LTC2927CDDB View Datasheet(PDF) - Linear Technology
Part Name
Description
MFG CO.
LTC2927CDDB Datasheet PDF : 16 Pages
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APPLICATIO S I FOR ATIO
Offset Tracking Example
1V/DIV
MASTER
SLAVE2
SLAVE1
LTC2927
1V/DIV
10ms/DIV
10ms/DIV
2927 F13
Figure 13. Offset Tracking (from Figure 14)
Converting the circuit in the coincident tracking example
to the offset tracking shown in Figure 13 is relatively
simple. Here the 1.8V slave 1 supply ramps up 1V below
the master. The ramp rate remains the same (100V/s), so
there are no changes necessary to steps 1 and 2 of the
3-step design procedure. Only step 3 must be considered.
Be sure to verify that the chosen voltage offset will allow
the slave supply to ramp up completely. In this example,
if the voltage offset were 2V, the slave supply would only
ramp to 3.3V – 2V = 1.3V.
3. Choose RTA to obtain desired delay.
First, convert the desired voltage offset, VOS, to a delay
tD, using the ramp rate:
tD
=
VOS
SS
=
1V
100V
/
s
= 10ms
(6)
From Equation 4:
RTA″
=
0.8V •16.5kΩ
10ms•100V /s
=
13.2kΩ
From Equation 5:
EARLY VIN
3.3V
RONB
138k
RONA
100k
RTB1
16.5k
RTA1
6.65k
VCC
ON
RAMP
LTC2927
SDO
RAMPBUF
FB
TRACK
GND
0.1μF
0.1μF 3.3V
MASTER
3.3V
RUN/SS IN
DC/DC
FB = 1.235V
OUT
RFA1
35.7k
RFB1
16.5k
SLAVE1
1.8V
EARLY
3.3V
RTB2
887k
RTA2
316k
VCC
ON
RAMP
LTC2927
SDO
RAMPBUF
FB
TRACK
GND
2927 F14
0.1μF
3.3V
RUN/SS IN
DC/DC
FB = 0.8V
OUT
RFA2
412k
RFB2
887k
SLAVE2
2.5V
Figure 14. Offset Tracking Example
RTA = 13.1kΩ 13.2kΩ ≈ 6.65kΩ
2927fb
11
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