Mitsubishi M51995AP Switching regulator control Datasheet

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
PIN CONFIGURATION (TOP VIEW)
supply.
This IC can directly drive the MOS-FET with fast rise and fast fall
COLLECTOR
1
16
Vcc
VOUT
2
15
CLM+
EMITTER
3
14
CLM-
VF
4
13
GND
ON/OFF
5
12
CT
It has another big feature of current protection to short and over
OVP
6
11
T-OFF
current,owing to the integrated timer-type protection circuit,if few
DET
7
10
CF
F/B
8
9
T-ON
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.
parts are added to the primary side.
The M51995A is equivalent to the M51977 with externally re-
Outline 16P4
settable OVP(over voltage protection)circuit.
FEATURES
500kHz operation to MOS FET
•Output current...............................................................±2A
•Output rise time 60ns,fall time 40ns
•Modified totempole output method with small through current
COLLECTOR
1
20
Vcc
VOUT
2
19
CLM+
EMITTER
3
18
CLM-
VF
4
17
GND
5
16
6
15
ON/OFF
7
14
CT
Compact and light-weight power supply
HEAT SINK PIN
•Small start-up current............................................90µA 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.
HEAT SINK PIN
OVP
8
13
T-OFF
DET
9
12
CF
F/B
10
11
T-ON
Outline 20P2N-A
16-pin DIP,20-pin SOP 1.5W(at 25°C)
Simplified peripheral circuit with protection circuit and built-in
Connect the heat sink pin to GND.
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
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 75kΩ
•T-OFF pin resistance ROFF..........................2k to 30kΩ
( 1 / 27 )
MITSUBISHI (Dig./Ana. INTERFACE)
M51995AP/FP
SWITCHING REGULATOR CONTROL
BLOCK DIAGRAM
VCC
F/B
DET
GND
7.1V
5.8V
ON/OFF
UNDER
VOLTAGE
LOCKOUT
VOLTAGE
REGULATOR
500
3K
15.2K
6S
1S
OP AMP
1S
1S
OVP(shut down)
2.5V
LATCH
COLLECTOR
PWM
COMPARATOR
PWM
LATCH
VOUT
EMITTER
OSCILLATOR CAPACITANCE CF
OSCILLATOR RESISTANCE T-ON
(ON duty)
OSCILLATOR
(TRIANGLE)
+CURRENT
LIMIT LATCH
-CURRENT
LIMIT LATCH
INTERMITTENT
ACTION AND
OSC CONTROL
INTERMITTENT
ACTION
OSCILLATOR RESISTANCE T-OFF
(OFF duty)
VF
CLM+
+CURRENT LIMIT
CLM-CURRENT LIMIT
CT
INTERMITTENT OPERATION
DETERMINE CAPACITANCE
ABSOLUTE MAXIMUM RATINGS
Symbol
VCC
VC
Parameter
Supply voltage
Collector voltage
IO
Output current
VVF
VON/OFF
VCLMVCLM+
IOVP
VDET
IDET
VFB
ITON
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
ITOFF
Pd
K
Topr
Tstg
Tj
Conditions
Peak
Continuous
Ta=25˚C
Ta>25˚C
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
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=25°C, unless otherwise noted)
Block
Symbol
Parameter
Test conditions
∆Vcc
Difference voltage between
operation start and stop
IccL
Stand-by current
IccO
Operating circuit current
Icc OFF
Circuit current in OFF state
Icc CT
Circuit current in timer OFF state
Icc OVP
Circuit current in OVP state
VTHH ON/OFF
VTHL ON/OFF
∆VTHON/OFF
IFBMIND
IFBMAXD
∆IFB
VFB
RFB
VDET
IINDET
GAVDET
VTHOVPH
∆VTHOVP
ITHOVP
IINOVP
VCCOVPC
VCC(STOP)
-VCCOVPC
16.2
9.9
∆Vcc=Vcc(START) -Vcc(STOP)
5.0
6.3
7.6
V
Vcc=14.5V,Ta=25°C
Vcc=14.5V,-30≤Ta≤85°C
Vcc=30V
Vcc=25V
Vcc=14V
Vcc=25V
50
40
10
0.95
50
0.95
90
90
140
190
Vcc=14V
Vcc=25V
Vcc=9.5V
1.3
125
15
1.31
90
1.35
160
2.0
200
21
5.0
140
2.0
240
3.0
310
2.1
1.9
0.1
2.6
2.4
0.2
3.1
2.9
3.0
-2.1
-0.90
-1.35
4.9
420
2.4
-1.54
-0.55
-0.99
5.9
-1.0
-0.40
-0.70
7.1
600
2.5
780
2.6
3.0
µA
µA
mA
mA
µA
mA
µA
mA
µA
V
V
V
mA
mA
mA
V
Ω
V
µA
dB
mV
mV
µA
µA
V
ITHOVPC
ON/OFF terminal high threshold voltage
ON/OFF terminal hysteresis voltage
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
fTIMER
Timer frequency
ITIMECH
Timer charge current
TIMEOFF/ON
VTHCLMIINCLMTPDCLMVTHCLM+
IINCLM+
TPDCLM+
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
Unit
15.2
9.0
Vcc(STOP)
ON/OFF terminal low threshold voltage
Current at 0% duty
Current at maximum duty
Limits
Typ.
