LTM4600(RevA) View Datasheet(PDF) - Linear Technology
Part Name
Description
Manufacturer
LTM4600 Datasheet PDF : 24 Pages
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LTM4600
APPLICATIO S I FOR ATIO
inductor ripple current gets too high above 16V, and the
400ns minimum off-time is limited below 9V.
Equations for setting frequency:
tOFF = 2µs – 1.32ns ≅ 760ns
tON and tOFF are above the minimums with adquate guard
band.
ION = VIN – 0.7V/110k; for 5V input, ION = 39µA
frequency = (ION/[2.4V • 10pF]) • DC; DC = duty cycle,
duty cycle is (VOUT/VIN)
t = tON + tOFF, tON = on-time, tOFF = off-time of the
switching period; t = 1/frequency
tOFF must be greater than 400ns, or t – tON > 400ns.
tON = DC • t
~450kHz frequency or 2.22µs period is chosen for 5V to
3.3V. Frequency range is about 450kHz to 650kHz from
4.5V to 7V input.
Using the frequency = (ION/[2.4V • 10pF]) • DC, solve for
ION = (450kHz • 2.4V • 10pF) • (1/0.66) ≅ 16µA. ION current
calculated from 5V input was 39µA, so a resistor from fADJ
to ground = (0.7V/30.1k) = 23µA. 39µA – 23µA = 16µA,
sets the adequate ION current for proper frequency range
for the higher duty cycle conversion of 5V to 3.3V. Input
voltage range is limited to 4.5V to 7V. Higher input voltages
can be used without the 30.1k on fADJ. The inductor ripple
current gets too high above 7V, and the 400ns minimum
off-time is limited below 4.5V.
tON = 0.66 • 2.22µs ≅ 1.46ns
4.5V TO 7V
C3
10µF
25V
C1
10µF
25V
RUN/SOFT-START
5V to 3.3V at 8A
R1
30.1k
VIN
EXTVCC
fADJ
VOUT
FCB
LTM4600EV
RUN/SS
VOSET
SVIN
COMP
SGND
PGOOD
PGND
4600 F18
C5
100pF
3.3V AT 8A EFFICIENCY = 93%
R2
22.1k
1%
C2 +
22µF
C4
330µF
6.3V
OPEN DRAIN
5V TO 3.3V AT 8A WITH fADJ = 30.1k
C1, C3: TDK C3216X5R1E106MT
C2: TAIYO YUDEN, JMK316BJ226ML
C4: SANYO POS CAP, 6TPE330MIL
18
12V to 5V at 8A
9V TO 16V
C3
10µF
25V
C1
10µF
25V
RUN/SOFT-START
R1
15k
VIN
EXTVCC
fADJ
VOUT
FCB
LTM4600EV
RUN/SS
VOSET
SVIN
COMP
SGND
PGOOD
PGND
4600 F19
C5
100pF
5V AT 8A
R2
13.7k
1%
EFFICIENCY = 93%
C2 +
22µF
C4
330µF
6.3V
OPEN DRAIN
12V TO 5V AT 8A WITH fADJ = 15k
C1, C3: TDK C3216X5R1E106MT
C2: TAIYO YUDEN, JMK316BJ226ML
C4: SANYO POS CAP, 6TPE330MIL
4600fa
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