1、FA5304AP(S)/FA5305AP(S)1n DescriptionThe FA5304AP(S) and FA5305AP(S) are bipolar ICs forswitching power supply control and can directly drive a powerMOSFET. These ICs contain many functions in a small 8-pinpackage. With these ICs, a high-performance power supplycan be created compactly because not m
2、any externalcomponents are needed.n Features Drive circuit for connecting a power MOS-FET (IO = 1.5A) Wide operating frequency range (5 to 600kHz) Pulse-by-pulse overcurrent limiting functionPositive voltage detection: FA5304AP(S)Negative voltage detection: FA5305AP(S) Overload cutoff function (Latc
3、h or non-protection modeselectable) Output ON/OFF control function by external signals Overvoltage cutoff function in latch mode Undervoltage malfunction prevention function (ON at 16Vand OFF at 8.7V) Error amplifier for control by tertiary winding detection Low standby current (90m A typ.) 8-pin pa
4、ckage (DIP/SOP)n Applications Switching power supply for general equipmentn Dimensions, mm SOP-86.055.38.20.30.4 0.11.27 0.20.60.20+0.10.050101 48 52.0max DIP-8Bipolar ICFor Switching Power Supply ControlFA5304AP(S)/FA5305AP(S)18 549.36.57.63.44.5max1.53.0min0150150.5 0.12.54 0.250.3+0.10.05FA5304AP
5、(S)/FA5305AP(S)2n Block diagram FA5304AP(S)Pin Pin DescriptionNo. symbol1 IN () Inverting input to error amplifier2 FB Error amplifier output3 IS (+) Overcurrent (+) detection4 GND Ground5 OUT Output6 VCC Power supply7 CT Oscillator timing capacitor8 CS Soft-start and ON/OFF control FA5305AP(S)Pin P
6、in DescriptionNo. symbol1 IN () Inverting input to error amplifier2 FB Error amplifier output3 IS () Overcurrent () detection4 GND Ground5 OUT Output6 VCC Power supply7 CT Oscillator timing capacitor8 CS Soft-start and ON/OFF controlFA5304AP(S)/FA5305AP(S)3n Absolute maximum ratingsCommon to FA5304A
7、P(S) and FA5305AP(S)Item Symbol Rating UnitVCC 30 VIO 1.5 AVIN 4VVFBVIS 0.3 to +4 VICS 2mAPd 800 (DIP-8) *1mW550 (SOP-8) *2Topr 30 to +85 CTstg 40 to +150 Cn Recommended operating conditionsCommon to FA5304AP(S) and FA5305AP(S)Item Symbol Min. Max. UnitSupply voltage VCC 10 30 VError amplifier feedb
8、ack resistorRNF 100 kWSoft-start capacitor CS 0.1 1 m FOscillation frequency fOSC 5 600 kHzSupply voltageOutput currentError amplifier inputvoltageFeedback terminal input voltageOvercurrent detectionterminal input voltageCS terminal input currentTotal power dissipation(Ta = 25 C)Operating temperatur
9、eStorage temperatureNotes:*1 Derating factor Ta 25 C : 8.0mW/ C ( on PC board )*2 Derating factor Ta 25 C : 5.5mW/ C ( on PC board )n Electrical characteristics (Ta=25 C, VCC=18V,fosc=135kHz)Oscillator section Common to FA5304AP(S) and FA5305AP(S)Item Symbol Test condition Min. Typ. Max. UnitOscilla
10、tion frequency fOSC CT = 360pF 112 135 148 kHzFrequency variation 1 (due to supply voltage change) fdv VCC = 10 to 30V 1%Frequency variation 2 (due to temperature change) fdT Ta = 30 to +85 C 4%Error amplifier section Common to FA5304AP(S) and FA5305AP(S)Item Symbol Test condition Min. Typ. Max. Uni
11、tReference voltage VB 1.90 2.00 2.10 VInput bias current IB V1 = 2V 500 50 nAOpen-loop voltage gain AV 80 dBUnity-gain bandwidth fT 1.0 MHzMaximum output voltage (Pin 2) VOM+ RNF = 100kW 2.70 VVOM RNF = 100kW 200 mVOutput source current (Pin 2) IMO+ VOM = 1V 100 50 m APulse width modulation circuit
12、section Common to FA5304AP(S) and FA5305AP(S)Item Symbol Test condition Min. Typ. Max. UnitInput threshold voltage (Pin 2) VTH FBO Duty cycle = 0% 0.80 1.00 1.20 VVTH FBM Duty cycle = DMAX 1.70 1.90 2.10 VMaximum duty cycle DMAX 42 45 50 %Soft-start circuit section Common to FA5304AP(S) and FA5305AP