Max.
35
17.2
10.9
Operating supply voltage range
VCC
VCC(START) Operation start up voltage
VCC(STOP) Operation stop voltage
Min.
F/B terminal input current
F/B terminal input current
∆IFB=IFBMIND-IFBMAXD
F/B terminal input current=0.95mA
VDET=2.5V
80
80
7.5
1.0
40
750
30
150
150
9.0
0.55
1.20
-5≤Ta≤85°C
VCLM-=-0.1V
-480
-210
0.27
-193
-178
-147
7.0
-220
-170
-320
-140
0.40
-138
-127
-105
8.7
-200
-125
-213
-93
0.60
-102
-94
-78
11.0
-180
-90
-5≤Ta≤85°C
VCLM+=0V
180
-270
100
200
-205
100
220
-140
30
540
∆VTHOVP=VTHOVPH-VTHOVPL
VOVP=400mV
OVP terminal is open.
(high impedance)
Vcc=30V
Vcc=18V
CT=4.7µF
VCT=3.3V,Ta=-5°C
Ta=25°C
Ta=85°C
( 3
/ 27 )
960
250
250
10.0
V
V
V
V
µA
Hz
µA
mV
µA
ns
mV
µA
ns
MITSUBISHI (Dig./Ana. INTERFACE)
M51995AP/FP
SWITCHING REGULATOR CONTROL
ELECTRICAL CHARACTERISTICS (VCC=18V,Ta=25˚C, unless otherwise noted)(CONTINUE)
Block
Symbol
Parameter
Test conditions
Min.
Limits
Typ.
Max.
Unit
fOSC
Oscillating frequency
RON=20kΩ,ROFF=17kΩ
CF=220pF,-5≤Ta≤85°C
170
188
207
kHz
TDUTY
VOSCH
VOSCL
Maximum ON duty
Upper limit voltage of oscillation waveform
Lower limit voltage of oscillation waveform
fOSC=188kHz
fOSC=188kHz
47.0
3.97
1.76
50.0
4.37
1.96
53.0
4.77
2.16
%
V
V
∆VOSC
Voltage difference between upper limit and
lower limit of OSC waveform
VF=5V
OSC frequency in CLM
operating state
VF=2V
fOSC=188kHz
2.11
2.41
2.71
V
170
108
11.0
2.7
188
124
13.7
3.0
2
0.05
0.7
0.69
1.3
16.5
16.0
50
35
207
143
22.0
3.3
6
0.4
1.4
1.0
2.0
fOSCVF
TVFDUTY
VTHTIME
IVF
VOL1
VOL2
VOL3
VOL4
VOH1
VOH2
TRISE
TFALL
Duty in CLM operating state VF=0.2V
VF voltage at timer operating start
VF terminal input current
Output low voltage
Output high voltage
Output voltage rise time
Output voltage fall time
RON=20kΩ,ROFF=17kΩ
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
( 4 / 27 )
16.0
15.5
kHz
V
µA
V
V
V
V
V
V
ns
ns
MITSUBISHI (Dig./Ana. INTERFACE)
M51995AP/FP
SWITCHING REGULATOR CONTROL
TYPICAL CHARACTERISTICS
THERMAL DERATING
(MAXIMUM RATING)
1800
CIRCUIT CURRENT VS.SUPPLY VOLTAGE
(NORMAL OPERATION)
22m
RON=18kΩ
ROFF=20kΩ
18m
1500
fOSC=500kHz
16m
1200
14m
900
12m
fOSC=100kHz
10m
600
100µ
300
Ta=-30°C
Ta=25°C
Ta=85°C
50µ
0
0
25
75 85 100
50
125
10
20
30
SUPPLY VOLTAGE Vcc(V)
0
150
40
AMBIENT TEMPERATURE Ta(°C)
