LTC3608 LINER [Linear Technology], LTC3608 Datasheet - Page 15

• Manufacturer Part Number: LTC3608
• Description: 18V, 8A Monolithic Synchronous Step-Down DC/DC Converter
• Manufacturer: LINER [Linear Technology]

APPLICATIONS INFORMATION
within the LTC3608. The INTV
RMS and must be bypassed to ground with a minimum of
4.7μF tantalum or ceramic capacitor. Good bypassing is
necessary to supply the high transient currents required
by the MOSFET gate drivers.
The EXTV
and control power from the output or another external
source during normal operation. Whenever the EXTV
pin is above 4.7V the internal 5V regulator is shut off and
an internal 50mA P-channel switch connects the EXTV
pin to INTV
until this pin drops below 4.5V. Do not apply more than
7V to the EXTV
following list summarizes the possible connections for
EXTV
1. EXTV
2. EXTV
internal 5V regulator.
supply compatible with the MOSFET gate drive require-
ments (typically 5V) can improve overall effi ciency.
CC
:
CC
CC
CC
connected to an external supply. A high effi ciency
grounded. INTV
CC
pin can be used to provide MOSFET gate drive
V
= PGND
= SGND
OUT1
. INTV
C
C
V
CC
SEC
1μF
OUT
OUT2
pin and ensure that EXTV
+
+
CC
IN4148
power is supplied from EXTV
CC
C
1:N
T1
IN
CC
+
is always powered from the
V
pin can supply up to 50mA
IN
Figure 4. Secondary Output Loop and EXTV
GND
41
42
43
44
45
46
47
48
49
50
51
52
SW
SW
SW
SW
SW
SW
SW
PV
PV
PV
PV
PV
IN
IN
IN
IN
IN
40 39 38 37 36 35 34 33 32 31 30 29 28 27
1
CC
2
≤ V
3
4
IN
. The
5
CC
CC
CC
6
LTC3608
7
3. EXTV
Soft-Start and Latchoff with the RUN/SS Pin
The RUN/SS pin provides a means to shut down the
LTC3608 as well as a timer for soft-start and overcurrent
latchoff. Pulling the RUN/SS pin below 0.8V puts the
LTC3608 into a low quiescent current shutdown (I
30μA). Releasing the pin allows an internal 1.2μA current
source to charge up the external timing capacitor C
RUN/SS has been pulled all the way to ground, there is a
delay before starting of about:
8
SW
SW
The low voltage output can be boosted using a charge
pump or fl yback winding to greater than 4.7V. The
system will start-up using the internal linear regulator
until the boosted output supply is available.
9 10 11 12 13 14
t
DELAY
CC
=
CC
connected to an output derived boost network.
1.2μA
Connection
1.5V
PGOOD
SGND
SGND
SGND
V
C
SGND
3608 F04
FCB
RNG
V
I
NC
NC
NC
I
SS
ON
TH
FB
26
25
24
23
22
21
20
19
18
17
16
15
= 1.3s/μF
(
R4
R3
OPTIONAL EXTV
CONNECTION
5V < V
)
C
OUT2
SS
LTC3608
< 7V
CC
15
SS
3608fa
Q
. If
<