13、(S)Item Symbol Test condition Min. Typ. Max. UnitCharge current (Pin 8) ICHG Pin 8 = 0V 15 10 5 m AInput threshold voltage (Pin 8) VTH CSO Duty cycle = 0% 0.80 1.00 1.20 VVTH CSM Duty cycle = DMAX 1.70 1.90 2.10 VFA5304AP(S)/FA5305AP(S)4Overcurrent limiting circuit sectionItem Symbol Test condition
14、FA5304AP(S) FA5305AP(S) UnitMin. Typ. Max. Min. Typ. Max.Input threshold voltage (Pin 3) VTH IS 0.20 0.24 0.28 0.20 0.17 0.14 VOvercurrent detection terminal source current IIS Pin 3 = 0V 300 200 100 240 160 80 m ADelay time TPD IS 150 200 nsLatch-mode cutoff circuit section Common to FA5304AP(S) an
15、d FA5305AP(S)Item Symbol Test condition Min. Typ. Max. UnitCS terminal sink current ISINK CS Pin 8 = 6V, Pin 2 = 1V 40 70 150 m ACutoff threshold voltage (Pin 8) VTH CS 6.5 7.0 7.5 VOverload cutoff circuit section Common to FA5304AP(S) and FA5305AP(S)Item Symbol Test condition Min. Typ. Max. UnitCut
16、off threshold voltage (Pin 2) VTH FB 2.5 2.7 2.9 VUndervoltage lock-out circuit section Common to FA5304AP(S) and FA5305AP(S)Item Symbol Test condition Min. Typ. Max. UnitOFF-to-ON threshold voltage VTH ON 15.5 16.0 16.5 VON-to-OFF threshold voltage VTH OFF 8.20 8.70 9.20 VVoltage hysteresis VHYS 7.
17、30 VOutput section Common to FA5304AP(S) and FA5305AP(S)Item Symbol Test condition Min. Typ. Max. UnitL-level output voltage VOL IO = 100mA 1.30 1.80 VH-level output voltage VOH IO = 100mA, VCC = 18V 16.0 16.5 VRise time tr No load 50 nsFall time tf No load 50 nsOutput ON/OFF control circuit section
18、Common to FA5304AP(S) and FA5305AP(S)Item Symbol Test condition Min. Typ. Max. UnitCS terminal source current ISOURCE CS Pin 8 = 0V 15 10 5 m AOFF-to-ON threshold voltage (Pin 8) VTH ON CS pin voltage 0.56 0.76 VON-to-OFF threshold voltage (Pin 8) VTH OFF CS pin voltage 0.30 0.42 VOverall device Com
19、mon to FA5304AP(S) and FA5305AP(S)Item Symbol Test condition Min. Typ. Max. UnitStandby current ICC ST VCC = 14V 90 150 m AOperating-state supply current ICC OP 915mAOFF-state supply current ICC OFF 1.1 1.8 mACutoff-state supply current ICCL 1.1 1.8 mA5FA5304AP(S)/FA5305AP(S)Fig. 1 Configuration wit
20、h error amplifierFig. 2 Configuration with optocoupler (FB pin input)Fig. 3 PWM comparatorFig. 4 PWM comparator timing chartn Description of each circuit1. Oscillator (See block diagram on page 8.)The oscillator generates a triangular waveform by chargingand discharging a capacitor. CT pin voltage o
21、scillatesbetween an upper limit of approx. 3.0V and a lower limit ofapprox. 1.0V. The oscillation frequency is determined by aexternal capacitance CT connected to CT pin, andapproximately given by the following equation:(1)The recommended oscillation range is between 5k and600kHz.The oscillator outp
22、ut is connected to a PWM comparator.2. Feedback circuitFigure 1 gives an example of connection in which built-in erroramplifier is used to couple the feedback signal to IN(-) pin. Let n2be the number of turns of secondary winding L2 and n3 be thenumber of turns of tertiary winding L3. VCC and Vout a
23、re given byVcc= 2(V)(R1+R2)/R2(2)VOUTQ(n2/n3)(Vcc+VD3)VD2(3)(where VD2 and VD3 are the forward voltage drops across diodes D2and D3 respectively).Here, the following equation must be satisfied to prevent fromthe malfunction of OUT pin at shutdown.(R1R2)/ (R1+R2)L11kW .(4)Figure 2 gives an example of
24、 connection in which anoptocoupler is used to couple the feedback signal to the FBpin. If this circuit causes power supply instability, the frequencygain can be decreased by connecting R4 and C4 as shown infigure 2. R4 should be between several tens of ohms toseveral kiloohms and C4 should be betwee
