STLED524 datasheet(15/72 Pages) STMICROELECTRONICS

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STLED524

Detailed description

The STLED524 is a 5x24 LED dot matrix display driver. It includes 24 low-side current

mirrors (for each LED in a row). Rows are multiplexed by 5 internal PMOS transistors.

Current mirrors are supplied by the integrated boost converter. Its output voltage is

adjustable so it can be adapted to the forward voltage of LEDs. It reduces power dissipation

and improves efficiency.

4.1

Boost converter

The step-up bridge with current mode control regulation provides output voltage according

to the value of VOUT[3:0] register. This voltage should be adjusted to be high enough to

provide sufficient headroom to regulate current sources connected to COL 0-23 pins. On the

other hand, keeping boost output voltage unnecessarily high, increases power dissipation

and degrades efficiency.

Boost incorporates a zero current comparator. When the input voltage is close to the output

voltage, pulse-skipping is applied to keep the output voltage regulated.

If the input voltage is higher than desired output voltage, boost switches to bypass mode

automatically. In this mode, the output voltage is equal to the input voltage lowered by

voltage drop on the PMOS transistor.

Boost converter is enabled only when BSTEN bit in the boost control register is set to 1.

VOUT setting shouldn’t be changed when boost is on (BSTEN=1).

BSTEN = 0, boost is disabled

BSTEN = 1, boost is enabled

One step = 120 mV

Table 7. Boost control register bits

Boost control

Bit 7

Bit 6

Bit 5

Bit 4

Bit 3

Bit 2

Bit 1

Bit 0

Add = 16h

BSTEN

VOUT3

VOUT2

VOUT1

VOUT0

Default

000

0101

Table 8. Boost output voltage

VOUT[3:0]

0001

0203040506

0708

VOUT[V]

2.80 2.92 3.04 3.16 3.28 3.40 3.52 3.64 3.76 3.88 4.00 4.12 4.24 4.36 4.48 4.60

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