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MITSUBISHI (Dig./Ana. INTERFACE)
M51995AP/FP
SWITCHING REGULATOR CONTROL DESCRIPTION
M51995A is the primary switching regulator controller which is especially designed to get the regulated DC voltage from AC power supply. This IC can directly drive the MOS-FET with fast rise and fast fall output pulse. Type M51995A has the functions of not only high frequency OSC and fast output drive but also current limit with fast response and high sensibility so the true "fast switching regulator" can be realized. It has another big feature of current protection to short and over current,owing to the integrated timer-type protection circuit,if few parts are added to the primary side. The M51995A is equivalent to the M51977 with externally resettable OVP(over voltage protection)circuit. COLLECTOR VOUT EMITTER VF ON/OFF OVP DET F/B
1 2 3 4 5 6 7 8 16 15 14 13 12 11 10 9
PIN CONFIGURATION (TOP VIEW)
Vcc CLM+ CLMGND CT T-OFF CF T-ON
Outline 16P4
FEATURES
500kHz operation to MOS FET *Output current...............................................................2A *Output rise time 60ns,fall time 40ns *Modified totempole output method with small through current Compact and light-weight power supply *Small start-up current............................................90A typ. *Big difference between "start-up voltage" and "stop voltage" makes the smoothing capacitor of the power input section small. Start-up threshold 16V,stop voltage 10V *Packages with high power dissipation are used to with-stand the heat generated by the gate-drive current of MOS FET. 16-pin DIP,20-pin SOP 1.5W(at 25C) Simplified peripheral circuit with protection circuit and built-in large-capacity totempole output *High-speed current limiting circuit using pulse-by-pulse method(Two system of CLM+pin,CLM-pin) *Protection by intermittent operation of output over current...... ..........................................................Timer protection circuit *Over-voltage protection circuit with an externally re-settable latch(OVP) *Protection circuit for output miss action at low supply voltage(UVLO) High-performance and highly functional power supply *Triangular wave oscillator for easy dead time setting HEAT SINK PIN
6 15 14 13 12 11
COLLECTOR VOUT EMITTER VF
1 2 3 4 5
20 19 18 17 16
Vcc CLM+ CLMGND HEAT SINK PIN
ON/OFF OVP DET F/B
7 8 9 10
CT T-OFF CF T-ON
Outline 20P2N-A Connect the heat sink pin to GND.
APPLICATION
Feed forward regulator,fly-back regulator
RECOMMENDED OPERATING CONDITIONS
Supply voltage range............................................12 to 36V Operating frequency.................................less than 500kHz Oscillator frequency setting resistance *T-ON pin resistance RON...........................10k to 75k *T-OFF pin resistance ROFF..........................2k to 30k
( 1 / 27 )
MITSUBISHI (Dig./Ana. INTERFACE)
M51995AP/FP
SWITCHING REGULATOR CONTROL BLOCK DIAGRAM
VCC 7.1V 5.8V ON/OFF UNDER VOLTAGE LOCKOUT VOLTAGE REGULATOR 15.2K 1S 3K 500 F/B DET GND
6S
OP AMP
1S OVP(shut down) LATCH
1S 2.5V COLLECTOR
PWM COMPARATOR
PWM LATCH
VOUT EMITTER
OSCILLATOR CAPACITANCE CF
OSCILLATOR RESISTANCE T-ON (ON duty) OSCILLATOR RESISTANCE T-OFF (OFF duty)
OSCILLATOR (TRIANGLE)
+CURRENT LIMIT LATCH
-CURRENT LIMIT LATCH
INTERMITTENT ACTION AND OSC CONTROL
INTERMITTENT ACTION
VF
CLM+ +CURRENT LIMIT
CLM-CURRENT LIMIT
CT INTERMITTENT OPERATION DETERMINE CAPACITANCE
ABSOLUTE MAXIMUM RATINGS
Symbol VCC VC IO VVF VON/OFF VCLMVCLM+ IOVP VDET IDET VFB ITON ITOFF Pd K Topr Tstg Tj Parameter Supply voltage Collector voltage Output current VF terminal voltage ON/OFF terminal voltage CLM-terminal voltage CLM+terminal voltage OVP terminal current DET terminal voltage DET terminal input current F/B terminal voltage T-ON terminal input current T-OFF terminal input current Power dissipation Thermal derating factor Operating temperature Storage temperature Junction temperature Peak Continuous Conditions Ratings 36 36 2 0.15 Vcc Vcc -4.0 to +4.0 -0.3 to +4.0 8 6 5 0~10 -1 -2 1.5 12 -30 to +85 -40 to +125 150 Unit V V A V V V V mA V mA V mA mA W mW/C C C C
Ta=25C Ta>25C
Note 1."+" sign shows the direction of current flow into the IC and "-" sign shows the current flow from the IC. 2.This terminal has the constant voltage characteristic of 6 to 8V,when current is supplied from outside.The maximum allowable voltage is 6V when the constant voltage is applied to this terminal.And maximum allowable current into this terminal is 5mA. 3.The low impedance voltage supply should not be applied to the OVP terminal.
( 2 / 27 )
MITSUBISHI (Dig./Ana. INTERFACE)
M51995AP/FP
SWITCHING REGULATOR CONTROL ELECTRICAL CHARACTERISTICS (VCC=18V, Ta=25C, unless otherwise noted)
Block
Symbol
Parameter
Test conditions
Min.
Vcc(STOP)
Limits Typ. 16.2 9.9 6.3 90 90 15 1.31 90 1.35 160 2.0 200 2.6 2.4 0.2 -1.54 -0.55 -0.99 5.9 600 2.5 1.0 40 750 30 150 150 9.0 1.20 -320 -140 0.40 -138 -127 -105 8.7 -200 -125 100 200 -205 100
Operating supply voltage range VCC VCC(START) Operation start up voltage VCC(STOP) Operation stop voltage Vcc IccL IccO Icc OFF Icc CT Icc OVP VTHH ON/OFF VTHL ON/OFF VTHON/OFF IFBMIND IFBMAXD IFB VFB RFB VDET IINDET GAVDET VTHOVPH VTHOVP ITHOVP IINOVP VCCOVPC VCC(STOP)
