LTC3616 LINER [Linear Technology], LTC3616 Datasheet - Page 13

• Manufacturer Part Number: LTC3616
• Description: 6A, 4MHz Monolithic Synchronous Step-Down DC/DC Converter
• Manufacturer: LINER [Linear Technology]

APPLICATIONS INFORMATION
OPERATION
If the output voltage drops below 50% of its nominal value,
the clamp voltage at ITH pin is lowered causing the maxi-
mum peak inductor current to decrease gradually with the
output voltage. When the output voltage reaches 0V the
clamp voltage at the ITH pin drops to 40% of the clamp
voltage during normal operation. The short-circuit peak
inductor current is determined by the minimum on-time
of the LTC3616, the input voltage and the inductor value.
This foldback behavior helps in limiting the peak inductor
The basic LTC3616 application circuit is shown in Figure 1.
Operating Frequency
Selection of the operating frequency is a trade-off between
efficiency and component size. High frequency operation
allows the use of smaller inductor and capacitor values.
Operation at lower frequencies improves efficiency by
reducing internal gate charge losses but requires larger
inductance values and/or capacitance to maintain low
output ripple voltage.
The operating frequency of the LTC3616 is determined
by an external resistor that is connected between the
RT/SYNC pin and ground. The value of the resistor sets
2.25V TO 5.5V
V
IN
R
2M
SS
C
22nF
C
470pF
SS
C
15k
R
C
Figure 1. 1.8V, 6A Step-Down Regulator
C
10pF
(OPT)
C1
R
130k
T
RUN
TRACK/SS
RT/SYNC
PGOOD
ITH
MODE
SV
IN
LTC3616
SRLIM/DDR
current when the output is shorted to ground. It is disabled
during internal or external soft-start and tracking up/down
operation (see the Applications Information section).
A secondary limit is also imposed on the valley inductor
current. If the inductor current measured through the
bottom MOSFET increases beyond 12A typical, the top
power MOSFET will be held off and switching cycles will
be skipped until the inductor current is reduced.
the ramp current that is used to charge and discharge an
internal timing capacitor within the oscillator and can be
calculated by using the following equation:
Although frequencies as high as 4MHz are possible, the
minimum on-time of the LTC3616 imposes a minimum
limit on the operating duty cycle. The minimum on-time
is typically 60ns; therefore, the minimum duty cycle is
equal to 60ns • f
Tying the RT/SYNC pin to SV
operating frequency to 2.25MHz ±20%.
PV
V
FB
SGND
PGND
IN
R
R2
196k
SW
T
=
3.82 • 10
f
220nH
OSC
392k
R1
L1
C
22μF
( )
OSC
IN1
4
Hz
11
3616 F01
(Hz)•100%.
Hz
C
47μF
Ω – 16kΩ
OUT1
IN
C
100μF
OUT2
sets the default internal
V
1.8V
6A
OUT
LTC3616
13
3616f