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April 2006

FAN7602 Rev. 1.0.1

AN76

02 Green Current

Mode PWM Controller

FAN7602
Green Current Mode PWM Controller

Features

Green Current Mode PWM Control
Fixed 65kHz Operation with Frequency Modulation
Internal High-Voltage Start-up Switch
Burst Mode Operation
Line Voltage Feed Forward to Limit Maximum Power
Line Under-Voltage Protection
Latch Protection & Internal Soft-Start (10ms) Function
Overload Protection
Over Voltage Protection
Low Operation Current: Typ. 1mA
8-pin DIP

Applications

Adapter
LCD Monitor Power
Auxiliary Power Supply

Related Application Notes

AN6014 - Green Current Mode PWM Controller
FAN7602

Description

The FAN7602 is a green current mode PWM controller.
It is specially designed for off-line adapter application,
DVDP, VCR, LCD monitor application, and auxiliary
power supplies.

The internal high-voltage start-up switch and the burst
mode operation reduce the power loss in standby mode.
Because of the internal start-up switch and the burst
mode, it is possible to supply 0.5W load limiting the input
power under 1W when the input line voltage is 265Vac.
On no-load condition, the input power is under 0.3W.

The maximum power can be limited constantly, regard-
less of the line voltage change using the power limit
function.

The switching frequency is internally fixed to be 65kHz
and the frequency modulation technique reduces EMI.

The FAN7602 includes various protections for the sys-
tem reliability and the internal soft start prevents the out-
put voltage over-shoot at start-up.

Ordering Information

Part Number

Operating Temp.

Range

Pb-Free

Package Packing

Method

Marking

Code

FAN7602N

-25

°C to +125°C

Yes

8-DIP

Rail

FAN7602

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FAN7602 Rev. 1.0.1

AN7602 Green Curren

t Mode PWM Controller

Pin Assignments

Figure 3. Pin Configuration (Top View)

Pin Definitions

Pin Number Pin Name

Pin Function Description

LUVP

Line Under Voltage Protection Pin. This pin is used to protect the set when the
input voltage is lower than the rated input voltage range.

Latch/Plimit

Latch Protection and Power Limit Pin. When the pin voltage exceeds 4V, the latch
protection works and the latch protection is reset when the Vcc voltage is lower than
5V. For the power limit function, the OCP level decreases as the pin voltage
increases.

CS/FB

Current Sense and Feedback Pin. This pin is used to sense the MOSFET current
for the current mode PWM and OCP. The output voltage feedback information and
the current sense information are added using external RC filter.

GND

Ground Pin. This pin is used for the ground potential of all the pins. For proper oper-
ation, the signal ground and the power ground should be separated.

OUT

Gate Drive Output Pin. This pin is an output pin to drive an external MOSFET. The
peak sourcing current is 450mA and the peak sinking current is 600mA. For proper
operation, the stray inductance in the gate driving path must be minimized.

Vcc

Supply Voltage Pin. IC operating current and MOSFET driving current are supplied
using this pin.

No Connection.

Vstr

Start-up Pin. This pin is used to supply IC operating current during IC start-up. After

start-up, the internal JFET is turned off to reduce power loss.

F A N 7 6 0 2

Y W W

Latch/

Plimit

GND

CS/FB

LUVP

Vstr

Vcc

Out

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FAN7602 Rev. 1.0.1

AN7602 Green Curren

t Mode PWM Controller

Absolute Maximum Ratings

The "Absolute Maximum Ratings" are those values beyond which the safety of the device cannot be guaranteed. The
device should not be operated at these limits. The parametric values defined in the Electrical Characteristics tables
are not guaranteed at the absolute maximum ratings. The "Recommended Operating Conditions" table defines the
conditions for actual device operation.

Thermal Impedance

Note:
1. Regarding the test environment and PCB type, please refer to JESD51-2 and JESD51-10.

Symbol

Parameter

Value

Unit

Vcc

Supply Voltage

, I

Peak Drive Output Current

+450/-600

CS/FB

CS/FB Input Voltage

-0.3 to 20

LUVP

LUVP Input Voltage

-0.3 to 10

Latch

Latch/Plimit Input Voltage

-0.3 to 10

Vstr

Vstr Input Voltage

600

Operating Junction Temperature

150

°C

Topr

Operating Temperature Range

-25 to 125

°C

Tstg

Storage Temperature Range

-55 to 150

°C

Power Dissipation

1.2

ESD_HBM

ESD Capability, Human Body Model

2.0

ESD_MM

ESD Capability, Machine Model

300

ESD_CDM

ESD Capability, Charged Device Model

500

Symbol

Parameter

Value

Unit

Thermal Resistance, Junction to Ambient

8-DIP

100

°C/W

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FAN7602 Rev. 1.0.1

AN7602 Green Curren

t Mode PWM Controller

Electrical Characteristics

(Vcc = 14V, T

= -25

°C~125°C, unless otherwise specified)

Note:

1. These parameters, although guaranteed by design, are not tested in mass production.

Symbol

Parameter Condition

Min.

