LTC2925IUF#PBF Linear Technology, LTC2925IUF#PBF Datasheet - Page 9

• Manufacturer Part Number: LTC2925IUF#PBF
• Description: IC POWER SUPPLY CONTROLLER 24QFN
• Manufacturer: Linear Technology

Specifications of LTC2925IUF#PBF

• Applications: Power Supply Controller
• Voltage - Supply: 2.9 V ~ 5.5 V
• Current - Supply: 1.5mA
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 24-QFN
• Voltage Supervisor Type: Power Supply Tracker
• Number Of Voltage Supervisors: 4
• Operating Supply Voltage (min): 2.9V
• Operating Supply Voltage (max): 5.5V
• Operating Temperature Classification: Industrial
• Operating Temp Range: -40C to 85C
• Pin Count: 24
• Mounting: Surface Mount
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Voltage - Input: -
• Lead Free Status / Rohs Status: Compliant

APPLICATIONS INFORMATION
Tracking Cell
The LTC2925’s operation is based on the tracking cell
shown in Figure 5, which uses a proprietary wide-range
current mirror. The tracking cell shown in Figure 5 servos
the TRACK pin at 0.8V. The current supplied by the TRACK
pin is mirrored at the FB pin to establish a voltage at the
output of the slave supply. The slave output voltage varies
with the master signal, enabling the slave supply to be
controlled as a function of the master signal with terms
set by R
R
in Figures 1 to 4.
Controlling the Ramp-Up and Ramp-Down Behavior
The operation of the LTC2925 is most easily understood by
referring to the simplifi ed functional diagram in Figure 6.
When the ON pin is low, the GATE pin is pulled to ground
causing the master signal to remain low. Since the current
through R
low, the current from FB1 is also at its maximum. This cur-
rent drives the slave’s output to its minimum voltage.
When the ON pin rises above 1.23V, the master signal rises
and the slave supply tracks the master signal. The ramp
rate is set by an external capacitor driven by a 10μA current
source from an internal charge pump. If no external FET
is used, the ramp rate is set by tying the RAMP and GATE
pins together at one terminal of the external capacitor (see
the Ratiometric Tracking Example).
TA
MASTER
and R
R
R
TB
TA
TA
TRACK
TB
TB1
and R
, it is possible to generate any of the profi les
is at its maximum when the master signal is
Figure 5. Simplifi ed Tracking Cell
TB
. By selecting appropriate values of
V
CC
+
–
+
–
0.8V
FB
R
2925 F05
FA
FB OUT
DC/DC
R
FB
SLAVE
In a properly designed system, when the master signal
has reached its maximum voltage the current from the
TRACK1 pin is zero. In this case, there is no current from
the FB1 pin and the LTC2925 has no effect on the output
voltage accuracy, transient response or stability of the
slave supply.
When the ON pin falls below V
cally 1.225V, the GATE pin pulls down with 10μA and the
master signal and the slave supplies will fall at the same
rate as they rose previously.
The ON pin can be controlled by a digital I/O pin or it
can be used to monitor an input supply. By connecting a
resistive divider from an input supply to the ON pin, the
supplies will ramp up only after the monitored supply has
reached a preset voltage.
R
R
R
R
ONB
ONA
TB1
TA1
1.2V
1.2V
SCTMR
ON
RAMPBUF
TRACK1
Figure 6. Simplifi ed Functional Block Diagram
+
–
+
–
1
50μA
2μA
V
CC
V
SENSEP – SENSEN > 50mV
CC
10μA
10μA
+
–
50mV
ON(TH)
0.8V
SENSEN
SENSEP
RAMP
GATE
FB1
– ΔV
LTC2925
ON(HYST)
R
2925 F06
FA1
C
DC/DC
GATE
R
FB1
Q1
, typi-
MASTER
SLAVE1
2925fc
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