IC-HTP Datasheet, PDF (15/51 Pages) IC-Haus GmbH – DUAL CW P-TYPE LASER DIODE DRIVER

iC-HTP
DUAL CW P-TYPE
LASER
DIODE
DRIVER
preliminary
DISP1
0
1
Addr. 0x10; bit 2
PLR enabled for channel 1
PLR disabled for channel 1
Table 14: Disable PLR channel 1
R/W 0
Rev B1, Page 15/51
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):
DISP2
0
1
Addr. 0x15; bit 2
PLR enabled for channel 2
PLR disabled for channel 2
Table 15: Disable PLR channel 2
R/W 0
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.
Rmd
= Rmd₀(1 +
∆
Rmd(%)
100
)ⁿ
+
1_,
n
from
0
to
255
Rmda(RMDx
= 0x00, max)
= Rmd₀(1 +
∆
Rmd(%)
100
)¹
6
286
= Rmd₀(1 +
3.3
100
)¹⁶
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
register ILIMx using the following equations:
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.
For calculating the maximum value of Imon, Vref(0x3FF, Register CRNGx splits each current range into 4 addi-
min value) (cf. Electrical Characteristics No. 303) and tional current ranges. k is a current range factor, with a
Rmda(RMDx = 0x00, max vaule) (cf. Electrical Char- value depending on CRNGx(1:0) register: