Datasheet KA7541 Datasheet (Fairchild Semiconductor)

KA7541

Simple Ballast Controller

www.fairchildsemi.com

Features

• Internal soft start

• Flexible soft start frequency

• No lamp protection

• Trimmed 1.5% internal bandgap reference

• Under voltage lock out with 1.8V of hysteresis

• Totem pole output with high state clamp

• Low start up and operating current

Descriptions

The KA7541 provides simple and high performance
electronic ballast control functions. KA7541 is optimized for
electronic ballast requiring a minimum b oard area, reduced
component count and low power dissipation. Internal soft
start circuitry eliminates the need for an external soft sta rt
PTC resistor. The initial soft start switching frequency and
soft start time can be adjusted depending on the types of
lamps. Protection circuitry has also been adde d to prevent
burning out of switches in no lamp condition. output gate
drive circuit clamps power MOSFET gate voltage
irrespective of supply voltage

8-DIP

1

8-SOP

1

©2001 Fairchild Semiconductor Corporation

Rev. 1.0.3

KA7541

Internal Block Diagram

0.22µF

180pF

22k

1.8V

UVLO

+

−

9.5V

8

V

CC

V

CC

OUT 1

7

V

CC

OUT 2

6

GND

5

2V Ref

V

40k

30k

5pF

Z

3pF

2k

−

+

Vref

I

H

I

+

S

R
latch

+

Q

C

Oscilator

I

S

Shut down signal

Ict

+

-

3V

-

+

1V

Ω

−

+

Vref

Ω

Ω

−

+

2V

Ik = IS / 6

Oscilator

Current

mirror

Internal

bias

UVLO

F.D

Frequency
divider

I

= Ik × (Vref − VSS) / Vref

H

= Vref / RS

I

S

Ldet

1

2.5µA

2

8Ict

3

4

C

S

Ct

R

S

Ω

Absolute Maximum Ratings

Parameter Symbol Value Unit

Supply voltage V
Peak drive output current I
Drive output clamping diodes

V

O>VCC

, or VO<−0.3

OH

Iclamp ±10 mA

Soft start, and no lamp detection input voltage V

CC

, I

IN

OL

30 V

±300 mA

−0.3 to 6 V

Operating temperature range Topr -25 to 125 °C
Storage temperature range Tstg −65 to 150 °C

Power dissipation

Thermal resistance (Junction-to-air)

8-DIP
8-SOP 0.5
8-DIP
8-SOP 165

Pd

θja

0.8

100

Absolute Maximum Ratings (-25°°°°C≤≤≤≤Ta≤≤≤≤125°°°°C)

Parameter Symbol Value Unit

Temperature stability for reference voltage (Vref) ∆Vref(Typ) 15 mV
Temperature stability for operating frequency (fos) ∆fos(Typ) 5 kHz

W

°C/W

2

Pin Assignments

KA7541

V

1

S

CC

8C

Ct

R

Ldet

2

S

3

4

7

6

5

(Top View)

Pin Definitions

Pin Number Pin Name Pin Function Descrition

1C

2C

3R

S

T

S

4 Ldet
5 GND The ground potential of all the pins.
6OUT 2

7OUT 1
8V

CC

Soft start capacitor connection pin. The pin voltage determines the phase of soft
start, normal mode.

Timing capacitor connection pin. The timing capacitor is charged and discharged
to generate the sawtooth waveform that determines the oscillation frequency in
the internal oscillator block.

Soft start resistor connection pin. The soft start resistor value determines the initial
preheating switching frequency during soft start mode.

Input to the protection circuit. If the pin voltage is lower than 2V, the output of the
gate driver is inhibited.

The output of a high-current power driver capable of driving the gate of a power
MOSFET

The output of a high-current power driver capable of driving the gate of a power
MOSFET.

The logic and control power supply connection.

