LTM4601A View Datasheet(PDF) - Linear Technology
Part Name
Description
MFG CO.
'LTM4601A' PDF : 28 Pages View PDF
LTM4601A/LTM4601A-1
APPLICATIONS INFORMATION
Run Enable
The RUN pin is used to enable the power module. The
pin has an internal 5.1V zener to ground. The pin can be
driven with a logic input not to exceed 5V.
The RUN pin can also be used as an undervoltage lockout
(UVLO) function by connecting a resistor divider from the
input supply to the RUN pin:
VUVLO
=
R1+ R2
R2
ā¢
1.5V
See Figure 1, Simpliļ¬ed Block Diagram.
Power Good
The PGOOD pin is an open-drain pin that can be used to
monitor valid output voltage regulation. This pin monitors
a Ā±10% window around the regulation point and tracks
with margining.
COMP Pin
This pin is the external compensation pin. The module
has already been internally compensated for most output
voltages. Table 2 is provided for most application require-
ments. A spice model will be provided for other control
loop optimization.
PLLIN
The power module has a phase-locked loop comprised
of an internal voltage controlled oscillator and a phase
detector. This allows the internal top MOSFET turn-on
to be locked to the rising edge of the external clock. The
frequency range is Ā±30% around the operating frequency
of 850kHz. A pulse detection circuit is used to detect a
clock on the PLLIN pin to turn on the phase-lock loop.
The pulse width of the clock has to be at least 400ns and
2V in amplitude. During the start-up of the regulator, the
phase-lock loop function is disabled.
INTVCC and DRVCC Connection
An internal low dropout regulator produces an internal
5V supply that powers the control circuitry and DRVCC
for driving the internal power MOSFETs. Therefore, if the
system does not have a 5V power rail, the LTM4601A
can be directly powered by VIN. The gate driver current
14
through the LDO is about 20mA. The internal LDO power
dissipation can be calculated as:
PLDO_LOSS = 20mA ā¢ (VIN ā 5V)
The LTM4601A also provides the external gate driver
voltage pin DRVCC. If there is a 5V rail in the system, it is
recommended to connect DRVCC pin to the external 5V
rail. This is especially true for higher input voltages. Do
not apply more than 6V to the DRVCC pin. A 5V output can
be used to power the DRVCC pin with an external circuit
as shown in Figure 16.
Parallel Operation of the Module
The LTM4601A device is an inherently current mode
controlled device. Parallel modules will have very good
current sharing. This will balance the thermals on the de-
sign. Figure 19 shows a schematic of the parallel design.
The voltage feedback equation changes with the variable
N as modules are paralleled:
VOUT
=
0.6V
60.4k
N
+
RSET
RSET
N is the number of paralleled modules.
Figure 19 shows an LTM4601A and an LTM4601A-1 used
in a parallel design. The 2nd LTM4601A device does
not require the remote sense ampliļ¬er, therefore, the
LTM4601A-1 device is used. An LTM4601A device can be
used without the diff amp. VOSNS+ can be tied to ground
and the VOSNSā can be tied to INTVCC. DIFFVOUT can ļ¬oat.
When using multiple LTM4601A-1 devices in parallel with
an LTM4601A, limit the number to ļ¬ve for a total of six
modules in parallel.
Thermal Considerations and Output Current Derating
The power loss curves in Figures 7 and 8 can be used
in coordination with the load current derating curves in
Figures 9 to 14 for calculating an approximate ĪøJA for the
module with various heat sinking methods. Thermal models
are derived from several temperature measurements at
the bench and thermal modeling analysis. Thermal Ap-
plication Note 103 provides a detailed explanation of the
analysis for the thermal models and the derating curves.
4601afb
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