-VCCOVPC
15.2 9.0 Vcc=Vcc(START) -Vcc(STOP) Vcc=14.5V,Ta=25C Vcc=14.5V,-30Ta85C Vcc=30V Vcc=25V Vcc=14V Vcc=25V Vcc=14V Vcc=25V Vcc=9.5V 5.0 50 40 10 0.95 50 0.95 1.3 125 2.1 1.9 0.1 F/B terminal input current F/B terminal input current IFB=IFBMIND-IFBMAXD F/B terminal input current=0.95mA -2.1 -0.90 -1.35 4.9 420 2.4 30 540 VTHOVP=VTHOVPH-VTHOVPL VOVP=400mV OVP terminal is open. (high impedance) Vcc=30V Vcc=18V CT=4.7F VCT=3.3V,Ta=-5C Ta=25C Ta=85C -5Ta85C VCLM-=-0.1V -5Ta85C VCLM+=0V 80 80 7.5 0.55 -480 -210 0.27 -193 -178 -147 7.0 -220 -170 180 -270
Max. 35 17.2 10.9 7.6 140 190 21 5.0 140 2.0 240 3.0 310 3.1 2.9 3.0 -1.0 -0.40 -0.70 7.1 780 2.6 3.0 960 250 250 10.0
Unit V V V V A A mA mA A mA A mA A V V V mA mA mA V V A dB mV mV A A V V
Difference voltage between operation start and stop Stand-by current Operating circuit current Circuit current in OFF state Circuit current in timer OFF state Circuit current in OVP state
ON/OFF terminal high threshold voltage ON/OFF terminal low threshold voltage ON/OFF terminal hysteresis voltage
Current at 0% duty Current at maximum duty
Current difference between max and 0% duty
Terminal voltage Terminal resistance Detection voltage Input current of detection amp Voltage gain of detection amp OVP terminal H threshold voltage OVP terminal hysteresis voltage OVP terminal threshold current OVP terminal input current OVP reset supply voltage Difference supply voltage between operation stop and OVP reset Current from OVP terminal for OVP reset Timer frequency Timer charge current OFF time/ON time ratio CLM- terminal threshold voltage CLM- terminal current Delay time from CLM- to VOUT CLM+ terminal threshold voltage CLM+ terminal current Delay time from CLM+ to VOUT
VDET=2.5V
ITHOVPC fTIMER ITIMECH TIMEOFF/ON VTHCLMIINCLMTPDCLMVTHCLM+ IINCLM+ TPDCLM+
-213 -93 0.60 -102 -94 -78 11.0 -180 -90 220 -140
A Hz A
mV A ns mV A ns
(3
/ 27 )
MITSUBISHI (Dig./Ana. INTERFACE)
M51995AP/FP
SWITCHING REGULATOR CONTROL ELECTRICAL CHARACTERISTICS (VCC=18V,Ta=25C, unless otherwise noted)(CONTINUE)
Block
Symbol fOSC TDUTY VOSCH VOSCL VOSC fOSCVF TVFDUTY VTHTIME IVF VOL1 VOL2 VOL3 VOL4 VOH1 VOH2 TRISE TFALL
Parameter Oscillating frequency Maximum ON duty Upper limit voltage of oscillation waveform Lower limit voltage of oscillation waveform Voltage difference between upper limit and lower limit of OSC waveform VF=5V OSC frequency in CLM operating state VF=2V Duty in CLM operating state VF=0.2V VF voltage at timer operating start VF terminal input current Output low voltage
Test conditions RON=20k,ROFF=17k CF=220pF,-5Ta85C fOSC=188kHz fOSC=188kHz fOSC=188kHz RON=20k,ROFF=17k CF=220pF Min off duty/Max on duty Source current Vcc=18V,Io=10mA Vcc=18V,Io=100mA Vcc=5V,Io=1mA Vcc=5V,Io=100mA Vcc=18V,Io=-10mA Vcc=18V,Io=-100mA No load No load
Min. 170 47.0 3.97 1.76 2.11 170 108 11.0 2.7
Limits Typ. 188 50.0 4.37 1.96 2.41 188 124 13.7 3.0 2 0.05 0.7 0.69 1.3 16.5 16.0 50 35
Max. 207 53.0 4.77 2.16 2.71 207 143 22.0 3.3 6 0.4 1.4 1.0 2.0
Unit kHz % V V V kHz
Output high voltage Output voltage rise time Output voltage fall time
16.0 15.5
V A V V V V V V ns ns
( 4 / 27 )
MITSUBISHI (Dig./Ana. INTERFACE)
M51995AP/FP
SWITCHING REGULATOR CONTROL
TYPICAL CHARACTERISTICS
1800 THERMAL DERATING (MAXIMUM RATING) 22m 18m 16m 1200 14m 900 12m
fOSC=100kHz RON=18k ROFF=20k fOSC=500kHz
CIRCUIT CURRENT VS.SUPPLY VOLTAGE (NORMAL OPERATION)
1500
600 300
10m 100 50
Ta=-30C Ta=25C Ta=85C
0 0 25 50
75 85 100
125
150
0
10 20 30 SUPPLY VOLTAGE Vcc(V)
40
AMBIENT TEMPERATURE Ta(C) CIRCUIT CURRENT VS.SUPPLY VOLTAGE (OVP OPERATION) 8.0 OVP RESET POINT 8.87V(-30C) 7.0 8.94V(25C) 9.23V(85C) 6.0 5.0 4.0 3.0 2.0 1.0 0 0 0 40 Ta=-30C Ta=25C Ta=85C 1.0 3.0 CIRCUIT CURRENT VS.SUPPLY VOLTAGE (OFF STATE)
2.0
Ta=25C Ta=85C Ta=-30C
10.0
20.0
30.0
40.0
0
10
20
30
SUPPLY VOLTAGE Vcc(V) CIRCUIT CURRENT VS.SUPPLY VOLTAGE (TIMER OFF STATE) 3.0 1.0 0.9 2.0 Ta=25C Ta=85C Ta=-30C 0.7 0.6 1.0 0.5 0.4 0 40 0.3 -40 0.8
SUPPLY VOLTAGE Vcc(V) OVP TERMINAL THRESHOLD VOLTAGE VS.AMBIENT TEMPERATURE
1.1
H threshold voltage (VTHOVPH)
L threshold voltage (VTHOVPL)
0
10 20 30 SUPPLY VOLTAGE Vcc(V)
-20 0 20 40 60 80 100 AMBIENT TEMPERATURE Ta(C)
( 5 / 27 )
MITSUBISHI (Dig./Ana. INTERFACE)
M51995AP/FP
SWITCHING REGULATOR CONTROL
THRESHOLD VOLTAGE OF ON/OFF TERMINAL VS.AMBIENT TEMPERATURE
3.4 3.2 3.0 25.0
THRESHOLD VOLTAGE OF ON/OFF TERMINAL VS.AMBIENT TEMPERATURE
ON ON OFF
20.0
OFF
2.8 2.6 2.4
15.0
OFF
2.2 2.0 1.8
ON
5.0
OFF
ON
-40
-20
0
20
40
60
80
100
0 -60
-40
-20
0
20
40
60
80
100
AMBIENT TEMPERATURE Ta(C) INPUT CURRENT OF VF TERMINAL VS.INPUT VOLTAGE
-10 -9 -8 16 -7 -6 -5 -4 -3 -2 15 14 13
AMBIENT TEMPERATURE Ta(C) DISCHARGE CURRENT OF TIMER VS.AMBIENT TEMPERATURE
18 17
Ta=-30C Ta=25C Ta=85C
12 11 10 -60
-1 0
0
1
2
3
4
5
6
7
8
9
10
-40
-20
0
20
40
60
80
100
VF TERMINAL VOLTAGE VVF(V) CHARGE CURRENT OF TIMER VS.AMBIENT TEMPERATURE
AMBIENT TEMPERATURE Ta(C) ON AND OFF DURATION OF TIMER VS.AMBIENT TEMPERATURE (INTERMITTENT OPERATION)
TIMER ON***CIRCUIT OPERATION ON TIMER OFF**CIRCUIT OPERATION OFF
-200 -180 -160 -140 -120 -100 -80 -60 -40 -60
175
1.4
150
1.3
TIMER ON
125 1.2
100
TIMER OFF
1.1
-40
-20
0
20
40
60
80
100
75 -60
-40
-20
0
20
40
60
80
1.0 100
AMBIENT TEMPERATURE Ta(C) ( 6 / 27 )
AMBIENT TEMPERATURE Ta(C)
