LTM4603HV
15
4603hvfa
For more information www.linear.com/LTM4603HV
applicaTions inForMaTion
to be locked to the rising edge of the external clock. The
frequency range is ±30% around the operating frequency
of 1MHz. A pulse detection circuit is used to detect a clock
on the PLLIN pin to turn on the phase-locked loop. The
pulse width of the clock has to be at least 400ns and the
amplitude at least 2V. The PLLIN pin must be driven from a
low impedance source such as a logic gate located close to
the pin. During start-up of the regulator, the phase-locked
loop function is disabled.
INTV
CC
and DRV
CC
Connection
An internal low dropout regulator produces an internal
5V supply that powers the control circuitry and DRV
CC
for driving the internal power MOSFETs. Therefore, if the
system does not have a 5V power rail, the LTM4603HV
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:
P
LDO_LOSS
= 20mA•(V
IN
– 5V)
The LTM4603HV also provides the external gate driver
voltage pin DRV
CC
. If there is a 5V rail in the system, it is
recommended to connect DRV
CC
pin to the external 5V
rail. This is especially true for higher input voltages. Do
not apply more than 6V to the DRV
CC
pin. A 5V output can
be used to power the DRV
CC
pin with an external circuit
as shown in Figure 18.
Parallel Operation of the Module
The LTM4603HV device is an inherently current mode
controlled 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:
V
OUT
= 0.6V
n
+R
SET
R
n is the number of paralleled modules.
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 12, and Figures 13 to 16 for calculating an
approximate θ
JA
for the module with various heat sinking
methods. Thermal models are derived from several tem-
perature measurements
at
the bench and thermal modeling
analysis. Thermal Application Note 103 provides a detailed
explanation of the analysis for the thermal models and the
derating curves. Tables 3 and 4 provide a summary of the
equivalent θ
JA
for the noted conditions. These equivalent
θ
JA
parameters are correlated to the measured values,
and are improved with air flow. The case temperature is
maintained at 100°C or below for the derating curves.
Figure 7. 1.5V Power Loss Figure 8. 3.3V Power Loss Figure 9. No Heat Sink
OUTPUT CURRENT (A)
0
2.0
2.5
3 5
4603HV F07
1.5
1.0
1 2
4 6 7
0.5
0
POWER LOSS (W)
12V LOSS
5V LOSS
OUTPUT CURRENT (A)
0
2.0
2.5
3.5
3 5
4603HV F08
1.5
1.0
1 2
4 6 7
0.5
0
3.0
POWER LOSS (W)
24V LOSS
12V LOSS
AMBIENT TEMPERATURE (C)
75
0
MAXIMUM LOAD CURRENT (A)
1
2
3
4
5
6
80 85 90 95
4603HV F09
5V
IN
, 1.5V
OUT
, 0LFM
5V
IN
, 1.5V
OUT
, 200LFM
5V
IN
, 1.5V
OUT
, 400LFM
