Features: Integrated half-bridge mosfet floating channel for bootstrap operation below +550V Low start-up and operating current: 120 μA, 2.6MA under-voltage lockout, hysteresis 1.8V Adjustable operating frequency and warm-up time Internal active ZVS control Internal protection function (No light) Internal clamp Zener diode High precision oscillator soft start function

Application: Compact Fluorescent Lamp Ballast Description: Developed using Fairchild's unique High Voltage Process and Package System (SIP) concept, the Fan 7710 is a compact ballast controlled integrated circuit fluorescent lamp (CFL). FAN7710 controls internal high voltage stress, at 310V DC voltage. Fan 7710 incorporates a preheat/ignition function, externally controlled capacitors selected by the user, extending bulb life. Fan 7710 detects switching from post ignition mode to an internal active zero voltage switching (zvs) control circuit. This control scheme enables the FAN7710 to detect the state of an open lamp without costing external circuitry and preventing stress on the mosfet. The high-side driver built into the FAN7710 has a common-mode noise cancellation circuit that provides robust operation against high dv/dt noise intrusion.

Typical application information: 1. Under voltage lockout (uvlo) function High side and low side circuits of Fan 7710. When vdd reaches vddth(st+), uvlo is released and fan 7710 works normally. In the uvlo state, the fan7710 consumes very little current, note yes. Once the uvlo is released, the fan7710 will work usually until the vdd is below vddth(st-), the uvlo is hysteretic. Under uvlo conditions, the states of all identified ICs are reset. When the IC is in shutdown mode, the IC can restart by lowering the VDD voltage below VDDTH (ST-). The FAN7710 has a high-side gate drive circuit. The supply uses high-end drivers between vb and vout. To prevent driver failure under low supply voltages between vb and vout, the fan7710 provides additional UVLO circuitry between the supply rails. If vb-vout is below vhsth(st+), the driver remains low to close the high-side switch as shown. As long as vb-vout is higher than vhsth(st-) after vb-vout exceeds vhsth(st+), the driver continues to work. 2. The ballast circuit of the oscillator fluorescent lamp is based on the lcc resonant tank and the half-bridge inverter circuit as shown in the figure. The driving frequency of the switch (ZVS) lcc that realizes the zero-voltage half-bridge inverter circuit is higher than its resonant frequency, which is determined by l, cs, cp and rl; where rl is the impedance of the equivalent lamp.

The transfer function of the lcc resonator is strongly dependent on the lamp impedance rl, as the oscillator in the FAN7710 produces efficient auxiliary lamp ignition and improved driving frequency for long lamp life. Therefore, the oscillation frequency is changed in the following order: preheat frequency -> ignition frequency -> normal operating frequency. Before the lamp is ignited, the impedance of the lamp is very high. Once the lamp is turned on, the impedance of the lamp is significantly reduced. Because the resonance peak is very high due to the instantaneous high resistance of the lamp when the lamp is turned on, the lamp must be turned on at a higher frequency than the resonant frequency, as shown in (a). In this mode, the inverter mainly passes through the CP. CP connects the two filaments and grounds the current path. As a result, the current causes the filament to easily heat up and ignite. The magnitude of the current can be controlled by controlling the oscillation frequency or changing the capacitance of Cp. The drive frequency fpre is called the preheat frequency and is derived from the following equation: Equation 2 only 5 volts before vcph is between 3v and the fan 7710 enters run mode. Once VCPH reaches 5V, the internal latch registers the slave firing mode. Preheat and ignition modes transition at lamp start unless vdd is below vddth(st-). Finally, the lamp is connected by an external resistor, Rt, as shown in (c) in the figure. If VDD is above vddth(st+) and uvlo is released, the voltage of RT pin is regulated to 4V. This voltage is set according to the oscillation frequency because this current and a capacitor, FAN7710 does not need any external capacitor. The proposed oscillation characteristics are given by:

3. Operating Modes FAN7710 has four operating modes: (a) preheat mode, (b) ignition mode, (c) active zero voltage switching mode, and (d) shutdown mode as shown. The mode is automatically selected by the cph capacitor voltage as shown. In modes (a) and (b), the cph action acts as a timer to determine preheat and ignition times. After warm-up and ignition modes, the role of CPH changes to stabilize the active zvs control circuit. In this mode, the dead time of the inverter is determined by the voltage of cph. Is it possible to use the CPH pin only when the FAN7710 is in active ZVS mode. Pulling the CPH pin below 2.6V activates ZVS mode to put the Fan 7710 into shutdown mode. In shutdown mode, all active operations will stop except for UV and some bias circuits. Off mode is controlled by external CPH or active zero voltage switching circuit. Automatic control of active zvs circuit detects lamp disassembly (turn on lamp state) and reduces CPH voltage below 2.6V to protect inverter switch from damage.

