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KA7540
Simple Dimming Ballast Control IC
Features
* * * * * * * * Internal soft start No lamp protection Voltage controlled dimming 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 8-pin DIP & 8-pin SOP
Descriptions
The KA7540 provides simple and high performance electronic ballast control functions. KA7540 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. Voltage controlled dimming circuit is built into the IC to control the lighting output in a wide range. Protection circuitry has also been added to prevent switches from burning out in no lamp condition. Output gate drive circuit clamps power MOSFET gate voltage irrespective of supply voltage.
8-DIP
Applications
* Electronic Ballast * Lighting Control System * Half-bridge Drive Control System
1
8-SOP
1
Rev. 1.0.1
(c)2001 Fairchild Semiconductor Corporation
KA7540
Internal Block Diagram
UVLO 2V Ref CS 6.8F 25A VZ Vref 1 - + 17A VZ IS UVLO Internal bias 1.8V + - 12.5V 8 VCC
Oscillator Ct 180pF 8Ict 2
Ict latch + Q
+ +
IC 7 OUT 1
F.D from VCS
Vdim
3 80k Vd 20k 100A 3pF
VCC Id + - kVref VZ 40k 25A - + 2V Shut down signal IS = 17A x (Vref - VSS) / Vref Id = 25A x (Vref - Vd) / Vref Frequency divider
6
OUT 2
Ldet
4 5pF
5
GND
IC Characteristics
Parameter Initial soft start frequency Voltage controlled dimming KA7540 1.33 x normal operating frequency 1 ~ 10V
2
KA7540
Pin Assignments
CS
1
8
VCC
Ct
2
7
OUT1
Vdim
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 Vdim Ldet GND OUT 2 OUT 1 VCC Pin Function Description Soft start capacitor connection pin. The pin voltage determines the phase of soft start, normal and dimming 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. Input to the dimming stage. The pin voltage sets the switching frequency in dimming 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
KA7540
Absolute Maximum Ratings
Parameter Supply voltage Peak drive output current Drive output clamping diodes VO>VCC, or VO<-0.3 Dimming, soft start, and no lamp detection input voltage Operating temperature range Storage temperature range 8-DIP Power dissipation 8-SOP 8-DIP Thermal resistance (Junction-to-air) 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
(-25 125 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
4
KA7540
Electrical Characteristics
Unless otherwise specified, for typical values Vcc=14V, Ta=25C, For Min/Max values Ta is the operating ambient temperature range with -25C Ta 125C and 14V 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(Note1) Line regulation
(Note1)
Symbol VTH(st) HY(st)
Conditions VCC increasing VCCMin. 11.5 1.3
Typ. 12.5 1.8
Max. 13.5 2.3
Unit V V
IST ICC IDCC Vref Vref 1 Vref 2
1.95 -
0.2 6 7 2 0.1 15
0.3 10 14 2.05 10 -
mA mA mA V mV mV
Temperature stability of Vref(Note1) OSCILLATOR SECTION Operating frequency Operating dead time Soft start frequency Soft start time current Soft start dead time Dimming frequency OUTPUT SECTION Rising time (Note2) Falling time
(Note2)
fos tod fss ISS tsd fd tr tf Vomax(o) Vomin(o) Vnd
44 2.4 56 17 1.8 58 12 1.9
50 2.9 65 25 2.3 72 120 50 15 2
56 3.4 74 33 2.8 86 200 100 18 1 2.1
kHz s kHz A s kHz ns ns V V V
Maximum output voltage Output voltage with UVLO activated NO LAMP PROTECTION SECTION No lamp detect voltage
Notes : 1. This parameter is not tested in production but tested in wafer. 2. This parameter, although guaranteed, is not 100% tested in production.
5
KA7540
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 AC line voltage. The following equation can be used to calculate the value of Rst.
R
Vin ( ac ) x 2 - Vth ( st ), max --------------------------------------------------------------------------st lst, max 85 x 2 - 13.5 = ------------------------------------- = 356K -3 0.3 x 10
2 ( Vin ( ac_max ) 2 - V CC ) --------------------------------------------------------------------------- 1W P Rst = Rst 2 Rst ( Vin ( ac_max ) 2 - V CC ) Rst 130K
130K Rst 356K
The value of start-up capacitor (Cst) is normally determined in terms of the start-up time and operating current build up time with the 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 value 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 frequency of the gate drive output 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 (7 x 50A). During the charging period, one of the two MOSFETs remains ON state. On the contrary both of MOSFETs are OFF during the discharging period. 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 470pF, V(Vhigh - Vlow) = (2.86V - 1.0V) = 1.86V, Tch = 17.5s, Tdis = 2.5s
6
KA7540
Vct (Pin #2)
Vhigh
Vlow 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) = 40s fsw = 1 / TS = 25kHz The explicit equation calculating the value of the timing capacitor for a certain switching frequency is written below.
11.76 x 10 Ct = -------------------------------fsw
-6
Soft Start
The switching frequency is decreasing linearly from the pre-heating frequency to the normal switching frequency. In KA7540, the normal timing capacitor charging current is increased by 25A during the pre-heating mode. This addition of the charging current sets the pre-heating frequency to be 1.33 times the switching frequency at the normal mode.
fsw, VCS fsw (pre) fsw (dim) fsw (nor) 3.5V 2.7V 2V 0.95 ts/s td1 td2
Figure 3. Frequency & Soft start capacitor voltage variation during soft start and dimming mode
7
KA7540
No Lamp Protection
When the voltage at pin #4 is lower than 2V, the gate drive output is off-state, so the external power MOSFETs stop 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.
