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FAN7554 Versatile PWM Controller
©2003 Fairchild Semiconductor Corporation
www.fairchildsemi.com
Rev. 1.0.3
Features
Current mode control
Pulse by pulse current limiting
Low external components
Under voltage lockout(UVLO): 9V/15V
Stand-by current: typ. 100uA
Power saving mode current: typ. 200uA
Operating current: typ. 7mA
Soft start
On/off control
Over load protection(OLP)
Over voltage protection(OVP)
Over current protection(OCP)
Over current limit(OCL)
Operating frequency up to 500kHz
1A totem-pole output current
Applications
Off-Line & DC-DC converter
Description
The FAN7554 is a fixed frequency current mode PWM
controller. It is specially designed for off-line and DC to DC
converter applications with minimal external components.
These integrated circuits feature a trimmed oscillator for
precise duty cycle control, a temperature compensated
reference, an ON/OFF control, a high gain error amplifier, a
current sensing comparator, and a high current totem-pole
output. The FAN7554 has various protection functions such
as an over load protection, an over current protection, and
the over voltage protection, which include built-in auto
restart circuit. The FAN7554 is available in the 8-DIP
package as well as the 8-SOP package.
FAN7554
Versatile PWM Controller
8-DIP
8-SOP
1
1 FAN7554
2
Internal Block Diagram
Absolute Maximum Ratings
( Ta = 25
°
C, unless otherwise specified )
Note:
1. Junction -to -air thermal resistance test environments.
- JESD51-2 : Integrated circuits thermal test method environmental conditions-natural convection (still air).
- JESD51-3 : Low effective thermal conductivity test board for leaded surface mount packages.
- JESD51-10 : Test boards for through-hole perimeter leaded package thermal measurements.
Parameter
Symbol
Value
Unit
Supply voltage
Vcc
30
V
Output current
I
O
±1
A
Input voltage to FB pin
V
FB
-0.3 to V
SD
V
Input voltage to IS pin
V
IS
-0.3 to V
OC
V
Power dissipation at T
A
25
°
C
8-DIP
8-SOP
P
D
0.85
0.42
W
Operating temperature
T
OPR
-25 to +85
°
C
Storage temperature
T
STG
-55 to +150
°
C
Thermal resistance, junction-to-air (Note1)
8-DIP
8-SOP
R ja
147.8
291.4
°
C/W
OSC
6
7
1
5
4
3
8
FB
Rt/Ct
Vcc
OUT
GND
I S
2
S/S
1.5V
+
3.5V
0.3V
14V
15V/9V
UVLO
2V
OLP
6V
5uA
Vcc
Offset(0.1V)
PWM
R
MAX. 1V
2R
UVLO-out
S Q
R
CLK
PWR
/
SAVE
on
off
Vref
S
Q
R
1k
Vref
100uA
Vref
1mA
Vref
S
R
Q
OVP
34V
OVP-out
OCL-out
OCL
_
+
_
+
_
+
_
+
_
+
_
+
_
+
_
OSC
6
6
7
7
1
1
5
5
4
4
3
3
8
8
FB
Rt/Ct
Vcc
OUT
GND
I S
2
2
S/S
1.5V
+
3.5V
0.3V
14V
15V/9V
UVLO
2V
OLP
6V
5uA
Vcc
5uA
Vcc
Offset(0.1V)
PWM
R
MAX. 1V
2R
UVLO-out
S Q
R
CLK
PWR
/
SAVE
on
off
Vref
S
Q
R
1k
1k
Vref
100uA
Vref
1mA
Vref
S
R
Q
OVP
34V
OVP-out
OCL-out
OCL
_
+
_
+
_
+
_
+
_
+
_
+
_
+
_ FAN7554
3
Temperature Characteristics
( -25
°
C

Ta
85
°
C )
PIN Array
PIN Definitions
Parameter
Symbol
Value
Unit
Vref temperature stability V
REF
3
±0.5
%
Fosc temperature stability F
OSC
2
±5
%
Pin Number
Pin Name
Pin Function Description
1
FB
Inverting(-) input of pwm comparator, on/off control & OLP sensing terminal.
