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FAN7710 -- Ballast Control IC for Compact Fluorescent Lamps
June 2007
FAN7710 Ballast Control IC for Compact Fluorescent Lamps
Features
Integrated Half-Bridge MOSFET Floating Channel for Bootstrap Operation up to +550V Low Start-up and Operating Current: 120A, 2.6mA Under-Voltage Lockout with 1.8V of Hysteresis Adjustable Run Frequency and Preheat Time Internal Active ZVS Control Internal Protection Function (No Lamp) Internal Clamping Zener Diode High Accuracy Oscillator Soft-Start Functionality
Description
The FAN7710, developed using Fairchild's unique highvoltage process and system-in-package (SiP) concept, is a ballast control integrated circuit (IC) for a compact fluorescent lamp (CFL). The FAN7710 controls internal high-voltage stress and delivers 20W to the lamp at 310VDC voltage. FAN7710 incorporates a preheating / ignition function, controlled by an user-selected external capacitor, to increase lamp life. The FAN7710 detects switch operation from after ignition-mode through an internal active Zero-Voltage Switching (ZVS) control circuit. This control scheme enables the FAN7710 to detect an open-lamp condition, without the expense of external circuitry, and prevents stress on MOSFETs. The high-side driver built into the FAN7710 has a commonmode noise cancellation circuit that provides robust operation against high-dv/dt noise intrusion. 8-DIP
Applications
Compact Fluorescent Lamp Ballast
Ordering Information
Part Number
FAN7710N
Package
8-DIP
Pb-Free
Yes
Operating Temperature Range
-25C ~ 125C
Packing Method
Tube
(c) 2007 Fairchild Semiconductor Corporation FAN7710 Rev. 1.0.2
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FAN7710 -- Ballast Control IC for Compact Fluorescent Lamps
Typical Application Diagrams
* Refer to the BOM and design guide provided on page16.
Figure 1. Typical Application Circuit for Compact Fluorescent Lamp
Internal Block Diagram
VDD 1
10V REG 15V SHUNT REGULATOR VDD Sense
VDC
HIGH-SIDE DRIVER
VB UVLO
8 7 VB
Reference
IPH =0.6*IRT
BIAS & SYSTEM LATCH
BGR CPH 3V 5V UVLO UVLO SDH R S BIAS TSD SYSHALT Q Q SHORT-PULSE GENERATOR SDL SET
Noise Canceller
S R VS
Q Q
4V
IRT
IPH
IPH*
IRT
RT
2
PRE-HEAT Control
CPH<3V Yes 2A 12A No
CPH
0A
6 OUT
LOW-SIDE GATE DRIVER
DELAY
DEAD TIME Control
OSCILLATOR
RESET
IPH*
VDDH/VDD LSH VDDH/VDD LSH SDL
SDH
5 PGND CPH 3
SDL 5V/3V S SDH R Q Q RESET SYSHALT ADAPTIVE ZVS CONTROLLER TRANSITION SENSING
ADAPTIVE ZVS ENABLE LOGIC
4 SGND
FAN7710 Rev. 1.00
Figure 2. Functional Block Diagram
(c) 2007 Fairchild Semiconductor Corporation FAN7710 Rev. 1.0.2 2
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FAN7710 -- Ballast Control IC for Compact Fluorescent Lamps
Pin Configuration
VDC 8 VB 7 OUT 6 PGND 5
FAN7710
YWW
(YWW : Work Week Code)
1 VDD
2 RT
3 CPH
4 SGND
FAN7710 Rev. 1.00
Figure 3. Pin Configuration (Top View)
Pin Definitions
Pin #
1 2 3 4 5 6 7 8
Name
VDD RT CPH SGND PGND OUT VB VDC Supply voltage Oscillator frequency set resistor Preheating time set capacitor Signal ground Power ground High-side floating supply return High-side floating supply High-voltage supply
Description
(c) 2007 Fairchild Semiconductor Corporation FAN7710 Rev. 1.0.2 3
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FAN7710 -- Ballast Control IC for Compact Fluorescent Lamps
Absolute Maximum Ratings
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. TA=25C unless otherwise specified.