MITSUBISHI (Dig./Ana. INTERFACE)
M51995AP/FP
SWITCHING REGULATOR CONTROL
VF THRESHOLD VOLTAGE FOR TIMER VS. AMBIENT TEMPERATURE THRESHOLD VOLTAGE OF CLM+ TERMINAL VS. AMBIENT TEMPERATURE
3.5
205
3.0
200
2.5
195
-60
-40
-20
0
20
40
60
80
100
-60
-40
-20
0
20
40
60
80
100
AMBIENT TEMPERATURE Ta(C) THRESHOLD VOLTAGE OF CLM- TERMINAL VS. AMBIENT TEMPERATURE -400
AMBIENT TEMPERATURE Ta(C) CLM+ TERMINAL CURRENT VS. CLM+ TERMINAL VOLTAGE
205
-300 Ta=-30C Ta=25C
200
-200
Ta=85C
195
-100
-60
-40
-20
0
20
40
60
80
100
0 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 CLM+ TERMINAL VOLTAGE VCLM+(V) OUTPUT HIGH VOLTAGE VS. OUTPUT SOURCE CURRENT Vcc=18V Ta=25C
AMBIENT TEMPERATURE Ta(C) CLM- TERMINAL CURRENT VS. CLM- TERMINAL VOLTAGE -500 2.6 2.4 -400 2.2 2.0 -300 Ta=-30C 1.6 -200 Ta=25C Ta=85C 1.2 -100 1.0 0.8 0 0 -0.2 -0.4 -0.6 -0.8 CLM- TERMINAL VOLTAGE VCLM-(V) -1.0 0.6 1m ( 7 / 27 ) 1.4 1.8
100m 10m 1 OUTPUT SOURCE CURRENT IOH(A)
10
MITSUBISHI (Dig./Ana. INTERFACE)
M51995AP/FP
SWITCHING REGULATOR CONTROL
OUTPUT LOW VOLTAGE VS. OUTPUT SINK CURRENT 5.0 Ta=25C 4.0 2.55
DETECTION VOLTAGE VS. AMBIENT TEMPERATURE
3.0
2.50
2.0
Vcc=18V Vcc=5V 2.45
1.0
0 1m 10m 100m 1 10 OUTPUT SINK CURRENT IOL(A) INPUT CURRENT OF DETECTION AMP VS. AMBIENT TEMPERATURE 1.6 1.5
2.40 -60
-40
-20
0
20
40
60
80
100
AMBIENT TEMPERATURE Ta(C) DETECTION AMP VOLTAGE GAIN VS. FREQUENCY 50.0
40.0 1.4 1.3 1.2 1.1 1.0 10.0 0.9 0.8 -60 -40 -20 0 20 40 60 80 100 0 100 1k 10k 100k 1M 10M 20.0 30.0
AMBIENT TEMPERATURE Ta(C) ON duty VS. F/B TERMINAL INPUT CURRENT (fOSC=100kHz) RON=18k ROFF=20k
FREQUENCY f(Hz) ON duty VS. F/B TERMINAL INPUT CURRENT 50 (fOSC=200kHz) RON=18k ROFF=20k
50
40
40
30 Ta=-30C 20 Ta=25C Ta=85C 10
30 Ta=-30C 20 Ta=25C Ta=85C 10
00
1.5 2.0 1.0 2.5 0.5 F/B TERMINAL INPUT CURRENT IF/B (mA) ( 8 / 27 )
0
0
1.5 2.0 1.0 2.5 0.5 F/B TERMINAL INPUT CURRENT IF/B (mA)
MITSUBISHI (Dig./Ana. INTERFACE)
M51995AP/FP
SWITCHING REGULATOR CONTROL
ON duty VS. F/B TERMINAL INPUT CURRENT 50 (fOSC=500kHz) RON=18k ROFF=20k 5.2 4.8 4.4 30 Ta=-30C Ta=25C 20 Ta=85C 4.0 2.2 2.0 10 1.8 0 0 0.5 1.0 1.5 2.0 2.5 F/B TERMINAL INPUT CURRENT IF/B(mA) OSCILLATING FREQUENCY VS. CF TERMINAL CAPACITY 10000
UPPER & LOWER LIMIT VOLTAGE OF OSC VS. AMBIENT TEMPERATURE RON=18k ROFF=20k
40
fOSC=500kHz fOSC=200kHz fOSC=100kHz
fOSC=100kHz fOSC=200kHz fOSC=500kHz
-60
-40 -20 0 20 40 60 80 AMBIENT TEMPERATURE Ta(C)
100
ON duty VS. ROFF 100 90 80
1000 RON=22k ROFF=12k 100 RON=36k ROFF=6.2k RON=24k ROFF=20k 10
70 RON=75k 60 50 40 30 20 10 51k 36k 24k 22k 18k 15k 10k
1
1
3
10
3
100
3
1000
3
0 10000
1
3
5
7
10
3
5
7
100
CF TERMINAL CAPACITY(pF) OSCILLATING FREQUENCY VS. AMBIENT TEMPERATURE 120 RON=24k ROFF=20k CF=330pF 700
ROFF(k) OSCILLATING FREQUENCY VS. AMBIENT TEMPERATURE RON=24k ROFF=20k CF=47pF
600
110
500 100 400 90 300
80 -60
-40 -20 0 20 40 60 80 AMBIENT TEMPERATURE Ta(C)
100
200 -60 ( 9 / 27 )
-40
-20 0 20 40 60 80 AMBIENT TEMPERATURE Ta(C)
100
MITSUBISHI (Dig./Ana. INTERFACE)
M51995AP/FP
SWITCHING REGULATOR CONTROL
ON duty VS. AMBIENT TEMPERATURE 100 90 80 70 60 50 40 30 20 10 0 -60 -40 -20 0 20 40 60 80 100
RON=22k,ROFF=12k RON=24k,ROFF=20k RON=22k,ROFF=22k RON=18k,ROFF=24k RON=15k,ROFF=27k
ON duty VS. AMBIENT TEMPERATURE 100 90 80 70 60 50 40 30 20 10 0 -60 -40 -20 0 20 40 60 80 AMBIENT TEMPERATURE Ta(C) INPUT VOLTAGE OF TERMINAL VS. EXPANSION RATE OF PERIOD (fOSC=100kHz) 4.0 100
RON=22k,ROFF=12k RON=24k,ROFF=20k RON=22k,ROFF=22k RON=18k,ROFF=24k RON=15k,ROFF=27k
(fOSC=100kHz)
RON=36k,ROFF=6.2k
(fOSC=200kHz)
RON=36k,ROFF=6.2k
AMBIENT TEMPERATURE Ta(C)
ON duty VS. AMBIENT TEMPERATURE 100 (fOSC=500kHz) 90 80 70 60 50 40 30 20 10 0 -60 -40 -20 0 20 40 60 80 100 0
RON=22k,ROFF=12k RON=24k,ROFF=20k RON=22k,ROFF=22k RON=18k,ROFF=24k RON=15k,ROFF=27k RON=36k,ROFF=6.2k
5.0
1 RON=15k,ROFF=27k 2 RON=18k,ROFF=24k 3 RON=22k,ROFF=22k 4 RON=24k,ROFF=20k 5 RON=22k,ROFF=12k 6 RON=36k,ROFF=6.2k
3.0
2.0
1.0
1
2
3
4
5
6
0
2
4
6
8
10
12
14 16
18
20
AMBIENT TEMPERATURE Ta(C) INPUT VOLTAGE OF TERMINAL VS. EXPANSION RATE OF PERIOD 5.0 (fOSC=500kHz) 4.0
1 RON=15k,ROFF=27k 2 RON=18k,ROFF=24k 3 RON=22k,ROFF=22k 4 RON=24k,ROFF=20k 5 RON=22k,ROFF=12k 6 RON=36k,ROFF=6.2k
EXPANSION RATE OF PERIOD(TIMES) OVP TERMINAL INPUT VOLTAGE VS. INPUT CURRENT Ta=85C Ta=25C Ta=-30C 100
1m
3.0
2.0 10 1.0
0
1
2
3
4
5
6
0
2 46 8 10 12 14 16 18 EXPANSION RATE OF PERIOD(TIMES)
20
1
0.2 0.4 0.6 0.8 1.0 OVP TERMINAL INPUT VOLTAGE VOVP(V)
( 10 / 27 )
MITSUBISHI (Dig./Ana. INTERFACE)
M51995AP/FP
SWITCHING REGULATOR CONTROL
CURRENT FROM OVP TERMINAL FOR OVP RESET VS. SUPPLY VOLTAGE 800 700 600 500 400 300 200 100 0 0 5 10 15 20 25 30 35 40
Ta=-30C Ta=25C Ta=85C
SUPPLY VOLTAGE Vcc(V)
( 11 / 27 )
MITSUBISHI (Dig./Ana. INTERFACE)
M51995AP/FP
SWITCHING REGULATOR CONTROL
FUNCTION DESCRIPTION
Type M51995AP and M51995AFP are especially designed for off-line primary PWM control IC of switching mode power supply (SMPS) to get DC voltage from AC power supply. Using this IC,smart SMPS can be realized with reasonable cost and compact size as the number of external electric parts can be reduced and also parts can be replaced by reasonable one. In the following circuit diagram,MOS-FIT is used for output transistor,however bipolar transistor can be used with no problem.
