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FA551X series
FA5510P (N), FA5511P (N) FA5514P (N), FA5515P (N)
Description
The FA551X series are the PWM type switching power supply control ICs that can directly drive power MOSFET. These ICs use a CMOS device with high dielectric strength (30V) to implement low power consumption. These ICs contain many function in a small 8-pin package. With these ICs, a highperformance and compact power supply can be created because not many external discrete components are needed.
CMOS IC For Switching Power Supply Control FA551X
Dimensions, mm SOP-8
8 5
1 4.9
4
+0.1 -0.05
6.00.2
3.9
Features
* Low current consumption by CMOS process with high dielectric strength (30V) * Standby current of 2A or less (at Vcc=14V), and operating current of 1.5mA (typ) * Overvoltage protection function detecting the Vcc voltage * A drive circuit for connecting a power MOSFET directly * Output peak current: 1.5A * Pulse-by-pulse overcurrent limiting function * Overload protection function (latch or non-latch mode selectable) * Output ON-OFF function by external signal * Latch-mode overvoltage shutdown function * Undervoltage lockout function (16.5V ON / 9V OFF) * Reference voltage output (5V) * 8-pin package (DIP/SOP)
0.40.1 1.27
DIP-8
8
5
1
9.3
4
1.50.3
6.4
3.0min 4.5max
3.3
0~8
Block diagram FA5510P (N), FA5511P (N)
CS(8) REF (7)
5V VCC ENB 5V REF 8.5V/7.9V 0.8V 3.5V ENB 4V PWM Dmax FA5510: 46% FA5511: 70% OSC RT CT OUT PUT 0.8V/0.68V 5.2A 0.95mA 15.5V 15.5V UVLO
0.05 0.25 -
7.62
0~15
0~1 5
VCC(6)
2.54
0.460.1
16.5V/9V
FB (2)
OUT (5)
Pin Pin Function No. symbol 1 RT FB IS GND OUT VCC REF CS Oscillator timing resistor Feedback Overcurrent detection Ground Output Power supply Reference voltage Soft-start and ON/OFF control
Description Setting oscillation frequency Input of PWM comparator Input of the overcurrent limiting function Ground Output for driving a power MOSFET Power supply Reference voltage output (5V) Soft-start, ON/OFF function and latch-mode shutdown operations
R +0.24V
GND (4)
2 3 4 5 6 7 8
QB SQ FF
5V Controlled block
RT(1)
IS+(3)
FA5514P (N), FA5515P (N)
CS(8) REF (7)
5V VCC ENB 5V REF 8.5V/7.9V 0.8V 3.5V ENB 4V PWM Dmax FA5514: 46% FA5515: 70% OSC RT CT OUT PUT 0.8V/0.68V 5.2A 0.95mA 15.5V 15.5V UVLO
VCC(6)
Type FA5510P
OUT (5)
Max. duty cycle (typ.) 46% 70% 46% 70%
Polarity of overcurrent Package detection + + - - DIP-8 SOP-8 DIP-8 SOP-8 DIP-8 SOP-8 DIP-8 SOP-8
16.5V/9V
FA5510N FA5511P FA5511N
FB (2)
R -0.17V
GND (4)
FA5514P FA5514N FA5515P FA5515N
QB SQ FF
5V Controlled block
RT(1)
IS-(3)
1.8max
+0.1
0.20
1
FA551X
Absolute maximum ratings
Item
Supply Voltage Low impedance source (ICC>15mA) Internal zener clamp (ICC<15mA) Symbol VCC1 VCC2 IOUT VFB VIS IREF ICS Pd Ta Tj Tstg Rating 30 Self limiting 1.5 -0.3 to 5.0 -0.3 to 5.0 -10 +2.0 800 (DIP-8) 400 (SOP-8) -30 to +85 125 -40 to +150 Unit V V A V V mA mA mW C C C
Output peak current FB pin input voltage IS pin input voltage REF pin source current CS pin sink current Total power dissipation (Ta=25C) Ambient temperature Maximum junction temperature Storage temperature
Note: There are cases where the IC cannot output the rating current depending on Vcc voltage or temperature.
Maximum power dissipation curve
400mW (SOP) 800mW (DIP)
Max. power dissipation
0 -30
25
85
125
Ambient temperature Ta [C]
Recommended operating conditions
Item Supply voltage Oscillation frequency REF-GND capacitor Soft start capacitor Symbol VCC fOSC Cref CS Min. 10 10 0.1 0.01 0.47 1 Typ. Max. 28 500 Unit V kHz F F
2
FA551X
Electrical characteristics (VCC=18V, RT=47k, Ta=25C) Reference voltage section (REF pin)
Item Reference voltage Line regulation Load regulation Temperature stability Symbol VREF Vdv1 Vdv2 VdT Test condition Tj=25C VCC=10 to 28V IL=0 to 10mA, VCC=18V Ta=-30 to 85C -40 Min. 4.75 Typ. 5.00 6 -12 0.5 Max. 5.25 20 Unit V mV mV mV/C
Oscillator section (RT pin)
Item Oscillation frequency Voltage stability Temperature stability Symbol fOSC fdv fdT Test condition RT=47k, Tj=25C VCC=10 to 28V Ta=-30 to 85C Min. 92.6 Typ. 100 1.0 0.02 Max. 107.4 Unit kHz % %/C
Pulse width modulation circuit section (FB pin)
Item FB pin source current Input threshold voltage (FB pin) Maximum duty cycle Symbol Test condition FA5510/14 Min. Typ. 1 1.92 42 46 50 66 FA5511/15 Max. Min. 0.9 Typ. 1 2.40 70 74 Max. V V % Unit
IFB VTH FB0 VTH FBM DMAX
VFB=0
Duty cycle =0% Duty cycle =DMAX
-855 -720 -585 -855 -720 -585 A 0.9
Overcurrent limiting circuit section (IS pin)
Item Input threshold voltage (IS pin) Source current (IS pin) Delay time Symbol VTHIS IIS tpdIS VIS=0V 150 Test condition FA5510/11 Min. 220 Typ. 240 260 5 FA5514/15 Max. Min. -28 Typ. -20 150 Max. -12 A ns Unit
-190 -170 -150 mV
Soft start circuit section (CS pin)
Item Charge current (CS pin) Input threshold voltage (CS pin) Symbol Test condition FA5310/14 Min. Typ. -5.2 1.0 1.92 -3.2 FA5311/15 Max. Min. -7.2 0.90 Typ. -5.2 1.0 2.40 Max. -3.2 A V V Unit
ICHG VTH CS0 VTH CSM
VCS=1V, Tj=25C -7.2 Duty cycle =0% Duty cycle =DMAX 0.90
Output ON/OFF control circuit section (CS pin)