Symbol
VB VOUT VIN ICL dVOUT/dt TA TSTG PD JA Note: High-side floating supply
Parameter
High-side floating supply return RT, CPH pins input voltage Clamping current level Allowable offset voltage slew rate Operating temperature range Storage temperature range Power dissipation Thermal resistance (junction-to-air)
Min. Typ. Max. Unit
-0.3 -0.3 -0.3 50 -25 -65 2.1 70 125 150 575 550 8 25 V V V mA V/ns C C W C/W
1. Do not supply a low-impedance voltage source to the internal clamping Zener diode between the GND and the VDD pin of this device.
(c) 2007 Fairchild Semiconductor Corporation FAN7710 Rev. 1.0.2 4
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FAN7710 -- Ballast Control IC for Compact Fluorescent Lamps
Electrical Characteristics
VBIAS (VDD, VB -Vout) = 14.0V, TA = 25C, unless otherwise specified.
Symbol
VDC
Parameter
High-voltage supply voltage
Condition
Min. Typ. Max. Unit
550 V 13.4 11.6 1.8 15.2 120 2.6 8.5 7.9 9.2 8.6 0.6 50 250 A 10.0 9.5 V A mA 14.4 12.4 V
High-Voltage Supply Section Low-Side Supply Section (VDD) VDDTH(ST+) VDD UVLO positive going threshold VDDTH(ST-) VDD UVLO negative going threshold VDDHY(ST) VCL IST IDD VDD-side UVLO hysteresis Supply clamping voltage Start-up supply current Dynamic operating supply current IDD =20mA VDD = 10V Running freq,CL = 1nF 14.8 VDD increasing VDD decreasing 12.4 10.8
High-Side Supply Section (VB-VOUT) VHSTH(ST+) High-side UVLO positive going threshold VB -VOUT increasing VHSTH(ST-) High-side UVLO negative going threshold VB -VOUT decreasing VHSHY(ST) IHST IHD High-side UVLO hysteresis High-side quiescent supply current High-side dynamic operating supply current CPH pin preheating voltage range CPH pin charging current during preheating CPH pin charging current during ignition CPH pin voltage level at running mode Preheating frequency Running frequency Maximum dead time Minimum dead time RT = 80k, VCPH = 2V RT = 80k VCPH = 1V, VOUT = GND during preheat mode VCPH = 6V, VOUT= GND during run mode 2.6 250 165 VDS = 500V VGS = 12V, ID = 100mA VGS = 12V, ID = 500mA VGS = 12V, VDS = 30V 800 6.2 6.5 10 450 72 48.7 VCPH = 1V VCPH = 4V VB -VOUT = 14V Running freq,CL = 1nF
Oscillator Section VMPH IPH IIG VMO fPRE fOSC DTMAX DTMIN 2.5 1.25 8 3.0 2.00 12 7.0 85 53.0 3.1 1.0 98 57.3 3.5 2.85 16 V kHz kHz s s V A
Protection Section VCPHSD ISD TSD ILKMOS RON ISAT Shutdown voltage Shutdown current Thermal shutdown
(2)
VRT = 0 after run mode
V A C A mA
MOSFET Section MOSFET leakage current On resistance (dynamic) Saturation current(2)
Note: 2. This parameter, although guaranteed, is not 100% tested in production.
(c) 2007 Fairchild Semiconductor Corporation FAN7710 Rev. 1.0.2 5
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FAN7710 -- Ballast Control IC for Compact Fluorescent Lamps
Typical Characteristics
Figure 4. Start-up Current vs. Temp.
Figure 5. Preheating Current vs. Temp.
Figure 6. Ignition Current vs. Temp.
Figure 7. Operating Current vs. Temp.
Figure 8. High-Side Quiescent Current vs. Temp.
Figure 9. Shutdown Current vs. Temp.
(c) 2007 Fairchild Semiconductor Corporation FAN7710 Rev. 1.0.2 6
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FAN7710 -- Ballast Control IC for Compact Fluorescent Lamps
Typical Characteristics (Continued)
Figure 10. VDD UVLO+ vs. Temp.
Figure 11. VDD UVLO- vs. Temp.
Figure 12. VHS UVLO+ vs. Temp.
Figure 13. VHS UVLO- vs. Temp.
Figure 14. VDD Clamp Voltage vs. Temp.
Figure 15. Running Frequency vs. Temp.
(c) 2007 Fairchild Semiconductor Corporation FAN7710 Rev. 1.0.2 7
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FAN7710 -- Ballast Control IC for Compact Fluorescent Lamps
Typical Characteristics (Continued)
Figure 16. Preheating Frequency vs. Temp.