VOUT2 AC CFIN R1 A
1 2 16
VOUT1 M51995AP
4 3 14 13 15 9 10 11 12 8 6 7 5
R2 Cvcc
OVP CF CT F/B RON A Pin No.is related with M51995AP Fig.1 Example application circuit diagram of feed forward regulator ROFF ON/OFF
AC CFIN R1
1 2 16
OVP F/B
VOUT R21 M51995AP Cvcc
4 3 14 13 15 9 10 11 12 8 6 7
5
R22 CF
RON
ROFF
Pin No.is related with M51995AP Fig.2 Example application circuit diagram of fly-back regulator
( 12 / 27 )
MITSUBISHI (Dig./Ana. INTERFACE)
M51995AP/FP
SWITCHING REGULATOR CONTROL Start-up circuit section
The start-up current is such low current level as typical 90 A,as shown in Fig.3,when the Vcc voltage is increased from low level to start-up voltage Vcc(START). In this voltage range,only a few parts in this IC,which has the function to make the output voltage low level,is alive and Icc current is used to keep output low level.The large voltage difference between Vcc(START) and Vcc(STOP) makes start-up easy,because it takes rather long duration from Vcc(START) to Vcc(STOP). CF is discharged by the summed-up of ROFF current and one sixteenth (1/16) of RON current by the function of Q2,Q3 and Q4 when SW1,SW2 are switched to "discharge side". 5.8V
Q4 T-ON RON T-OFF ROFF FROM VF SIGNAL Vz ~ 4.2V 1/16 Q3 Q1 CHARGING SW1
SWITCHED BY CHARGING AND DISCHARGING SIGNAL SW2 Q2 DISCHARGING
Icco ~ 14mA
CF CF
M51995 IccL ~ 90A Vcc
(STOP)
Vcc
(START)
Fig.4 Schematic diagram of charging and discharging control circuit for OSC.capacitor CF
~ 9.9V ~ 16.2V SUPPLY VOLTAGE Vcc(V) Fig.3 Circuit current vs.supply voltage
VOSCL ~ 2.0V VOSCH ~ 4.4V
Oscillator section
The oscillation waveform is the triangle one.The ON-duration of output pulse depends on the rising duration of the triangle waveform and dead-time is decided by the falling duration. The rising duration is determined by the product of external resistor RON and capacitor CF and the falling duration is mainly determined by the product of resistor ROFF and capacitor CF.
VOH
(1)Oscillator operation when intermittent action and OSC control circuit does not operate
Fig.4 shows the equivalent charging and discharging circuit diagram of oscillator when the current limiting circuit does not operate.It means that intermittent action and OSC control circuit does not operate. The current flows through RON from the constant voltage source of 5.8V.CF is charged up by the same amplitude as RON current,when internal switch SW1 is switched to "charging side".The rise rate of CF terminal is given as
VOL
Fig.5 OSC.waveform at normal condition (nooperation of intermittent action and OSC.control circuit) So fall rate of CF terminal is given as VT - OFF VT - ON + (V/s) .....................(3) ROFF X CF 16 X RON X CF The minimum off duration approximately is given as ~ (VOSCH-VOSCL) X CF (s) .....................................(4) VT-OFF + VT-ON ROFF 16 X RON where VT - OFF
~
~
VT - ON (V/s) ................................................(1) RON X CF
where VT - ON ~ 4.5V The maximum on duration is approximately given as ~ (VOSCH-VOSCL) X RON X CF (s)........................(2) VT - ON where VOSCH ~ 4.4V VOSCL ~ 2.0V
~
3.5V
The cycle time of oscillation is given by the summation of Equations 2 and 4. The frequency including the dead-time is not influenced by the temperature because of the built-in temperature compensating circuit.
( 13 / 27 )
MITSUBISHI (Dig./Ana. INTERFACE)
M51995AP/FP
SWITCHING REGULATOR CONTROL (2)Oscillator operation when intermittent action and OSC control circuit operates.
When over current signal is applied to CLM+ or CLMterminal,and the current limiting circuit,intermittent action and OSC control circuit starts to operate.In this case T-OFF terminal voltage depends on VF terminal voltage,so the oscillation frequency decreases and dead-time spreads.
VOSCH ~ 4.4V
VOSCL ~ 2.0V
The rise rate of oscillation waveform is given as
~
VT - ON (V/s) ................................................(5) RON X CF
VOH
The fall rate of oscillation waveform is given as
VOL
~
VVF - VVFO + VT - ON (V/s) ...............(6) ROFF X CF 16 X RON X CF
where VT - ON
~ 4.5V
Fig.6 OSC.waveform with operation of intermittent and OSC.control circuit operation
VVF;VF terminal voltage VVFO ~ 0.4V VVF-VFO=0 if VVF-VVFO<0 VVF-VVFO=VT-OFF if VVF-VVFO>VT-OFF ~ 3.5V
VOSCH
START FROM 0V
So when VVF>3.5V,the operation is just same as that in the no current limiting operation state. The maximum on-duration is just same as that in the nooperation state of intermittent and oscillation control circuit and is given as follows; (VOSCH - VOSCL) X ROFF X CF VT - ON
VOSCL
0
~
(s) ...............(7)
VOH
FIRST PULSE NO GENERATE PULSE
The minimum off-duration is approximately given as;
VOL
~
(VOSCH - VOSCL) X CF VVF - VVFO + VT - ON (s)...............(8) ROFF X CF 16 X RON X CF
0 OPERATION START Fig.7 Relation between OSC. and output waveform circuit operation at start up
The oscillation period is given by the summation of Equation(7) and (8). As shown in Fig.7,the internal circuit kills the first output pulse in the output waveform.The output waveform will appear from the second pulse cycle because the duration of first cycle takes CF charging time longer comparing with that at the stable operating state. Usually the applied voltage to VF terminal must be proportional the output voltage of the regulator. So when the over current occurs and the output voltage of the regulator becomes low,the off-duration becomes wide. There are two methods to get the control voltage,which depends on the output voltage,on primary side.For the fly back type regulator application,the induced voltage on the third or bias winding is dependent on output voltage.On the other hand,for the feed forward type regulator application,it can be used that the output voltage depends on the product of induced voltage and "on-duty",as the current of choke coil will continue at over load condition,it means the "continuous current" condition. Fig.8 shows one of the examples for VF terminal application for the feed forward type regulator.
M51995 VOUT RVFFB VF CVFFB
Fig.8 Feedback loop with low pass filter from output to VF terminal choke coil will continue at over load condition,it means the "continuous current" condition. Fig.8 shows one of the examples for VF terminal application for the feed forward type regulator.
( 14 / 27 )
MITSUBISHI (Dig./Ana. INTERFACE)
M51995AP/FP
SWITCHING REGULATOR CONTROL PWM comparator and PWM latch section
Fig.9 shows the PWM comparator and latch section. The onduration of output waveform coincides with the rising duration of CF terminal waveform,when the infinitive resistor is connected between F/B terminal and GND. When the F/B terminal has finite impedance and current flows out from F/B terminal,"A" point potential shown in Fig.9 depends on this current.So the "A" point potential is close to GND level when the flow-out current becomes large. "A" point potential is compared with the CF terminal oscillator waveform and PWM comparator,and the latch circuit is set when the potential of oscillator waveform is higher than "A" point potential. On the other hand,this latch circuit is reset by high level signal during the dead-time of oscillation(falling duration of oscillation waveform).So the "B" point potential or output waveform of latch circuit is the one shown in Fig.10. The final output waveform or "C" point potential is got by combining the "B" point signal and dead-time signal logically.(please refer to Fig.10)
Current limiting section
When the current-limit signal is applied before the crossing instant of "A" pint potential and CF terminal voltage shown in Fig.9,this signal makes the output "off" and the off state will continue until next cycle.Fig.11 shows the timing relation among them. The current limiting circuit has two input terminals,one has the detector-sensitivity of +200mV to the GND terminal and the other has -200mV.The circuit will be latched if the input signal is over the limit of either terminal. If the current limiting circuit is set,no waveform is generated at output terminal however this state is reset during the succeeding dead-time. So this current limiting circuit is able to have the function in every cycle,and is named "pulse-by-pulse current limit".