Item Source current (CS pin) ON/OFF control threshold voltage (CS pin) Hysteresis voltage Symbol IS0CS VTHON VTHOFF VTHOHS Test condition VCS=0V, Tj=25C OFFON, Tj=25C ONOFF, Tj=25C 0.50 Min. -7.2 Typ. -5.2 0.8 0.68 0.12 Max. -3.2 0.93 Unit A V V V
3
FA551X
Latch-mode cutoff circuit section (CS pin)
Item Sink current (CS pin) Cutoff threshold voltage (CS pin) Hysteresis voltage Symbol ISICS VTH CSF VTH CSN VTHHIS Test condition VCS=6.5V, VFB=1V, Tj=25C ONOFF, Tj=25C OFFON, Tj=25C Min. 18 8.0 7.4 Typ. 30 8.5 7.9 0.6 Max. 45 9.0 8.4 Unit A V V V
Overload cutoff circuit section (FB pin)
Item Overload threshold voltage (FB pin) Symbol VTH FB Test condition Min. 3.2 Typ. 3.5 Max. 3.8 Unit V
Overvoltage cutoff circuit section (VCC pin)
Item Overvoltage threshold voltage (VCC pin) Cutoff operating supply current (VCC pin) Charge current (CS pin) Symbol VTH VCC IVCC IS0CS2 Test condition Tj=25C Tj=25C, VCC=VTHVCC VCS=6.5V -1.4 Min. 30 Typ. 31.8 14 -0.95 -0.5 Max. 34 Unit V mA mA
Undervoltage lockout circuit section (VCC pin)
Item OFF-to-ON threshold voltage ON-to-OFF threshold voltage Hysteresis voltage Symbol VCC ON VCC OFF VHYS Test condition Tj=25C Tj=25C Tj=25C Min. 15.5 8.5 6.8 Typ. 16.5 9.0 7.5 Max. 17.5 10.0 8.2 Unit V V V
Output circuit section (OUT pin)
Item Low output voltage High output voltage Rise time Fall time Symbol VOL VOH tr tf Test condition IOL=100mA IOH=-100mA, VCC=18V CL=1nF CL=1nF 15 Min. Typ. 0.7 16.5 40 25 Max. 1.5 Unit V V ns ns
Supply current (VCC pin)
Item Stand-by current Startup current Operating-state supply current OFF-state supply current Latch mode supply current Symbol ICCSTB ICCST ICCOP ICCOF ICCL Test condition VCC=14V VCC=OFF-to-ON threshold voltage No load VCC=17V, CS=0V VCC=10V 12 1.5 80 45 Min. Typ. Max. 2 30 2.5 200 80 Unit A A mA A A
4
FA551X
Characteristic curves (VCC=18V, RT=47k, Ta=25C) Oscillation frequency (fOSC) vs. timing resistor resistance (RT)
1000
Oscillation frequency (fOSC) vs. supply voltage (VCC)
100.1 100.08 100.06
100
100.04
fosc (kHz)
fosc (kHz)
100.02 100 99.98 99.96 99.94 99.92
10
1
1
10
100
1000
RT (k)
99.9 10
15
20
25
30
Vcc (V)
Oscillation frequency (fOSC) vs.
junction temperature (Tj)
102 101.5 101
FB pin source current (IFB) vs. FB pin voltage (VFB)
0 -100 -200
fosc (kHz)
-300
100.5 100 99.5 99 98.5 -50
IFB (A)
-400 -500 -600 -700 -800 0 1 2 3 4 5
0
50
100
150
VFB (V)
Tj (C)
Maximum duty cycle (DMAX) vs. timing resitor resistance (RT) FA5510/14
49 48
Maximum duty cycle (DMAX) vs. timing resitor resistance (RT) FA5511/15
72
71
47
DMAX (%)
DMAX (%)
1 10 100 1000
46 45 44 43 42
70
69
68
67 1 10 100 1000
RT (k)
RT (k)
5
FA551X
Maximum duty cycle (DMAX) vs. junction temperature (Tj) FA5510/14
47 46.8 46.6 46.4
Maximum duty cycle (DMAX) vs. junction temperature (Tj) FA5511/15
71 70.8 70.6 70.4
DMAX (%)
DMAX (%)
46.2 46 45.8 45.6 45.4 45.2 45 -50 0 50 100 150
70.2 70 69.8 69.6 69.4 69.2
69
-50 0 50 100 150
Tj (C)
Tj (C)
IS (+) pin current (IIS (+)) vs. IS (+) pin voltage (VIS (+)) FA5510/11
0 -0.05 -0.1 -0.15
IS (-) pin current (IIS (-)) vs. IS (-) pin voltage (VIS (-)) FA5514/15
5 0
IIS (+) (A)
IIS (-) (A)
-5 -10 -15 -20
-0.2 -0.25 -0.3 -0.35 -0.4 -1 0 1 2 3 4
-25 -1 0 1 2 3 4
VIS (+) (V)
VIS (-) (V)
CS pin current (ICS) vs. CS pin voltage (VCS) FB=open
40 35 30
CS pin current (ICS) vs. CS pin voltage (VCS) FB=0V
40 35 30
ICS (A)
ICS (A)
25 20 15 10 5 0 -5 -10 0 2 4 6 8 10 12
25 20 15 10 5 0 -5 -10 0 2 4 6 8 10 12
VCS (V)
VCS (V)
6
FA551X
CS pin charge current (ICHG) vs. junction temperature (Tj)
-4.5
-4.7
ICHG (A)
-4.9
-5.1
-5.3
-5.5 -50
0
50
100
150
Tj (C)
UVLO OFF-to-ON threshold voltage (VCCON) vs. junction temperature (Tj)
16.9 16.8
UVLO ON-to-OFF threshold voltage (VCCOFF) vs. junction temperature (Tj)
9.1
9.05
VCCON (V)
16.6 16.5 16.4 16.3 -50
VCCOFF (V)
0 50 100 150
16.7
9
8.95
8.9 -50
0
50
100
150
Tj (C)
Tj (C)
H-level output voltage (VOH) vs. supply voltage (VCC) IO= -100mA
1.8 1.7 1.6
L-level output voltage (VOL) vs. supply voltage (VCC) IO=100mA
0.8 0.75 0.7 0.65 0.6 0.55 0.5 0.45 0.4 0.35 0.3 10
VCC-VOH (V)
1.4 1.3 1.2 1.1 1 0.9 0.8 10 15 20 25 30
VOL (V)
1.5
15
20
25
30
VCC (V)
VCC (V)
7
FA551X
Operating state supply current (ICCOP) vs. supply voltage (VCC)
1.8 1.7 1.6
Operating state supply current (ICCOP) vs. junction temperature (Tj)
1.72
FB=0V
1.7 1.68 1.66
ICCOP (mA)
1.5 1.4 1.3 1.2 1.1 1 0.9 0.8 10 15 20 25 30
ICCOP (mA)
FB=0V
1.64
FB=Open
1.62 1.6 -50
0
50
100
150
VCC (V)
Tj (C)
OFF state supply current (ICCOFF) vs. supply voltage (VCC)
3000 2500 2000 1500 1000 500 0 10
OFF state supply current (ICCOFF) vs. supply voltage (VCC) Enlarged
200 180 160
ICCOFF (A)
ICCOFF (A)
140 120 100 80 60 40 20
15
20
25
30
0 10
12
14
16
18
20
VCC (V)
VCC (V)
Latch mode supply current (ICCL) vs. supply voltage (VCC)
3000 2500 2000
Latch mode supply current (ICCL) vs. supply voltage (VCC) Enlarged
200 180 160 140
ICCL (A)
ICCL (A)
120 100 80 60 40
1500 1000 500 0 10
20 0 10 15 20 25 30 12 14 16 18 20
VCC (V)
VCC (V)
8
FA551X
Description of each circuit
