STODD01 datasheet(15/31 Pages) STMICROELECTRONICS

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STODD01

Detailed description

Doc ID 17789 Rev 2

15/31

Figure 32 shows the in-rush current at enable transient. Initially, the C4 capacitor is

completely discharged and the current limitation is due only to the equivalent series resistor

of the inductor, the power MOSFET parasitic diode, and the cut-off MOSFETs’ RDSon. As

soon as the output voltage reaches the input voltage level, the device begins to switch and

the current is limited cycle by cycle.

The EN pin does not have an internal pull-up, which means that the enable pin cannot be

left floating.

If the enable function is not used, the EN pin must be connected to VIN.

7.3

TX pin

The device implements an S-wire bus communication, which uses one control signal coming

from the microprocessor to program the step-up STODD01 output voltage (see Figure 11).

S-wire protocol allows the feedback voltage of the step-up section to be changed from 0.8 to

1.25 V, with steps of 15 mV (see Table 9).

This feature allows complete and easy control of the laser diode power during read and

write operation.

If this function is not used, the TX pin must be connected to GND.

7.4

Reset function

This flag shows that input voltage is in the correct range.

A comparator senses the input voltage. When it is higher than VR_TH, the reset pin goes to

high impedance, with a delay of 100 ms (typ.). If it is below VR_TL, the reset pin goes to low

impedance (see Figure 12).

Figure 11.

S-Wire connection

Reset

GND

Reset

STODD01

GND

µP

GND

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