OSC WAVEFORM OF CF TERMINAL VTHCLM~ 200mV
~ 7.1V
5.8V POINT A LATCH POINT B
WAVEFORM OF CLM+ TERMINAL TO OUTPUT CURRENT LIMIT SIGNAL TO SET LATCH
6S
1S
+
PWM COMP
POINT C
F/B
WAVEFORM OF VOUT TERMINAL FROM OSC
M51995A
CF
(a) +current limit
Fig.9 PWM comparator and latch circuit
OSC WAVEFORM OF CF TERMINAL
OSC WAVEFORM POINT A
WAVEFORM OF CLM- TERMINAL VTHCLM~ -200mV CURRENT LIMIT SIGNAL TO SET LATCH
WAVEFORM OF O.S.C. & POINT A
POINT B WAVEFORM OF VOUT TERMINAL POINT C
(b) -current limit Fig.10 Waveforms of PWM comparator input point A, latch circuit points B and C Fig.11 Operating waveforms of current limiting circuit
( 15 / 27 )
MITSUBISHI (Dig./Ana. INTERFACE)
M51995AP/FP
SWITCHING REGULATOR CONTROL
It is rather recommended to use not "CLM+" but "CLM-" terminal,as the influence from the gate drive current of MOS-FIT can be eliminated and wide voltage rating of + 4V to -4V is guaranteed for absolute maximum rating. There happen some noise voltage on RCLM during the switching of power transistor due to the snubber circuit and stray capacitor of the transformer windings. To eliminate the abnormal operation by the noise voltage,the low pass filter,which consists of RNF and CNF is used as shown in Fig.12. It is recommended to use 10 to 100 for RNF because such range of RNF is not influenced by the flow-out current of some 200A from CLM terminal and CNF is designed to have the enough value to absorb the noise voltage.
+ +
OSC WAVEFORM OF CF TERMINAL
CURRENT LIMIT SIGNAL OUTPUT OF CURRENT LIMIT LATCH OUTPUT OF INTERMITTENT ACTION and OSC. CONTROL CIRCUIT
GND
GND
GND
(b) Without current limit signal Fig.13 Timing chart of intermittent and OSC.control circuit
M51995A
M51995A
Intermittent action circuit section
VOUT VOUT
CLM+
RNF GND CNF RCLM CLMRNF CNF RCLM
GND
(a)In case of CLM+
(b)In case of CLM-
Fig.12 How to connect current limit circuit
Intermittent action and oscillation control section
When the internal current limiting circuit states to operate and also the VF level decreases to lower than the certain level of some 3V,the dead-time spreads and intermittent action and OSC control circuit(which is one of the timer-type-protection circuit)starts to operate. The intermittent action and OSC control circuit is the one to generate the control signal for oscillator and intermittent action circuit. Fig.13 shows the timing-chart of this circuit.When the output of intermittent action and oscillation control is at "high" level,the waveform of oscillator depends on the VF terminal voltage and the intermittent action circuit begins to operate.
Intermittent action circuit will start to operate when the output signal from the intermittent action and oscillation control circuit are "high" and also VF terminal voltage is lower than VTHTIME of about 3V. Fig.14 shows the block diagram of intermittent action circuit.Transistor Q is on state when VF terminal voltage is higher than VTHTIME of about 3V,so the CT terminal voltage is near to GND potential. When VF terminal voltage is lower than VTHTIME,Q becomes "off" and the CT has the possibility to be charged up. Under this condition,if the intermittent action and oscillation control signal become "high" the switch SWA will close only in this "high" duration and CT is charged up by the current of 120A through SWA (SWB is open) and CT terminal potential will rise.The output pulse can be generated only this duration. When the CT terminal voltage reaches to 8V,the control logic circuit makes the SWA "off" and SWB "on",in order to flow in the ITIMEOFF of 15A to CT terminal. The IC operation will be ceased in the falling duration. On the other hand,when CT terminal voltage decreases to lower than 2V,the IC operation will be reset to original state,as the control logic circuit makes the SWA "on" and SWB "off". Therefore the parts in power circuit including secondary rectifier diodes are protected from the overheat by the over current.
ITIMEON (~120A) VTHTIME (~ 3V) CT A SWA SWB B CT ITIMEOFF (~15A) CONTROL LOGIC
OSC WAVEFORM OF CF TERMINAL
Q VF
CURRENT LIMIT SIGNAL
Fig.14 Block diagram of intermittent action circuit
OUTPUT OF CURRENT LIMIT LATCH OUTPUT OF INTERMITTENT ACTION and OSC. CONTROL CIRCUIT
(a) With current limit signal ( 16 / 27 )
MITSUBISHI (Dig./Ana. INTERFACE)
M51995AP/FP
SWITCHING REGULATOR CONTROL
NO OPERATING DURATION
8V
2V
of primary and secondary in feed forward system. The circuit diagram is quite similar to that of shunt regulator type 431 as shown in Fig.17.As well known from Fig.17 and Fig.18,the output of OP AMP has the current-sink ability,when the DET terminal voltage is higher than 2.5V but it becomes high impedance state when lower than 2.5V DET terminal and F/B terminal have inverting phase characteristics each other,so it is recommended to connect the resistor and capacitor in series between them for phase compensation.It is very important,one can not connect by resistor directly as there is the voltage difference between them and the capacitor has the DC stopper function.
Fig.15 Waveform of CT terminal
~7.1V 3k 500
Fig.16 shows the Icc versus Vcc in this timer-off duration. In this duration the power is not supplied to IC from the third winding of transformer but through from the resistor R1 connected toVcc line. If the R1 shown in Fig.1 and 2 is selected adequate value,Vcc terminal voltage will be kept at not so high or low but adequate value,as the Icc versus Vcc characteristics has such the one shown in Fig.16.
1S
6S F/B DET
5.4k 10.8k 10.8k
10S
1.2k
2.0 Fig.17 Equivalent circuit diagram of voltage detector 1.5
~7.1V 3k 500
1.0
1S 6S F/B
0.5
OP AMP
DET
+
2.5V
0
0
5
10
15
20
25
30 Fig.18 Equivalent circuit diagram of voltage detector
SUPPLY VOLTAGE Vcc(V) Fig.16 Icc vs.Vcc in timer-off duration of intermittent action circuit
To ground the CT terminal is recommended,when the intermittent mode is not used. In this case the oscillated frequency will become low but the IC will neither stop the oscillation nor change to the intermittent action mode,when the current limit function becomes to operate and the VF terminal voltage becomes low.
ON-OFF circuit section
Fig.19 shows the circuit diagram of ON-OFF circuit.The current flown into the ON-OFF terminal makes the Q4 "on" and the switching operation stop.On the other hand.the switching operation will recover as no current flown into ON/OFF terminal makes Q4 "off" As the constant current source connected to Q4 base terminal has such the hysteresis characteristics of 20A at operation and 3A at stopping.So the unstable operation is not appeared even if the ON/OFF terminal voltage signal varies slowly.