1. Oscillator The oscillator generates a triangular waveform by charging and discharging the built-in capacitor. A desired oscillation frequency can be set by the value of the resistor connected to the RT pin (See Figure 1). The built-in capacitor voltage oscillates between about 3V and 1V, with almost the same charging and discharging gradients (Figure 2). You can set the desired oscillation frequency by changing the gradients using the resistor connected to the RT pin. (Large RT=Low frequency, small RT=High frequency) The relationship between RT and the oscillation frequency is approximately given by: fOSC RT 4880 [kHz] ........................................................ (1) RT + 1.4 4880 - 1.4 [k] ........................................................ (2) fOSC
OSC
1
RT RT
Fig. 1
Oscillator
RT=Small
3V
RT=Large
1V
Fig. 2
Oscillator output
fOSC: Oscillation frequency [kHz] RT: Timing resistance [k]
The oscillator waveform cannot be observed from the outside because the oscillator output is not pinned out. The oscillator output is connected to a PWM comparator. 2. PWM comparator The PWM comparator has four inputs as shown in Figure 3. Oscillator output is compared with CS pin voltage , FB pin voltage , and DT voltage . The lowest of three inputs , , and has priority and is compared with oscillator output . While the voltage is lower than the oscillator output, the comparator output is high. While the voltage is higher than the oscillator output, the PWM comparator output is low (see Figure 4). The IC OUT pin voltage is high while the PWM comparator output is low. When the IC is powered up, CS pin voltage controls soft start operation. The output pulse then begins to widen gradually. During normal operation, the output pulse width is determined within the maximum duty cycle (FA5510/14: 46%, FA5511/15: 70%) set by DT voltage under the condition set by FB pin voltage , to stabilize the output voltage.
DT voltage FB pin voltage CS pin voltage Oscillator output
PWM comparator output
Fig. 3
PWM comparator
FB pin voltage DT voltage Oscillator output CS pin voltage PWM comparator output OUT pin voltage
(4.0V)
Fig. 4
PWM comparator timing chart
9
FA551X
3. CS pin circuit As shown in Figure 5, capacitor Cs is connected to the CS pin. The CS pin voltage varies depending on the charging voltage of this capacitor Cs. When the power is turned on, the constant current source (5.2A) begins to charge capacitor. Accordingly, the CS pin voltage rises as shown in Figure 6. The CS pin voltage is connected to the PWM comparator, which is characterized to make output based on the lowest of input voltages. The device enters soft-start mode while the CS pin voltage is between 1.0V and VTHCSM (FA5510/14: 1.92V, FA5511/15: 2.4V). During normal operation, the CS pin is clamped at 4.0V by internal zener diode. If the output voltage drops due to an overload and the FB voltage rises to 3.5V or more, the clamp voltage 4.0V is canceled and the CS pin voltage rises to 9.5V. The CS pin is also connected to latch comparator C2. If the CS pin voltage rises to 8.5V or more, comparator C2 toggles to turn off the 5V REF circuit, thereby shutting the output down. Since the CS pin is also connected to comparator C1, the 5V REF circuit can be turned off to shut the output down by dropping the CS pin voltage below 0.68V. In this way, comparator C1 can be used for output on-off control. As explained above, the CS pin can be used for soft-start, overload output shutdown, and output on-off control by varying the voltage. Further details on the above three major functions of the CS pin are given below. 3.1 Soft start function Figure 7 shows the soft start circuit. Figure 8 is a soft-start operation timing chart. The CS pin is connected to capacitor Cs. When the power is turned on, the constant current source (5.2A) begins to charge the capacitor. As shown in the timing chart, the CS pin voltage rises slowly in accordance with the capacitor Cs charging current. The CS pin is also connected to the IC internal PWM comparator, which has such characteristics that the voltage is determined to output on the basis of the lowest of input voltages. The comparator output pulse slowly widens to cause a soft start as shown in the timing chart. The soft start period can be approximately estimated by the period tS, from the time the IC is activated to the time the output pulse width widens to 30%. The period tS is given by the following equation: tS [ms] 310 CS [ms] ..................................................... (3)
Cs
CS VCC
8 0.8/0.68V 5.2A C2 8.5/7.9V 3.5V UVLO C3 4V PWM 6
REF 7
C1 5V VCC ENB 5V REF
FB 2
DMAX OSC
Output circuit
1
RT
Fig. 5
CS pin circuit
CS pin voltage Vcs [V]
9.5 8.5 Shutdown 4.0 VTHCSM 1.0 0.68/0.8 0 Soft start Time t OFF mode
Momentary overload or overvoltage
Overload or overvoltage
Fig. 6
CS pin waveform
Cs
CS
8 6
VCC
5.2A
FB
2 DMAX
PWM Output circuit
Cs: Soft start capacitor [F]
OSC
1
RT Soft start circuit
Fig. 7
FB pin voltage Oscillator output DT voltage CS pin voltage
OUT pin output
Fig. 8
Soft start timing chart
10
FA551X
