LTM4601A LINER [Linear Technology], LTM4601A Datasheet - Page 15

• Manufacturer Part Number: LTM4601A
• Description: Ultralow EMI 28VIN, 6A DC/DC ?Module Regulator
• Manufacturer: LINER [Linear Technology]

applicaTions inForMaTion
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 ±30% around the operating frequency. 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.
INTV
An internal low dropout regulator produces an internal
5V supply that powers the control circuitry and DRV
for driving the internal power MOSFETs. Therefore, if
the system does not have a 5V power rail, the LTM4606
can be directly powered by Vin. The gate driver current
through the LDO is about 20mA. The internal LDO power
dissipation can be calculated as:
The LTM4606 also provides an external gate driver voltage
pin DRV
mended to connect DRV
especially true for higher input voltages. Do not apply more
than 6V to the DRV
the DRV
Parallel Operation of the Module
The LTM4606 device is an inherently current mode con-
trolled device. Parallel modules will have very good current
sharing. This will balance the thermals on the design. The
voltage feedback equation changes with the variable N as
modules are paralleled:
N is the number of paralleled modules.
P
V
LDO_LOSS
OUT
CC
and DRV
CC
CC
= 0.6V
. If there is a 5V rail in the system, it is recom-
pin with an external circuit as shown in Figure 18.
= 20mA • (V
60.4k
CC
CC
N
Connection
R
pin. A 5V output can be used to power
FB
+ R
CC
pin to the external 5V rail. This is
IN
FB
– 5V)
CC
Thermal Considerations and Output Current Derating
In different applications, LTM4606 operates in a variety
of thermal environments. The maximum output current is
limited by the environment thermal condition. Sufficient
cooling should be provided to help ensure reliable opera-
tion. When the cooling is limited, proper output current
derating is necessary, considering ambient temperature,
airflow, input/output condition, and the need for increased
reliability.
The power loss curves in Figures 6 and 7 can be used
in coordination with the load current derating curves in
Figures 8 to 15 for calculating an approximate θ
module. The graphs delineate between no heat sink, and
a BGA heat sink. Each of the load current derating curves
will lower the maximum load current as a function of the
increased ambient temperature to keep the maximum junc-
tion temperature of the power module at 125°C maximum.
Each of the derating curves and the power loss curve that
corresponds to the correct output voltage can be used to
solve for the approximate θ
has three curves that are taken at three different air flow
conditions. Tables 3 and 4 provide the approximate θ
for Figures 8 to 15. A complete explanation of the thermal
characteristics is provided in the thermal application note
AN110.
Safety Considerations
The LTM4606 modules do not provide isolation from V
to V
fuse with a rating twice the maximum input current needs
to be provided to protect each unit from catastrophic failure.
Radiated EMI Noise
High radiated EMI noise is a disadvantage for switching
regulators by nature. Fast switching turn-on and turn-off
make large di/dt change in the converters, which act as
the radiation sources in most systems. The LTM4606
integrates the feature to minimize the radiated EMI noise
for applications with low noise requirements. Optimized
gate driver for the MOSFET and noise cancellation network
are installed inside the LTM4606 to achieve low radiated
EMI noise. Figure 16 shows a typical example for LTM4606
to meet the Class B of EN55022 radiated emission limit.
OUT
. There is no internal fuse. If required, a slow blow
JA
of the condition. Each figure
LTM4606
JA
15
for the
4606fb
JA
IN