LTM4601 LINER [Linear Technology], LTM4601 Datasheet - Page 21

• Manufacturer Part Number: LTM4601
• Description: 12A DC/DC ?Modules with PLL, Output Tracking and Margining
• Manufacturer: LINER [Linear Technology]

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
or 1.35µs. The f
the I
APPLICATIO S I FOR ATIO
fSET
current equates to 38µA with the internal 39.2k.
SET
10V TO 20V
pin voltage compliance is 1/3 of V
FOR ≥12V INPUT
U
10µF
V
25V
IN
C2
EFFICIENCY
IMPROVE
U
5% MARGIN
C1
10µF
25V
100k
392k
1%
R2
CMSSH-3C3
R1
Figure 16. 5V at 8A Design Without Differential Amplifi er
V
OUT
DUAL
W
100k
ON
R4
= DC/frequency,
SOT-323
PGOOD
MPGM
RUN
COMP
INTV
DRV
CC
CC
SGND
U
V
IN
OFF
IN
LTM4601-1
, and
PLLIN
PGND
, or
MARGIN CONTROL
TRACK/SS
f
SET
V
OUT_LCL
The I
A resistor can be placed from V
effective I
f
will source 14µA into the f
current to 24µA. This enables the 540kHz operation and
the 4.5V to 20V 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.
MARG0
MARG1
SET
R
100k
fSET
V
NC3
NC1
NC2
OUT
V
FB
pin is 4.5V/3 =1.5V and V
fSET
TRACK/SS CONTROL
C6 100pF
REVIEW TEMPERATURE
current needs to be 24µA for 540kHz operation.
fSET
DERATING CURVE
8.25k
R
SET
current out of the f
LTM4601/LTM4601-1
4601 F16
+
C3
100µF
6.3V
SANYO POSCAP
SET
OUT
V
5V
8A
node and lower the I
OUT
OUT
= 3.3V, therefore 130k
SET
REFER TO
TABLE 2
to f
pin to 24µA. The
SET
to lower the
21
fSET
4601f