LTC2925CUF Linear Technology, LTC2925CUF Datasheet - Page 15

• Manufacturer Part Number: LTC2925CUF
• Description: IC POWER SUPPLY CONTROLLER 24QFN
• Manufacturer: Linear Technology

Specifications of LTC2925CUF

• Applications: Power Supply Controller
• Voltage - Supply: 2.9 V ~ 5.5 V
• Current - Supply: 1.5mA
• Operating Temperature: 0°C ~ 70°C
• Mounting Type: Surface Mount
• Package / Case: 24-QFN
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Voltage - Input: -

APPLICATIONS INFORMATION
Ratiometric Tracking Example
This example converts the coincident tracking example to
the ratiometric tracking profi le shown in Figure 13, using
three supplies without an external FET. The ramp rate of
the master signal remains unchanged (step 1) and there
is no delay in ratiometric tracking (step 3), so only the
result of step 2 in the 3-step design procedure needs to
be considered. In this example, the ramp rate of the 1.8V
slave 1 supply ramps up at 60V/s, the 2.5V slave 2 supply
ramps up at 85V/s, and the 1.5V slave 3 supply ramps up
at 50V/s. Always verify that the chosen ramp rate will al-
low the supplies to ramp-up completely before RAMPBUF
reaches V
it would only reach 1.65V because the RAMPBUF signal
would reach its fi nal value of V
supply reached 1.8V.
2. Solve for the pair of resistors that provide the desired
slave supply behavior, assuming no delay.
From Equation 2:
R
TB
=
16 5
CC
. If the 1.8V supply were to ramp-up at 50V/s
.
k
•
100
60
V s
V s
1V/DIV
/
/
≈
27 4
CC
.
k
= 3.3V before the slave
10ms/DIV
Figure 13. Ratiometric Tracking from Figure 14
SLAVE2
SLAVE1
SLAVE3
3.3V V
From Equation 3:
Step 3 is unnecessary because there is no delay, so
R
TA
R
27.4k
R
10k
38.3k
R
TB1
TA1
R
IN
TA2
= R
TA
V
V
IN
IN
10k
10k
R
100k
R
138k
R
100k
63.4k
′ =
R
174k
TA
TB2
R
ONB
ONA
TB3
TA3
´.
0.1μF
Figure 14. Ratiometric Tracking Example
1 235
16 5
10ms/DIV
.
ON
REMOTE
STATUS
FAULT
V
RAMPBUF
TRACK1
TRACK2
TRACK3
GND
CC
.
SENSEP SENSEN
SCTMR
k
V
C
0.41μF
+
SCTMR
1 235
0 8
35 7
LTC2925
.
.
SDTMR
.
V
C
0.082μF
2925 F13
GATE
SDTMR
k
V
1V/DIV
–
PGTMR
C
0.1μF
27 5
0 8
GATE
C
0.82μF
RAMP
.
PGTMR
.
SD1
SD3
SD2
FB1
FB2
FB3
PGI
V
k
≈
LTC2925
R
35.7k
R
41.2k
R
100k
2925 F14
RST
RUN/SS
FB = 1.235V
RUN/SS
FB = 0.8V
RUN/SS
FB = 0.8V
FA1
FA2
FA3
10
MONITOR
SUPPLY
k
DC/DC
DC/DC
DC/DC
16.5k
86.6k
R
88.7k
R
R
FB1
FB3
FB2
3.3V
OUT
3.3V
OUT
3.3V
OUT
IN
IN
IN
15
1.8V
SLAVE1
2.5V
SLAVE2
1.5V
SLAVE3
2925fc