CIRCUIT CURRENT VS.SUPPLY VOLTAGE
(OVP OPERATION)
CIRCUIT CURRENT VS.SUPPLY VOLTAGE
(OFF STATE)
8.0
OVP RESET POINT
8.87V(-30°C)
7.0
8.94V(25°C)
9.23V(85°C)
6.0
3.0
5.0
2.0
4.0
Ta=-30°C
Ta=25°C
3.0
Ta=85°C
Ta=25°C
Ta=85°C
Ta=-30°C
1.0
2.0
1.0
0
0
10.0
20.0
30.0
0
40.0
10
0
SUPPLY VOLTAGE Vcc(V)
20
30
40
SUPPLY VOLTAGE Vcc(V)
CIRCUIT CURRENT VS.SUPPLY VOLTAGE
(TIMER OFF STATE)
1.1
OVP TERMINAL THRESHOLD VOLTAGE
VS.AMBIENT TEMPERATURE
3.0
1.0
0.9
Ta=25°C
2.0
H threshold voltage
(VTHOVPH)
0.8
Ta=85°C
0.7
Ta=-30°C
L threshold voltage
(VTHOVPL)
0.6
1.0
0.5
0.4
0
0
10
20
30
SUPPLY VOLTAGE Vcc(V)
40
0.3
( 5 / 27 )
-40
-20
0
20 40
60
80 100
AMBIENT TEMPERATURE Ta(°C)
MITSUBISHI (Dig./Ana. INTERFACE)
M51995AP/FP
SWITCHING REGULATOR CONTROL
THRESHOLD VOLTAGE OF ON/OFF
TERMINAL VS.AMBIENT TEMPERATURE
THRESHOLD VOLTAGE OF ON/OFF
TERMINAL VS.AMBIENT TEMPERATURE
3.4
25.0
3.2
3.0
ON
OFF
ON
OFF
40
60
20.0
2.8
2.6
15.0
2.4
OFF
ON
2.2
OFF
5.0
ON
2.0
1.8
-40
-20
0
20
40
60
80
0
-60
100
-40
-20
0
20
80
AMBIENT TEMPERATURE Ta(°C)
AMBIENT TEMPERATURE Ta(°C)
INPUT CURRENT OF VF TERMINAL
VS.INPUT VOLTAGE
DISCHARGE CURRENT OF TIMER
VS.AMBIENT TEMPERATURE
18
-10
-9
100
17
-8
16
-7
15
-6
-5
14
-4
13
Ta=-30°C
-3
Ta=25°C
12
-2
Ta=85°C
11
-1
0
0
1
2
-200
3
4
5
6
7
8
9
10
10
-60
-40
-20
0
20
40
60
80
VF TERMINAL VOLTAGE VVF(V)
AMBIENT TEMPERATURE Ta(°C)
CHARGE CURRENT OF TIMER
VS.AMBIENT TEMPERATURE
ON AND OFF DURATION OF TIMER
VS.AMBIENT TEMPERATURE
(INTERMITTENT OPERATION)
175
100
1.4
TIMER ON•••CIRCUIT OPERATION ON
TIMER OFF••CIRCUIT OPERATION OFF
-180
150
-160
1.3
-140
TIMER ON
125
-120
1.2
-100
TIMER OFF
100
-80
1.1
-60
-40
-60
-40
-20
0
20
40
60
80
100
75
-60
AMBIENT TEMPERATURE Ta(°C)
-40
-20
0
20
40
60
80
AMBIENT TEMPERATURE Ta(°C)
( 6 / 27 )
1.0
100
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
AMBIENT TEMPERATURE Ta(°C)
AMBIENT TEMPERATURE Ta(°C)
THRESHOLD VOLTAGE OF CLM- TERMINAL
VS. AMBIENT TEMPERATURE
CLM+ TERMINAL CURRENT
VS. CLM+ TERMINAL VOLTAGE
100
-400
-300
205
Ta=-30°C
Ta=25°C
200
-200
195
-100
-60
-40
-20
0
20
40
60
80
Ta=85°C
0
100
0
AMBIENT TEMPERATURE Ta(°C)
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)
CLM- TERMINAL CURRENT
VS. CLM- TERMINAL VOLTAGE
-500
2.6
2.4
-400
OUTPUT HIGH VOLTAGE VS.