3.2 Overload shutdown function Figure 9 shows the overload shutdown circuit, and Figure 10 is a timing chart that illustrates overload shutdown operation. If the output voltage drops due to an overload or short circuit, the FB pin output voltage rises. If the FB pin voltage exceeds the reference voltage (3.5V) of comparator C3, the output of comparator C3 goes low to turn off the switch. With the switch off, the CS pin voltage clamped at 4.0V by zener diode in normal operation is unclamped, and the constant current source (5.2A) begins to charge capacitor Cs again and the CS pin voltage rises. When the CS pin voltage exceeds the reference voltage (8.5V) of comparator C2, the output of comparator C2 toggles to turn off the 5V REF circuit. The IC then enters the latched mode and shuts down the output. IC current consumption for shutdown is 45A (typ) (Vcc=10V). This current must be supplied through the startup resistor. The IC enters output off (low voltage) state. The overload shutdown operation can be reset by lowering the supply voltage Vcc to below the OFF threshold voltage (9.0V) or forcing the CS pin voltage below 7.9V. The period tOL from the time the output is short-circuited to the time the output circuit goes off is given by the following equation: tOL [ms] 870 CS [ms] ..................................................... (4)
Comparator C2 reference voltage (8.5V) CS pin voltage DT voltage FB pin voltage Oscillator output OUT pin voltage REF pin voltage
H L ON OFF
(9.5V)
(4V)
(0V)
Overload detection Overload shutdown
Fig. 10
Overload shutdown timing chart
ON/OFF control
Cs CS VCC
8 0.8/0.68V 5.2A 6
REF 7
5V VCC ENB
C1 C2
5V REF
8.5/7.9V
Cs: Soft start capacitor [F]
UVLO PWM FB 2
DMAX
When you want to disable the overload shutdown function, see item 9 in "Design advice" 3.3 Output ON/OFF control function The IC can be turned on or off via an external signal applied to the CS pin. Figure 11 shows the output on/off control circuit, and Figure 12 is a timing chart. The IC is turned off when the CS pin voltage is externally made to drop below 0.68V (typ). The output of comparator C1 goes high to turn the 5V REF circuit off. This shuts the output down. The IC enters output off (low voltage) state. Required IC current consumption during shutdown is 80A (typ) (Vcc=17V). This current must be supplied through the startup resistor. The IC goes on when the CS pin is opened and the CS pin voltage exceeds 0.80V (typ). This turns the 5V REF circuit on and results in automatic soft start. The power supply then restarts operation.
Output circuit
OSC
1
RT
Fig. 11
External output ON/OFF control circuit
CS pin voltage DT voltage FB pin voltage Oscillator output Comparator C1 reference voltage (0.8/0.68V) OUT pin output
(4V)
H L
Cs
CS VCC
8 0.8/0.68V 5.2A C2 8.5/7.9V 3.5V UVLO C3 4V PWM 6
REF pin voltage
ON OFF
REF 7
C1 5V VCC ENB 5V REF
ON mode
OFF mode
Fig. 12
Output ON/OFF control circuit timing chart
FB 2
DMAX OSC
Output circuit
1
RT
Fig. 9
Overload shutdown circuit
11
FA551X
4. Overcurrent limiting circuit The overcurrent limiting circuit detects the peak value of every drain current pulse (pulse by pulse method) of the main switching MOSFET to limit the overcurrent. The detection threshold voltage is +0.24V for FA5510/11 or -0.17V for FA5514/15 with respect to the ground as shown in Figure 13 and Figure 14. The drain current of the MOSFET is converted to voltage by resistor Rs and fed to the IS pin of the IC. If the voltage exceeds the reference voltage +0.24V (FA5510/11) or -0.17V (FA5514/15) of comparator C4, comparator C4 works to set flip-flop output Q to high. The output is immediately turned off to shut off the current. Flip-flop output Q is reset on the next cycle to turn on the output again. This operation is repeated to limit the overcurrent. If the overcurrent limiting circuit malfunctions due to noise, place an RC filter between the IS pin and MOSFET as shown in Figure 13 and Figure 14. (See item 12 in "Design advice.") Figure 15 is a timing chart that illustrates overcurrent-limiting operations. 5. Vcc overvoltage protection circuit The IC contains a Vcc overvoltage protection circuit to protect the IC from damage by overvoltage. Figure 16 shows the overvoltage protection circuit. Figure 17 is a timing chart that illustrates overvoltage protection operations. Overvoltage is detected if the supply voltage Vcc rises to 31.8V (Icc=14mA) or more and current flows in the built-in zener diode. The output of comparator C5 then goes high and the constant current source (0.95mA) raises the CS pin voltage. When the CS pin voltage exceeds 8.5V, the output of comparator C2 goes high to turn off the 5V REF circuit. The IC then enters the latched mode and the IC output is put in the off (low voltage) state. When latched mode, the IC current consumption is 45A (typ) (Vcc=10V). This current must be supplied through the startup resistor. The overvoltage shutdown operation can be reset by lowering the supply voltage to below 9.0V or forcing the CS pin voltage below 7.9V. (When you want to enable Vcc overvoltage shutdown at a desired voltage, see item 6 in "Design advice.")
