STV9326 datasheet(6/14 Pages) STMICROELECTRONICS

6 / 14 page

Application Hints

STV9326

6/14

4.1.1.1 Centering

Display will be centered (null mean current in yoke) when voltage on pin 7 is (R1 is negligible):

4.1.1.2 Peak Current

Example: for Vm =2 V, VM = 5 V and IP =1A

Choose R1 in the1 Ω range, for instance R1=1 Ω

From equation of peak current:

Then choose R2 or R3. For instance, if R2 = 10 kΩ, then R3 = 15 kΩ

Finally, the bias voltage on pin 7 should be:

4.1.2

Ripple Rejection

When both ramp signal and bias are provided by the same driver IC, you can gain natural rejection

of any ripple caused by a voltage drop in the ground (see Figure 5), if you manage to apply the

same fraction of ripple voltage to both booster inputs. For that purpose, arrange an intermediate

point in the bias resistor bridge, such that (R8 / R7) = (R3 / R2), and connect the bias filtering

capacitor between the intermediate point and the local driver ground. Of course, R7 should be

connected to the booster reference point, which is the ground side of R1.

Figure 5: Ripple Rejection

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2.5

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1.4V

Yoke

Power

Amplifier

Flyback

Generator

Thermal

Safety

Reference

Voltage

Ramp

Signal

Driver

Ground

Source of Ripple

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