Datasheet

LTM4608A
17
4608afd
Figure 7. 3.3V
IN
, 2.5V and 1.5V
OUT
Power Loss Figure 8. 5V
IN
, 3.3V and 1.5V
OUT
Power Loss
LOAD CURRENT (A)
0
POWER LOSS (W)
2.0
2.5
3.0
8
4608A F07
1.5
1.0
0
2
4
6
0.5
4.0
3.5
3.3V
IN
1.5V
OUT
3.3V
IN
2.5V
OUT
LOAD CURRENT (A)
0
POWER LOSS (W)
2.0
2.5
3.0
8
4608A F08
1.5
1.0
0
2
4
6
0.5
4.0
3.5
5V
IN
1.5V
OUT
5V
IN
3.3V
OUT
applicaTions inForMaTion
Slope Compensation
The module has already been internally compensated for
all output voltages. Table 3 is provided for most applica-
tion requirements. A spice model will be provided for other
control loop optimization. For single module operation,
connect I
THM
pin to SGND. For parallel operation, tie I
THM
pins together and then connect to SGND at one point. Tie
I
TH
pins together to share currents evenly for all phases.
Output Margining
For a convenient system stress test on the LTM4608A’s
output, the user can program the LTM4608A’s output to
±5%, ±10% or ±15% of its normal operational voltage.
The margin pin with a voltage divider is driven with a small
three-state gate as shown in Figure 18, for the three margin
states (high, low, no margin). When the MGN pin is <0.3V,
it forces negative margining in which the output voltage
is below the regulation point. When MGN is >V
IN
– 0.3V,
the output voltage is forced above the regulation point.
The amount of output voltage margining is determined by
the BSEL pin. When BSEL is low, it is 5%. When BSEL is
high, it is 10%. When BSEL is floating, it is 15%. When
margining is active, the internal output overvoltage and
undervoltage comparators are disabled and PGOOD re-
mains high. Margining is disabled by tying the MGN pin
to a voltage divider as shown in Figure 20.
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 16 for calculating an approximate θ
JA
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.
Tables 4 and 5 provide a summary of the equivalent θ
JA
for the noted conditions. These equivalent θ
JA
parameters
are correlated to the measured values and improve with
air flow. The junction temperature is maintained at 125°C
or below for the derating curves.