2
S/S
Soft start
3
IS
Non-inverting(+) input of PWM comparator, OCL sensing terminal
4
Rt/Ct
Oscillator time constant(Rt/Ct)
5
GND
Ground
6
OUT
Output of gate driver
7
Vcc
Power supply
8
Vref
Output of 5V reference
Vref
Vcc
OUT
GND
7
7
7
7
6
6
6
6
5
5
5
5
8
8
8
8
2
2
2
2
3
3
3
3
4
4
4
4
1
1
1
1
Y
Y
Y
Y W
W
W
W W
W
W
W
A
A
A
A N
N
N
N 7
7
7
7 5
5
5
5 5
5
5
5 4
4
4
4
F
F
F
F
Rt/Ct
IS
S/S
FB FAN7554
4
Electrical Characteristics
(Ta = 25
°
C, Vcc=16V, Rt=10k , Ct=3.3nF unless otherwise specified)
Parameter
Symbol
Conditions
Min.
Typ.
Max.
Unit
< REFERENCE SECTION >
Reference output voltage
V
REF
T
j
=25
°
C , Iref =1mA
4.90
5.00
5.10
V
Line regulation V
REF1
Vcc =12V ~ 25V
-
6
20
mV
Load regulation V
REF2
Iref =1mA ~ 20mA
-
6
25
mV
Short circuit output current
I
SC
T
j
= 25
°
C
-
0.1
0.18
A
< OSCILLATOR SECTION >
Oscillation frequency
F
OSC
T
j
= 25
°
C
45
50
55
kHz
Frequency change with Vcc F
OSC1
Vcc = 12V ~ 25V
-
0.05
1.0
%
Ramp high voltage
V
RH
-
-
2.8
-
V
Ramp low voltage
V
RL
-
-
1.2
-
V
Discharge current
Idisch
V
RT/CT
= 3.3V
6.1
-
9.4
mA
< PWM SECTION >
Sense threshold voltage
V
TH(IS)
V
FB
= 5V
0.8
1.0
1.2
V
Feedback threshold voltage
V
TH(FB)
V
IS
= 0V
0.2
0.3
0.4
V
Feedback source current
I
FB
V
FB
= 0V, V
S/S
= 5V
-
1.0
-
mA
Max. duty cycle
D
(MAX)
-
92
95
98
%
Min. duty cycle
D
(MIN)
-
-
-
0
%
< PROTECTION SECTION >
Shutdown delay current
I
SD
4V V
FB
V
SD
3.5
5
6.5
uA
Shutdown feedback voltage
V
SD
V
FB
> 5V
5.4
6
6.6
V
Over current protection
V
OC
V
IS
> 1.5V,

t
on
> 500nS
1.6
2
2.4
V
Over voltage protection
V
OVP
-
30
34
38
V
< ON/OFF CONTROL SECTION >
Off mode sink current
I
SINK
V
FB
< V
TH(FB)
, V
S/S
= 5V
-
4
-
mA
Off threshold voltage
V
OFF
V
FB
< V
TH(FB)
1.2
1.5
1.8
V
< SOFT-START SECTION >
Soft start current
I
S/S
V
FB
= 5V, V
S/S
= 0V
-
1.1
-
mA
Soft start limit voltage
V
LIM(S/S)
Vcc = 16V
-
5.2
-
V
<OUTPUT SECTION>
Low output voltage1
V
OL1
V
CC
= 18V, I
O
= 50mA
-
0.15
0.4
V
High output voltage1
V
OH1
V
CC
= 18V, I
O

= -50mA
13
15
17
V
Low output voltage2
V
OL2
V
CC
= 18V, I
O
= 200mA
-
1.5
2.5
V
High output voltage2
V
OH2
Vcc = 18V, Io = -200mA
12
14
16
V
Rising time (Note1)
t
R
T
j
= 25
°
C, C
L
= 1nF
-
80
-
ns
Falling time (Note1)
t
F
T
j
= 25
°
C, C
L
= 1nF
-
40
-
ns
<UVLO SECTION>
Start threshold voltage
V
TH(ST)
-
13.2
15
16.2
V
Min. operating voltage
V
OPR(M)
-
8.2
9
10.2
V FAN7554
5
Electrical Characteristics
(Continued)
(Ta = 25
°
C, Vcc=16V, Rt =10k ,
Ct = 3.3nF unless otherwise specified)
Note:
1. These parameters, although guaranteed, are not 100% tested in production.
Parameter
Symbol
Conditions
Min.
