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KA7541
Simple Ballast Controller
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 board area, reduced component count and low power dissipation. Internal soft start circuitry eliminates the need for an external soft start 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 added 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
Rev. 1.0.3
(c)2001 Fairchild Semiconductor Corporation
KA7541
Internal Block Diagram
UVLO 2V Ref CS 0.22F
2.5A
1
- + Vref VZ Ict + + 3V 8Ict 1V + + - + Vref 2k 40k IS SQ Oscilator R latch Current mirror Frequency divider F.D IC Oscilator Internal bias IH Ik = IS / 6
1.8V
+ -
8
VCC
UVLO
9.5V
VCC
Ct 180pF
2
7
OUT 1
VCC
RS 22k
30k 3 3pF
6
OUT 2
Ldet
4 5pF 2V
- + Shut down signal
IH = Ik x (Vref - VSS) / Vref IS = Vref / RS
5
GND
Absolute Maximum Ratings
Parameter Supply voltage Peak drive output current Drive output clamping diodes VO>VCC, or VO<-0.3 Soft start, and no lamp detection input voltage Operating temperature range Storage temperature range Power dissipation Thermal resistance (Junction-to-air) 8-DIP 8-SOP 8-DIP 8-SOP Symbol VCC IOH, IOL Iclamp VIN Topr Tstg Pd ja Value 30 300 10 -0.3 to 6 -25 to 125 -65 to 150 0.8 0.5 100 165 Unit V mA mA V C C W C/W
Absolute Maximum Ratings (-25CTa125C)
Parameter Temperature stability for reference voltage (Vref) Temperature stability for operating frequency (fos) Symbol Vref(Typ) fos(Typ) Value 15 5 Unit mV kHz
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KA7541
Pin Assignments
CS
1
8
VCC
Ct
2
7
OUT1
RS
3
6
OUT2
Ldet
4
5
GND
(Top View)
Pin Definitions
Pin Number 1 2 3 4 5 6 7 8
Pin Name CS CT RS Ldet GND OUT 2 OUT 1 VCC
Pin Function Descrition 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 ground potential of all the pins. 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.
3
KA7541
Electrical Characteristics
Unless otherwise specified, for typical values Vcc=14V, Ta=25oC, For Min/Max values Ta is the operating ambient temperature range with -25oC Ta 125oC and 11V VCC 30V Parameter UNDER VOLTAGE LOCK OUT SECTION Start threshold voltage UVLO hysteresis SUPPLY CURRENT SECTION Start up supply current Operating supply current Dynamic operating supply current REFERENCE SECTION Reference voltage Line regulation Temperature stability of Vref OSCILLATOR SECTION Operating frequency Operating dead time Soft start frequency Soft start dead time OUTPUT SECTION Rising time (note1) Falling time
(note1)
Symbol VTH(st) HY(st) IST ICC IDCC Vref Vref 1 Vref 2 fos tod fss tsd tr tf Vomax(o) Vomin(o) Vnd
Conditions VCC increasing VCCMin. 8.5 1.3 1.95 44 2.4 56 1.8 12 1.9
Typ. 9.5 1.8 0.15 6 7 2 0.1 15 50 2.9 65 2.3 120 50 15 2
Max. 10.5 2.3 0.25 10 14 2.05 10 56 3.4 74 2.8 200 100 18 1 2.1
Unit V V mA mA mA V mV mV KHz s KHz s ns ns V V V
Maximum output voltage Output voltage with UVLO activated NO LAMP PROTECTION SECTION No lamp detect voltage
Note: 1. These parameters, although guaranteed, are not 100% tested in production.
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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 ) x 2 - Vth ( st ) ,max Rst < -------------------------------------------------------------------------Ist ,max = 85 x 2 - 10.5 = 440k -------------------------------------3 0.25 x 10 ( Vin ( ac_max ) 2 - Vcc ) P RSt = ------------------------------------------------------------------------ 0.5W R St R St 2 x ( Vin ( ac_max ) 2 - Vcc ) R St 260K
2 2
260K R St 440K
The size of start up capacitor (Cst) is normally decided in terms of the start up time and 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 VCC voltage of the Cst is also increased.