25、n several thousandpicofarads to one microfarads.3. PWM comparatorThe PWM comparator has four inputs as shown in Figure 3.Oscillator output is compared with CS pin voltage , FB pin , and DT voltage fl . The lowest of three inputs , , and flis compared with output . If it is lower than the oscillatoro
26、utput, the PWM comparator output is high, and if it is higherthan the oscillator output, the PWM comparator output is low(see Fig. 4).The IC output voltage is high during when the comparatoroutput is low, and the IC output voltage is low during when thecomparator output is high.When the IC is powere
27、d up, CS pin voltage controls softstart operation. The output pulse then begins to widengradually. During normal operation, the output pulse width isdetermined within the maximum duty cycle (FA5304A,FA5305A: 45%) set by DT voltage fl under the condition setby feedback signal , to stabilize the outpu
28、t voltage.CT (pF)f (kHZ) =4.8 1046FA5304AP(S)/FA5305AP(S)4. CS pin circuitAs shown in Figure 5, capacitor CS is connected to the CS pin.When power is turned on, the constant current source (10m A)begins to charge capacitor CS. Accordingly, the CS pin voltagerises as shown in Figure 6. The CS pin is
29、connected to aninput of the PWM comparator. The device is in soft-start modewhile the CS pin voltage is between 1.0V and 1.9V common toFA5304A and FA5305A. During normal operation, the CS pinis clamped at 3.6V by internal zener diode Zn. If the outputvoltage drops due to an overload, etc., the clamp
30、 voltage shiftsfrom 3.6V to 8.0V. As a result, the CS pin voltage rises to 8.0V.The CS pin is also connected to latch comparator C2. If the pinvoltage rises above 7.0V, the output of comparator C2 goeshigh to turn off the bias circuit , thereby shutting the outputdown. Comparator C2 can be used not
31、only for shutdown inresponse to an overload, but also for shutdown in response toan overvoltage. Comparator C1 is also connected to the CSpin, and the bias circuit is turned off and the output is shutdown if the CS pin voltage drops below 0.42V. In this way,comparator C1 can also be used for output
32、on/off control.As explained above, the CS pin can be used for soft-startoperation, overload and overvoltage output shutdown andoutput on/off control.Further details on the four functions of the CS pin are givenbelow.4.1 Soft start functionFigure 7 shows the soft start circuit. Figure 8 is the soft-s
33、tartoperation timing chart. The CS pin is connected to capacitorCS . When power is turned on, a 10m A constant-current sourcebegins to charge the capacitor. As shown in the timing chart,the CS pin voltage rises slowly in response to the chargingcurrent. The CS pin is connected internally to the PWMc
34、omparator. The comparator output pulse slowly widens asshown in the timing chart.The soft start period can be approximately evaluated by theperiod ts from the time the IC is activated to the time the outputpulse width widens to 30%. Period ts is given by the followingequation:tS (mS) = 160CS (m F).(
35、2)Fig. 5 CS pin circuitFig. 6 CS pin waveformFig. 7 Soft-start circuitFig. 8 Soft-start timing chart7FA5304AP(S)/FA5305AP(S)4.2 Overload shutdownFigure 9 shows the overload shutdown circuit, and Figure 10 isa timing chart which illustrates overload shutdown operation.Ifthe output voltage drops due t
36、o an overload or short-circuit, theoutput voltage of the FB pin rises. If FB pin voltage exceedsthe reference voltage (2.7V) of comparator C3, the output ofcomparator C3 switches low to turn transistor Q off. In normaloperation, transistor Q is on and the CS pin is clamped at 3.6Vby zener diode Zn.