FA5510/11
PWM CS pin FB pin Oscillator O.C.P. 0.24V C4 3 C R R Q S F.F 4 Rs OSC UVLO OUT Output pin circuit
Comparator C2 reference voltage (8.5V) CS pin voltage DT voltage FB pin voltage Osillator output OUT pin voltage REF pin voltage
H L ON OFF
CS pin voltage (4V) DT voltage FB pin voltage Oscillator output OUT pin output Comparator C4 reference voltage
FA5510/11:+0.24V FA5514/15:-0.17V H L
IS pin voltage REF pin voltage ON
OFF
Overcurrent limiting
Fig. 15
Overcurrent timing chart
~
Vin
+
~
-
Cs
8 0.8/0.68V 0.95mA
CS
6
VCC
15.5V
REF 7
5V VCC ENB
C1 C2
5V REF
C5
0.8V
15.5V
8.5/7.9V 3.5V
UVLO C3
4V
PWM FB 2
DMAX
Output circuit
OSC
1
RT
Fig. 16
Overvoltage shutdown circuit
(9.5V)
(4V)
IS(+)
GND
(0V)
Fig. 13
Overcurrent limiting circuit (FA5510/11)
Overvoltage detection
Shutdown
FA5514/15
PWM CS pin FB pin Oscillator O.C.P. -0.17V C4 R Q S F.F 4 C R OSC UVLO OUT Output pin circuit
Fig. 17
Overvoltage shutdown timing chart
Rs
IS(-)
3
GND
Fig. 14
Overcurrent limiting circuit (FA5514/15)
12
FA551X
6. Undervoltage lockout circuit (U.V.L.O.) The IC incorporates a circuit that prevents the IC from malfunctioning when the supply voltage drops. When the supply voltage is raised from 0V, the IC starts operation with Vcc=16.5V (typ). If the supply voltage drops, the output is shut down when Vcc=9.0V (typ). When the undervoltage lockout circuit operates, the outputs of the OUT and CS pins go low to reset the IC. 7. Output circuit The IC contains a push-pull output stage and can directly drive the MOSFET. The absolute maximum rating of OUT pin peak current is 1.5A. But when using in actual circuit, the output peak current depends on the characteristics of the MOSFET, resistance between the OUT pin and the MOSFET, supply voltage, temperature and so. When supply voltage is relatively low or temperature is relatively high, the output peak current may not reach the maximum ratings. Note that the output current causes loss of the output stage. The total loss caused by the operating current and the output current should be within the ratings in actual circuit.
13
FA551X
Design advice
1. Deciding the startup circuit These ICs, which use CMOS process, consume less current, and therefore can use larger startup resistance than the conventional bipolar type of IC. To decide the startup resistance, the following conditions must be satisfied: (a) The IC is started when the power is turned on. (b) The IC consumption current is supplied during latch mode operation to maintain the latch state. (c) The IC consumption current is supplied during the off state under the on/off function to maintain the off state. However, these are the minimum conditions for using the IC. The startup time required for the power supply must also be decided on.
Fig. 18 Startup circuit (1)
AC INPUT
~
DB
~ +
T1 C1
R1
D1 C2
6
VCC
FA551X
5
MOSFET
OUT
Rs
1.1 Connecting the startup resistor before rectification (AC line) When the startup resistor is connected before rectification (AC line) as shown in Figure 18, the voltage applied to the startup resistor forms a half-wave rectified waveform of the AC input voltage. Startup resistor R1 must satisfy the three equations shown below. Select a smaller-side value for R1 in consideration of the temperature characteristics. (a) To supply startup current 30A at ON threshold voltage 17.5V (max.) of UVLO: 2 Vac - 17.5 ...................................................... (5) 0.03
R1
(b) To supply IC consumption current 80A (max.) (Vcc=10V) in latch mode: 2 Vac - 10 ........................................................ (6) 0.08
R1
(c) To supply IC consumption current 200A (max.) (Vcc=17V) in the off state under the on/off function: 2 Vac - 17 ........................................................ (7) 0.2
R1
R1: Startup resistance [k] Vac: Effective value of AC input voltage [V]
If neither the latch mode operation nor the on/off functions are used, only the expression in (5) needs to be satisfied. In this method, the supply current to the IC via the start-up resistor is stopped when AC input is shut down. Therefore, after latch mode operation, shutting the AC input down resets the latch mode in a very short period of time.
14
FA551X
1.2 Connecting the startup resistor after rectification (DC line) When the startup resistor is connected after rectification (DC line) as shown in Figure 19, the voltage applied to the startup resistor becomes the peak value of the AC input voltage. Startup resistor R1 must satisfy the three equations shown below. Select a smaller-side value for R1 in consideration of temperature characteristics. (a) To supply startup current 30A at ON threshold voltage 17.5V (max.) of UVLO: R1 2 Vac - 17.5 ...................................................... (8) 0.03
DB AC INPUT
~+
C1
T1
~-
R1 D1 C2
6
VCC
FA551X
5
MOSFET
OUT
Rs
(b) To supply IC consumption current 80A (max.) (Vcc =10V) in latch mode: R1 2 Vac - 10 0.08 ........................................................ (9)
Vcc
Fig. 19
Startup circuit (2)
(c) To supply IC consumption current 200A (max.) (Vcc = 17V) in the off state under the on/off function: R1 2 Vac - 17 ...................................................... (10) 0.2
UVLO ON UVLO OFF
Vcc must not drop to UVLO OFF.