Figure 17. Maximum Dead Time vs. Temp.
Figure 18. Minimum Dead Time vs. Temp.
Figure 19. Internal MOSFET Turn-on Resistance vs. Temp.
(c) 2007 Fairchild Semiconductor Corporation FAN7710 Rev. 1.0.2 8
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FAN7710 -- Ballast Control IC for Compact Fluorescent Lamps
Typical Application Information
1. Under-Voltage Lockout (UVLO) Function
The FAN7710 has UVLO circuits for both high-side and low-side circuits. When VDD reaches VDDTH(ST+), UVLO is released and the FAN7710 operates normally. At UVLO condition, FAN7710 consumes little current, noted as IST. Once UVLO is released, FAN7710 operates normally until VDD goes below VDDTH(ST-), the UVLO hysteresis. At UVLO condition, all latches that determine the status of the IC are reset. When the IC is in the shutdown mode, the IC can restart by lowering VDD voltage below VDDTH(ST-). FAN7710 has a high-side gate driver circuit. The supply for the high-side driver is applied between VB and VOUT. To protect from malfunction of the driver at low supply voltage between VB and VOUT, FAN7710 provides an additional UVLO circuit between the supply rails. If VBVOUT is under VHSTH(ST+), the driver holds low state to turn off the high-side switch, as shown in Figure 20. As long as VB-VOUT is higher than VHSTH(ST-) after VB-VOUT exceeds VHSTH(ST+), operation of the driver continues. Before the lamp is ignited, the lamp impedance is very high. Once the lamp is turned on, the lamp impedance significantly decreases. Since the resonant peak is very high due to the high-resistance of the lamp at the instant of turning on the lamp, the lamp must be driven at higher frequency than the resonant frequency, shown as (A) in Figure 21. In this mode, the current supplied by the inverter mainly flows through CP. CP connects both filaments and makes the current path to ground. As a result, the current warms up the filament for easy ignition. The amount of the current can be adjusted by controlling the oscillation frequency or changing the capacitance of CP. The driving frequency, fPRE, is called preheating frequency and is derived by:
fPRE = 1.6 x fOSC
(EQ 1)
2. Oscillator
The ballast circuit for a fluorescent lamp is based on the LCC resonant tank and a half-bridge inverter circuit, as shown in Figure 20. To accomplish Zero-Voltage Switching (ZVS) of the half-bridge inverter circuit, the LCC is driven at a higher frequency than its resonant frequency, which is determined by L, CS, CP, and RL; where RL is the equivalent lamp's impedance.
After the warm-up, the FAN7710 decreases the frequency, shown as (B) of Figure 21. This action increases the voltage of the lamp and helps the fluorescent lamp ignite. The ignition frequency is described as a function of CPH voltage, as follows:
fIG = 0.3 x ( 5-VCPH ) + 1 x fOSC
(EQ 2)
where VCPH is the voltage of CPH capacitor. Equation 2 is valid only when VCPH is between 3V and 5V before FAN7710 enters running mode. Once VCPH reaches 5V, the internal latch records the exit from ignition mode. Unless VDD is below VDDTH(ST-), the preheating and ignition modes appear only once during lamp start transition. Finally, the lamp is driven at a fixed frequency by an external resistor, RT, shown as (C) in Figure 21. If VDD is higher than VDDTH(ST+) and UVLO is released, the voltage of the RT pin is regulated to 4V. This voltage adjusts the oscillator's control current according to the resistance of RT. Because this current and an internal capacitor set the oscillation frequency, the FAN7710 does not need any external capacitors. The proposed oscillation characteristic is given by:
FAN7710
VDD Inverter VDC
VDC
RT VDD RT
Oscillator High-side driver
VB L OUT Low-side driver PGND equivalent lamp impedance LCC resonant tank Filament CS
CPH CPH SGND
Dead-time controller
RL
CP
FAN7710 Rev. 1.00
Figure 20. Resonant Inverter Circuit Based on LCC Resonant Tank The transfer function of LCC resonant tank is heavily dependent on the lamp impedance, RL, as illustrated in Figure 20. The oscillator in FAN7710 generates effective driving frequencies to assist lamp ignition and improve lamp life longevity. Accordingly, the oscillation frequency is changed in the following sequence: Preheating freq->Ignition freq-> Normal running freq.
fOSC =
4 x 10 9 RT
(EQ 3)
The oscillation frequency is not changed even in the active ZVS mode, shown as (D) in Figure 21. The dead time is varied according to resonant tank characteristics.
