LTC2925CUF Linear Technology, LTC2925CUF Datasheet - Page 14

• 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: -

LTC2925
APPLICATIONS INFORMATION
Coincident Tracking Example
A typical four supply application is shown in Figure 12.
The master signal is a 3.3V module. The slave 1 supply
is a 1.8V switching power supply, the slave 2 supply is a
2.5V switching power supply, and the slave 3 supply is
a 1.5V supply. All three slave supplies track coincidently
with the 3.3V supply that is controlled with an external
FET. The ramp rate of the supplies is 100V/s. The 3-step
design procedure detailed previously can be used to
determine component values. Only the slave 1 supply
is considered here as the procedure is the same for the
other supplies.
1. Set the ramp rate of the master signal.
From Equation 1:
2. Solve for the pair of resistors that provide the desired
slave supply behavior, assuming no delay.
From Equation 2:
From Equation 3:
3. Choose RTA to obtain the desired delay.
Since no delay is desired, R
14
R
R
C
GATE
TB
TA
′ =
=
16 5
=
1 235
16 5
100
.
.
10
k
.
μA
•
V s
k
V
/
100
100
+
=
1 235
0 8
V s
V s
35 7
1V/DIV
0 1
.
.
/
/
.
.
V
μF
=
k
V
TA
16 5
–
= R
.
16 5
0 8
k
.
TA
.
V
´.
k
10ms/DIV
Figure 11. Coincident Tracking from Figure 12
≈
13
k
MASTER
SLAVE2
SLAVE1
SLAVE3
In this example, all supplies remain low while the ON pin
is held below 1.23V. When the ON pin rises above 1.23V,
10μA pulls up CGATE and the gate of the FET at 100V/s.
As the gate of the FET rises, the source follows and pulls
up the output to 3.3V at 100V/s. This output serves as
the master signal and is buffered from the RAMP pin
to the RAMPBUF pin. As this output and the RAMPBUF
pin rise, the current from the TRACKx pins is reduced.
Consequently, the voltages at the slave supplies’ outputs
increase, and the slave supplies track the master supply.
When the ON pin is again pulled below 1.23V, 10μA will
pull down C
loads on the outputs are suffi cient, all outputs will track
down coincidently at 100V/s.
3.3V V
R
16.5k
R
13k
41.2k
TB1
TA1
R
IN
TA2
V
V
IN
IN
10k
10k
R
88.7k
R
138k
R
100k
86.6k
R
R
100k
TB2
ONB
ONA
TB3
TA3
0.1μF
Figure 12. Coincident Tracking Example
GATE
10ms/DIV
ON
REMOTE
STATUS
FAULT
RAMPBUF
TRACK1
TRACK2
TRACK3
V
GND
CC
SENSEP SENSEN
SCTMR
and the gate of the FET at 100V/s. If the
0.015Ω
C
0.47μF
SCTMR
LTC2925
SDTMR
10Ω
Si4412ADY
C
0.082μF
2925 F11
GATE
SDTMR
Q1
1V/DIV
C
0.1μF
GATE
PGTMR
C
0.82μF
RAMP
PGTMR
SD1
SD2
SD3
PGI
FB1
FB2
FB3
MASTER
R
35.7k
R
41.2k
R
100k
2925 F12
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
2925fc
1.8V
SLAVE1
2.5V
SLAVE2
1.5V
SLAVE3