3.1 Preheating mode (t0~t1) When VDD exceeds VDDTH (ST+), the fan 7710 starts to operate. At this time, the internal current source (IPH) charges CPH. The cph voltage was increased from 0v to 3v in preheat mode. Therefore, the oscillation frequency Equation 4. In this mode, the lamp does not ignite, but preheats for easy ignition. The warm-up time depends on the size of the CPH. According to the warm-up process, the lit lamps are reduced and the life of the lamps is shortened and increased. In this mode, the dead time is fixed at the maximum value. 3.2 Ignition mode (T1~T2) When the CPH voltage exceeds 3V, the cph of the internal current charging source increases about 6 times more than the iph, which is called iig, causing the cph to increase the voltage rapidly. The internal oscillator reduces the frequency of oscillation from fpre to fosc as the cph voltage increases. Decreasing the frequency increases the lights as shown. Finally, the lights came on. When the CPH voltage is between 3V and 5V. Once the CPH voltage reaches 5V, the fan 7710 does not return to firing mode, even if the CPH voltage is within this range, until the fan 7710 restarts from below VDDTH (ST-). Because the firing mode continues from 3V to 5V at CPH, the firing time is given by: 3.3 Operation mode and active zero voltage switching (AZVS) mode (T2~) When the CPH voltage exceeds 5V, the operating frequency is fixed to FOSC through RT. However, active ZVS operation does not start until CPH reaches ~6V. Fan 7710 is ready to exceed 5V during active ZVS operation T2 to T3 starting from instantaneous CPH. The zvs operation is activated when cph is elevated greater than ~6v at t3. To determine the switch state, the FAN7710 detects the transition time of the inverter output (output pin) using the vb pin. Converting information from the output, the FAN7710 controls the dead time to satisfy the ZVS condition. If the ZVS is satisfied, the fan 7710 slightly increases the CPH voltage to reduce the dead time and find the optimal dead time, thereby increasing the efficiency and reducing the inverter switching. If ZVS fails, the fan 7710 will decrease the cph voltage increasing the dead time. The CPH voltage is adjusted for optimum zero voltage switching operation. In active zvs mode, the charge/discharge current is the same as iph. Figure depicts normal operating waveforms.

3.4 Shutdown Mode If the voltage of the capacitor cph drops to ~2.6V, the IC enters shutdown mode through the external application circuit or the internal application circuit protection circuit. Once the IC enters shutdown mode, this state persists until the internal latch reduces vdd to VDDTH (ST-). Figure shows an external shutdown control circuit.

The size of the CPH charging current is the same as the iph, and a small signal transistor can be used. FAN7710 provides active zero voltage switching according to cph voltage. If ZVS loses time even at the maximum dead zone, the FAN7710 stops driving the inverter. The fan 7710 thermal shutdown circuit senses the junction temperature of the integrated circuit. A thermal shutdown circuit stops the operation of the fan 7710 if the temperature exceeds about 160°C. The current usage of shutdown mode and undervoltage lockout state is different. In shutdown mode, some circuit blocks, such as bias circuits, remain active. Therefore, the current consumption is slightly higher during undervoltage lockout. 4. Automatic light-on detection FAN7710 can automatically detect an open light condition. When the lamp is on, the resonant tank cannot form a closed loop to ground, as shown in Fig. The charge pump capacitor is charged and discharged using the current provided by the output pin. Because the light-on state means that when the resonant tank does not exist, it is impossible to satisfy the ZVS condition. At this condition, the power dissipation of the fan 7710, due to capacitive load drive, is estimated as:

Assuming that Cp, Vdc and F are 1nF, 311V and 50kHz, the power consumption reaches about 2.4W respectively and the temperature of the fan 7710 rises rapidly. Without protection, the IC can be thermally attacked. Note that hard switching conditions can cause EMI during capacitive load driving. The figure shows the waveform in the light-on state. In this case, the charging and CP discharging currents are directly determined by and take into account the hard switching conditions. The FAN7710 increases the dead time by reducing the cph voltage. If ZVS fails and CPH is below 2.6V, FAN7710 shuts down the IC to protect against damage even if the dead time reaches its maximum value. To restart the FAN7710, VDD must be lower than vddth(st-) to reset the internal latch circuit to remember the state of the IC.

5. Power When vdd is lower than vddth (st+), it consumes a very small current, IST, so that the current can be supplied to the VDD pin using a high resistance resistor (R start-up diagram). Once the UVLO is released, the current consumption increases and the entire circuit operates, requiring additional power for stable operation. Supplies must deliver at least a few. A charge pump circuit is a cost-effective way to create an additional power supply and allow the CP to be used to reduce EMI.

Current flows along path (1). It charges to CVDD, which is a bypass capacitor to lower the supply rails. If CVDD charges above the threshold voltage in the internal shunt regulator, the shunt regulator is turned on and regulates VDD with the trigger voltage. When the outside world changes from high to low, the CCP is discharged through DP2, as shown by path (2) in Figure 27. These charging and discharging operations will continue until the fan 7710 is turned off to stop the operation. This charging current, i, must be large enough to supply the operating current of the fan 7710. The power supply for the high-side gate driver is provided by guided band technology, as shown in Figure 28. When the low-voltage side mosfet is connected to the output, the pgnd pin is turned on, and the charging current of vb flows through the database. Every low tide has a chance to recharge the circuit breaker. Therefore, the CB voltage will only increase when the fan 7710 is operating normally. When the output voltage is too high, the diode's decibel reverse-biased circuit breaker supplies current to the high-side driver. At this time, the VB-VOUT voltage decreases due to CB discharge. If vb-vout is lower than vhsth(st-), the high-side driver cannot operate the protection circuit due to the high-side uvlo. A large enough CB must be chosen not to be in the UV range because of half the oscillation period, especially when the high-side mosfet is turned on.