LTC2927ITS8#PBF Linear Technology, LTC2927ITS8#PBF Datasheet - Page 12

• Manufacturer Part Number: LTC2927ITS8#PBF
• Manufacturer: Linear Technology

Specifications of LTC2927ITS8#PBF

• Operating Temperature (max): 85C
• Operating Temperature (min): -40C
• Pin Count: 8
• Mounting: Surface Mount
• Package Type: TSOT-23
• Case Length: 2.9mm
• Screening Level: Industrial
• Lead Free Status / RoHS Status: Compliant

APPLICATIO S I FOR ATIO
LTC2927
Supply Sequencing Example
In Figure 15, the slave 1 supply and the slave 2 supply are
sequenced instead of tracking. The 3.3V master ramps up
at 100V/s. 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
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 supply yields:
1. Set the ramp rate of the master signal.
2. Solve for the pair of resistors that provide the desired
12
From Equation 1:
slave supply behavior, assuming no delay.
From Equation 3:
R
R
C
TB
TA
RAMP
′ =
=
16 5
=
16 5
1 235
.
.
100
1V/DIV
.
10
k
Ω
k
Ω
μ
V s
V
•
A
/
U
+
1000
100
35 7
1 235
=
0 8
.
0 1
V s
.
.
V s
.
U
/
V
k
μ
/
Ω
V
F
=
−
1 65
1 65
.
10ms/DIV
.
0 8
W
.
k
k
V
Figure 15. Supply Sequencing (from Figure 16)
Ω
Ω
= −
2 13
.
U
k
Ω
MASTER
SLAVE2
SLAVE1
3. Choose R
EARLY V
EARLY
From Equation 4:
From Equation 5:
R
R
3.3V
3.3V
TA
TA
IN
″ =
R
R
1.65k
3.48k
88.7k
36.5k
138k
100k
R
R
= −
R
R
ONB
ONA
TB1
TA1
TB2
TA2
10
Figure 16. Supply Sequencing Example
2 13
0 8
TA
.
.
ms
to obtain desired delay.
V
ON
RAMPBUF
TRACK
ON
RAMPBUF
TRACK
k
•
10ms/DIV
Ω
•
1 65
100
LTC2927
LTC2927
1 32
.
GND
GND
V
V
.
CC
CC
V s
k
Ω
k
/
RAMP
RAMP
Ω
SDO
SDO
2927 F16
FB
FB
=
=
1 32
3 48
.
.
R
35.7k
R
412k
FA1
FA2
0.1μF
0.1μF
0.1μF
RUN/SS
FB = 1.235V
RUN/SS
FB = 0.8V
k
k
2927 F15
Ω
Ω
DC/DC
DC/DC
16.5k
887k
1V/DIV
3.3V
R
3.3V
R
IN
IN
FB1
FB2
OUT
OUT
MASTER
3.3V
SLAVE1
1.8V
SLAVE2
2.5V
2927fb