37、With Q off, the clamp is released and the10m A constant-current source begins to charge capacitor CSagain and the CS pin voltage rises. When the CS pin voltageexceeds the reference voltage (7.0V) of comparator C2, theoutput of comparator C2 switches high to turn the bias circuitoff. The IC then ente
38、rs the latched mode and shuts the outputdown. Shutdown current consumption is 400m A(VCC=9V).This current must be supplied through the startup resistor. TheIC then discharges the MOSFET gates.Shutdown operation initiated by an overload can be reset bylowering supply voltage VCC below 8.7V or forcing
39、 the CS pinvoltage below 7.0V.The period tOL from the time that the outputis short-circuited to the time that the bias circuit turns off isgiven by the following equation:tOL(mS) = 340Cs(m F).(3)4.3 Overvoltage shutdownFigure 11 shows the overvoltage shutdown circuit, and Figure12 is a timing chart
40、which illustrates overvoltage shutdownoperation.The optocoupler PC1 is connected between the CS and VCCpins. If the output voltage rises too high, the PC1 turns on toraise the voltage at the CS pin via resistor R6. When the CSpin voltage exceeds the reference voltage (7.0V) ofcomparator C2, comparat
41、or C2 switches high to turn the biascircuit off. The IC then enters the latched mode and shuts theoutput down. The shutdown current consumption of the IC is400m A(VCC=9V). This current must be applied via startupresistor R5.The IC then discharges the MOSFET gates.The shutdown operation initiated by
42、an overvoltage conditioncan be reset by lowering supply voltage VCC below 8.7V orforcing the CS pin voltage below 7.0V.During normal operation, the CS pin is clamped by a 3.6Vzener diode with a sink current of 150m A max. Therefore, acurrent of 150m A or more must be supplied by the optocouplerin or
43、der to raise the CS pin voltage above 7.0V.Fig. 9 Overload shutdown circuitFig. 10 Overload shutdown timing chartFig. 11 Overvoltage shutdown circuitFig. 12 Overvoltage shutdown timing 8FA5304AP(S)/FA5305AP(S)4.4 Output ON/OFF controlThe IC can be turned on and off by an external signal applied toth
44、e CS pin.Figure 13 shows the external output on/off control circuit, andFigure 14 is the timing chart.The IC is turned off if the CS pin voltage falls below 0.42V. Theoutput of comparator C1 switches high to turn the bias circuitoff. This shuts the output down. The IC then discharges theMOSFET gates
45、.The IC turns on if the CS pin is opened for automatic soft start.The power supply then restarts operation.5. Overcurrent limiting circuitThe overcurrent limiting circuit detects the peak value of everydrain current pulse of the main switching MOSFET to limit theovercurrent.The detection threshold i
46、s +0.24V for FA5304A with respect toground as shown in Figure 15.The drain current of the MOSFET is converted to voltage byresistor R7 and fed to the IS pin of the IC. If the voltage exceedsthe reference voltage (0.24V) of comparator C4, the output ofcomparator C4 goes high to set flip-flop output Q
47、 high. Theoutput is immediately turned off to shut off the current. Flip-flopoutput Q is reset on the next cycle by the output of the PWMcomparator to turn the output on again. This operation isrepeated to limit the overcurrent.If the overcurrent limiting circuit malfunctions due to noise,place an R
48、C filter between the IS pin and the MOSFET.Figure 16 is a timing chart which illustrates current-limitingoperations.Fig. 13 External output on/off control circuitFig. 14 Timing chart for external output on/off controlFig. 16 Overcurrent timing chart for FA5304AFig. 15 Overcurrent limiting circuit fo
49、r FA5304A9FA5304AP(S)/FA5305AP(S)The detection threshold is -0.17v for FA5305A with respect toground as shown in Figure 17.The operation is similar to that of FA5304A except thethreshold is minus voltage compared to that which is plusvoltage for FA5304A.Figure 18 is a timing chart which illustrates current limitingoperations.6. Undervoltage lockout circuitThe IC incorporates a circuit which prevents the IC frommalfunctioning when the supply voltage