Voltage detector circuit(DET) section
The DET terminal can be used to control the output voltage which is determined by the winding ratio of fly back transformer in fly-back system or in case of common ground circuit
( 17 / 27 )
MITSUBISHI (Dig./Ana. INTERFACE)
M51995AP/FP
SWITCHING REGULATOR CONTROL
Fig.20 shows how to connect the ON/OFF terminal.The switching operation will stop by swich-off and operate by switchon. Transistor or photo transistor can be replaced by this switch,of course.No resistor of 30 to 100k is connected and ON/OFF terminal is directly connected to GND,when it is not necessary to use the ON/OFF operation. Fig.21 shows the Icc versus Vcc characteristics in OFF state and Vcc will be kept at not so high or low but at the adequate voltage,when R1 shown in Fig.1 and 2 is selected properly. 2k ON/OFF
OVP circuit(over voltage protection circuit)section
OVP circuit is basically positive feedback circuit constructed by Q2,Q3 as shown in Fig.22. Q2,Q3 turn on and the circuit operation of IC stops,when the input signal is applied to OVP terminal.(threshold voltage ~ 750mV) The current value of I2 is about 150A when the OVP does not operates but it decreases to about 2A when OVP operates. It is necessary to input the sufficient larger current(800A to 8mA)than I2 for triggering the OVP operation. The reason to decrease I2 is that it is necessary that Icc at the OVP rest supply voltage is small. It is necessary that OVP state holds by circuit current from R1 in the application example,so this IC has the characteristic of small Icc at the OVP reset supply voltage(~stand-by current + 20A) On the other hand,the circuit current is large in the higher supply voltage,so the supply voltage of this IC doesn't become so high by the voltage drop across R1. This characteristic is shown in Fig.23. The OVP terminal input current in the voltage lower than the OVP threshold voltage is based on I2 and the input current in the voltage higher than the OVP threshold voltage is the sum of the current flowing to the base of Q3 and the current flowing from the collector of Q2 to the base. For holding in the latch state,it is necessary that the OVP terminal voltage is kept in the voltage higher than VBE of Q3. So if the capacitor is connected between the OVP terminal and GND,even though Q2 turns on in a moment by the surge voltage,etc,this latch action does not hold if the OVP terminal voltage does not become higher than VBE of Q3 by charging this capacitor. For resetting OVP state,it is necessary to make the OVP terminal voltage lower than the OVP L threshold voltage or make Vcc lower than the OVP reset supply voltage. As the OVP reset voltage is settled on the rather high voltage of 9.0V,SMPS can be reset in rather short time from the switch-off of the AC power source if the smoothing capacitor is not so large value.
Q2
Q3 Q4 OPERATE STOP AT Q4 ON I:3A AT STOPPING I:20A AT OPERATING I
Fig.19 ON/OFF circuit
Vcc
30k~100k
M51995A ON/OFF
Fig.20 Connecting of ON/OFF terminal
1.6
1.2
0.8
0.4
0
0
5
10
15
20
25
30
SUPPLY VOLTAGE Vcc(V) Fig.21 Icc vs.Vcc in OFF state
( 18 / 27 )
MITSUBISHI (Dig./Ana. INTERFACE)
M51995AP/FP
SWITCHING REGULATOR CONTROL
Output section
Vcc 7.8V 100A 8k 12k Q1 I1 It is required that the output circuit have the high sink and source abilities for MOS-FET drive.It is well known that the "totempole circuit has high sink and source ability.However,it has the demerit of high through current. For example,the through current may reach such the high current level of 1A,if type M51995A has the "conventional" totempole circuit.For the high frequency application such as higher than 100kHz,this through current is very important factor and will cause not only the large Icc current and the inevitable heat-up of IC but also the noise voltage. This IC uses the improved totempole circuit,so without deteriorating the characteristic of operating speed,its through current is approximately 100mA.
Q2 400 OVP 2.5k GND I2
I1=0 when OVP operates
Q3
APPLICATION NOTE OF TYPE M51995AP/FP Design of start-up circuit and the power supply of IC
(1)The start-up circuit when it is not necessary to set the start and stop input voltage Fig.24 shows one of the example circuit diagram of the start-up circuit which is used when it is not necessary to set the start and stop voltage. It is recommended that the current more than 300A flows through R1 in order to overcome the operation start-up current Icc(START) and Cvcc is in the range of 10 to 47F.The product of R1 by Cvcc causes the time delay of operation,so the response time will be long if the product is too much large.
RECTIFIED DC VOLTAGE FROM SMOOTHING CAPACITOR
Fig.22 Detail diagram of OVP circuit
8 7 6 5 4 3 OVP RESET POINT 8.82V(-30C) 8.97V(25C) 9.07V(85C)
Ta=-30C Ta=25C Ta=85C
MAIN TRANSFORMER R1 VF
Vcc
THIRD WINDING OR BIAS WINDING
2 1 0 M51995A 0 5 10 15 20 25 30 35 40
GND
CVcc
SUPPLY VOLTAGE Vcc(V) Fig.23 CIRCUIT CURRENT VS. SUPPLY VOLTAGE (OVP OPERATION)
Fig.24 Start-up circuit diagram when it is not necessary to set the start and stop input voltage Just after the start-up,the Icc current is supplied from Cvcc,however,under the steady state condition ,IC will be supplied from the third winding or bias winding of transformer,the winding ratio of the third winding must be designed so that the induced voltage may be higher than the operation-stop voltage Vcc(STOP). The Vcc voltage is recommended to be 12V to 17V as the normal and optimum gate voltage is 10 to 15V and the output voltage(VOH) of type M51995AP/FP is about(Vcc-2V).
( 19 / 27 )
MITSUBISHI (Dig./Ana. INTERFACE)
M51995AP/FP
SWITCHING REGULATOR CONTROL
It is not necessary that the induced voltage is settled higher than the operation start-up voltage Vcc(START),and the high gate drive voltage causes high gate dissipation,on the other hand,too low gate drive voltage does not make the MOS-FET fully onstate or the saturation state.
RECTIFIED DC VOLTAGE FROM SMOOTHING CAPACITOR VIN NP PRIMARY WINDING OF TRANSFORMER
It is required that the VIN(START) must be higher than VIN(STOP). When the third winding is the "fly back winding" or "reverse polarity",the VIN(START) can be fixed,however,VIN(STOP) can not be settled by this system,so the auxiliary circuit is required.
R1 VF Vcc NB THIRD WINDING OF TRANSFORMER
M51995A
R2
CVcc
GND
(3)Notice to the Vcc,Vcc line and GND line To avoid the abnormal IC operation,it is recommended to design the Vcc is not vary abruptly and has few spike voltage,which is induced from the stray capacity between the winding of main transformer. To reduce the spike voltage,the Cvcc,which is connected between Vcc and ground,must have the good high frequency characteristics. To design the conductor-pattern on PC board,following cautions must be considered as shown in Fig.26. (a)To separate the emitter line of type M51995A from the GND line of the IC (b)The locate the CVCC as near as possible to type M51995A and connect directly (c)To separate the collector line of type M51995A from the Vcc line of the IC (d)To connect the ground terminals of peripheral parts of ICs to GND of type M51995A as short as possible
Fig.25 Start-up circuit diagram when it is not necessary to set the start and stop input voltage
MAIN TRANSFORMER THIRD WINDING
COLLECTOR
Vcc
(2)The start-up circuit when it is not necessary to set the start and stop input voltage It is recommend to use the third winding of "forward winding" or "positive polarity" as shown in Fig.25,when the DC source voltages at both the IC operation start and stop must be settled at the specified values. The input voltage(VIN(START)),at which the IC operation starts,is decided by R1 and R2 utilizing the low start-up current characteristics of type M51995AP/FP. The input voltage(VIN(STOP)),at which the IC operation stops,is decided by the ratio of third winding of transformer. The VIN(START) and VIN(STOP) are given by following equations. M51995A
OUTPUT CVcc
RCLM
EMITTER GND
Fig.26 How to design the conductor-pattern of type M51995A on PC board(schematic example) (4)Power supply circuit for easy start-up When IC start to operate,the voltage of the CVCC begins to decrease till the CVCC becomes to be charged from the third winding of main-transformer as the Icc of the IC increases abruptly.In case shown in Fig.24 and 25,some "unstable startup" or "fall to start-up" may happen, as the charging interval of CVCC is very short duration;that is the charging does occur only the duration while the induced winding voltage is higher than the CVCC voltage,if the induced winding voltage is nearly equal to the "operation-stop voltage" of type M51995. It is recommended to use the 10 to 47F for CVCC1,and about 5 times capacity bigger than CVCC1 for CVCC2 in Fig.27.