(c) 2007 Fairchild Semiconductor Corporation FAN7710 Rev. 1.0.2 9
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FAN7710 -- Ballast Control IC for Compact Fluorescent Lamps
40dB
CPH voltage [V] 8 7
RL=100k
(C) Active ZVS mode
CPH voltage varies by active ZVS control circuit
(B) Ignition Mode
6
DTMAX
5 4 (A) Preheating Mode
20dB
DTMIN
3 2 1 0 Preheating Frquency:fPRE Preheating Mode Ignition Mode t0
RL=10k
Preheating frequency (B)
(D) Shutdown mode
0dB RL=1k Running frequency RL=500 (C)
(A)
3 21 0 Dead-Time[s] Oscillation frequency
time
Running frequency: fOSC
Running Mode
t1 t2 t3
time
FAN7710 Rev. 1.00
(D) Dead-time control mode at fixed frequency
FAN7710 Rev. 1.00
Figure 21. LCC Transfer Function in Terms of Lamp Impedance
Figure 22. Operation Modes 3.1 Preheating Mode (t0~t1) When VDD exceeds VDDTH(ST+), the FAN7710 starts operation. At this time, an internal current source (IPH) charges CPH. CPH voltage increases from 0V to 3V in preheating mode. Accordingly, the oscillation frequency follows Equation 4. In this mode, the lamp is not ignited, but warmed up for easy ignition. The preheating time depends on the size of CPH:
fpreheat = 3 x CPH IPH
[Sec.]
3. Operation Modes
FAN7710 has four operation modes: (A) preheating mode, (B) ignition mode, (C) active ZVS mode, and (D) shutdown mode, depicted in Figure 22. The modes are automatically selected by the voltage of CPH capacitor shown in Figure 20. In modes (A) and (B), the CPH acts as a timer to determine the preheating and ignition times. After preheating and ignition modes, the role of the CPH is changed to stabilize the active ZVS control circuit. In this mode, the dead time of the inverter is selected by the voltage of CPH. Only when FAN7710 is in active ZVS mode, is it possible to shut off the whole system using the CPH pin. Pulling the CPH pin below 2.6V in active ZVS mode causes the FAN7710 to enter shutdown mode. In shutdown mode, all active operation is stopped except UVLO and some bias circuitry. The shutdown mode is triggered by the external CPH control or the active ZVS circuit. The active ZVS circuit automatically detects lamp removal (open-lamp condition) and decreases CPH voltage below 2.6V to protect the inverter switches from damage.
(EQ 4)
According to the preheating process, the voltage across the lamp to ignite is reduced and the lifetime of the lamp is increased. In this mode, the dead time is fixed at its maximum value. 3.2 Ignition Mode (t1~t2) When the CPH voltage exceeds 3V, the internal current source to charge CPH is increased about six times larger than IPH, noted as IIG, causing rapid increase in CPH voltage. The internal oscillator decreases the oscillation frequency from fPRE to fOSC as CPH voltage increases. Lowering the frequency increases the voltage across the lamp, as depicted in Figure 22. Finally, the lamp ignites. Ignition mode is defined when CPH voltage lies between 3V and 5V. Once CPH voltage reaches 5V, the FAN7710 does not return to ignition mode, even if the CPH voltage is in that range, until the FAN7710 restarts from below VDDTH(ST-). Since the ignition mode continues when CPH is from 3V to 5V, the ignition time is given by:
tignition = 2 x CPH IIG
[Sec.]
(EQ 5)
In this mode, dead time varies according to the CPH voltage.
(c) 2007 Fairchild Semiconductor Corporation FAN7710 Rev. 1.0.2 10
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FAN7710 -- Ballast Control IC for Compact Fluorescent Lamps
3.3 Running Mode and Active Zero-Voltage Switching (AZVS) Mode (t2~) When CPH voltage exceeds 5V, the operating frequency is fixed to fOSC by RT. However, active ZVS operation is not activated until CPH reaches ~6V. The FAN7710 prepares for active ZVS operation from the instant CPH exceeds 5V during t2 to t3. When CPH becomes higher than ~6V at t3, the active ZVS operation is activated. To determine the switching condition, FAN7710 detects the transition time of the output (VOUT pin) of the inverter by using the VB pin. From the output-transition information, FAN7710 controls the dead time to meet the ZVS condition. If ZVS is satisfied, the FAN7710 slightly increases the CPH voltage to reduce the dead time and to find optimal dead time, which increases the efficiency and decreases the thermal dissipation and EMI of the inverter switches. If ZVS fails, the FAN7710 decreases CPH voltage to increase the dead time. CPH voltage is adjusted to meet optimal ZVS operation. During the active ZVS mode, the amount of the charging/ discharging current is the same as IPH. Figure 23 depicts normal operation waveforms.