OUT1

OUT2

GND

3

KA7541

Electrical Characteristics

o

Unless otherwise specified, for typical values Vcc=14V, Ta=25

temperature range with

-25

o

≤ Ta ≤ 125

C

o

C

and 11V ≤ V

CC

Parameter Symbol Conditions Min. Typ. Max. Unit

UNDER VOLTAGE LOCK OUT SECTION

Start threshold voltage V
UVLO hysteresis HY

TH(st)

(st)

SUPPLY CURRENT SECTION

Start up supply current I
Operating supply current I
Dynamic operating supply current I

ST

CC

DCC

REFERENCE SECTION

Reference voltage V
Line regulation ∆V
Temperature stability of Vref ∆V

ref
ref 1
ref 2

OSCILLATOR SECTION

Operating frequency fos V
Operating dead time tod V
Soft start frequency fss V
Soft start dead time tsd V

OUTPUT SECTION

Rising time
Falling time
Maximum output voltage V
Output voltage with UVLO activated V

(note1)

(note1)

tr CI=1nF, Vcc=12V - 120 200 ns
tf CI=1nF, Vcc=12V - 50 100 ns

omax(o)VCC

omin(o)

NO LAMP PROTECTION SECTION

No lamp detect voltage Vnd - 1.9 2 2.1 V

Note:

1. These parameters, although guaranteed, are not 100% tested in production.

C, For Min/Max values Ta is the operating ambient

≤ 30V

VCC increasing 8.5 9.5 10.5 V

- 1.3 1.8 2.3 V

VCC<VTH(st) - 0.15 0.25 mA
Output not switching - 6 10 mA
50kHz, CI=1nF - 7 14 mA

Iref=0mA, Vcc=14V 1.95 2 2.05 V
14V≤V

≤25V - 0.1 10 mV

CC

-25≤Ta≤125°C, Vcc=14V - 15 - mV

=3V, CT=470pF 44 50 56 KHz

SS

=3V, Vcc=14V 2.4 2.9 3.4 µs

SS

=0V, CT=470pF 56 65 74 KHz

SS

=0V, Vcc=14V 1.8 2.3 2.8 µs

SS

=20V 12 15 18 V

VCC=5V, IO=100µA--1V

4

KA7541

Start-up Circuit

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 equation can be used to calculate the size of Rst

Vin ac() 2Vthst()max,–×

-------------------------------------------------------------------------- -

Rst

<

85 2 10.5–×

------------------------------------- - 440kΩ==

0.25 10

×

Ist max,

3–

P

Vin ac_max()2Vcc–⋅()

----------------------------------------------------------------------- -

RSt

2 Vi n ac_max()2Vcc–⋅()

R

×≥

St

R

St

R

260K≥

St

The size of start up capacitor (Cst) is normally decided in terms o f the start up time a nd operating current build up time with
auxiliary operating current source.

The turn off snubber capacitor (Cq2) and two diodes (D1, D2) constitute the auxiliary operating current source for the IC. The
charging current through the Cq2 flows into the IC and also charges the start-up capacitor. If the size of Cq2 is increased, the
V

voltage of the Cst is also increased.

CC

Q1

2

0.5W≤=

2

260K R

440K≤≤∴

St

Rectifier

To V
(Pin 8)

Output

Rst

CC

+

−

Cst

Q2

D2

Cq2

D1

Figure 1. Start up circuit

Oscillator

The gate drive output frequency is as half as that of the triangular waveform in timing capacitor (Ct) at pin #2. In normal
operating mode, the timing capacitor charging current is 50µA. The discharging current is seven times of the charging current
(7× 50µA). The charging period of the timing capacitor is the on duty of the gate drive. The discharging period is the off duty
of the gate drive.
The rising slope and falling slope of the triangular waveform are as following.

Rising slope: dv / dt = i / C = 50µA / Ct
Falling slope: dv / dt = i / C = 7 × 50µA / Ct

For example, when the timing capacitor is 180pF,

∆Tch = 6.69µ
∆Tdis = 0.956µ

5

KA7541

Vct
(Pin #2)

Voutput
(Pin #6, 7)

Charging
Period(∆Tch)

Figure 2. Oscillator sawtooth & Output gate drive waveform

Discharging
Period(∆Tdis)

2.86V

1.0V
14V

0V

As a result, the switching frequency is as following
Ts = 2 × (∆Tch + ∆Tdis) = 15.29µ

fsw = 1 / T

= 65KHz

S

The explicit equation calculating the size of the timing capacitor for a certain switching frequency is written below.