VIN(START)~ R1 * ICCL + ( R1 + 1) * Vcc(START) ...............(9) R2 NP + 1 VIN(STOP)~ (Vcc(STOP)-VF) * 2 V'IN RIP(P-P)..........(10) NB where ICCL is the operation start-up current of IC Vcc(START) is the operation start-up voltage of IC Vcc(STOP) is the operation stop voltage of IC VF is the forward voltage of rectifier diode V'IN(P-P) is the peak to peak ripple voltage of Vcc terminal ~ NB NP V'IN RIP(P-P)
( 20 / 27 )
MITSUBISHI (Dig./Ana. INTERFACE)
M51995AP/FP
SWITCHING REGULATOR CONTROL
R1
Vcc
MAIN TRANSFORMER THIRD WINDING
TO MAIN TRANSFORMER R1
M51995A
CVcc1 CVcc2 Vcc GND
~
CFIN R2
Cvcc
M51995A
GND
Fig.27 DC source circuit for stable start-up
THE TIME CONSTANT OF THIS PART SHOULD BE SHORT
OVP circuit
(1)To avoid the miss operation of OVP It is recommended to connect the capacitor between OVP terminal and GND for avoiding the miss operation by the spike noise. The OVP terminal is connected with the sink current source (~150A) in IC when OVP does not operate,for absorbing the leak current of the photo coupler in the application. So the resistance between the OVP terminal and GND for leakcut is not necessary. If the resistance is connected,the supply current at the OVP reset supply voltage becomes large. As the result,the OVP reset supply voltage may become higher than the operation stop voltage. In that case,the OVP action is reset when the OVP is triggered at the supply voltage a little high than the operation stop voltage. So it should be avoided absolutely to connect the resistance between the OVP terminal and GND.
Fig.29 Example circuit diagram to make the OVP-reset-time fast
Vcc
MAIN TRANSFORMER THIRD WINDING 470 OVP CVcc
M51995A
GND
FIG.30 OVP setting method using the induced third winding voltage on fly back system (2)Application circuit to make the OVP-reset time fast The reset time may becomes problem when the discharge time constant of CFIN * (R1+R2) is long. Under such the circuit condition,it is recommended to discharge the CVCC forcedly and to make the Vcc low value.This makes the OVP-reset time fast.
Vcc
10k (3)OVP setting method using the induced third winding voltage on fly back system
M51995A
OVP
PHOTO COUPLER
For the over voltage protection (OVP),the induced fly back type third winding voltage can be utilized,as the induced third winding voltage depends on the output voltage.Fig.30 shows one of the example circuit diagram.
GND
Fig.28 Peripheral circuit of OVP terminal
( 21 / 27 )
MITSUBISHI (Dig./Ana. INTERFACE)
M51995AP/FP
SWITCHING REGULATOR CONTROL
Current limiting circuit
(1)Peripheral circuit of CLM+,CLM- terminal Fig.31 and 32 show the example circuit diagrams around the CLM+ and CLM- terminal.It is required to connect the low pass filter,as the main current or drain current contains the spike current especially during the turn-on duration of MOS-FIT. 1,000pF to 22,000pF is recommended for CNF and the RNF1 and RNF2 have the functions both to adjust the "currentdetecting-sensitivity" and to consist the low pass filter.
I2
CLM RCLM I1
(a) Feed forward system
R1 I1 CFIN INPUT SMOOTHING CAPACITOR COLLECTOR Cvcc VOUT I2 IP1
Vcc
IP2
M51995A
CLM+ GND EMITTER CNF RNF1 RNF2 RCLM
(b) Primary and secondary current Fig.33 Primary and secondary current waveforms under the current limiting operation condition on feed forward system
Fig.31 Peripheral circuit diagram of CLM+ terminal
R1
CFIN INPUT SMOOTHING CAPACITOR COLLECTOR VOUT
Vcc
Cvcc
M51995A
EMITTER GND
CLM+
CNF
RNF2 RCLM RNF1
OUTPUT CURRENT
Fig.32 Peripheral circuit diagram of CLM- terminal To design the RNF1 and RNF2,it is required to consider the influence of CLM terminal source current(IINCLM+ or INFCLM-), which value is in the range of 90 to 270A. In order to be not influenced from these resistor paralleled value of RNF1 and RNF2,(RNF1/RNF2)is recommended to be less than 100. The RCLM should be the non-inductive resistor.
Fig.34 Over current limiting curve on feed forward system
(2)Over current limiting curve (a)In case of feed forward system Fig.33 shows the primary and secondary current wave-forms under the current limiting operation. At the typical application of pulse by pulse primary current detecting circuit,the secondary current depends on the primary current.As the peak value of secondary current is limited to specified value,the characteristics curve of output voltage versus output current become to the one as shown in Fig.34.
The demerit of the pulse by pulse current limiting system is that the output pulse width can not reduce to less than some value because of the delay time of low pass filter connected to the CLM terminal and propagation delay time TPDCLM from CLM terminal to output terminal of type M51995A.The typical TPDCLM is 100ns. As the frequency becomes higher,the delay time must be shorter.And as the secondary output voltage becomes higher,the dynamic range of on-duty must be wider;it means that it is required to make the on-duration much more narrower. So this system has the demerit at the higher oscillating frequency and higher output voltage applications. To improve these points,the oscillating frequency is set low using the characteristics of VF terminal.When the current limiting circuit operates under the over current condition,the oscillating frequency decreases in accordance with the decrease of VF terminal voltage,if the VF is lower than 3.5V.And also the dead time becomes longer.
( 22 / 27 )
MITSUBISHI (Dig./Ana. INTERFACE)
M51995AP/FP
SWITCHING REGULATOR CONTROL
Under the condition of current limiting operation,the output current I2 continues as shown in Fig.33.So the output voltage depends on the product of the input primary voltage VIN and the on-duty. If the third winding polarity is positive ,the Vcc depends on VIN,so it is concluded that the smoothed voltage of VOUT terminal depends on the output DC voltage of the SMPS. So the sharp current limiting characteristics will be got,if the VOUT voltage if feed back to VF terminal through low pass filter as shown in Fig.35.
POINT THAT Vcc VOLTAGE OR THIRD WINDING VOLTAGE DECREASES UNDER "OPERATION-STOP VOLTAGE"
DC OUTPUT CURRENT
Fig.37 Over current limiting curve on fly back system M51995A
VOUT RVFFB VF CVFFB
Fig.35 Feed back loop through low pass filter from VOUT to VF terminal It is recommended to use 15k for RVFFB,and 10,000pF for CVFFB in Fig.35. Fig.36 shows how to control the knee point where the frequency becomes decrease.
FROM VOUT TO VF FROM VOUT TO VF FROM VOUT TO VF
However,the M51995A will non-operate and operate intermittently,as the Vcc voltage rises in accordance with the decrease of Icc current. The fly back system has the constant output power characteristics as shown in Fig.37 when the peak primary current and the operating frequency are constant. To control the increase of DC output current,the operating frequency is decreased using the characteristics of VF terminal when the over current limiting function begins to operate. The voltage which mode by dividing the Vcc is applied to VF terminal as shown in Fig.38,as the induced third winding voltage depends on the DC output voltage of SMPS. 15k or less is recommended for R2 in Fig.38,it is noticed that the current flows through R1 and R2 will superpose on the Icc(START) current. If the R1 is connected to Cvcc2 in Fig.27,the current flows through R1 and R2 is independent of the Icc(START).
Vcc
COLLECTOR
TO MAKE THE KNEE POINT HIGH
TO MAKE THE KNEE POINT LOW
M51995A
VF
R1 CVcc R2
Fig.36 How to control the knee point
(b)In case of fly back system The DC output voltage of SMPS depends on the Vcc voltage of type M51995A when the polarity of the third winding is negative and the system is fly back.So the operation of type M51995A will stop when the Vcc becomes lower than "Operation-stop voltage" of M51995A when the DC output voltage of SMPS decreases under specified value at over load condition.
Fig.38 Circuit diagram to make knee point low on fly back system
(c)Application circuit to keep the non-operating condition when over load current condition will continue for specified duration The CT terminal voltage will begin to rise and the capacitor connected to CT terminal will be charged-up,if the current limiting function starts,and VF terminal voltage decreases below VTHTIME(~3V). If the charged-up CT terminal voltage is applied to OVP terminal through the level-shifter consisted of buffer transistor and resistor,it makes type M51995A keep non-operating condition.
