LTM4630IV View Datasheet(PDF) - Linear Technology
Part Name
Description
Manufacturer
LTM4630IV Datasheet PDF : 34 Pages
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LTM4630
APPLICATIONS INFORMATION
tracking is desired, then MR and SR are equal, thus RTB
is equal the 60.4k. RTA is derived from equation:
RTA =
VFB
0.6V
+ VFB − VTRACK
60.4k RFB RTB
where VFB is the feedback voltage reference of the regula-
tor, and VTRACK is 0.6V. Since RTB is equal to the 60.4k
top feedback resistor of the slave regulator in equal slew
rate or coincident tracking, then RTA is equal to RFB with
VFB = VTRACK. Therefore RTB = 60.4k, and RTA = 60.4k in
Figure 6.
In ratiometric tracking, a different slew rate maybe desired
for the slave regulator. RTB can be solved for when SR is
slower than MR. Make sure that the slave supply slew rate
is chosen to be fast enough so that the slave output voltage
will reach it final value before the master output.
For example, MR = 1.5V/1ms, and SR = 1.2V/1ms. Then
RTB = 76.8k. Solve for RTA to equal to 49.9k.
Each of the TRACK pins will have the 1.3µA current source
on when a resistive divider is used to implement tracking
on that specific channel. This will impose an offset on the
TRACK pin input. Smaller values resistors with the same
ratios as the resistor values calculated from the above
equation can be used. For example, where the 60.4k is
used then a 6.04k can be used to reduce the TRACK pin
offset to a negligible value.
Power Good
The PGOOD pins are open drain pins that can be used to
monitor valid output voltage regulation. This pin monitors
a 10% window around the regulation point. A resistor can
be pulled up to a particular supply voltage no greater than
6V maximum for monitoring.
Stability Compensation
The module has already been internally compensated
for all output voltages. Table 4 is provided for most ap-
plication requirements. The Linear Technology µModule
Power Design Tool will be provided for other control loop
optimization.
Run Enable
The RUN pins have an enable threshold of 1.4V maximum,
typically 1.25V with 150mV of hysteresis. They control the
turn on each of the channels and INTVCC. These pins can be
pulled up to VIN for 5V operation, or a 5V Zener diode can be
placed on the pins and a 10k to 100k resistor can be placed
up to higher than 5V input for enabling the channels. The
RUN pins can also be used for output voltage sequencing.
In parallel operation the RUN pins can be tie together and
controlled from a single control. See the Typical Applica-
tion circuits in Figure 23.
INTVCC and EXTVCC
The LTM4630 module has an internal 5V low dropout
regulator that is derived from the input voltage. This regu-
lator is used to power the control circuitry and the power
MOSFET drivers. This regulator can source up to 70mA,
and typically uses ~30mA for powering the device at the
maximum frequency. This internal 5V supply is enabled
by either RUN1 or RUN2.
EXTVCC allows an external 5V supply to power the LTM4630
and reduce power dissipation from the internal low dropout
5V regulator. The power loss savings can be calculated by:
(VIN – 5V) • 30mA = PLOSS
EXTVCC has a threshold of 4.7V for activation, and a
maximum rating of 6V. When using a 5V input, connect
this 5V input to EXTVCC also to maintain a 5V gate drive
level. EXTVCC must sequence on after VIN, and EXTVCC
must sequence off before VIN.
Differential Remote Sense Amplifier
An accurate differential remote sense amplifier is provided
to sense low output voltages accurately at the remote
load points. This is especially true for high current loads.
The amplifier can be used on one of the two channels, or
on a single parallel output. It is very important that the
DIFFP and DIFFN are connected properly at the output,
and DIFFOUT is connected to either VOUTS1 or VOUTS2.
In parallel operation, the DIFFP and DIFFN are connected
properly at the output, and DIFFOUT is connected to
one of the VOUTS pins. Review the parallel schematics in
Figure 24 and review Figure 2.
For more information www.linear.com/LTM4630
4630fa
17
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