C

t

11.76 10

-------------------------------- -=

6–

×

f

sw

Soft Start

The switching frequency is linearly decreasing from the pre-heating frequency to the normal switching fr equency.
In KA7541, the initial pre-heating frequency can be adjusted depending on the types of the lamps used. During the pre-heating
mode, a sixth of the soft start current (I
timing capacitor charging current (50µA). The rising and falling slope o f the triangular waveform are increased due to this
added current .
Soft start current (I

) = 2V / R

S

S

) which flows through the soft start resistor (RS) at pin #3 is added to the normal

S

Rising slope: dv / dt = i / C = (50µA + IS / 6) / Ct
Falling slope: dv / dt = i / C = 7 × (50µA + I

So, once the value of R

and Ct are known, the pre-heating frequency can be calculated straightforward by using the

S

/ 6) / Ct

S

following equation.

6–

0.33

-----------+×

Rs

fsw pre()

50 10

------------------------------------------ -=

Ct 4.25×

The dead time ratio during pre-heating mode is maintained to be constant as well as in normal mode.
(on duty: dead time = 7:1 )

The voltage of the soft start capacitor (C

) determines the soft start time (tss). When VCC voltage exceeds the start-up voltage

S

(Vth(st)), the soft start capacitor start to be charged by the current source (313nA). The switching frequency decreases linearly
to fsw(nor) from fsw(pre) until the soft start capacitor vo ltage (V

) touches 2V. Therefore the soft start duration time (tss)

CS

can be acquired by the following formula.

6

Cs V×

----------------- -=

tss

0.2 10

----------------------------------- -

313 10

i

6–

2××

1.28s==

9–

×

For example, the soft start capacitor of 0.2µF makes the soft start time (tss) to be 1.28sec.

fsw, V

CS

fsw (pre)

fsw (nor)

2V

tss

KA7541

Figure 3. Frequency & Soft start capacitor voltage variation during soft start

No Lamp Protection

When the voltage at pin #4 is lower than 2V , the gate drive output is off state, so the external power MOSFET stops switching.
In no lamp protection circuit the dc link voltage is divided by a couple of resistors including both lamp filaments, and The
divided voltage is applied to the pin #4 before the MOSFETs start switching.

R

15KΩ

R

3

4

×++

f

2

4

2

---------------------------------------------------------------------

×=

Vdd

-------------------------------------------------------------------------------------- -------

×

180KΩ

V

3V2

R2R32R

------------------------------------------ R

R

++

1

330KΩ 680KΩ+

-------------------------------------------- - 15KΩ++

--------------------

× 200V≅=

R2R3+

400≅

V

R4

When in normal mode the average voltage of the V3 is the half of the dc link voltage (Vdd). So, in order to make stable start
condition, the resistors are designed to make the voltage of V3 to be the half of the dc link voltage.

7

KA7541

DC Link Voltage (Vdd)