R1: Startup resistance [k] Vac: Effective value of AC input voltage [V]
Auxiliary winding voltage Time t
Fig. 20 Vcc voltage at startup with a adequate capacitor
If neither the latch nor the on/off functions are used, only the expression in (8) needs to be satisfied. In this method, after latch mode operation, smoothing capacitor C1 in the main circuit supplies current to the IC via the startup resistor even if the AC input is shut down. Therefore, some time must elapse before the latch mode is reset. 2. Determining the Vcc capacitor value To properly start the power supply, a certain value is required for the capacitor connected to the VCC pin. Figure 20 shows the Vcc voltage at start-up when a proper value is given to the capacitor. When the input power is turned on, the capacitor connected to the VCC pin is charged via the startup resistor and the voltage increases. The IC is then in standby state and almost no current is consumed. (Icc<2A) Thereafter, Vcc reaches the ON threshold voltage of UVLO and the IC begins operation. When the IC begins operation to make output, the IC operates based on the voltage from the auxiliary winding. When the IC is just starting up, however, it takes time for the voltage from the auxiliary winding to rise enough, and Vcc drops during this period. Determine the Vcc capacitor value so that Vcc will not drop down to the OFF threshold voltage of UVLO during this period. If the Vcc capacitor value is too small, Vcc will drop to the OFF threshold voltage of UVLO before the auxiliary winding voltage rises enough. If so, Vcc repeatedly goes up and down between the UVLO threshold voltages, and the power supply cannot start up. (Figure 21)
Vcc UVLO ON UVLO OFF
Time t
Fig. 21 Vcc voltage at startup with a inadequate capacitor
15
FA551X
3. The startup period The start up period from the time the power is on to the time the IC is turn to on is approximately given by: tstart-up = -C2 R1 In 1 -
R1
D1 C2
(
16.5 V1
)
VCC
................................. (11)
6
Where: R1: Startup resistor [] C2: Capacitor between VCC and GND pin [F] Vac: Effective value of AC input voltage [V]
FA551X
Fig. 22 Startup circuit (3)
V1=
To shorten the start-up period, the capacitor C2 or resistor R1 should be decreased. But in some case, such as when the load current of the power supply is changed rapidly, you may want to prolong the hold time of the Vcc voltage over the off threshold. In this case the capacitor C2 cannot be decreased and the resistor R1 should be decreased. But loss of the resistor R1 increases. In such case, the circuit shown in Fig. 23 is effective to shorten start-up period without increasing the loss of the resistor R1. The capacitor C2 is decreased to shorten the start-up period and, after the IC starts up, Vcc voltage supplied from C3 to prolong the hold time of the Vcc voltage. The start-up period of this circuit also is approximately given by the expression in (11) 4. Setting soft start period and OFF latch delay independently Figure 24 shows a circuit for setting the soft start period and OFF latch delay independently. In this circuit, capacitance CS determines the soft start period, and capacitance CL determines the OFF latch delay. If the overload shutdown or overvoltage shutdown functions raise the CS pin voltage to around 5V, zener diode Zn becomes conductive to charge capacitor CL. The OFF latch delay can be thus prolonged by capacitance CL. 5. Overvoltage protection using the VCC pin These ICs contain an overvoltage protection function detecting the Vcc voltage using internal ZD (See item 5 in "Description of each circuit"). If Vcc voltage exceed 31.8V, the current of 14mA flows through the internal ZD and the overvoltage protection function operates. After this protection function operates, the IC continues to consume the large current if high voltage continues to be applied to the Vcc pin. Mind that total IC loss does not exceed the rating. If the voltage source applied to Vcc pin has relatively high impedance and cannot supply the current of 14mA, overvoltage protection function does not operate. But the internal ZD maintains the Vcc voltage 32V or less and protects the IC.
16

2 2
Vac ..... (Connecting a startup resistor before rectification) Vac ....... (Connecting a startup resistor after rectification)
R1
D1 C2
D2 C3
VCC
6
FA551X
Fig. 23
Startup circuit (4)
CL Zn 5V
Cs
CS
8
FA551X
4
GND
Fig. 24 Independent setting of soft start period and OFF latch deley
FA551X
6. Overvoltage protection using CS pin These ICs contain the overvoltage protection function detecting Vcc voltage. However, the threshold voltage is fixed. Adding a circuit to CS pin enables the overvoltage protection detecting desired voltage. 6.1 Detecting on secondary side Figure 25 shows the overvoltage shutdown circuit based on the signal from the secondary side. The optocoupler output transistor is connected between the CS and VCC pins. When the output voltage is put in the overvoltage state, the optocoupler output transistor goes on to raise the CS pin voltage via resistor R2. When the CS pin voltage exceeds the reference voltage (8.5V) of internal comparator, the IC enters the OFF latch mode and shuts the output down. The IC consumes current 45A (typ) (Vcc=10V) in latch mode. This current must be supplied via startup resistor R1. The overvoltage protection circuit can be reset by lowering the supply voltage Vcc to below 9.0V or forcing the CS pin voltage below 7.9V. In normal operation, the CS pin voltage is clamped by the 4V zener diode with maximum sink current 45A . Therefore, to raise the CS pin voltage to 8.5V or more, 45A or a higher current needs to be supplied from the optocoupler. Set the current input to the CS pin to 1mA or less. 6.2 Detecting on primary side (detecting Vcc voltage) To attain overvoltage protection, the CS pin voltage is forcibly raised from outside the IC until it exceeds the reference voltage (8.5V) of the internal comparator C2. When the reference voltage is exceeded, the IC enters latch mode and shuts the output down. Connect a zener diode (ZD) and resistor between the VCC and CS pins as shown in Figure 26. When the Vcc voltage exceeds about ZD voltage +8.5V, the IC enters the OFF latch mode and shuts the output down. If Vcc remains high even after shutdown and current is input to the CS pin, set the current to 1mA or lower. Set the zener voltage of the ZD connected to the CS pin higher than the UVLO ON threshold voltage. Startup is disabled below this voltage. Figure 27 shows another circuit for enabling latch mode shutdown by detecting a desired Vcc voltage using the CS pin. In this circuit, overvoltage shutdown works when the Vcc voltage is about the same as the ZD voltage. For this circuit also, use a ZD voltage higher than the UVLO ON threshold voltage. Set the current flowing into the CS pin to 1mA or lower. 7. Feedback pin circuit Figure 28 gives an example of connection in which a feedback signal is input to the FB pin. If this circuit causes power supply instability, connect R3 and C4 as shown in Figure 28 to decrease the frequency gain. Set R3 between several tens of ohms to several kilohms and C4 between several thousand picofarads to one microfarad. If noise is applied to the FB pin, the output pulses may be lacked or disturbed. In this case, connect a capacitor C5 as shown in Fig. 29 to suppress the noise applied to the FB pin. Set the capacitance of C5 less than 10% of capacitance of C4 and connect C5 as near the IC as possible.
