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Page 2
FAN7602C
Green Current Mode PWM Controller
FAN7602C — Green Current Mode PWM Controller
November 2013
Features
Green Current Mode PWM Controller
Random Frequency Fluctuation for Low EMI
Internal High-Voltage Startup Switch
Burst Mode Operation
Line Voltage Feedforward to Limit Maximum Power
Line Under-Voltage Protection
Latch Protection & Internal Soft-Start (10ms) Function
Overload Protection (OLP)
Over-Voltage Protection (OVP)
Over-Temperature Protection (OTP)
Low Operation Current: 1 mA Typical
Available in the 8-Lead SOP Package
Applications
Adapter
LCD Monitor Power
Auxiliary Power Supply
Related Resources
AN-6014- Green Current Mode PWM Controller
(Except for frequency fluctuation part in AN-6014)
Description
The FAN7602C is a green current-mode PWM controller.
It is specially designed for off-line adapter applications;
DVDP, VCR, LCD monitor applications; and auxiliary
power supplies.
The internal high-voltage startup switch and the burst
mode operation reduce the power loss in standby mode.
As a result, the input power is lower than 1 W when the
input line voltage is 265 V
no-load condition, input power is under 0.15 W.
The maximum power can be limited constantly,
regardless of the line voltage change, using the power
limit function.
The switching frequency is not fixed and has random
frequency fluctuation.
The FAN7602C includes various protections for the
system reliability and the internal soft-start prevents the
output voltage over-shoot at startup.
and the load is 0.5 W. At
AC
Ordering Information
Part Number
FAN7602CMX -40°C to +150°C 8-Lead Small Outline Package (SOP) Tape and Reel FAN7602C
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 Protection and Power Limit Pin. When the pin voltage exceeds 4 V, the latch
protection works. The latch protection is reset when the V
voltage is lower than 5 V. For
CC
the power limit function, the OCP level decreases as the pin voltage increases.
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 an external RC filter.
Ground Pin. This pin is used for the ground potential of all the pins. For proper operation,
the signal ground and the power ground should be separated.
Gate Drive Output Pin. This pin is an output pin to drive an external MOSFET. The peak
sourcing current is 450 mA and the peak sinking current is 600 mA. For proper operation,
the stray inductance in the gate driving path must be minimized.
Supply Voltage Pin. IC operating current and MOSFET driving current are supplied
using this pin.
No Connection.
Startup Pin. This pin is used to supply IC operating current during IC startup. After
startup, the internal JFET is turned off to reduce power loss.
Stresses exceeding the absolute maximum ratings may damage the device. The device may not function or be
operable above the recommended operating conditions and stressing the parts to these levels is not recommended. In
addition, extended exposure to stresses above the recommended operating conditions may affect device reliability.
The absolute maximum ratings are stress ratings only.
Symbol Parameter Min. Max. Unit
VCC Supply Voltage 25 V
IO Output Current -600 +450 mA
V
CS/FB Input Voltage -0.3 20.0 V
CS/FB
V
LUVP Input Voltage -0.3 10.0 V
LUVP
V
Latch/Plimit Input Voltage -0.3 10.0 V
Latch
V
V
STR
TJ
T
Storage Temperature Range -55 +150 °C
STG
Input Voltage 600 V
STR
Junction Temperature +150
Recommended Operating Junction Temperature -40 +150
PD Power Dissipation 1.2 W
ESD Electrostatic Discharge Capability
Human Body Model, JESD22-A114 3500
Charged Device Model, JESD22-C101 2000
°C
V
Thermal Impedance
Symbol Parameter Value Unit
θ
Thermal Resistance
JA
Note:
1. Regarding the test environment and PCB type, please refer to JESD51-2 and JESD51-10.
The FAN7602C contains a startup switch to reduce the
power loss of the external startup circuit of the
conventional PWM converters. The internal startup
circuit charges the V
source if the AC line is connected. The startup switch is
turned off 15 ms after IC starts up, as shown in Figure
19. The soft-start function starts when the V
reaches the start threshold voltage of 12 V and ends
when the internal soft-start voltage reaches 1 V. The
internal startup circuit starts charging the V
again if the V
CC
operating voltage, 8 V. 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 V
threshold voltage, the IC starts switching again and the
soft-start block works as well.
During the soft-start, pulse-width modulated (PWM)
comparator compares the CS/FB pin voltage with the
soft-start voltage. The soft-start voltage starts from 0.5 V
and the soft-start ends when it reaches 1 V and the softstart time is 10 ms. The startup switch is turned off when
the soft-start voltage reaches 1.3 V.
capacitor with 0.9 mA current
CC
voltage
CC
capacitor
CC
voltage is lowered to the minimum
voltage reaches the start
CC
Figure 20. Frequency Fluctuation Waveform
3. Current Sense and Feedback Block
The FAN7602C performs the current sensing for the
current mode PWM and the output voltage feedback
with only one pin, pin 3. To achieve the two functions
with one pin, an internal Leading-Edge Blanking (LEB)
circuit to filter 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.
Figure 21 shows the current sense and feedback circuits.
