LTM4602 LINER [Linear Technology], LTM4602 Datasheet - Page 18

• Manufacturer Part Number: LTM4602
• Description: 6A High Effi ciency DC/DC ?Module
• Manufacturer: LINER [Linear Technology]

APPLICATIONS INFORMATION
LTM4602
Equations for setting frequency for 5V to 3.3V:
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.
t
band.
18
OFF
ON
I
frequency = (I
DC = duty cycle, duty cycle is (V
t
switching period; t
t
t
t
ON
S
ON
ON
OFF
and t
must be greater than 400ns, or t
= t
= (V
= DC • t
= 0.66 • 2.22μs ≅ 1.46μs
= 2.22μs – 1.46μs ≅ 760ns
ON
OFF
IN
+ t
are above the minimums with adequate guard
– 0.7V)/110k; I
S
OFF
, t
ON
ON
/[2.4V • 10pF]) • DC = 1.07MHz;
S
= on-time, t
= 1/frequency
ON
= 39μA
OUT
OFF
S
/V
– t
= off-time of the
IN
ON
)
> 400ns.
Using the frequency = (I
I
calculated from 5V input was 39μA, so a resistor from f
to ground = (0.7V/30.1k) = 23μA. 39μA – 23μA = 16μA,
sets the adequate I
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 f
current gets too high above 7V, and the 400ns minimum
off-time is limited below 4.5V.
In 12V to 3.3V applications, if a 35k resistor is added from
the f
achieved as shown in the 12V effi ciency graph in the Typi-
cal Performance Characteristics. This is due to the lower
transition losses in the power MOSFETs after lowering the
switching frequency down from 1.3MHz to 950kHz.
ON
= (450kHz • 2.4V • 10pF) • (1/0.66) ≅ 16μA. I
ADJ
pin to ground, then a 2% effi ciency gain will be
ON
current for proper frequency range
ON
/[2.4V • 10pF]) • DC, solve for
ADJ
. The inductor ripple
ON
current
4602fa
ADJ