feature

Low start-up and operating current: 140µA , 6.5mA undervoltage lockout with 1.9V hysteresis, 600mA totem pole output with high state clamp, trimmed 1.5% internal bandgap reference, programmable warm-up time and frequency, available Programmable operating frequency high precision oscillator

describe

7544 -ic/" title="FAN7544 Product Specifications, Documentation and Sourcing Information" target="_blank">FAN7544 provides simple and high-performance electronic ballast control. The fan 7544 is optimized for electronic ballasts requiring minimal board area current radiator, by reducing component count and power consumption. Features include programmable warm-up time and frequency and programmable operating frequency. Initial warm-up time and frequency can be based on the type of fixture using CPH, CT and RPH. The output gate drive circuit will The power MOSFET gate voltage is clamped to the supply voltage.

Internal block diagram

Electrical Characteristics

Unless otherwise specified, for typical values Vcc=15V, Ta=25°C, for min/max Ta is operating ambient temperature range -25°C≤Ta≤125°C and 12.7V≤VCC≤30V

Note:

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

application information

start circuit

The startup current is supplied to the IC through the startup resistor (Rst). To reduce power dissipation in Rst Rst is connected to the full-wave rectified output voltage. The following equations can be used to calculate the magnitude of Rst

The size of the supply capacitor (Cs) is usually determined by the start-up time and the running current to use as an auxiliary operating current source. The off-snubber capacitor (CQ) and the two diodes (d1, d2) form the source of the auxiliary operating current IC. The charging current through CQ flows into the IC and charges the supply capacitors. If the size of CQ increases, Cs also increases. Under Voltage Lockout (UVLO) The UVLO mode of the fan 7544 is designed to keep the ultra-low supply current less than 140uA and ensure that the IC is fully functional before activating the two output drivers. The oscillator gate drive output frequency is half of the triangular waveform of the timing capacitor (CT) at pin #2. In normal working mode, the charging current of the timing capacitor is 4×Irt (=Vref/RT). The discharge current is 5.25 times the charging current (5.25×4×1rt). The charging cycle of the timing capacitor is the on-time of the MOSFET. Both mosfets were closed during unloading.

Operating mode

Fan 7544 has three working modes as shown in the picture.

(1) Preheat mode The preheat mode is defined as the internal state of the IC at temperature when the filament is heated to the correct discharge amount. This is necessary to maximize lamp life and reduce the required ignition voltage. Once Vcc exceeds the UVLO high threshold, the warm-up time sets the capacitor and CPH starts to be charged by the internal 1.6µA current source until VCPH reaches 2.9V. After the VCPH starts charging, from 0V to 2.9V, the switching frequency of the entire preheat mode is determined by CT and RPH, and the preheat time is determined by CPH and a 1.6µA current source. (∏TPRE=CPH×2.9V/1.6uA)

(2) Ignition method

Ignition mode is defined as when the necessary high voltage is built across the lamp, the internal state of the IC is lit. When VCPH exceeds 2.9V, the fan 7544 enters ignition mode, when

VCPH exceeds 5V. During this time, the internal 10μA current source charges the external preheat timing capacitor (CPH) to improve the noise immunity of VCPH. Ignition time is determined by CPH and internal 10µA current source (∏TIGN=CPH×∏VCPH2/ICPHH). In this mode, the switching frequency is determined by CT, RPH and RT, since ICT is determined by the following equation

(3) Operation mode

After the lamp has successfully ignited, the fan 7544 goes into run mode. The operating mode is defined as the internal state of the ICI when the lamp is driven at normal power levels after discharge. The operating mode switching frequency is determined by the timing resistor RT and the timing capacitor CT. Once VCPH exceeds 5V, the protection mask mode is disabled and the IC can enter the protection mode. Protection Mode If the voltage on the RPH pin falls below 2V in run mode, the FAN7544 enters protection mode and the full gate drive outputs (OUT1 and OUT2) are latched in the low state, reducing VCpH to 0V. Vcc must fall below the UVLO low threshold.

Application circuit

<32W×2 lamp ballast>

Parts List (for wide range 32W x 2LAMP applications)