ltm4601ahv Linear Technology Corporation, ltm4601ahv Datasheet - Page 21

• Manufacturer Part Number: ltm4601ahv
• Description: 12a, 28vin Dc/dc ?module With Pll, Output Tracking And Margining
• Manufacturer: Linear Technology Corporation

APPLICATIONS INFORMATION
Solution
Lower the switching frequency at lower input voltages to
allow for higher duty cycles, and meet the 400ns mini-
mum off-time at 4.5V input voltage. The off-time should
be about 500ns with 100ns guard band. The duty cycle
for (3.3V/4.5) = ~73%. Frequency = (1 – DC)/t
(1 – 0.73)/500ns = 540kHz. The switching frequency
needs to be lowered to 540kHz at 4.5V input. t
frequency, or 1.35μs. The f
is 1/3 of V
the internal 39.2k. The I
10V TO 28V
IN
, and the I
FOR ≥12V INPUT
10μF
V
35V
IN
C2
EFFICIENCY
IMPROVE
fSET
5% MARGIN
fSET
C1
10μF
35V
current equates to 38μA with
100k
392k
current needs to be 24μA for
1%
SET
R2
CMSSH-3C3
R1
V
OUT
100k
pin voltage compliance
R4
Figure 18. 5V at 8A Design Without Differential Amplifi er
SOT-323
PGOOD
MPGM
RUN
COMP
INTV
DRV
CC
CC
SGND
V
IN
LTM4601AHV
ON
PLLIN
PGND
OFF
= DC/
MARGIN CONTROL
TRACK/SS
f
or
V
DIFFV
SET
OUT_LCL
MARG0
MARG1
V
V
R
100k
OSNS
OSNS
V
fSET
OUT
OUT
V
FB
+
–
540kHz operation. As shown in Figure 19, a resistor can
be placed from V
current out of the f
=1.5V and V
into the f
This enables the 540kHz operation and the 4.5V to 28V
input operation for down converting to 3.3V output. The
frequency will scale from 540kHz to 1.1 MHz over this
input range. This provides for an effective output current
of 8A over the input range.
TRACK/SS CONTROL
REVIEW TEMPERATURE
DERATING CURVE
8.25k
R
SET
SET
4601AHV F18
OUT
node and lower the I
= 3.3V, therefore 130k will source 14μA
OUT
SET
+
to f
pin to 24μA. The f
C3
100μF
6.3V
SANYO
POSCAP
SET
LTM4601AHV
to lower the effective I
22μF
6.3V
fSET
V
5V
8A
OUT
current to 24μA.
REFER TO
SET
TABLE 2
pin is 4.5V/3
21
4601ahvf
fSET