3.4 Shutdown Mode If the voltage of capacitor CPH is decreased below ~2.6V by an external application circuit or internal protection circuit, the IC enters shutdown mode. Once the IC enters shutdown mode, this status continues until an internal latch is reset by decreasing VDD below VDDTH(ST-). Figure 24 shows an example of external shutdown control circuit.
3 Shutdown Q1 CPH 4
CPH
FAN7710
SGND
FAN7710 Rev. 1.00
Figure 24. External Shutdown Circuit The amount of the CPH charging current is the same as IPH, making it possible to shut off the IC using small signal transistor. FAN7710 provides active ZVS operation by controlling the dead time according to the voltage of CPH. If ZVS fails even at the maximum dead time, FAN7710 stops driving the inverter. The FAN7710 thermal shutdown circuit senses the junction temperature of the IC. If the temperature exceeds ~160C, the thermal shutdown circuit stops operation of the FAN7710. The current usages of shutdown mode and undervoltage lockout status are different. In shutdown mode, some circuit blocks, such as bias circuits, are kept alive. Therefore, the current consumption is slightly higher than during under-voltage lockout. 4. Automatic Open-Lamp Detection The FAN7710 can automatically detect an open-lamp condition. When the lamp is opened, the resonant tank fails to make a closed-loop to the ground, as shown in Figure 25. The supplied current from the OUT pin is used to charge and discharge the charge pump capacitor, CP. Since the open-lamp condition means resonant tank absence, it is impossible to meet ZVS condition. In this condition, the power dissipation of the FAN7710, due to capacitive load drive, is estimated as:
Figure 23. Typical Transient Waveform from Preheating to Active ZVS Mode
Pdissipation =
1 x CP x VDC 2 x f 2
[W ]
(EQ 6)
where f is driving frequency and VDC is DC-link voltage.
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FAN7710 -- Ballast Control IC for Compact Fluorescent Lamps
VDC=311VDC DB
5. Power Supply
When VDD is lower than VDDTH(ST+), it consumes very little current, IST, making it possible to supply current to the VDD pin using a resistor with high resistance (Rstart in Figure 27). Once UVLO is released, the current consumption is increased and the whole circuit is operated, which requires additional power supply for stable operation. The supply must deliver at least several mA. A charge pump circuit is a cost-effective method to create an additional power supply and allows CP to be used to reduce the EMI.
VDC
Charge Pump
1 2 CVDD 3 4
VDD RT CPH SGND
VDC VB OUT PGND
8 7 6 5
CB L LCC resonant tank C Filament open
S
RL
CP
Dp1
CCP Dp2
FAN7710 Rev. 1.00
Rstart VDD RT CVDD CPH SGND
Figure 25. Current Flow When the Lamp is Open Assuming that CP, VDC, and f are 1nF, 311V, and 50kHz, respectively; the power dissipation reaches about 2.4W and the temperature of FAN7710 is increased rapidly. If no protection is provided, the IC can be damaged by the thermal attack. Note that the hard switching condition during the capacitive-load drive causes EMI. Figure 26 illustrates the waveforms during the openlamp condition. In this condition, the charging and discharging current of CP is directly determined by FAN7710 and considered hard switching condition. The FAN7710 tries to meet ZVS condition by decreasing CPH voltage to increase dead time. If ZVS fails and CPH goes below 2.6V, even though the dead time reaches its maximum value, FAN7710 shuts off the IC to protect against damage. To restart FAN7710, VDD must be below VDDTH(ST-) to reset an internal latch circuit, which remembers the status of the IC.
