LTC3415 Datasheet, PDF (15/28 Pages) Linear Technology – 7A, PolyPhase Synchronous Step-Down Regulator

LTC3415
OPERATION
Otherwise, an internal open-drain pull down device (20Ω)
will pull the PGOOD pin low. In certain computer systems
today, the PGOOD pin is used as a resetting signal while
the output voltage is dynamically changed from one level
to another. To prevent unwanted power resetting during
output voltage changes, the LTC3415’s PGOOD falling
and rising edges include a blanking delay equivalent to
approximately 10μs per every volt of V_IN.
Output Voltage Programming
The output voltage is set by an external resistive divider
according to the following equation:
V_OUT
=
0.596V
•

₁₊
R2 ^
R1
The resistive divider allows pin V_FB to sense a fraction of
the output voltage as shown in Figure 9.
V_OUT
R2
C_FF
V_FB
LTC3415
SGND
R1
3415 F09
Figure 9. Setting the Output Voltage
Output Tracking and Sequencing
Some microprocessor, ASIC and DSP chips need two
power supplies with different voltage levels. These sys-
tems often require voltage sequencing between the core
power supply and the I/O power supply. Without proper
sequencing, latch-up failure or excessive current draw
may occur that could result in damage to the processor’s
I/O ports or the I/O ports of supporting system devices
such as memory, FPGAs or data converters. To ensure
that the I/O loads are not driven until the core voltage is
properly biased, tracking of the core supply voltage and
the I/O supply voltage is necessary.
Voltage tracking is enabled by applying a voltage to the
TRACK pin. When the voltage on the TRACK pin is below
0.57V, the feedback voltage will regulate to this tracking
voltage. When the tracking voltage exceeds 0.57V, tracking
is disabled and the feedback voltage will regulate to the
internal reference voltage.
Voltage Tracking
The LTC3415 allows the user to program how its output
voltage ramps during start-up by means of the TRACK
pin. Through this pin, the output voltage can be set up to
either coincidentally or ratiometrically track another output
voltage as shown in Figure 10.
V_OUT2
V_OUT1
V_OUT2
V_OUT1
TIME
TIME
3415 F10
(10a) Coincident Tracking
(10b) Ratiometric Sequencing
Figure 10. Two Different Modes of Output Voltage Sequencing
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