow). Therefore be careful when using high frequency. 3. Restriction of external discrete components To achieve a stable operation of the ICs, the value of external discrete components connected to Vcc, REF, CS, FB terminals should be within the recommended operational conditions. 4. Loss calculation Since it is difficult to measure IC loss directly, the calculation to obtain the approximate loss of the IC connected directly to a MOSFET is described below. When the supply voltage is Vcc, the current consumption of the IC is Icc, the total input gate charge of the driven MOSFET is Qg, the switching frequency is fsw, the total loss Pd of the IC can be calculated by: Pd ⱌ Vcc ⫻ (Icc + Qg ⫻ fsw). The values in this expression is influenced by the effects of the dependency of supply voltage, the characteristics of temperature, or tolerance. Therefore, be sure to verify appropriateness of the value considering the factors above under all applicable conditions. Example: When VCC = 6V, in the case of a typical IC, from the characteristic curve, Icc=1.2mA. When operating in Qg = 6nC, fsw = 500kHz, Pd should be: Pd ⱌ 6 ⫻ (1.2mA + 6nC ⫻ 500kHz) ⱌ 25.2mW 11 FA7700V, FA7701V ■ Application circuit FA7700 Vin 2.5~11V Vout 12V/0.2A 8 7 6 5 CS VCC OUT GND ON /OFF FA7700 RT 1 REF 2 IN3 FB 4 Vin Vout 8 CS ON /OFF 6 5 OUT GND FA7700 RT 1 12 7 VCC REF 2 IN3 FB 4 FA7700V, FA7701V ■ Application circuit FA7701 Vin 7~18V Vout 5V/0.5A 8 CS ON /OFF 7 VCC 6 OUT 5 GND FA7701 RT 1 REF 2 IN3 FB 4 Parts tolerances characteristics are not defined in the circuit design sample shown above. When designing an actual circuit for a product, you must determine parts tolerances and characteristics for safe and economical operation. 13