Shutdown Release Restart
FAN7710 VDC VB (2) OUT PGND RL CP L CS dv/dt
Shunt regulator
(1) Dp1 Dp2 FAN7710 Rev. 1.00
CCP
Charge pump
Figure 27. A Local Power Supply for VDD Using a Charge Pump Circuit As presented in Figure 27; when OUT is high, the inductor current and CCP create an output transition with the slope of dv/dt. The rising edge of OUT charges CCP. At that time, the current that flows through CCP is:
I CCP x dv dt
(EQ 7)
VDD VDDTH(ST+) VDDTH(ST-)
CPH 6V 5V 3V 2V
Active ZVS activated Automatic Shutdown
time
This current flows along the path (1). It charges CVDD, which is a bypass capacitor to reduce the noise on the supply rail. If CVDD is charged over the threshold voltage of the internal shunt regulator, the shunt regulator is turned on and regulates VDD with the trigger voltage. When OUT is changing from HIGH to LOW state, CCP is discharged through Dp2, shown as path (2) in Figure 27. These charging/discharging operations are continued until FAN7710 is halted by shutdown operation. The charging current, I, must be large enough to supply the operating current of FAN7710. The supply for the high-side gate driver is provided by the boot-strap technique, as illustrated in Figure 28. When the low-side MOSFET connected between OUT and PGND pins is turned on, the charging current for VB flows through DB. Every low OUT gives the chance to charge the CB. Therefore, CB voltage builds up only when FAN7710 operates normally.
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time
Running mode
OUT
Active ZVS mode
0V Preheating period (Filament warm-up) Shutdown Ignition period mode
time
FAN7710 Rev. 1.00
Figure 26. CPH Voltage Variation in Open-Lamp Condition
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FAN7710 -- Ballast Control IC for Compact Fluorescent Lamps
When OUT goes HIGH, the diode DB is reverse-biased and CB supplies the current to the high-side driver. At this time, since CB discharges, VB-VOUT voltage decreases. If VB-VOUT goes below VHSTH(ST-), the highside driver cannot operate due to the high-side UVLO protection circuit. CB must be chosen to be large enough not to fall into UVLO range, due to the discharge during a half of the oscillation period, especially when the highside MOSFET is turned on.
VDC DB Rstart VDD RT CVDD CPH SGND FAN7710 VDC VB OUT PGND RL CP CB L CS Bootstrap circuit
Chraging path Dp1 Dp2 FAN7710 Rev. 1.00
Cp
Figure 28. Implementation of Floating Power Supply Using the Bootstrap Method
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FAN7710 -- Ballast Control IC for Compact Fluorescent Lamps
Design Guide
1. Start-up Circuit
The start-up current (IST) has to be supplied to the IC through the start-up resistor, Rstart. Once operation starts, the power is supplied by the charge pump circuit. To reduce the power dissipation in Rstart, select Rstart as high as possible, considering the current requirements at start-up. For 220VAC power, the rectified voltage by the full-wave rectifier makes DC voltage, as shown in Equation 8. The voltage contains lots of AC component, due to poor regulation characteristic of the simple fullwave rectifier:
VDC = 2 x 220[V ] 311[V ]
As shown in Equation 14, if Rstart meets Equation 14, restart operation is possible. However, it is not recommended to choose Rstart at that range since VDD rising time could be long and increase the lamp's turn-on delay time, as depicted in Figure 29.
VDD VCL VDDTH(ST+) VDDTH(ST-) tstart
(EQ 8)
0
FAN7710 Rev. 1.00
Considering the selected parameters, Rstart must satisfy the following equation:
VDC - VDDTH (ST + ) R start > IST
time
(EQ 9)
Figure 29. VDD Build-up Figure 30 shows the equivalent circuit for estimating tstart. From the circuit analysis, VDD variation versus time is given by:
VDD (t ) = (VDC - Rstart IST ) 1 - e -t /(Rstart CVDD )
From Equation 9, Rstart is selected as:
VDC - VDDTH (ST + ) IST > R start
(EQ 10)
(
)
(EQ 15)
Note that if choosing the maximum Rstart, it takes a long time for VDD to reach VDDTH(st+). Considering VDD rising time, Rstart must be selected as shown in Figure 29. Another important concern for choosing Rstart is the available power rating of Rstart. To use a commercially available, low-cost 1/4 resistor, Rstart must obey the following rule:
where CVDD is the total capacitance of the bypass capacitors connected between VDD and GND. From Equation 15, it is possible to calculate tstart by substituting VDD(t) with VDDTH(ST+):
tstart = -Rstart CVDD ln VDC - Rstart IST - VDDTH (ST + ) VDD - Rstart IST
(EQ 16)
(VDC
- VCL )
2
R start
<
1 [W ] 4
(EQ 11)
In general, Equation 16 can be simplified as:
tstart Rstart CVDD VDDTH (ST + ) VDC - Rstart IST - VDDTH (ST + )
Assuming VDC=311V and VCL=15V, the minimum resistance of Rstart is about 350k. When the IC operates in shutdown mode due to thermal protection, open-lamp protection, or hard-switching protection; the IC consumes shutdown current, ISD, which is larger than IST. To prevent restart during this mode, Rstart must be selected to cover ISD current consumption. The following equation must be satisfied:
VDC - VDDTH (ST + ) ISD > R start
(EQ 17)
Accordingly, tstart can be controlled by adjusting the value of Rstart and CVDD. For example, if VDC=311V, Rstart=560k, CVDD=10F, Ist=120A, and VDDTH(ST+)= 13.5V, tstart is about 0.33s.
