LED1642GW datasheet(19/42 Pages) STMICROELECTRONICS

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LED1642GW

Configuration register

8.1

Gain control (from CFG 0 to 5) and current ranges (CFG- 6)

The LED current can be programmed using an external resistor connected to GND from

REXT pin and can be fixed using the dedicated bits of the configuration register (from CFG -

0 to CFG - 5 bits define the gain, while CFG - 6 bit defines the current range within the which

the gain can be adjusted). The device can regulate the current up to 36 mA and down to 0.5

mA. The accuracy of the LED current depends on the selected range and it is guaranteed in

the ranges indicated in the static electrical characteristics only (see Table 3 and 9). When

the device is switched on, the selected current range and the resistor connected to the REXT

pin fix the default LED current:

Where VREF=1.23 V is the voltage of the REXT pin and K is the mirroring current ratio, whose

value depends on the selected current range:

•

K = 28 with low current range selected (CFG - 6 = "0")

•

K = 80 with high current range selected (CFG - 6 = "1")

The relation between the programmed current and the current gain settings is the following:

where G is the current gain value (decimal value) defined by the dedicated bits of the

current gain register. The current gain is managed by 6-bits of the configuration register

(CFG - 0 to CFG - 5, CFG - 0 is LSB and CFG - 5 is MSB) and can be adjusted within two

ranges (selectable through the bit CFG - 6) over 64 steps. The width of each step depends

on the default current (Iol_default) as well as the selected REXT. Finally, each step is as

follows:

CFG-14

Gradual output

delay

R/W

“0” a progressive delay is applied to output (10 ns per

channel)

”1” no delay is applied to output

CFG-15

12/16 PWM

counter

R/W

“0” to select 16-bit brightness register (65536 grayscale

rightness steps).

“1” to select 12-bit brightness register (4096 grayscale

brightness steps)

Table 8. Configuration register (continued)

Bit

Definition

R/W

Description

Default

EXT

REF

default

⋅

)

(

ste p

default

⋅

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