R
is the current sense resistor to sense the switch
S
current. The current sense information is filtered by an
RC filter composed of R
output voltage feedback information, I
stops charging C
zero, C
is discharged through RF and RS to lower the
F
to adjust the offset voltage. If IFB is
F
offset voltage.
and CF. According to the
F
charges or
FB
Figure 19. Startup Current and VCC Voltage
2. Oscillator Block
The oscillator frequency is set internally and FAN7602C
has a random frequency fluctuation function.
Fluctuation of the switching frequency of a switched
power supply can reduce EMI by spreading the energy
over a wider frequency range than the bandwidth
measured by the EMI test equipment. The amount of
EMI reduction is directly related to the range of the
frequency variation. The range of frequency variation is
fixed internally; however, its selection is randomly
chosen by the combination of external feedback voltage
and internal free-running oscillator. This randomly
chosen switching frequency effectively spreads the EMI
noise nearby switching frequency and allows the use of
a cost-effective inductor instead of an AC input line filter
to satisfy the world-wide EMI requirements.
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 22. The CS/FB pin
voltage is compared with PWM that is 1 V - Plimit offs et.
If the CS/FB voltage meets PWM+, the output drive is
shut off. If the feedback offset voltage is LOW, the
switch on-time is increased. If the feedback offset
voltage is HIGH, the switch on-time is decreased. In this
way, the duty cycle is controlled according to the output
load condition. Generally, the maximum output power
increases as input voltage increases because the
current slope during switch on-time increases.
Page 12
FAN7602C — Green Current Mode PWM Controller
PWM+
CS/FB
GND
On Time
FB
Offset
1V
Power Limit
Offset
(a) Low Power Limit Offset Case
PWM+
CS/FB
GND
On Time
FB
Offset
1V
Power Limit
Offset
(b) High Power Limit Offset Case
CS/FB
Delay
Circuit
3
+
−
0.95V/0.88V
Burst+
Offset
OLP
50mV
22ms
Timer
Soft-Start
Clock
CS/FB
3
2V/1.5V
1
+
−
LUVP
V
IN
To limit the output power of the converter constantly, the
power limit function is included in FAN7602C. Sensing
the converter input voltage through the Latch/Plimit pin,
the Plimit offset voltage is subtracted from 1 V. As
shown in Figure 22, the Plimit offset voltage is
subtracted from 1 V and the switch on-time decreases
as the Plimit offset voltage increases. If the converter
input voltage increases, the switch on-time decreases,
keeping the output power constant. The offset voltage is
proportional to the Latch/Plimit pin voltage and the gain
is 0.16. If the Latch/Plimit voltage is 1 V, the offset
voltage is 0.16 V.
5.1 Overload Protection (OLP)
The FAN7602C 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 representing the feedback information is
almost zero. As shown in Figure 24, the CS/FB voltage
is compared with 50 mV reference when the internal
clock signal is HIGH and, if the voltage is lower than
50 mV, the OLP timer starts counting. If the OLP
condition persists for 22 ms, the timer generates the
OLP signal. The protection is reset by the UVLO. The
OLP block is enabled after the soft-start finishes.
Figure 24. Overload Protection Circuit
5.2 Line Under-Voltage Protection
If the input voltage of the converter is lower than the
minimum operating voltage, the converter input current
increases too much, causing components failure.
Therefore, if the input voltage is LOW, the converter
should be protected. The LUVP circuit senses the input
voltage using the LUVP pin and, if this voltage is lower
than 2 V, the LUVP signal is generated. The comparator
has 0.5 V hysteresis. If the LUVP signal is generated,
the output drive block is shut down, the output voltage
feedback loop is saturated, and the OLP works if the
Figure 22. CS/FB Pin Voltage Waveforms
LUVP condition persists more than 22 ms.
4. Burst-Mode Block
The FAN7602C contains the burst-mode block to reduce
the power loss at a light-load and no load. A hysteresis
comparator senses the offset voltage of the Burst+ for
the burst mode, as shown in Figure 23. The Burst+ is
the sum of the CS/FB voltage and Plimit offset voltage.
The FAN7602C enters the burst mode when the offset
voltage of the Burst+ is higher than 0.95 V and exits the
burst mode when the offset voltage is lower than 0.88 V.
The offset voltage is sensed during the switch off time.
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 overvoltage protection and/or other protections. If the Latch/
Plimit pin voltage is made higher than 4 V by an external
circuit, the IC is shut down. The latch protection is reset
when the V
5.4 Over-Voltage Protection (OVP)
Figure 23. Burst-Mode Block
If the V
the OVP protection is reset when the V
lower than 5 V.
5. Protection Block
The FAN7602C contains several protection functions to
improve system reliability.
sinking current with typical rise and fall time of 45 ns and
35 ns, respectively, with a 1 nF load.
stage to drive a power MOSFET. The drive output is
capable of up to 450 mA sourcing current and 600 mA
Typical Application Circuit
Application Output Power Input Voltage Output Voltage
Adaptor 48 W Universal Input (85 ~ 265 VAC) 12V
Features
Low stand-by power (<0.15 W at 265 V
Constant output power control
AC
)
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 V
no load.
R110 should be designed carefully to make the V
at full load.
R103 should be designed to keep the MOSFET V
shorted.
voltage higher than 8 V when the input voltage is 265 VAC at
CC
voltage lower than OVP level when the input voltage is 85 VAC
CC
voltage lower than maximum rating when the output is
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