Typ.

Max.

Unit

START UP SECTION

str

Vstr Start-up Current

str

= 30V,

= 25

°C

0.7

1.4

UNDER VOLTAGE LOCK OUT SECTION

Vth(start)

Start Threshold Voltage

Vcc increasing

Vth(stop)

Stop Threshold Voltage

Vcc decreasing

HY(uvlo)

UVLO Hysteresis

3.6

4.4

SUPPLY CURRENT SECTION

Ist

Start-up Supply Current

= 25

°C

250

320

Icc

Operating Supply Current

Output no switching

1.5

SOFT START SECTION

Tss

Soft Start Time

(1)

PWM SECTION

OSC

Operating Frequency

CS/FB

= 0.2V,

= 25

°C

kHz

Frequency Modulation

±2

kHz

CS/FB1

CS/FB Threshold Voltage

= 25

°C

0.9

1.0

1.1

Propagation Delay to Output

(1)

100

150

MAX

Maximum Duty Cycle

MIN

Minimum Duty Cycle

BURST MODE SECTION

CS/FB2

Burst On Threshold Voltage

= 25

°C

0.84

0.95

1.06

CS/FB3

Burst Off Threshold Voltage

= 25

°C

0.77

0.88

0.99

POWER LIMIT SECTION

Plimit

Offset Gain

Latch/Plimit

= 2V,

= 25

°C

0.12

0.16

0.20

OUTPUT SECTION

Output Voltage High

= 25

°C, Isource = 100mA

11.5

Output Voltage Low

= 25

°C, Isink = 100mA

2.5

Rising Time

(1)

= 25

°C, Cl = 1nF

150

Falling Time

(1)

= 25

°C, Cl = 1nF

150

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FAN7602 Rev. 1.0.1

AN7602 Green Curren

t Mode PWM Controller

Typical Performance Characteristics

Figure 4. Start Threshold Voltage vs. Temp.

Figure 6. UVLO Hysteresis vs. Temp.

Figure 8. Operating Supply Current vs. Temp.

Figure 5. Stop Threshold Voltage vs. Temp.

Figure 7. Start-up Supply Current vs. Temp.

Figure 9. Vstr Star-up Current vs. Temp.

-25

100

125

11.2

11.6

12.0

12.4

12.8

]

Temperature

[°C]

-25

100

125

3.6

3.7

3.8

3.9

4.0

4.1

4.2

4.3

4.4

LO Hy

steresi

s
[
V

]

Temperature

[°C]

-25

100

125

0.8

0.9

1.0

1.1

1.2

1.3

1.4

1.5

p
[m

Temperature

[°C]

-25

100

125

7.2

7.6

8.0

8.4

8.8

]

Temperature

[°C]

-25

100

125

150

200

250

300

350

t [u

]

Temperature

[°C]

-25

100

125

0.8

0.9

1.0

1.1

1.2

1.3

t
r
[m

Temperature

[°C]

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FAN7602 Rev. 1.0.1

AN7602 Green Curren

t Mode PWM Controller

Typical Performance Characteristics

(Continued)

Figure 10. Burst On/Off Voltage vs. Temp.

Figure 12. Offset Gain vs. Temp.

Figure 14. OVP Voltage vs. Temp.

Figure 11. Operating Frequency vs. Temp.

Figure 13. Maximum Duty Cycle vs. Temp.

Figure 15. Latch Voltage vs. Temp.

-25

100

125

0.70

0.75

0.80

0.85

0.90

0.95

1.00

1.05

1.10

/
F

B T

h
r
e
shold

[
V

]

Temperature

[°C]

CSFB2
CSFB3

-25

100

125

0.10

0.12

0.14

0.16

0.18

0.20

l
i
m

i
t

Temperature

[°C]

-25

100

125

18.0

18.4

18.8

19.2

19.6

20.0

OVP

[
V

]

Temperature

[°C]

-25

100

125

Fos

c
[
k
H

z
]

Temperature

[°C]

-25

100

125

a
x
[%

]

Temperature

[°C]

-25

100

125

3.6

3.8

4.0

4.2

4.4

LATC

[
V

]

Temperature

[°C]