OUTPUT SOURCE CURRENT
Vcc=18V
Ta=25°C
2.2
2.0
-300
1.8
Ta=-30°C
1.6
Ta=25°C
-200
1.4
Ta=85°C
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 )
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
DETECTION VOLTAGE
VS. AMBIENT TEMPERATURE
5.0
Ta=25°C
2.55
4.0
2.50
3.0
Vcc=18V
2.0
Vcc=5V
2.45
1.0
0
10m
1m
100m
10
1
2.40
-60
-40
-20
0
20
40
60
80
100
AMBIENT TEMPERATURE Ta(°C)
OUTPUT SINK CURRENT IOL(A)
DETECTION AMP VOLTAGE GAIN
VS. FREQUENCY
INPUT CURRENT OF DETECTION AMP
VS. AMBIENT TEMPERATURE
1.6
50.0
1.5
40.0
1.4
1.3
30.0
1.2
20.0
1.1
1.0
10.0
0.9
0.8
-60
-40
-20
0
20
40
60
80
100
0
100
AMBIENT TEMPERATURE Ta(°C)
50
40
100k
1M
10M
ON duty
VS. F/B TERMINAL INPUT CURRENT
ON duty
VS. F/B TERMINAL INPUT CURRENT
50
(fOSC=100kHz)
RON=18kΩ
ROFF=20kΩ
(fOSC=200kHz)
RON=18kΩ
ROFF=20kΩ
40
30
Ta=-30°C
Ta=-30°C
Ta=25°C
Ta=25°C
20
Ta=85°C
Ta=85°C
10
10
00
10k
FREQUENCY f(Hz)
30
20
1k
0
1.5
2.0
1.0
2.5
0.5
F/B TERMINAL INPUT CURRENT IF/B (mA)
( 8 / 27 )
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
UPPER & LOWER LIMIT VOLTAGE OF OSC
VS. AMBIENT TEMPERATURE
ON duty VS.
F/B TERMINAL INPUT CURRENT
50
(fOSC=500kHz)
RON=18kΩ
ROFF=20kΩ
40
RON=18kΩ
ROFF=20kΩ
5.2
fOSC=500kHz
fOSC=200kHz
fOSC=100kHz
4.8
4.4
30
Ta=-30°C
4.0
Ta=25°C
Ta=85°C
20
fOSC=100kHz
fOSC=200kHz
fOSC=500kHz
2.2
2.0
10
1.8
0
0
0.5
1.0
1.5
2.0
-60
2.5
F/B TERMINAL INPUT CURRENT IF/B(mA)
OSCILLATING FREQUENCY VS. CF
TERMINAL CAPACITY
100
-40 -20
0
20
40 60 80
AMBIENT TEMPERATURE Ta(°C)
ON duty VS. ROFF
100
10000
90
80
1000
70
RON=75kΩ
RON=22kΩ
ROFF=12kΩ
100
60
51kΩ
50
RON=36kΩ
ROFF=6.2kΩ
36kΩ
24kΩ
22kΩ
18kΩ
15kΩ
10kΩ
40
RON=24kΩ
ROFF=20kΩ
30
10
20
10
1
1
3
10
3
100
3
1000
3
0
10000
5
7
10
3
5
CF TERMINAL CAPACITY(pF)
ROFF(kΩ)
OSCILLATING FREQUENCY VS.
AMBIENT TEMPERATURE
OSCILLATING FREQUENCY VS.
AMBIENT TEMPERATURE
120
110
3
1
700
RON=24kΩ
ROFF=20kΩ
CF=330pF
7
100
RON=24kΩ
ROFF=20kΩ
CF=47pF
600
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
ON duty VS. AMBIENT TEMPERATURE
100
100
(fOSC=100kHz)
90
80
(fOSC=200kHz)
90
RON=36k,ROFF=6.2k
80
RON=36k,ROFF=6.2k
70
70
60
RON=22k,ROFF=12k
60
RON=22k,ROFF=12k
50
RON=24k,ROFF=20k
RON=22k,ROFF=22k
50
RON=24k,ROFF=20k
RON=22k,ROFF=22k
40
RON=18k,ROFF=24k
40
RON=18k,ROFF=24k
30
RON=15k,ROFF=27k
30
RON=15k,ROFF=27k
20
20
10
10
0
-60
-40
-20
0
20
40
60
0
-60
100
80
AMBIENT TEMPERATURE Ta(°C)
100
INPUT VOLTAGE OF TERMINAL VS.