~+
Vin
~-
C1
Vout
R1 R2 PC Cs C2
VCC
6
8
CS
FA551X
4
GND
Fig. 25 Overvoltage shutdown circuit (1)
CS VCC
R2 ZD
8 6
Fig. 26
Overvoltage shutdown circuit (2)
VCC
6
R2
8
ZD
CS
Fig. 27
Cs
Overvoltage shutdown circuit (3)
Vout
5
PC1 FA551X OUT Rs 2 FB R3 C4 PC1
Shunt regulator
Fig. 28
FB pin circuit (1)
FA551X OUT Rs 4 2 FB GND
C5 R3 C4 PC1
5
Fig. 29
FB pin circuit (2)
17
FA551X
8. Simple voltage control on the primary side In a flyback type power supply, the output voltages of the power supply and auxiliary winding voltage are almost proportional to the number of winding turns of the transformer. This characteristic can be used in the circuit shown in Figure 30, where the output voltage can easily be made constant by detecting the auxiliary winding voltage. However, this is an easy output voltage control method, and the output voltage precision and regulation are therefore not as good. To reduce output pulse width completely to 0%, the FB pin voltage must fall below 0.9V and R5 must be set below about 1k from the characteristics of the FB pin voltage and source current. 9. Disabling the overload shutdown function As shown in Figure 31, connect a 10k resistor R6 between the FB pin and the ground. The FB pin voltage then does not rise sufficiently high to reach the shutdown threshold voltage when an overload occurs so that IC does not enter OFF latch mode. Use a 5% or better-precision resistor for R6. Even with this connection, the overvoltage shutdown function is available. 10. Polarities for overcurrent detecting and their characteristics The FA5510/11 uses positive polarity detection for overcurrent limiting (number 3 pin of IS pin) and the FA5514/15 uses negative polarity detection. The characteristics of positive and negative polarity detection are summarized below. Select one in accordance with the circuit used. (See item 4 in "Description of each circuit.") Positive detection (FA5510/11) * Wiring is easy because the ground can be shared by the main circuit and IC peripherals. * It is easy to correct the current detected as overload against the input voltage. Negative detection (FA5514/15) * The MOSFET drive current does not flow to the current detection resistor and therefore it hardly affects overcurrent detection. 11. Correcting overload detection current (FA5510/11 only) If the power supply output is overloaded, the overcurrent limiting function restricts the output power and the overload shutdown function stops the IC. The output current when an overload occurs varies depending on the input voltage; the higher the input voltage, the more the overload detection current may increase. If any problems occur as a result of the appearance of this symptom, connect resistor R8 between current detection resistor Rs and the IS (+) pin and add resistor R7 for correction as shown in Figure 32. The standard resistance of R8 is several hundred ohms, and that of R7 is from several hundred kilohms to several megohms. Note that the above correction slightly lowers the output current when overload even where the input voltage is low. This correction is available only for the FA5510/11 that uses positive polarity for overcurrent detection.
C1
n1
n2
Vout
VCC
6
7
REF FA551X 2 GND 4 FB
R5
n3 C2
Fig. 30
Simple voltage control circuit
FA551X GND FB 2 4
R3 R6 10k C4
Fig. 31
Disabling overload shutdown function
DB
~+
T1 C1
AC input
~-
FA5510/11 IS(+)
3
R7 R8 Rs
Fig. 32
Correction of overload detection current
18
FA551X
12. Preventing malfunction caused by noise Noise applied to each pin may cause malfunction of the IC. If noise causes malfunction, see the notes summarized below and confirm in actual circuit to prevent malfunction. * The IS pin for overcurrent limiting function detects the MOSFET current converted to the voltage. The parasitic capacitor and inductor of the MOSFET, transformer, wiring, etc. cause a noise in switching operation. If this switching noise causes a malfunction of overcurrent limitimg function, insert the RC filter into IS pin as shown in Figure 13 and 14. Connect this capacitor as near the IC as possible to suppress noise effectively. * Connect a noise prevention capacitor (0.1F or more) to the REF pin that outputs the reference voltage for each component. * If noise is applied to the FB pin, the output pulses may be disturbed. In this case, see item 7 in "Design advice." * Relatively large noise may occur at the VCC pin because large current flows from VCC pin to drive the MOSFET. Then this noise may cause malfunction of the IC. In addition, the IC may stop operation when Vcc voltage drops below the off threshold voltage by noise. Mind that capacitance and characteristics of the capacitor connected between VCC and GND pin not to allow the large noise at the VCC pin. To prevent malfunction, suppress the noise width below about 0.5s or less and noise voltage below about 0.6V or less. 13. Preventing malfunction caused by negative voltage applied to a pin When large negative voltage is applied to each IC pin, a parasitic element in the IC may operate and cause malfunction. Be careful not to allow the voltage applied to each pin to drop below -0.3V. Especially for the OUT pin, voltage oscillation caused after the MOSFET turns off may be applied to the OUT pin via the parasitic capacitance of the MOSFET, causing the negative voltage to be applied to the OUT pin. If the voltage falls below -0.3V, add a Schottky diode between the OUT pin and the ground. The forward voltage of the Schottky diode can suppress the voltage applied to the OUT pin. Use the low forward voltage of the Schottky diode. Similarly, be careful not to cause the voltages at other pins to fall below -0.3V. 14. Gate circuit configuration To adjust switching speeds or prevent oscillation at gate terminals, resistors are normally inserted between the power MOSFET gate terminal to be driven and the OUT pin of the IC. You may prefer to decide on the drive current independently, to turn the MOSFET on and off. If so, connect the MOSFET gate terminal to the OUT pin of the IC as shown in Figure 34. In this circuit, Rg1 and Rg2 restrict the current when the MOSFET is turned on, and only Rg1 restricts the current when it is turned off.