V2

Rfilament

Rfilament

To pin #4

R1

Rfilament

R2

Rfilament

V3

R3

R4

C4

Figure 4. Lamp detection resistor networ k

8

Application Circuit

<85 ~ 265VAC Input, 400VDC, 32W×2 Lamps Ballast>

KA7541

Full-wave Rectified Output

D3

D1

D4

D2

C5

NTC

C3 C4

C2

L1

C1

TNR

F1

AC INPUT

R1

R2

C8

R3

C6

R6 R4

D6

7

8

Vcc

OUT

FAN7527

INV

EA_OUT

1

2

C7

6

3

L2

GND

MULT

PFC Output

D5

R8

R5

5

Idet

CS

4

Q1

R7

C9

R9

To PFC Output

To full-wave

rectified voltage

R12

C10

Z1

R10

C21

C11

8

Vcc

CS

1

C12

T1

6

7

OUT1

KA7541

Ct

2

3

R11

OUT2

Rs

R13

5

4

GND

Ldet

C13

Q2

Q3

D8

R17

R19

R14

C14

R18

D7

L3
L4

R15

C15

C16

R16

C17

C18

C19

C20

9

KA7541

Component Listing

Part number Value Note Manufacturer

R1 2.7MΩ 1/4W -

R2 18kΩ 1/4W ­R3, 12 150kΩ 1W ­R4, 13 22kΩ 1/4W -

R5, 10, 11 47Ω 1/4W -

R6 3.3Ω 1/4W -

R7 0.2Ω 1W -

R8 1.2MΩ 1/4W -

R9 103 Variable resistor -

R14 180kΩ 1/4W ­R15, 16 330kΩ 1/4W ­R17, 18 680kΩ 1/4W -

R19 15kΩ 1/4W -

C1, 2 150nF, 275vac Box-Cap ­C3, 4 2200pF, 3000V Y-Cap -

C5 0.22µF, 630V Miller-Cap -

C6, 10 47µF, 35V Electrolytic -

C7 0.33µFMLCC ­C8 1nF, 25V Ceramic ­C9 47µF, 450V Electrolytic -

C11, 21 0.22µF, 25V Ceramic -

C12 180pF, 25V Ceramic -

C13 0.1µF, 25V Ceramic -

C14 1nF, 630V Miller-Cap ­C15, 16 4700pF, 1000V Miller-Cap -

C17, 18, 19, 20 6800pF, 630V Miller-Cap -

Q1, 2, 3 500V, 3.6A FQPF6N50 FairChild

D1, 2, 3, 4 1000V, 1A 1N4007 -

D5 1000V, 1A UF4007 ­D6 75V, 150mA 1N4148 -

D7, 8 600V, 1A 1N4937 -

ZD1 15V, 1W 1N4744 -

L1 45mH Line Filter ­L2 590µH (62T:5T) EI3026

L3, 4 3.1mH (120T) EI2820 -

T1 1.2mH(30T:60T) EE1614

F1 250V, 3A Fuse ­TNR 470V 471 ­NTC 10Ω 10D09 -

10

Mechanical Dimensions

Package

8-SOP

1.55 ±0.20

0.061 ±0.008

Dimensions in millimeters

0.1~0.25

MIN

0.004~0.001

0.56

0.022

()

KA7541

0.006

0.15

+

-0.002

-0.05

0.004

0.50 ±0.20

0.020 ±0.008

+

0.10

#1

#4

6.00 ±0.30

0.236 ±0.012

3.95 ±0.20

0.156 ±0.008

5.72

0.225

#8

#5

0~8°

MAX

5.13

0.202

1.80

0.071

4.92 ±0.20

MAX

0.194 ±0.008

MAX0.10

MAX0.004

1.27

0.050

0.41 ±0.10

0.016 ±0.004

11

KA7541

Mechanical Dimensions

Package

6.40

±0.20

±0.008

0.252

#1

#4 #5

#8

(Continued)

9.60

8-DIP

MAX

±0.20

9.20

0.378

±0.008

0.362

Dimensions in millimeters

0.79

0.031

()

±0.10

0.46

2.54

±0.004

0.018

0.100

±0.10

±0.004

1.524

0.060

0~15°

7.62

0.300

0.25

0.010

5.08

0.200

3.40

0.134

+0.10
–0.05

+0.004

–0.002

MAX

±0.20

±0.008

0.33

0.013

MIN

3.30

0.130

±0.30
±0.012

12

Ordering Information

Product Number Package Operating Temperature

KA7541 8-DIP

KA7541D 8-SOP

-25°C ~ +125°C

KA7541

13

KA7541

DISCLAIMER

FAIRCHILD SEMICONDUCTOR RESERVES THE RIGHT TO MAKE CHANGES WITHOUT FURT HER NOTICE TO ANY
PRODUCTS HEREI N TO IMPROVE RELIABILITY, FUNCTIO N OR DESIGN. FAIRCH IL D DOES NOT ASSUME ANY
LIABILITY ARISING OUT OF THE APPLICATION OR USE OF ANY PRODUCT OR CIRCUIT DESCRIBED HEREIN; NEITHER
DOES IT CONVEY ANY LICENSE UNDER IT S PATENT RIGHTS, NOR THE RIGHTS OF OTHE RS.

LIFE SUPPORT POL I CY

FAIRCHILD’S PR ODUCTS ARE NOT AUTH ORIZED FOR USE AS C RITICAL COMPONENT S IN LIFE SUPPORT DE VICES
OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT OF FAIRCHILD SEMICONDUCTOR
CORPORATION. As used herein :

1. Life support devices or systems are devices or systems
which, (a) are intended for surgical implant into the body,
or (b) support or sustain life, and (c) whose failure to
perform when properly used in accordance with

2. A critical component in any component of a life support
device or sy stem whose fai lure to perform can be
reasonably expec ted to cause the failur e of the life support
device or system, or to affect its safety or effec t iv ene ss .

instructions for use provided in the labeling, can be
reasonably expected to result in a significant injury of the
user.

www.fairchildsemi.com

9/27/01 0.0m 001

 2001 Fairchild Semiconductor Corporation

Stock#DSxxxxxxxx