EXPANSION RATE OF PERIOD
ON duty VS. AMBIENT TEMPERATURE
100
-40 -20
0
20
40 60 80
AMBIENT TEMPERATURE Ta(°C)
5.0
(fOSC=500kHz)
(fOSC=100kHz)
90
RON=36k,ROFF=6.2k
80
4.0
1 RON=15k,ROFF=27k
2 RON=18k,ROFF=24k
70
60
RON=22k,ROFF=12k
50
RON=24k,ROFF=20k
RON=22k,ROFF=22k
40
RON=18k,ROFF=24k
3 RON=22k,ROFF=22k
4 RON=24k,ROFF=20k
5 RON=22k,ROFF=12k
3.0
6 RON=36k,ROFF=6.2k
2.0
RON=15k,ROFF=27k
30
20
1.0
10
0
-60
-40
-20
0
20
40
60
80
0
100
1
0
4
2
3
6
4
8
6
5
10
12
14 16
18
EXPANSION RATE OF PERIOD(TIMES)
AMBIENT TEMPERATURE Ta(°C)
INPUT VOLTAGE OF TERMINAL VS.
EXPANSION RATE OF PERIOD
5.0
1m
(fOSC=500kHz)
OVP TERMINAL INPUT VOLTAGE VS.
INPUT CURRENT
Ta=85°C
Ta=25°C
Ta=-30°C
4.0
1 RON=15k,ROFF=27k
2 RON=18k,ROFF=24k
100µ
3 RON=22k,ROFF=22k
4 RON=24k,ROFF=20k
5 RON=22k,ROFF=12k
3.0
2
6 RON=36k,ROFF=6.2k
2.0
10µ
1.0
0
1
0
2
3
4
5
6
2
4 6
8 10 12 14 16 18
EXPANSION RATE OF PERIOD(TIMES)
20
1µ
( 10 / 27 )
0.2
0.4
0.6
0.8
1.0
OVP TERMINAL INPUT VOLTAGE VOVP(V)
20
MITSUBISHI (Dig./Ana. INTERFACE)
M51995AP/FP
SWITCHING REGULATOR CONTROL
CURRENT FROM OVP TERMINAL FOR OVP
RESET VS. SUPPLY VOLTAGE
800
700
600
500
Ta=-30°C
Ta=25°C
Ta=85°C
400
300
200
100
0
0
5
10
15
20
25
30
35
40
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
R1
CFIN
A
1
2
16
VOUT1
R2
Cvcc
M51995AP
4
5
3
14 13 15
9
10
11 12
8
6
7
OVP
CF
CT
F/B
RON
ROFF
A
ON/OFF
Pin No.is related with M51995AP
Fig.1 Example application circuit diagram of feed forward regulator
AC
R1
CFIN
1
VOUT
2
16
OVP
F/B
R21
M51995AP
Cvcc
4
5
3
14 13 15
9
10
11 12
8
6
7
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
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".
Start-up circuit section
The start-up current is such low current level as typical 90µ
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).
5.8V
Q4
T-ON
1/16
Q3
RON
T-OFF
ROFF
Q1
CHARGING
SW1
FROM
VF SIGNAL
Vz ~ 4.2V
SWITCHED BY
CHARGING AND
DISCHARGING
SIGNAL
CF
Icco
~ 14mA
CF
SW2
Q2
DISCHARGING
M51995
IccL
~ 90µA
Vcc
Vcc
(STOP)
(START)
Fig.4 Schematic diagram of charging and discharging
control circuit for OSC.capacitor CF
~ 9.9V ~ 16.2V
VOSCH
~ 4.4V
SUPPLY VOLTAGE Vcc(V)
Fig.3 Circuit current vs.supply voltage
VOSCL
~ 2.0V
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
VOL
(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
~
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
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
~
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.
VOSCH
~ 4.4V
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.