Typ.
Max.
Unit
<TOTAL STAND-BY CURRENT SECTION>
Start-up current
I
ST
-
-
0.1
0.2
mA
Operating supply current
I
OP
-
-
7
10
mA
Off State current
I
OFF
V
FB
<V
TH(FB)
,V
S/S
<V
OFF
-
0.2
0.4
mA FAN7554
6
Typical Perfomance Characteristics
[ Rt vs. Freqency ]
[ Rt vs. Freqency ]
[ Rt vs. Freqency ]
[ Rt vs. Freqency ]
0.1
1.0
10.0
100.0
1000.0
10000.0
1
10
100
Rt[Kohm]
F
r
e
q
u
en
cy
[
k
Hz
]
0.33n
1.1n
3.3n
11n
33n
[ Ct vs Dead time ]
[ Ct vs Dead time ]
[ Ct vs Dead time ]
[ Ct vs Dead time ]
0.100
1.000
10.000
100.000
0.1
1
10
100
Ct[nF]
D
e
ad Ti
m
e
[
u
s
e
c
]
1K
2K
5K
10K
20K
50K
100K
[ Ct vs Duty ]
[ Ct vs Duty ]
[ Ct vs Duty ]
[ Ct vs Duty ]
15.0
25.0
35.0
45.0
55.0
65.0
75.0
85.0
95.0
0.1
1
10
100
Ct [nF]
Du
t
y
[%]
1K
2K
5K
10K
20K
50K
100K
[ Cload vs Tr & Tf ]
[ Cload vs Tr & Tf ]
[ Cload vs Tr & Tf ]
[ Cload vs Tr & Tf ] 50Khz,95% duty
0
100
200
300
400
500
600
700
800
1
10
100
Cload [ nF]
Tim
e
[n
s
ec]
Tr
Tf
Figure 1. Rt vs. Frequency
Figure 2. Ct vs. Dead Time
Figure 3. Ct vs. Duty
Figure 4. Cload vs. Tr & Tf FAN7554
7
Typical Performance Characteristics
(Continued)
Figure 5. Temperature vs. Start-up Current
Figure 6. Temperature vs. Operating Supply Current
Figure 8. Temperature vs. Oscillation frequency
Figure 10. Temperature vs. Min. Operating Voltage
Figure 7. Temperature vs. Reference Voltage
Figure 9. Temperature vs. Start Threshold Voltage FAN7554
8
Operation Description
The FAN7554 has all the basic features of the current mode SMPS control IC. Its basic configuration includes the UVLO with
6V hysteresis, a band gap reference, the oscillator that can oscillate up to 500kHz according to R
t
/C
t
(connected externally), a
PWM logic circuit , a gate driver, and the feedback circuit that has the current source and soft start function. The FAN7554 has
various functions such as an over load protection, an over current protection, and an over voltage protection. The over load
protection forces the FAN7554 to stop its operation if the load current is higher than the preset value. The protection circuit
can also be prevented from operating during transient states by ensuring that a certain amount of the time passes before the
protection circuit operates. The shutdown circuit is configured for an auto-restart, so the FAN7554 automatically restarts when
Vcc drops to 9V (stop voltage).
Start-Up
The start-up circuit is made up of an under voltage lock out (UVLO), the protection for low voltage conditions, and the 5V
reference (V
ref
), which supplies bias voltage to the control circuit after start-up. The start voltage of the UVLO is 15V , and
the stop voltage af