When 2 Lamp V R4 R19 = Vdd x -------------------------------------------------------------------------------------R15 + R18 + 2 x Rf R14 + -------------------------------------------------- + R19 2
15k 400 x ---------------------------------------------------------------------------------------330k + 680k 180k + ------------------------------------------ + 15k 2 R18 V3 = V2 x ---------------------------- 200V R15 + R18 V R4 > 2V When 1 Lamp R19 V R4 = Vdd x -------------------------------------------------------------------------------R14 + R15 + R18 + 2Rf + R19 15k 400 x ---------------------------------------------------------------------------------------180k + 330k + 680k + 15k V R4 > 2V Stop switching
When No Lamp V = 0V ( <2V ) R4
In normal mode, the average voltage of the V3 is the half of the dc link voltage (Vdd, PFC_OUT). So, in order to make the start condition stable, the resistors are designed to make the voltage of V3 be the half of the dc link voltage.
DC Link Voltage (Vdd), PFC_OUT R14 V2 Rfilament R16 Rfilament VR4 R19 C13 R17 Rfilament R15 Rfilament V3 R18
To pin #4
Figure 4. Lamp detection resistor network
8
KA7540
Dimming Control
The lighting output of the lamp can be controlled by varying the switching frequency of the ballast circuit. In voltage source series resonant type converter, the output power is inversely proportional to the switching frequency. As a result, in order to make the lamp lighting output less bright (so called "dimming"), the switching frequency should be increased compared to that of the normal full lighting output frequency. With KA7540, the switching frequency can be controlled by the voltage level at the pin #3 (Vdim). Since the IC starts to operate, the voltage level at the dimming pin doesn't affect the oscillator frequency until the time of td1 in figure 3. At the time td1, the switching frequency starts to ramp up to the dimming switching frequency level that is determined by the voltage level at the pin #3 (Vdim). In dimming mode, the timing capacitor charging current is increased by the following amount of the dimming current (Id). Id = 25uA x (Vref - Vd) / Vref Vd = Vdim / 5 So, the equations for the dimming frequency are as following.
dV 50uA + Id ------ = ------------------------dt Ct dV x Ct dTch ( dim ) = ----------------------------------------------------------------------25uA ( Vref - Vd ) -------------------------------------------50uA + Vref dV x Ct dTdis ( dim ) = --------------------------------------------------------------------------------25uA ( Vref - Vd ) 7 x 50uA + -------------------------------------------- Vref Ts ( dim ) = 2 x ( Tch ( dim ) + Tdis ( dim ) ) 1 f SW ( dim ) = --------------------Ts ( dim )
If the dimming pin is open, the dimming pin voltage becomes 10V due to the internal 100A current source, which is equivalent to the normal full lighting output case. Dimming Control can be reallized by simple voltage source and current source of variable resistor at pin #3.
9
KA7540
Application Circuit
[85 ~ 265Vac Input, 400V Vdd, 32W x 2 Lamps Ballast,Group Dimming Control]
Full-wave Rectified Output
L2 D5 R3 R6 D6 R4
PFC Output
D3 D1 NTC
D4 D2
C5
R8 R5 Q1 R1
C3
C4 C6
8
7
6
Vcc
GND
OUT
5
C9
Idet
C2 L1 C1
1 INV
FAN7527
EA_OUT MULT 3 4 CS
TNR F1 R2 C8 C7
2
R7
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
KA7540
Vdim Ldet
R17
Ct
1
2
3
C11 C12 1~10V
4
R18 R19
C13
10
KA7540
Component List
Part number R1 R2 R3, 12 R4 R5, 10, 11 R6 R7 R8 R9 R14 R15, 16 R17, 18 R19 C1, 2 C3, 4 C5 C6, 10 C7 C8 C9 C11 C12 C13 C14 C15, 16 C17, 18, 19, 20 C21 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 6.8F, 35V 180pF, 25V 0.1F, 25V 1nF, 630V 4700pF, 1000V 6800pF, 630V 0.22F, 25V 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 Electrolytic Ceramic Ceramic Miller-Cap Miller-Cap Miller-Cap Ceramic FQPF6N50 1N4007 UF4007 1N4148 1N4937 1N4744 Line Filter EI3026 EI2820 EE1614 Fuse 471 10D09 Manufacturer FairChild -
11
KA7540
Mechanical Dimensions
Package Dimensions in millimeters
8-DIP
0.018 0.004 1.524 0.10 0.060 0.004 0.46 0.10 6.40 0.20 0.252 0.008 ( #1 #8 9.20 0.20 0.362 0.008 9.60 MAX 0.378 #4 #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
0.25 -0.05
0~15
+0.10
0.010 -0.002
+0.004
12
0.79 ) 0.031
KA7540
Mechanical Dimensions (Continued)
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
13
KA7540
Ordering Information
Product Number KA7540 KA7540D Package 8-DIP 8-SOP Operating Temperature -25C ~ +125C
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 10/29/01 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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