Ratiometric Tracking

The DS4426 can maintain a defined ratio between a

slave voltage and the master voltage where:

In Figure 5, this ratio is given by the following:

Power-Supply Tracking Loop Gain Stability

Slave DC-DC output tracking is controlled by the

DS4426 sourcing current into the slave DC-DC's feed-

back loop. This changes the stability of the loop during

tracking. The amount of gain used can be adjusted by

phase margin. If the slave DC-DC has a compensation

pin, the RC network connected to this pin can also be

adjusted to improve phase margin. This pin is often

labeled COMP or ITH. A larger compensation time con-

stant (increased R and/or increased C) often increases

the stability of the system during tracking; however, this

also modifies the DC-DC's transient response. In order

to prevent modification of the slave DC-DC’s transient

should first be modified before adjusting the compen-

sation network. The higher the gain, the less the gain

error. Reducing the gain increases the gain error during

tracking. See Figure 4 for more information.

Three Channels of Power-Supply Tracking

_______________________________________________________________________________________

9

DS4426

10k

Ω

10k

Ω

10k

Ω

0.1

μF

SDA

SCL

A0

A1

FS0

OUT0

INTERFACE

5.0V

5.0V

REF

1.24V

INP[3:1]

FS[3:1]

OUT[3:1]

INN[3:1]

THR[3:1]

GAIN[3:1]

10k

Ω

VOUT

FB

MASTER

DC-DC

CONVERTER

VOUT

FB

SLAVE

DC-DC

CONVERTER

COMP

x3

Figure 5. Typical DC-DC Power-Supply Tracking Application