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
Fig.6 OSC.waveform with operation of intermittent
and OSC.control circuit operation
~ 4.5V
VVF;VF terminal voltage
VVFO ~ 0.4V
VVF-VFO=0 if VVF-VVFO<0
START FROM 0V
VVF-VVFO=VT-OFF if VVF-VVFO>VT-OFF ~ 3.5V
VOSCH
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
FIRST
PULSE
(s) ...............(7)
VOH
The minimum off-duration is approximately given as;
NO GENERATE
PULSE
VOL
~
0
(VOSCH - VOSCL) X CF
VVF - VVFO +
VT - ON
(s)...............(8)
ROFF X CF
16 X RON X CF
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
Current limiting 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)
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
WAVEFORM OF
CLM+ TERMINAL
5.8V
POINT A
POINT B
LATCH
6S
+
1S
CURRENT LIMIT
SIGNAL TO SET
LATCH
POINT C
PWM
COMP
F/B
TO
OUTPUT
WAVEFORM OF
VOUT TERMINAL
FROM
OSC
M51995A
(a) +current limit
CF
Fig.9 PWM comparator and latch circuit
OSC WAVEFORM
OF CF TERMINAL
OSC WAVEFORM
POINT A
WAVEFORM OF
CLM- TERMINAL
VTHCLM~ -200mV
WAVEFORM
OF O.S.C. &
POINT A
CURRENT LIMIT
SIGNAL TO SET
LATCH
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
( 15 / 27 )
Fig.11 Operating waveforms of current limiting circuit
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 100Ω for RNF because such
range of RNF is not influenced by the flow-out current of some
200µA from CLM terminal and CNF is designed to have the
enough value to absorb the noise voltage.
+
CURRENT LIMIT
SIGNAL
GND
OUTPUT OF CURRENT
LIMIT LATCH
GND
OUTPUT OF INTERMITTENT
ACTION and OSC.
CONTROL CIRCUIT
GND
(b) Without current limit signal
Fig.13 Timing chart of intermittent and OSC.control circuit
+
M51995A
OSC WAVEFORM
OF CF TERMINAL
M51995A
Intermittent action circuit section
VOUT
VOUT
RNF
CLM+
GND
CNF
GND
RCLM
CNF
RCLM
CLMRNF
(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
120µA 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 15µA 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
(~120µA)
VTHTIME (~ 3V)
A
CT
OSC WAVEFORM
OF CF TERMINAL
Q
SWA
SWB
CONTROL
LOGIC
B
VF
CT
ITIMEOFF
(~15µA)
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
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.
NO OPERATING
DURATION
8V
2V
Fig.15 Waveform of CT terminal
~7.1V
500Ω
3k
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
500Ω
1.0
1S
6S
F/B
0.5
OP AMP
DET
+
2.5V
0
0
5
10
15
20
25
30
SUPPLY VOLTAGE Vcc(V)
Fig.18 Equivalent circuit diagram of
voltage detector
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.
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
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 20µA at
operation and 3µA at stopping.So the unstable operation is not
appeared even if the ON/OFF terminal voltage signal varies
slowly.
( 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 100kΩ 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
Q2
Q3
Q4
OPERATE STOP AT Q4 ON
I:3µA AT STOPPING
I:20µA AT OPERATING
I
Fig.19 ON/OFF circuit
Vcc
30k~100kΩ
M51995A
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 150µA when the OVP does not
operates but it decreases to about 2µA when OVP operates.
It is necessary to input the sufficient larger current(800µA 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 +
20µA)
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.
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
100µA
8k
I1
12k
Q1
Q2
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.
400
Q3
OVP
APPLICATION NOTE OF TYPE M51995AP/FP
Design of start-up circuit and the power supply
of IC
2.5k
I2
GND
I1=0 when OVP operates
(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 300µA flows
through R1 in order to overcome the operation start-up current
Icc(START) and Cvcc is in the range of 10 to 47µF.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.
Fig.22 Detail diagram of OVP circuit
8
OVP RESET POINT
8.82V(-30°C)
8.97V(25°C)
9.07V(85°C)
7
6
5
Ta=-30°C
Ta=25°C
Ta=85°C
4
RECTIFIED DC
VOLTAGE FROM
SMOOTHING CAPACITOR
MAIN TRANSFORMER
R1
VF
3
THIRD WINDING OR
BIAS WINDING
Vcc
2
1
0
M51995A
0
5
10
15
20
25
30
35
CVcc
40
SUPPLY VOLTAGE Vcc(V)
GND
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
R1
VF
Vcc
NB
M51995A
R2
THIRD WINDING OF
TRANSFORMER
CVcc
GND
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.
