LTC2925CUF Linear Technology, LTC2925CUF Datasheet - Page 8

• 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: -

Power Supply Tracking and Sequencing
The LTC2925 handles a variety of power-up profi les to
satisfy the requirements of digital logic circuits including
FPGAs, PLDs, DSPs and microprocessors. These require-
ments fall into one of the four general categories illustrated
in Figures 1 to 4.
Some applications require that the potential difference
between two power supplies must never exceed a speci-
fi ed voltage. This requirement applies during power-up
and power-down as well as during steady-state operation,
often to prevent destructive latch-up in a dual supply IC.
Typically, this is achieved by ramping the supplies up and
down together (Figure 1). In other applications it is desir-
able to have the supplies ramp up and down with fi xed
voltage offsets between them (Figure 2) or to have them
ramp up and down ratiometrically (Figure 3).
LTC2925
APPLICATIONS INFORMATION
8
1V/DIV
2V/DIV
Figure 3. Ratiometric Tracking
Figure 1. Coincident Tracking
10ms/DIV
10ms/DIV
2925 F03
2925 F01
MASTER
SLAVE1
SLAVE2
SLAVE3
MASTER
SLAVE1
SLAVE2
SLAVE3
Certain applications require one supply to come up after
another. For example, a system clock may need to start before
a block of logic. In this case, the supplies are sequenced
as in Figure 4 where the 1.8V supply ramps up completely
followed by the 2.5V supply and then the 1.5V supply.
Operation
The LTC2925 provides a simple solution to all of the power
supply tracking and sequencing profi les shown in Figures
1 to 4. A single LTC2925 controls up to four supplies with
three “slave” supplies that track a “master” signal. With
just two resistors, a slave supply is confi gured to ramp up
as a function of the master signal. This master signal can
be a fourth supply that is ramped up through an external
FET, whose ramp rate is set with a single capacitor, or it
can be a signal generated by tying the GATE and RAMP
pins to an external capacitor.
1V/DIV
2V/DIV
Figure 4. Supply Sequencing
Figure 2. Offset Tracking
10ms/DIV
10ms/DIV
2925 F02
2925 F04
MASTER
SLAVE1
SLAVE2
SLAVE3
SLAVE1
SLAVE2
SLAVE3
2925fc