MC33441 Datasheet, PDF (5/12 Pages) ON Semiconductor – Electroluminescent Lamp Driver IC

MC33441
will be turned off and the energy will release to the EL lamp.
And, those switches will remain off until the next clock cycle.
H–Bridge Network
To achieve the 140V peak–to–peak voltage, H–bridge
network is used to charge and discharge the EL lamp. The
switching frequency of the bridge network is controlled by a
clock signal from the divider with its frequency much lower than
the one to the coil–driver. Moreover, to reduce the current
consumption, the biasing current to the two low–side switches
of the H–bridge is not activated until the coil–driver circuit
needed to release the energy to the EL lamp. Then, the biasing
circuit will be on and be ready before the main switch in the
coil–driver really starts to turn off.
External Components
System designer will base on the application to decide the size
and the type of the EL lamp to be used. The external resistance
(REXT) at RT1 pin determines the excitation frequency (FEL) for
the lamp. The relationship between REXT and the frequency is:
B FEL = FOSC 384
By substitute the equation of FOSC from Oscillator &
Frequency Divider.
+ FEL
4.341 10⁷
REXT
Hz
so
+ W REXT
4.341 10⁷
FEL
Moreover, if a low TC resistor is used, the oscillator
frequency’s TC can be kept low. The filter capacitor is to provide
a smooth and more stable output waveform for the EL lamp.
The value of this capacitor depends on the input voltage and the
coil’s inductance value. Equations below can be used to estimate
filter capacitor’s value at different input voltage.
Best Case Approximation for the Filter Capacitor:
+ * ń CFILTER 0.026 (Vin VSW)² (L FOSC ²)
Worst Case Approximation for the Filter Capacitor:
+ * ń CFILTER 0.085 (Vin VSW)² (L FOSC ²)
where VIN is the input voltage, VSW is voltage across the
switch when it is on, L is the coil’s value and FOSC is the
clock frequency.
Measurement below is recorded with the condition: coil
= 1mH, EL lamp = 2.2nF and at room temperature.
Table 1: Reference for CFILTER
VDD
ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ _1.8V
ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ _2.0V
ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ _2.5V
ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ _3.0V
REXT
W 100K–130K
W 100K–130K
W 100K–130K
W 100K–130K
CFILTER
5n–10nF
10n–22nF
10n–22nF
22nF–33nF
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