Rstart IST VDD RT CVDD CPH GND
FAN7710 Rev. 1.00
(EQ 12)
From Equations 10 - 12; it is possible to select Rstart: (1) For safe start-up without restart in shutdown mode:
4 (VDC - VCL ) < Rstart <
2
VDC - VDDTH (ST + ) ISD VDC - VDDTH (ST + ) IST
(EQ 13)
(2) For safe start-up with restart from shutdown mode:
VDC - VDDTH (ST + ) ISD < Rstart <
(EQ 14)
Figure 30. Equivalent Circuit During Start
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FAN7710 -- Ballast Control IC for Compact Fluorescent Lamps
2. Current Supplied by Charge Pump
For the IC supply, the charge pump method is used in Figure 31. Since CCP is connected to the half-bridge output, the supplied current by CCP to the IC is determined by the output voltage of the half-bridge. When the half-bridge output shows rising slope, CCP is charged and the charging current is supplied to the IC. The current can be estimated as:
I = CCP V dV CCP DC dt DT
3. Lamp Turn-on Time
The turn-on time of the lamp is determined by supply build-up time tstart, preheating time, and ignition time; where tstart has been obtained by Equation 17. When the IC's supply voltage exceeds VDDTH(ST+) after turn-on or restart, the IC operates in preheating mode. This operation continues until CPH pin's voltage reaches ~3V. In this mode, CPH capacitor is charged by IPH current, as depicted in Figure 32. The preheating time is achieved by calculating:
(EQ 18)
where DT is the dead time and dV/dt is the voltage variation of the half-bridge output. When the half-bridge shows falling slope, CCP is discharged through Dp2. Total supplied current, Itotal, to the IC during switching period, t, is:
Itotal = I DT = CCP VDC
t preheat = 3
CPH IPH
(EQ 21)
The preheating time is related to lamp life (especially filament). Therefore, the characteristics of a given lamp should be considered when choosing the time.
VDD
(EQ 19)
From Equation 19, the average current, Iavg, supplied to the IC is obtained by:
RT IPH CPH
Iavg =
Itotal CCP VDC = = CCP VDC f t t
(EQ 20)
CPH
GND
FAN7710 Rev. 1.00
For the stable operation, Iavg must be higher than the required current. If Iavg exceeds the required current, the residual current flows through the shunt regulator implemented on the chip, which can cause unwanted heat generation. Therefore, CCP must be selected considering stable operation and thermal generation. For example, if CCP=0.5nF, VDC=311V, and f=50kHz, Iavg is ~7.8mA; it is enough current for stable operation.
