IC-HT datasheet(28/45 Pages) ICHAUS

28 / 45 page

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iC-HT

DUAL CW LASER DIODE DRIVER

Rev B1, Page 28/45

DC/DC CONVERTER OPTIMIZATION

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:

• 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

RDCO

Addr. 0x1B; bit 5:0

R/W 0x02

0x00

No current

. . .

0x3F

130 µA typ (cf. Electrical Characteristics No. D01)

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.

TPS63060

2x10μF

0.1μF

3x22μF

1MEG

VIN

VAUX

PS/SYNC

GND

VOUT

PGND

2.5...12V

Vin

Vout

1μH

1MEG

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 =

Vout

Vfb −1

= 100k

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.

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