Q1 Rectifier Output
Q2 Cq2
Rst To VCC (Pin 8)
D1
+ - Cst
D2
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 50A. The discharging current is seven times of the charging current (7x 50A). 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 = 50A / Ct Falling slope: dv / dt = i / C = 7 x 50A / Ct For example, when the timing capacitor is 180pF, Tch = 6.69 Tdis = 0.956
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KA7541
Vct (Pin #2)
2.86V
1.0V Voutput (Pin #6, 7) 14V 0V
Charging Period(Tch)
Discharging Period(Tdis)
Figure 2. Oscillator sawtooth & Output gate drive waveform
As a result, the switching frequency is as following Ts = 2 x (Tch + Tdis) = 15.29 fsw = 1 / TS = 65KHz The explicit equation calculating the size of the timing capacitor for a certain switching frequency is written below.
11.76 x 10 C t = -------------------------------f sw
-6
Soft Start
The switching frequency is linearly decreasing from the pre-heating frequency to the normal switching frequency. 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 (IS) which flows through the soft start resistor (RS) at pin #3 is added to the normal timing capacitor charging current (50A). The rising and falling slope of the triangular waveform are increased due to this added current. Soft start current (IS) = 2V / RS Rising slope: dv / dt = i / C = (50A + IS / 6) / Ct Falling slope: dv / dt = i / C = 7 x (50A + IS / 6) / Ct So, once the value of RS and Ct are known, the pre-heating frequency can be calculated straightforward by using the following equation.
- 6 0.33 50 x 10 + ---------Rs fsw ( pre ) = -----------------------------------------Ct x 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 (CS) determines the soft start time (tss). When VCC voltage exceeds the start-up voltage (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 voltage (VCS) touches 2V. Therefore the soft start duration time (tss) can be acquired by the following formula.
6
KA7541
----------------tss = Cs x V i 0.2 x 10 x 2 = ----------------------------------- = 1.28s -9 313 x 10
-6
For example, the soft start capacitor of 0.2F makes the soft start time (tss) to be 1.28sec.
fsw, VCS fsw (pre)
fsw (nor)
2V
tss
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.
R4 V R4 = Vdd x --------------------------------------------------------------------R2 + R 3 + 2 x Rf R 1 + ----------------------------------------- + R 4 2 15K 400 x -------------------------------------------------------------------------------------------180K + 330K + 680K + 15K -------------------------------------------2 R3 V 3 = V 2 x ------------------- 200V R2 + R3
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.
