LTC2925CUF Linear Technology, LTC2925CUF Datasheet - Page 17

• 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
Supply Sequencing Example
In Figure 17, the three slave supplies are sequenced in-
stead of tracking. As in the coincident tracking example,
the 3.3V master supply ramps up at 100V/s through an
external FET, so step 1 remains the same. The 1.8V slave
1 supply ramps up at 1000V/s beginning 10ms after the
master signal starts to ramp up. The 2.5V slave 2 supply
ramps up at 1000V/s beginning 20ms after the master
signal begins to ramp up. The 1.5V slave 3 supply ramps
up at 1000V/s beginning 25ms after the master signal
begins to ramp up. Note that not every combination of
ramp rates and delays is possible. Small delays and large
ratios of slave ramp rate to master ramp rate may result
in solutions that require negative resistors. In such cases,
either the delay must be increased or the ratio of slave
ramp rate to master ramp rate must be reduced. In this
example, solving for the slave 1 supply yields:
2. Solve for the pair of resistors that provide the desired
slave supply behavior, assuming no delay.
From Equation 2:
From Equation 3:
R
R
TB
TA
′ =
=
16 5
1 235
16 5
.
.
k
.
•
k
V
1000
100
+
1 235
0 8
35 7
V s
.
1V/DIV
.
V s
/
/
.
V
k
V
≈
1 65
–
.
1 65
0 8
.
.
k
V
k
10ms/DIV
≈
Figure 17. Supply Sequencing from Figure 18
– .
2 13
k
MASTER
SLAVE2
SLAVE1
SLAVE3
3. Choose R
From Equation 4:
From Equation 5:
3.3V V
R
1.65k
R
3.48k
4.87k
R
TB1
TA1
R
R
IN
TA2
TA
TA
V
V
IN
IN
″ =
10k
10k
R
8.87k
R
138k
R
100k
8.66k
3.74k
R
R
TB2
=
ONB
ONA
TB3
TA3
– .
0.1μF
10
2 13
Figure 18. Supply Sequencing Example
TA
0 8
10ms/DIV
V
ON
REMOTE
STATUS
FAULT
RAMPBUF
TRACK1
TRACK2
TRACK3
GND
CC
.
ms
to obtain the desired delay.
k
V
SENSEP SENSEN
SCTMR
|| .
•
• .
0.015Ω
C
0.41μF
100
1 32
1 65
SCTMR
LTC2925
V s
SDTMR
k
k
/
10Ω
Si4412ADY
≈
C
0.082μF
2925 F17
GATE
SDTMR
=
Q1
3 48
.
1 32
1V/DIV
C
0.1μF
.
GATE
PGTMR
k
C
0.82μF
RAMP
k
PGTMR
SD1
SD2
SD3
FB1
FB2
FB3
PGI
MASTER
LTC2925
R
35.7k
R
41.2k
R
100k
2925 F18
RST
RUN/SS
FB = 1.235V
RUN/SS
FB = 0.8V
RUN/SS
FB = 0.8V
FA1
FA2
FA3
MONITOR
SUPPLY
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
17
2925fc
1.8V
SLAVE1
2.5V
SLAVE2
1.5V
SLAVE3