LTM4604AIY View Datasheet(PDF) - Linear Technology
Part Name
Description
MFG CO.
'LTM4604AIY' PDF : 22 Pages View PDF
LTM4604A
Applications Information
pin must go beyond 0.8V to ensure the slave output has
reached its final value. Load current must be present for
proper tracking.
Ratiometric modes of tracking can be achieved by selecting
different resistor values to change the output tracking ratio.
The master output must be greater than the slave output
for ratiometric tracking to work. LTspice® can be used to
implement different tracking scenarios. The Master and
Slave data inputs can be used to implement the correct
resistor values for coincident or ratio tracking. The master
and slave regulators require load current for tracking down.
Power Good
The PGOOD pin is an open-drain pin that can be used to
monitor valid output voltage regulation. This pin monitors
a ±7.5% window around the regulation point.
COMP Pin
The COMP pin is the external compensation pin. The
LTM4604A has already been internally compensated for
all output voltages. Table 4 is provided for most applica-
tion requirements. The LTpowerCAD GUI is available for
other control loop optimizations.
Parallel Operation
The LTM4604A 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 16 shows a schematic of the parallel design.
The voltage feedback changes with the variable N as more
modules are paralleled. The equation:
VOUT
= 0.8V •
4.99
N
k
+
RFB
RFB
N is the number of paralleled modules.
Thermal Considerations and Output Current Derating
The power loss curves in Figures 4 and 5 can be used
in coordination with the load derating curves in Figures
6 through 13 for calculating an approximate θJA for the
module with and without heat sinking methods with vari-
ous airflow conditions. Thermal models are derived from
several temperature measurements at the bench, and are
correlated with thermal analysis software. Tables 2 and
3 provide a summary of the equivalent θJA for the noted
conditions. These equivalent θJA parameters are correlated
to the measured values and improve with air flow. The
maximum junction temperature is monitored while the
derating curves are derived.
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0
0
5V TO 1.2V
POWER LOSS
3.3V TO 1.2V
POWER LOSS
1
2
3
4
5
LOAD CURRENT (A)
4604A F04
Figure 4. 1.2V Power Loss
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0
0
5V TO 2.5V
POWER LOSS
3.3V TO 2.5V
POWER LOSS
1
2
3
4
5
LOAD CURRENT (A)
4604A F05
Figure 5. 2.5V Power Loss
12
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4604afc
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