OUT FA551X GND
4 5
SBD
Fig. 33
Protection of OUT pin against the negative voltage
Rg1 Rg2
FA551X
5
OUT
Gate circuit
Fig. 34
19
FA551X
15. Loss calculation IC loss must be confirmed to use the IC within the ratings. Since it is hard to directly measure IC loss, some examples of calculating approximate IC loss are given below. 15.1 Calculation example 1 Suppose the supply voltage is Vcc, IC current consumption is lccop, the total gate charge of the power MOSFET is Qg, and the switching frequency is fSW. Total IC loss Pd can be calculated by: Pd VCC (ICCOP + Qg fsw) ........................................ (12) When gate resistance differs between ON and OFF as shown in Figure 36, the loss is given by: Pdr = 1 2 VCC Qg fsw Ron Roff ( Rg1+Rg2+Ron + Rg1+Roff ) .... (15)
Example: When Vcc=18V, Qg=80nC, fsw=100kHz, and Rg=10, the typical IC loss is given by: Pdr = 1 2 18V 80nC 100kHz 15 7 ( 10+15 + 10+7 )
This expression calculates an approximate value of Pd, which is normally a little larger than the actual loss. Since various conditions such as temperature characteristics apply, thoroughly verify the appropriateness of the calculation under all applicable conditions. Example: When Vcc=18V, lccop=2.5mA (max.) is obtained from the specifications. Suppose Qg=80nC and fsw=100kHz. Pd 18V (2.5mA + 80nC 189mW 100kHz)
=72.8mW
15.2.3 Total loss The total loss (Pd) of the IC is the sum of the control circuit loss (Pop) and the output circuit loss (Pdr) calculated previously: Pd = Pop + Pdr .................................................................. (16) Example: The standard IC loss under the conditions used in (1) and (2) above are: Pd = Pop + Pdr = 27mW + 72.8mW = 99.8mW
15.2 Calculation example 2 The IC loss consists of the loss caused by operation of the control circuit and the loss caused at the output circuit to drive the power MOSFET. 15.2.1 Loss at the control circuit The loss caused by operation of the IC control circuit is calculated by the supply voltage and IC current consumption. When the supply voltage is Vcc and IC current consumption is lccop, loss Pop at the control circuit is: Pop = VCC ICCOP ........................................................... (13)
6
VCC OUT
5
Qon
Qoff
Rg
Example: When Vcc=18, lccop=1.9mA (typ) is obtained from the specifications. The typical IC loss is given by: Pop = 18V 1.5mA = 27mW
4
GND
Fig. 35 Output Circuit (1)
15.2.2 Loss at the output circuit The output circuit of the IC is a MOSFET push-pull circuit. When the ON resistances of MOSFETs making up the output circuit are Ron and Roff, the resistances can be determined as shown below based on Vcc=18V and Tj = 25C obtained from the output characteristics shown in the specifications: Ron = 15 (typ), Roff=7 (typ) When the total gate charge of the power MOSFET is Qg, the switching frequency is fSW, the supply voltage is Vcc, and gate resistance is Rg, the loss caused at the IC output circuit is given by: Pdr = 1 2 VCC Qg fsw
6
VCC OUT
5
Qon
Qoff
4
Rg1
Rg2
GND
Fig. 36 Output Circuit (2)
( RgRon + RgRoff ) ...... (14) + Ron + Roff
20
FA551X
Application circuit FA5510
T1 80 to F1 C114 C103 144V AC 250V/5A 0.47F 4700p R101 510K R102 510K C104 4700p L2 C102 D3SBA60 0.22F R103 100k R104 100k R109 10 R119 33k PC2 R107 680 IC1
1234 8765 R105 47k
D1
TH1 8D11
C203 1000pF C105 200V/1000F D2 ERA22-10
D201
L201 150H
+24V 0 to 8.4A
TH2 8D11
ESAD92M-02 C201 2200F C207 0.1F
FG
Q1 2SK1938
4.7k R110
R210 100 R209 470 PC2 R112 0.05 R102 D4 2.2 D4 ERA91-02 ZD201 27V R207 2.4k PC1 R208 1k R206 1k C205 1000pF R205 C202 IC2 10k 0.1F R203 2.2k
C204 0.022F
GND
R201 18k R202 1k C206 0.1F
C107
0.1F
PC1 R117 2k
C106 47F
FA5510
C115 1000pF 2200pF C108
C109 0.22F
C110 0.22F
R106 33
FA5511
C113 80 to 264V AC R101 510K R102 430K F1 250V/3A C104 470p L1 C102 D3SBA60 0.22F R103 130k R104 130k R109 10 R108 100 R107 680
1234 R105 62k D5 ERA91-02
C101 C103 0.22F 470p
2200p DB TH1 5D11 T1 C105 400V/220F ZD1 180V D2 ERA22-10 Q1 2SK2101
4.7k R110
D201
L201 10H
+24V 0 to 1.46A (Peak:2.71A)
YG902C C201 2200F C202 470F
FG
C204 0.022F R207 2.4k PC1 R112 0.1 R102 D4 ERA91-02 R206 1k R201 18k R202 1k
GND
R205 33k IC2
C203 0.1F R203 2.2k
IC1
8765
C107 0.1F
R117
1k
C106 10F
100pF
FA5511 C109 0.22F C110 0.22F
R106 24
C108
21
FA551X
FA5514
T1 80 to C114 C103 144V AC F1 250V/5A 0.47F 4700p R101 510K R102 510K C104 4700p L2 C102 D3SBA60 0.22F R103 100k R104 100k R109 10 R119 33k PC2 R107 680 IC1
1234 8765
D1
TH1 8D11 D2 ERA22-10
C203 1000pF C105 200V/1000F
D201
L201 150H
+24V 0 to 8.4A
TH2 8D11
ESAD92M-02 C201 2200F C207 0.1F
FG
Q1 2SK1938
R110 4.7k
R210 100 R209 470 PC2 R112 0.05 R102 D4 2.2 D4 ERA91-02 ZD201 27V R207 2.4k PC1 R208 1k R206 1k C205 1000pF R205 C202 IC2 10k 0.1F R203 2.2k
C204 0.022F
GND
R201 18k R202 1k C206 0.1F
R105 47k
C107
0.1F
PC1 R117 C108 820
C106 47F
C115 1000pF
2200pF
FA5514 C109 0.22F C110 0.22F
R106 33
FA5515
C113 80 to 264V AC R101 510K R102 430K F1 250V/3A C104 470p L1 C102 D3SBA60 0.22F R103 130k R104 R109 10 R108 100 R107 680
1234 R105 D5 ERA91-02
C101 C103 0.22F 470p
2200p DB TH1 5D11 T1 C105 400V/220F ZD1 180V D2 ERA22-10 Q1 2SK2101
4.7k R110
D201
L201 10H
+24V 0 to 1.46A (Peak:2.71A)
YG902C C201 2200F C202 470F
FG
C204 0.022F R207 2.4k PC1 R112 0.05 R206 1k R201 18k R202 1k
GND
130k
R205 33k D4 ERA91-02 IC2
C203 0.1F R203 2.2k
IC1
8765
62k C107 0.1F
C106 10F
FA5515
C108 100pF
C109 0.22F
C110 0.22F
R106 24
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.
22

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