IC-HT_15 Datasheet, PDF (28/45 Pages) IC-Haus GmbH – DUAL CW LASER DIODE DRIVER

iC-HT
DUAL CW LASER DIODE DRIVER
DC/DC CONVERTER OPTIMIZATION
preliminary
Rev B1, Page 28/45
iC-HT provides a 6 bit configurable current at pin DCO
that can be used to trim the output voltage of a DC/DC
converter.
Possible application benefits with using DCO:
RDCO
0x00
...
0x3F
Addr. 0x1B; bit 5:0
No current
R/W 0x02
130 µA typ (cf. Electrical Characteristics No. D01)
• DC/DC step down operation: regulation at voltages
lower than power supply
• DC/DC step up operation: regulation at voltages
higher than power supply
• Efficiency enhancement
Table 60: Digital current output register
The proposed applications can be demonstrated with
a standard DC/DC converter e.g. TPS63060DSC from
Texas Instruments. This converter allows an input volt-
age ranging from 2.5 V to 12 V and offers an output
voltages from 2.5 V to 8 V. It is capable of delivering up
to 2 A current, depending on the output voltage. Figure
17 shows a possible configuration.
2.5...12V
Vin
C1
2x10μF
C3
0.1μF
L1
1μH
L1 ^TPS63060
VIN
EN
VAUX
L2
VOUT
FB
PS/SYNC
GND
PG
PGND
Vout
R1
R3
1MEG
C2
3x22μF
R2
Figure 17: TPS63063 DC/DC converter from TI
DC/DC step down operation:
regulation at voltages lower than power supply
The resistors R1 and R2 in the feedback path allow
setting the desired output value Vout. The DC/DC con-
verter drives Vout pin in order to yield 0.5 V at feed-
back pin FB. The DCO output signal from iC-HT is
connected to FB pin. The Vout is controlled with the
internal register RDCO from iC-HT.
The DCO current into FB node controls the voltages
of the divider R1 and R2 and Vout changes in order to
maintain 0.5 V at FB pin. Selecting R1 and R2 needs
to consider:
• Resistors values:
R1
=
R2(
Vout
Vfb
− 1)
• Current of the voltage divider should be high enough,
in comparism to the current from the pin DCO, to of-
fer acceptable resolution. The programmable current
resolution from register RDCO is 2 µA.
• DCO current into the voltage divider will lower Vout
voltage, Vout is 8 V when no current is present at
DCO.
Choosing R1 to 100 kΩ, the value of R2 can be calcu-
lated:
R2
=
R1
Vout
Vfb
−1
=
100k
8
0.5
−1
= 6.7kΩ
With this configuration the current through the voltage
divider is 75 µA at 8 V . The resolution of each RDCO
step is then 200 mV.