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FAN7602 Rev. 1.0.1

AN7602 Green Curren

t Mode PWM Controller

Applications Information

1. Start-up Circuit and Soft Start Block

The FAN7602 contains a start-up switch to reduce the
power loss of the external start-up circuit of the conven-
tional PWM converters. The internal start-up circuit
charges the Vcc capacitor with 0.9mA current source if
the AC line is connected. The start-up switch is turned off
15ms after IC starts up, as shown in Fig. 19. The soft-
start function starts when the Vcc voltage reaches the
start threshold voltage of 12V and ends when the inter-
nal soft-start voltage reaches 1V. The internal start-up
circuit starts charging the Vcc capacitor again if the Vcc
voltage is lowered to the minimum operating voltage, 8V.
The UVLO block shuts down the output drive circuit and
some blocks to reduce the IC operating current and the
internal soft-start voltage drops to zero. If the Vcc volt-
age reaches the start threshold voltage, the IC starts
switching again and the soft start block works as well.

During the soft start, pulse-width modulated (PWM) com-
parator compares the CS/FB pin voltage with the soft
start voltage. The soft-start voltage starts from 0.5V and
the soft-start ends when it reaches 1V and the soft-start
time is 10ms. The start-up switch is turned off when the
soft start voltage reaches 1.5V.

Figure 19. Start-up Current and Vcc Voltage

2. Oscillator Block

The oscillator frequency is set internally and a frequency
modulation (FM) function reduces EMI. The average fre-
quency is 65kHz and the modulation frequency is

±2kHz.

The frequency varies from 63kHz to 67kHz with 16
steps. The frequency step is 250Hz and FM frequency is
125Hz, as shown in Fig. 20.

3. Current Sense and Feedback Block

The FAN7602 performs the current sensing for the cur-
rent mode PWM and the output voltage feedback with
only one pin, pin3. To achieve the two functions with one
pin, an internal LEB (leading edge blanking) circuit to fil-
ter the current sense noise is not included because the
external RC filter is necessary to add the output voltage

feedback information and the current sense information.
Fig. 21 shows the current sense and feedback circuits.
R

is the current sense resistor to sense the switch cur-

rent. The current sense information is filtered by an RC
filter composed of R

and C

. According to the output

voltage feedback information, I

charges or stops

charging C

to adjust the offset voltage. If I

is zero, C

is discharged through R

and R

to lower the offset volt-

age.

Figure 20. Frequency Modulation

Figure 22 shows typical voltage waveforms of the CS/FB
pin. The current sense waveform is added to the offset
voltage as shown in the figure. The CS/FB pin voltage is
compared with PWM

+ that is 1V - Plimit offset as shown

in Fig. 22. If the CS/FB voltage meets PWM+, the output
drive is shut off. As shown in Fig. 22, if the feedback off-
set voltage is low, the switch on time is increased. If the
feedback offset voltage is high, then the switch on time is
decreased. In this way, the duty cycle is controlled
according to the output load condition. In general, the
maximum output power increases as the input voltage
increases because the current slope during switch on-
time increases. To limit the output power of the converter
constantly, the power limit function is included in the
FAN7602. Sensing the converter input voltage through
the Latch/Plimit pin, the Plimit offset voltage is sub-
tracted from 1V. As shown in Fig. 22, the Plimit offset
voltage is subtracted from 1V and the switch on-time
decreases as the Plimit offset voltage increases. If the
converter input voltage increases, the switch on-time
decreases, controlling the output power constant. The
offset voltage is proportional to the Latch/Plimit pin volt-
age and the gain is 0.16; if the Latch/Plimit voltage is 1V,
the offset voltage is 0.16V.

Figure 21. Current Sense and Feedback Circuits

Soft Start

Time (10ms)

12V

Vcc

Start-up

Current

Soft Start

Voltage

1.5V

0.5V

5ms

63kHz

67kHz

16 steps

1 step=250Hz

125Hz

Soft

Start

CS/FB

PWM

Comparator

Vcc

Isw

Plimit

Offset

Power

Limit

PWM+

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FAN7602 Rev. 1.0.1

AN7602 Green Curren

t Mode PWM Controller

Figure 22. CS/FB Pin Voltage Waveforms

4. Burst Mode Block

The FAN7602 contains the burst mode block to reduce
the power loss at a light load and no load as the
FAN7601. A hysteresis comparator senses the offset
voltage of the Burst+ for the burst mode as shown in Fig.
23. The Burst+ is the sum of the CS/FB voltage and
Plimit offset voltage. The FAN7602 enters the burst
mode when the offset voltage of the Burst+ is higher
than 0.95V and exits the burst mode when the offset volt-
age is lower than 0.88V. The offset voltage is sensed
during the switch off time.

Figure 23. Burst Mode Block

. Protection Block

The FAN7602 contains several protection functions to
improve system reliability.

5.1 Overload Protection

(OLP)

The FAN7602 contains the overload protection function.
If the output load is higher than the rated output current,
the output voltage drops and the feedback error amplifier
is saturated. The offset of the CS/FB voltage represent-
ing the feedback information is almost zero. As shown in
Fig. 24, the CS/FB voltage is compared with 50mV refer-
ence when the internal clock signal is high and, if the
voltage is lower than 50mV, the OLP timer starts count-

ing. If the OLP condition persists for 22ms, the timer gen-
erates the OLP signal. And this protection is reset by the
UVLO. The OLP block is enabled after the soft start fin-
ishes.

Figure 24. Overload Protection Circuit

5.2 Line Under Voltage Protection
If the input voltage of the converter is lower than the min-
imum operating voltage, the converter input current
increases too much, causing component failure. There-
fore, if the input voltage is low, the converter should be
protected. In the FAN7602, the LUVP circuit senses the
input voltage using the LUVP pin and, if this voltage is
lower than 2V, the LUVP signal is generated. The com-
parator has 0.5V hysteresis. If the LUVP signal is gener-
ated, the output drive block is shut down, the output
voltage feedback loop is saturated, and the OLP works if
the LUVP condition persists more than 22ms.

Figure 25. Line UVP Circuit

5.3 Latch Protection
The latch protection is provided to protect the system
against abnormal conditions using the Latch/Plimit pin.
The Latch/Plimit pin can be used for the output over-
voltage protection and/or other protections. If the Latch/
Plimit pin voltage is made higher than 4V by an external
circuit, the IC is shut down. The latch protection is reset
when the Vcc voltage is lower than 5V.

5.4 Over-Voltage Protection

(OVP)

If the Vcc voltage reaches 19V, the IC shuts down and
the OVP protection is reset when the Vcc voltage is
lower than 5V.

6. Output Drive Block

The FAN7602 contains a single totem-pole output stage
to drive a power MOSFET. The drive output is capable of
up to 450mA sourcing current and 600mA sinking cur-
rent with typical rise and fall time of 45ns, 35ns respec-
tively with a 1nF load.

PWM+

CS/FB

GND

On Time

Offset

Power

Limit

Offset

(a) Low Power Limit Offset Case

PWM+

CS/FB

GND

On Time

Offset

Power

Limit

Offset

(b) High Power Limit Offset Case

C S /F B

D e la y

C ircu it

0 .9 5 V /0 .8 8 V

B u rst+

O ffse t

O LP

50mV

22ms

Timer

S oft S tart

C lock

C S /F B

2V/1.5V

LUVP

Vin

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FAN7602 Rev. 1.0.1

AN7602 Green Curren

t Mode PWM Controller

Typical application circuit

Features

Low stand-by power (<0.3W @ 265Vac)
Constant output power control

Key Design Notes

All the IC-related components should be placed close to IC, especially C107 and C110.
If R106 value is too low, there can be subharmonic oscillation.
R109 should be designed carefully to make the Vcc voltage higher than 8V when the input voltage is 265Vac at no
load.
R110 should be designed carefully to make the Vcc voltage lower than OVP level when the input voltage is 85Vac at
full load.
R103 should be designed to keep the MOSFET Vds voltage lower than maximum rating when the output is shorted.

1. Schematic

Figure 26. Schematic

Application

Output power

Input voltage

Output voltage

Adapter

48W

Universal input

(85~265Vac)

12V

FUSE

AC INPUT

C101

LF1

C102

RT
1
0
1

BD101

C105

C202

D204

L201

R204

R1
03

R101

Vstr

Vcc

Out

LUVP

CS/FB

Latch/

Plimit

GND

FAN

7
602

R205

C203

R203

R202

201

C201

D102

IC201

OP1

R111

R104

D103

R106

Q101

C1
06

D101

R105

IC101

C110

R113

C107

C204

R206

D202

C109

C103 C104

C222

C108

R207

ZD201

R108

OP2

R109

R112

R102

R107

R110

ZD101

R114

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FAN7602 Rev. 1.0.1

AN7602 Green Curren

t Mode PWM Controller

2. Inductor Schematic Diagram

Figure 27. Inductor Schematic Diagram

3. Winding Specification

4. Electrical Characteristics

5. Core & Bobbin

Core: EER2828
Bobbin: EER2828
Ae(mm

): 82.1

Pin (s

Wire

Turns

Winding Method

Np1

0.3

× 2

Solenoid Winding