Datasheet

Ballast section L6585DE
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6 Ballast section
6.1 Half-bridge drivers and integrated bootstrap diode
The half-bridge drivers are capable of 290 mA source and 480 mA sink current. This makes
them able to effectively drive also big MOSFETs Cg up to 2.2 nF. The high-side MOSFET is
driven by means of a bootstrapped structure reducing the number of external components.
6.2 Normal start-up description
Referring to Figure 7, normal startup proceeds as follows:
Figure 7. Normal start-up procedure
1. Startup: As soon as Vcc reaches the startup threshold voltage references are built up,
the RF and EOLP pin are biased, the EOI pin is pulled down and the TCH pin starts
sourcing 31 µA. The frequency of the half-bridge is generated by an internal CCO,
connected to
C
OSC
and using the RF current as the control signal. With the EOI pin
pulled down, the startup frequency will be due to the current flowing in parallel with
R
PRE
and R
RUN
(see typical application diagram).
2. Preheating: the TCH pin continues to source 31 µA until its voltage reaches 4.63 V,
therefore it is left in a high impedance status. As this pin loaded with an RC parallel
network, the voltage across this pin decreases exponentially. When it reaches 1.5 V the
TCH pin is pulled down and the preheating time ends. During this sequence the EOI
pin is pulled down and the half-bridge frequency is the startup frequency. A leading