( 23 / 27 )
MITSUBISHI (Dig./Ana. INTERFACE)
M51995AP/FP
SWITCHING REGULATOR CONTROL
Vcc
20
CT CT DRAIN
M51995A
OVP
15
VDS=80V VDS=200V VDS=320V 3 CGD
ID
CDS GATE CGS VGS VD
10 Fig.39 Application circuit diagram to keep the non-operating condition when over load current condition will continue for specified duration
2
SOURCE
5
1
ID=4A
Output circuit
(1)The output terminal characteristics at the Vcc voltage lower than the "Operation-stop" voltage
TO MAIN TRANSFORMER VOUT
0 0 4 8 12 16 TOTAL STORED GATE CHARGE(nC)
20
Fig.41 The relation between applied gate-source voltage and stored gate charge The charging and discharging current caused by this gate charge makes the gate power dissipation.The relation between gate drive current ID and total gate charge QGSH is shown by following equation; ID=QGSH * fOSC .....................................(11)
M51995A
100k RCLM
Fig.40 Circuit diagram to prevent the MOS-FIT gate potential rising The output terminal has the current sink ability even though the Vcc voltage lower than the "Operation-stop" voltage or Vcc(STOP) (It means that the terminal is "Output low state" and please refer characteristics of output low voltage versus sink current.) This characteristics has the merit not to damage the MOS-FIT at the stop of operation when the Vcc voltage decreases lower than the voltage of Vcc(STOP),as the gate charge of MOSFIT,which shows the capacitive load characteristics to the output terminal,is drawn out rapidly. The output terminal has the draw-out ability above the Vcc voltage of 2V,however,lower than the 2V,it loses the ability and the output terminal potential may rise due to the leakage current. In this case, it is recommended to connect the resistor of 100k between gate and source of MOS-FIT as shown in Fig.40.
Where fOSC is switching frequency As the gate drive current may reach up to several tenths milliamperes at 500kHz operation,depending on the size of MOS-FIT,the power dissipation caused by the gate current can not be neglected. In this case,following action will be considered to avoid heat up of type M51995A. (1) To attach the heat sink to type M51995A (2) To use the printed circuit board with the good thermal conductivity (3) To use the buffer circuit shown next section (3)Output buffer circuit It is recommended to use the output buffer circuit as shown in Fig.42,when type M51995A drives the large capacitive load or bipolar transistor.
(2)MOS-FIT gate drive power dissipation Fig.41 shows the relation between the applied gate voltage and the stored gate charge. In the region 1 ,the charge is mainly stored at CGS as the depletion is spread and CGD is small owing to the off-state of MOS-FIT and the high drain voltage. In the region 2 ,the CGD is multiplied by the "mirror effect" as the characteristics of MOS-FIT transfers from off-state to onstate. In the region 3 ,both the CGD and CGS affect to the characteristics as the MOS-FIT is on-state and the drain voltage is low.
( 24 / 27 )
MITSUBISHI (Dig./Ana. INTERFACE)
M51995AP/FP
SWITCHING REGULATOR CONTROL
Not to lack the output pulse,is recommended to connect the capacitor C4 as shown by broken line. Please take notice that the current flows through the R1 and R2 are superposed to Icc(START).Not to superpose,R1 is connected to Cvcc2 as shown in Fig.27.
VOUT
M51995A
How to get the narrow pulse width during the start of operation
Fig.45 shows how to get the narrow pulse width during the start of the operation.If the pulse train of forcedly narrowed pulsewidth continues too long,the misstart of operation may happen,so it is recommended to make the output pulse width narrow only for a few pulse at the start of operation.0.1F is recommended for the C.
F/B
Fig.42 Output buffer circuit diagram
DET
Fig.43 shows how to use the DET circuit for the voltage detector and error amplifier. For the phase shift compensation,it is recommended to connected the CR network between det terminal and F/B terminal.
M51995A
TO PHOTO COUPLER
100 C
C F/B
C1 R1
DETECTING VOLTAGE
Fig.45 How to get the narrow pulse width
during the start of operation
B
M51995A
DET
C2
R3
How to synchronize with external circuit
Type M51995A has no function to synchronize with external circuit,however,there is some application circuit for synchronization as shown in Fig.46.If this circuit is used,the synchronization may be out of order at the overload condition when the current limiting function starts to operate and VF terminal voltage becomes lower than 3V.
C4 R2
Fig.43 How to use the DET circuit for the voltage detector Fig.44 shows the gain-frequency characteristics between point B and point C shown in Fig.43. The G1, 1 and 2 are given by following equations; R3 G1= R1/R2 .............................................(11) 1 1= C2 * R3 ............................................(12) C1 + C2 2= C1 * C2 * R3 ....................................(13) At the start of the operation,there happen to be no output pulse due to F/B terminal current through C1 and C2,as the potential of F/B terminal rises sharply just after the start of the operation.
GAVDET (DC VOLTAGE GAIN)
M51995A
T-ON CF T-OFF CT
RON
CF
ROFF Q1 Q2
120A
SYNCHRONOU S PULSE
G1
Log
1
2
Fig.44 Gain-frequency characteristics between point B and C shown in Fig.43
0V
0V MINIMUM PULSE WIDTH OF SYNCHRONOUS PULSE
MAXIMUM PULSE WIDTH OF SYNCHRONOUS PULSE
Fig.46 How to synchronize with external circuit
( 25 / 27 )
MITSUBISHI (Dig./Ana. INTERFACE)
M51995AP/FP
SWITCHING REGULATOR CONTROL
COLLECTOR Vcc VOUT
Vcc
M51995A
-Vss (-2V to -5V) GND EMITTER
Fig.47 Driver circuit diagram (1) for bipolar transistor
COLLECTOR
Driver circuit for bipolar transistor
When the bipolar transistor is used instead of MOS-FIT,the base current of bipolar transistor must be sinked by the negative base voltage source for the switching-off duration,in order to make the switching speed of bipolar transistor fast one. In this case,over current can not be detected by detecting resistor in series to bipolar transistor,so it is recommended to use the CT(current transformer). For the low current rating transistor,type M51995A can drive it directly as shown in Fig.48.
Vcc VOUT
M51995A
GND EMITTER
BIPOLAR TRANSISTOR
Fig.48 Driver circuit diagram (2) for bipolar transistor
Attention for heat generation
The maximum ambient temperature of type M51995A is +85C,however,the ambient temperature in vicinity of the IC is not uniform and varies place by place,as the amount of power dissipation is fearfully large and the power dissipation is generated locally in the switching regulator. So it is one of the good idea to check the IC package temperature. The temperature difference between IC junction and the surface of IC package is 15C or less,when the IC junction temperature is measured by temperature dependency of forward voltage of pin junction,and IC package temperature is measured by "thermoviewer",and also the IC is mounted on the "phenol-base" PC board in normal atmosphere. So it is concluded that the maximum case temperature(surface temperature of IC) rating is 120C with adequate margin. As type M51995 has the modified totempole driver circuit, the transient through current is very small and the total power dissipation is decreased to the reasonable power level.Fig.49 shows the transient rush (through)current waveforms at the rising and falling edges of output pulse,respectively.
H-Axis : 20ns/div V-Axis : 50mA/div
AT RISING EDGE OF OUTPUT PULSE
H-Axis : 20ns/div V-Axis : 10mA/div
AT RISING EDGE OF OUTPUT PULSE Fig.49 Through current waveform of totempole driver circuit at no-load and Vcc of 18V condition ( 26 / 27 )
MITSUBISHI (Dig./Ana. INTERFACE)
M51995AP/FP
SWITCHING REGULATOR CONTROL
APPLICATION EXAMPLE
Feed forward types SMPS with multi-output.
AC CFIN R1 A
VOUT2
VOUT
COLLECTOR
Vcc
VOUT1 M51995AP
VF ON/OFF
R2 Cvcc
OVP CF CT F/B RON A ROFF ON/OFF
( 27 / 27 )

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