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KA7541
DC Link Voltage (Vdd) R1 V2 Rfilament Rfilament R2 Rfilament Rfilament V3 R3 To pin #4 R4 C4
Figure 4. Lamp detection resistor network
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KA7541
Application Circuit
<85 ~ 265VAC Input, 400VDC, 32Wx2 Lamps Ballast>
Full-wave Rectified Output
L2 D5
PFC Output
D3 D1 NTC
D4 D2
C5 R3 R6 D6 R1 R4 R8 R5 Q1
C3
C4 C6
8
7
6
GND
Vcc
OUT
5
C9
Idet
C2 L1 C1
1 INV
FAN7527
EA_OUT MULT 3 4 CS
TNR F1 R2 C8 C7 R7
2
R9
AC INPUT
To PFC Output R15 Q2 T1 R10 Q3 R11 C21 To full-wave rectified voltage R12 D8
8 7 6 OUT1 OUT2 5 GND Vcc
C17 R14 L3 L4 C18 D7 C16 R16 C15
C19
C14
C20
C10
Z1
CS
KA7541
Rs Ldet
R17
Ct
1
2
3
C11 C12
R13 C13
4
R18 R19
9
KA7541
Component Listing
Part number R1 R2 R3, 12 R4, 13 R5, 10, 11 R6 R7 R8 R9 R14 R15, 16 R17, 18 R19 C1, 2 C3, 4 C5 C6, 10 C7 C8 C9 C11, 21 C12 C13 C14 C15, 16 C17, 18, 19, 20 Q1, 2, 3 D1, 2, 3, 4 D5 D6 D7, 8 ZD1 L1 L2 L3, 4 T1 F1 TNR NTC Value 2.7M 18k 150k 22k 47 3.3 0.2 1.2M 103 180k 330k 680k 15k 150nF, 275vac 2200pF, 3000V 0.22F, 630V 47F, 35V 0.33F 1nF, 25V 47F, 450V 0.22F, 25V 180pF, 25V 0.1F, 25V 1nF, 630V 4700pF, 1000V 6800pF, 630V 500V, 3.6A 1000V, 1A 1000V, 1A 75V, 150mA 600V, 1A 15V, 1W 45mH 590H (62T:5T) 3.1mH (120T) 1.2mH(30T:60T) 250V, 3A 470V 10 Note 1/4W 1/4W 1W 1/4W 1/4W 1/4W 1W 1/4W Variable resistor 1/4W 1/4W 1/4W 1/4W Box-Cap Y-Cap Miller-Cap Electrolytic MLCC Ceramic Electrolytic Ceramic Ceramic Ceramic Miller-Cap Miller-Cap Miller-Cap FQPF6N50 1N4007 UF4007 1N4148 1N4937 1N4744 Line Filter EI3026 EI2820 EE1614 Fuse 471 10D09 Manufacturer FairChild -
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KA7541
Mechanical Dimensions
Package Dimensions in millimeters
8-SOP
MIN 1.55 0.20 0.061 0.008 0.1~0.25 0.004~0.001
#1
#8 4.92 0.20 0.194 0.008 5.13 MAX 0.202
( #4 #5 6.00 0.30 0.236 0.012
+0.10 0.15 -0.05 +0.004 0.006 -0.002
0.56 ) 0.022 1.80 MAX 0.071 MAX0.10 MAX0.004 3.95 0.20 0.156 0.008 5.72 0.225 0.50 0.20 0.020 0.008
0~
8
1.27 0.050
0.41 0.10 0.016 0.004
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KA7541
Mechanical Dimensions (Continued)
Package Dimensions in millimeters
8-DIP
1.524 0.10 0.018 0.004 0.060 0.004 0.46 0.10 6.40 0.20 0.252 0.008 0.79 ) 0.031 #8 9.20 0.20 0.362 0.008 9.60 MAX 0.378 #5 2.54 0.100 5.08 MAX 0.200 7.62 0.300 3.40 0.20 0.134 0.008 3.30 0.30 0.130 0.012 0.33 MIN 0.013
#1
#4
0.25 -0.05
0~15
+0.10
0.010 -0.002
+0.004
12
(
KA7541
Ordering Information
Product Number KA7541 KA7541D Package 8-DIP 8-SOP Operating Temperature -25C ~ +125C
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KA7541
DISCLAIMER FAIRCHILD SEMICONDUCTOR RESERVES THE RIGHT TO MAKE CHANGES WITHOUT FURTHER NOTICE TO ANY PRODUCTS HEREIN TO IMPROVE RELIABILITY, FUNCTION OR DESIGN. FAIRCHILD 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 ITS PATENT RIGHTS, NOR THE RIGHTS OF OTHERS. LIFE SUPPORT POLICY FAIRCHILD'S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES 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 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 Stock#DSxxxxxxxx 2001 Fairchild Semiconductor Corporation
2. A critical component in any component of a life support device or system whose failure to perform can be reasonably expected to cause the failure of the life support device or system, or to affect its safety or effectiveness.

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