(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
COLLECTOR
MAIN
TRANSFORMER
THIRD
WINDING
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.
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)
M51995A
CVcc
OUTPUT
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 47µF for CVCC1,and about 5
times capacity bigger than CVCC1 for CVCC2 in Fig.27.
( 20 / 27 )
MITSUBISHI (Dig./Ana. INTERFACE)
M51995AP/FP
SWITCHING REGULATOR CONTROL
R1
TO MAIN
TRANSFORMER
MAIN
TRANSFORMER
THIRD
WINDING
Vcc
R1
M51995A
CVcc1
CVcc2
Vcc
~
GND
CFIN R2
Cvcc
M51995A
GND
THE TIME CONSTANT OF
THIS PART SHOULD BE SHORT
Fig.27 DC source circuit for stable start-up
Fig.29 Example circuit diagram to make the
OVP-reset-time fast
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
(~150µA) 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.
MAIN
TRANSFORMER
THIRD
WINDING
Vcc
M51995A
470Ω
OVP
CVcc
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.
10k
Vcc
(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
I2
(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.
CLM
RCLM
I1
(a) Feed forward system
IP1
R1
I1
CFIN
INPUT
SMOOTHING
CAPACITOR
COLLECTOR
Vcc
IP2
Cvcc
VOUT
I2
M51995A
CLM+
GND
RNF1
EMITTER
CNF
(b) Primary and secondary current
RNF2 RCLM
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
Vcc
COLLECTOR
VOUT
M51995A
Cvcc
EMITTER
GND
CLM+
CNF
OUTPUT CURRENT
RNF2 RCLM
RNF1
Fig.34 Over current limiting curve on feed forward
system
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 270µA.
In order to be not influenced from these resistor paralleled value
of RNF1 and RNF2,(RNF1/RNF2)is recommended to be less than
100Ω.
The RCLM should be the non-inductive resistor.
(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 15kΩ 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
TO VF
VOUT
FROM
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.
15kΩ 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).
TO VF
VOUT
Vcc
TO MAKE THE KNEE
POINT HIGH
TO MAKE THE KNEE
POINT LOW
M51995A
COLLECTOR
VF
R1
Fig.36 How to control the knee point
CVcc
R2
(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
M51995A
DRAIN
VDS=80V
VDS=200V
15
OVP
ID
VDS=320V
CGD
CDS
3
GATE
10
VD
CGS
VGS
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
Output circuit
ID=4A
0
0
(1)The output terminal characteristics at the Vcc voltage
lower than the "Operation-stop" voltage
4
8
12
16
20
TOTAL STORED GATE CHARGE(nC)
Fig.41 The relation between applied gate-source
voltage and stored gate charge
TO MAIN
TRANSFORMER
VOUT
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;
M51995A
100kΩ
RCLM
ID=QGSH • fOSC .....................................(11)
Where
Fig.40 Circuit diagram to prevent the MOS-FIT gate
potential rising
fOSC is switching frequency
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 100kΩ
between gate and source of MOS-FIT as shown in Fig.40.
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.0.1µF is
recommended for the C.
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.
DET
C2
100Ω
TO PHOTO
COUPLER
C
Fig.45 How to get the narrow pulse width
R1
F/B
M51995A
M51995A
DETECTING
VOLTAGE
C1
C
F/B
during the start of operation
R3
How to synchronize with external circuit
B
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)
M51995A
CF
T-ON
RON
CF
T-OFF
CT
ROFF
120µA
Q1
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.
Q2
SYNCHRONOU
S
PULSE
GAVDET
(DC VOLTAGE GAIN)
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
Vcc
VOUT
M51995A
-Vss
(-2V to -5V)
GND
EMITTER
Fig.47 Driver circuit diagram (1) for bipolar transistor
COLLECTOR
Driver circuit for bipolar transistor
Vcc
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.
VOUT
M51995A
GND
BIPOLAR
TRANSISTOR
EMITTER
Fig.48 Driver circuit diagram (2) for bipolar transistor
Attention for heat generation
The maximum ambient temperature of type M51995A is
+85°C,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 15°C 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 120°C 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.
VOUT2
AC
R1
CFIN
A
VOUT
COLLECTOR
Vcc
VOUT1
M51995AP
ON/OFF
VF
R2
Cvcc
OVP
CF
CT
F/B
RON
ROFF
A
ON/OFF
( 27 / 27 )