STA333IS datasheet(35/43 Pages) STMICROELECTRONICS

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STA333IS

5.9

Reserved registers (addr 0x2E, 0x2F, 0x30, 0x31)

These registers are not to be used.

5.10

Postscale registers (addr 0x32, 0x33)

Postscale

The STA333IS provides one additional multiplication after the last interpolation stage and

the distortion compensation on each channel, which can be used to limit the maximum

modulation index and therefore the peak current through the power device. The register

values represent an 8-bit signed fractional number. This number is extended to a 24-bit

number, by adding zeros to the right, and then directly multiplied by the data on that

channel. An independent postscale is provided for each channel but all channels can use

channel 1 postscale factor by setting the postscale link bit. By default, all postscale factors

are set to 0x7F (pass-through).

5.11

Output limit register (addr 0x34)

5.11.1

Thermal and overcurrent warning output limit register

The STA333IS provides a simple mechanism for reacting to a thermal or overcurrent

warning in the power device. When the TWARN or OCWARN status bit is asserted, the

output is limited to the OLIM setting. The limit can be adjusted by modifying the thermal

warning/overcurrent output limit value. As for the normal postscale, the register value

represents an 8-bit signed fractional number. This number is extended to a 24-bit number,

by adding zeros to the right, and then directly multiplied by the data on both channels. The

scaling value range is from 0x80 = -1 to 0x7F = 0.992. To avoid phase changes in the output

signal only the positive range is used (0x00 to 0x7F). The default setting of 0x5A provides a

-3-dB limit.

If the cause of the limiting is a thermal warning, the output limiting is removed when the

thermal warning situation disappears. If the cause of the limiting is an overcurrent warning,

output limiting remains in effect until the device is reset.

C1PS7

C1PS6

C1PS5

C1PS4

C1PS3

C1PS2

C1PS1

C1PS0

01111111

C2PS7

C2PS6

C2PS5

C2PS4

C2PS3

C2PS2

C2PS1

C2PS0

01111111

OLIM7

OLIM6

OLIM5

OLIM4

OLIM3

OLIM2

OLIM1

OLIM0

01011

010

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