IC-HTP datasheet(15/51 Pages) ICHAUS

15 / 51 page

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iC-HTP

DUAL CW P-TYPE LASER DIODE DRIVER

Rev B1, Page 15/51

DISP1

Addr. 0x10; bit 2

R/W 0

PLR enabled for channel 1

PLR disabled for channel 1

Table 14: Disable PLR channel 1

DISP2

Addr. 0x15; bit 2

R/W 0

PLR enabled for channel 2

PLR disabled for channel 2

Table 15: Disable PLR channel 2

Both programmable logarithmic monitor resistors (PLR)

feature a wide logarithmic resistor range from 100 Ω to

407 kΩ, in steps of typically 3.3%. This covers a wide

range of monitor currents. More information about the

PLR can be found on page 28.

For fine-tuning the optical power, the reference volt-

age can be set with a 10 bit logarithmic D/A converter,

which is configurable through register REFx. This con-

verter has a voltage range that goes typically from 0.1 V

to 1.1 V, allowing an operation resolution of typically

0.235%. More information on the logarithmic D/A con-

verter can be found on page 29.

Inside the regulation loop there is the signal level con-

verter. This block is in charge of converting the values

coming from the PLRx which are referenced to MRHx

and reference them to GND. This is necessary because

the logarithmic D/A is referenced to GND. In addition

this signal level converter adds a 1:2 ratio between the

voltage regulated at PLRx and the one regulated at the

logarithmic D/A converter i.e. 1.1 V regulated at the

logarithmic D/A side are 0.55 V regulated at the PLRx

side.

For calculating the minimum value of the monitor cur-

rent, Imon, Vref(0x00, max value) (cf. Electrical Charac-

teristics No. 303) and Rmda(RMDx = 0xFF, min value)

(cf. Electrical Characteristics No. 201) are used. Also

the 1:2 ratio between PLRx regulation voltage and Vref

must be applied.

Imon(min) =

Vref (0x000,max)

2·Rmda(RMDx =0xFF,min) =

0.11

2·350000 = 0.16 ţA

It is not recommended to configure iC-HTP to have

such small Imon values, otherwise the leakage current

at MDKx may have an influence (cf. Electrical Char-

acteristics No. 204), especially at high temperatures.

To avoid this, Imon should be much greater than the

leakage current.

For calculating the maximum value of Imon, Vref(0x3FF,

min value) (cf. Electrical Characteristics No. 303) and

Rmda(RMDx = 0x00, max vaule) (cf. Electrical Char-

acteristics No. 201) are used. Also the 1:2 ratio be-

tween PLRx regulation voltage and Vref must be ap-

plied. Since only the 4 MSB from PLR can be accessed

at pin MDKx, the following formula needs to be used

for calculating Rmda(RMDx = 0x00, max value):

Rmd = Rmd0(1 +

∆

Rmd(%)

100

)n+1, n from 0 to 255

Rmda(RMDx = 0x00, max) = Rmd0(1 +

∆

Rmd(%)

100

)16

286 = Rmd0(1 + 3.3

100 )

Rmd0 = 170Ω

Therefore:

Imon(max) = Vref(0x3FF,min)

2·Rmd0

= 1.00

2·170 = 2.94 mA

Any other Imon value can be calculated using Rmd

formula above. Due to its logarithmic characteristic, the

steps between two consecutive values is kept within

3.3 % typical value.

A programmable overcurrent shutdown can be set to

protect the laser by disabling the channel. The over-

current protection value (Ilim) must be configured in

Ilim = (∆I(LDA), max) · n · k

n =

Ilim

k · ∆I(LDA), max

with n from 1 to 255.

ILIM set to 0x00 disables the overcurrent protection in

ACC mode. in APC mode, the overcurrent protection

cannot be disabled.

∆

I(LDA), max is the shutdown current threshold reso-

lution (maximum value) (cf. Electrical Characteristics

No. 108). Its value depend on the current range de-

fined by register bit RACCx. If RACCx = 1, the over-

current threshold is in the low range and ∆I(LDA), max

= 0.375 mA. If RACCx = 0, the overcurrent threshold is

in the high range and ∆I(LDA), max = 3 mA.

tional current ranges. k is a current range factor, with a

value depending on CRNGx(1:0) register:

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