Figure 32. Preheating Timer Compared to the preheating time, it is almost impossible to exactly predict the ignition time, whose definition is the time from the end of the preheating time to ignition. In general, the lamp ignites during the ignition mode. Therefore, assume that the maximum ignition time is the same as the duration of ignition mode, from 3V until CPH reaches 5V. Thus, ignition time can be defined as:
tignition = (5 - 3 ) CPH CPH =2 IIG IIG
Charging mode
CCP Dp1 Idp1 Dp2 To VDD
Discharging mode
CCP Dp1 Idp1=0 Dp2 To VDD CVDD
(EQ 22)
CVDD
f=1/t
Note that at ignition mode CPH is charged by IIG, which is six times larger than IPH. Consequently, total turn-on time is approximately: VDD Build-Time + Preheating Time + Ignition Time =
VDC
DT:dead time Half-bridge output
t ignition = (5 - 3 )
CPH CPH =2 [Sec.] IIG IIG
(EQ 23)
Idp1
FAN7710 Rev. 1.00
Figure 31. Charge Pump Operation
(c) 2007 Fairchild Semiconductor Corporation FAN7710 Rev. 1.0.2 15
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FAN7710 -- Ballast Control IC for Compact Fluorescent Lamps
Component List for 20W CFL Application
Part
R1(3) R2
Value
Resistor 470k 82k 1/4W
Note
Part
D1 D2 D3 D4 D6 D7 U1
Value
Diode 1N4007 1N4007 1N4007 1N4007 UF4007 UF4007 IC FAN7710 1kV/1A 1kV/1A 1kV/1A 1kV/1A
Note
1/4W,1% Electrolytic Capacitor, 105C Electrolytic Capacitor, 105C Miller Capacitor, 5% Miller Capacitor Ceramic Capacitor Miller Capacitor Miller Capacitor, 5% EE1916S
Capacitor C1 C2 C3(5) C4 C5 C6
(6) (6)
10F/400V 10F/50V 0.68F/25V 100nF/25V 470pF/1kV 33nF/630V 2.7nF/1kV Inductor 2.5mH (280T)
1kV/1A, Ultra Fast 1kV/1A, Ultra Fast Ballast IC
C7
L1(6)
Note: 3. Refer to the Typical Application circuit provided in Figure 1. 4. Refer to the Design Guide start-up circuit, in Figure 30. Due to reducing power loss on the start-up resistor (R1) for high-efficiency systems, it is possible to use a higher resistor value than recommended. In this case, the IC doesn't reliably keep SD (shutdown) state for protection. Carefully select the start-up resistor (R1) or use the recommended value (470k) to sufficiently supply shutdown current (ISD) and start-up current (IST). 5. Temperature dependency of the capacitance is important to prevent destruction of IC. Some capacitors show capacitance degradation at high temperatures and can not guarantee enough preheating time to safely ignite the lamp during the ignition period at high temperatures. If the lamp does not ignite during the ignition period, the IC cannot guarantee ZVS operation. Thus, the peak current of the switching devices can be increased above allowable peak current level of the switching devices. Especially in the high temperate, the switching device can be easily destroyed. Consequently, CPH capacitor (C3) must be large enough to warm the filaments of the lamp up over the target temperature range. 6. Consider the components (L1,C6,C7) of resonant tank variation over the target temperature range. Normally, these components would be changed toward increasing inductance and capacitance in high temperature. That means that the resonant frequency is decreased. In the lower resonant frequency condition, the preheating current is reduced, so the resonant tank cannot supply enough to preheat the filaments before lamps turn on. If the preheating current is insufficient, the ignition voltage/current is increased. With the ignition current at high temperature, the current capacity of internal MOSFETs on IC must be bigger than ignition current.
(c) 2007 Fairchild Semiconductor Corporation FAN7710 Rev. 1.0.2 16
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FAN7710 -- Ballast Control IC for Compact Fluorescent Lamps
Package Dimensions
8-DIP
Dimensions are in millimeters unless otherwise noted.
Figure 33. 8-Lead Dual Inline Package (DIP)
(c) 2007 Fairchild Semiconductor Corporation FAN7710 Rev. 1.0.2 17
www.fairchildsemi.com
FAN7710 -- Ballast Control IC for Compact Fluorescent Lamps
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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 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. 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.
PRODUCT STATUS DEFINITIONS Definition of Terms Datasheet Identification Advance Information Preliminary Product Status Formative or In Design First Production Definition This datasheet contains the design specifications for product development. Specifications may change in any manner without notice. This datasheet contains preliminary data; supplementary data will be published at a later date. Fairchild Semiconductor reserves the right to make changes at any time without notice to improve design. This datasheet contains final specifications. Fairchild Semiconductor reserves the right to make changes at any time without notice to improve design. This datasheet contains specifications on a product that has been discontinued by Fairchild Semiconductor. The datasheet is printed for reference information only.
Rev. I29
No Identification Needed
Full Production
Obsolete
Not In Production
(c) 2007 Fairchild Semiconductor Corporation FAN7710 Rev. 1.0.2 18
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