AN2846

Application guidelines

Doc ID 15130 Rev 1

5/35

format is 16 bits or 8 bits long according to SPM pin level. When SPM is grounded, 16 bits

the 8 input data bits are transmitted.

Table 1 defines the significance of the16 bits. Bit 15 is the most significant bit. Detailed SPI

functionality is described in Section 1.4.

1.2

Current-limited inputs

1.2.1

Maximum input current setting

All internal bias currents sources and particularly the input current limiter are defined by the

reference resistor connected to pin REF. A 15 k

Ω resistor will assure a typical input limited

formula:

Figure 2.

Current limiter diagram

The technology used allows a very low current dispersion according to the different

temperature range from -25 °C to 150 °C enabling a good stability of the limited current (see

Figure 3).

Table 1.

16-bit frame definition

Data bits

Bit15

Bit14

Bit13

Bit12

Bit11

Bit10

Bit09

Bit08

Control Bits

Bit07

Bit06

Bit05

Bit04

Bit03

Bit02

Bit01

Bit00

/UVA

/OTA

PC1

PC2

PC3

PC4

0

1

()

V

k

R

V

I

REF

BG

LIM

25

.

1

V

cal

with typi

5

.

1

30

+

·

=

LED_ON

1 : 20

R

REF =15k

REF

2

:

3

1 : 1

1.5k

LED

I

LIM

COMs

V