FAN7544M Fairchild Semiconductor, FAN7544M Datasheet - Page 7

• Manufacturer Part Number: FAN7544M
• Description: IC CTRLR BALLAST ELECT 8SOIC
• Manufacturer: Fairchild Semiconductor
• Type: Ballast Controllerr

Specifications of FAN7544M

• Frequency: 45.5 ~ 54.5 kHz
• Current - Supply: 6.5mA
• Current - Output: 500mA
• Voltage - Supply: 12.7 V ~ 30 V
• Operating Temperature: -25°C ~ 125°C
• Package / Case: 8-SOIC (3.9mm Width)
• Output Voltage: 17 V
• Operating Temperature Range: - 25 C to + 125 C
• Mounting Style: SMD/SMT
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: FAN7544M_NL; FAN7544M_NL

Application Information
Start-up Circuit
The start-up current is supplied to the IC through the start up resistor (Rst). In order to reduce the power dissipation in Rst, the
Rst is connected to the full wave rectified output voltage.
The following equations can be used to calculate the size of Rst
The size of supply capacitor (Cs) is normally decided in
terms of the start up time and operating current built up
by auxiliary operating current source.
The turn off snubber capacitor (CQ) and two diodes
(D1, D2) constitute the auxiliary operating current
source for the IC. The charging current through the CQ
flows into the IC and also charges the supply capacitor.
If the size of CQ is increased, the V
Cs is also increased.
Under Voltage Lock Out(UVLO)
UVLO mode of the FAN7544 is designed to maintain
an ultra low supply current of less than 140uA, and to
guarantee that the IC is fully functional before two out-
put drivers are activated.
Oscillator
The gate drive output frequency is as half as that of the triangular waveform on timing capacitor (CT) at pin #2. In normal
operating mode, the timing capacitor charging current is 4×Irt(=Vref/RT). The discharging current is 5.25 times of the charg-
ing current (5.25×4×Ιrt). The charging period of the timing capacitor is the on time of the MOSFET. During the discharging
period, both of the MOSFETs are off.
Rst
<
=
Vin ac
-------------------------------------------------------------------------- -
85
------------------------------------- -
0.2 10
(
×
×
)
2 12.5
×
–
Ist max
–
2 Vth st
3
,
–
OUT1
VCT
OUT2
=
539k Ω
( ) max
Period(∆T
,
Charging
CC
I
CH
voltage on the
CH
)
P
Figure 11. CT & Output Waveforms
Dead Time
RSt
Period(∆T
I
Discharging
DIS
R
=6.25*I
St
=
≥
(
----------------------------------------------------------------------- -
CH
Vin ac_max
DIS
3.7V
2
)
×
(
(
Vin ac_max
Vcc
Cs
Rst
R
(
St
Rectifier
Output
R
≥
St
)
260K
⋅
2 Vcc
ZD1
)
D2
–
⋅
2 Vcc
Figure 10. Start-up Circuit
–
)
2
≤
0.5W
)
D1
2
CQ
CT
DC 400V
M1
Vref
I
CH
M2
∴
I
DIS
260K R
G1
G2
≤
St
≤
539K
FAN7544
7