Datasheet

LTC3610
14
3610ff
applications inForMation
INTV
CC
Regulator and EXTV
CC
Connection
An internal P-channel low dropout regulator produces the
5V supply that powers the drivers and internal circuitry
within the LTC3610. The INTV
CC
pin can supply up to 50mA
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
CC
pin can be used to provide MOSFET gate drive
and control power from the output or another external
source during normal operation. Whenever the EXTV
CC
pin is above 4.7V the internal 5V regulator is shut off and
an internal 50mA P-channel switch connects the EXTV
CC
pin to INTV
CC
. INTV
CC
power is supplied from EXTV
CC
until this pin drops below 4.5V. Do not apply more than
7V to the EXTV
CC
pin and ensure that EXTV
CC
≤ V
IN
. The
following list summarizes the possible connections for
EXTV
CC
:
1. EXTV
CC
grounded. INTV
CC
is always powered from the
internal 5V regulator.
2. E
XTV
CC
connected to an external supply. A high efficiency
supply compatible with the MOSFET gate drive require-
ments (typically 5V) can improve overall efficiency.
3.
EXT
V
CC
connected to an output derived boost network.
The low voltage output can be boosted using a charge
pump or flyback winding to greater than 4.7V. The
system will start-up using the internal linear regulator
until the boosted output supply is available.
Soft-Start
and Latchoff with the RUN/SS Pin
The RUN/SS pin provides a means to shut down the LTC3610
as well as a timer for soft-start and overcurrent latchoff.
Pulling the RUN/SS pin below 0.8V puts the LTC3610 into
a low quiescent current shutdown (I
Q
< 30µA). Releasing
the pin allows an internal 1.2µA current source to charge
up the external timing capacitor C
SS
. If RUN/SS has been
pulled all the way to ground, there is a delay before start-
ing of about:
t
DELAY
=
1.5V
1.2µA
C
SS
= 1.3s/µF
( )
C
SS
Figure 4. Secondary Output Loop and EXTV
CC
Connection
LTC3610
SGND
48
SGND
47
SGND
46
SGND
45
EXTV
CC
44
V
FB
43
SGND
42
I
ON
41
R4
SGND
40
FCB
39
I
TH
38
V
RNG
37
PGOOD
36
V
ON
35
SGND
34
SGND
SGND
GND
33
PV
IN
17
PV
IN
18
PV
IN
19
PV
IN
20
PV
IN
21
PV
IN
22
PV
IN
23
PV
IN
24
PV
IN
25
SW
SW
SW
26
NC
27
SGND
28
BOOST
29
RUN/SS
30
SGND
31
SGND
32
PGND
64
PGND
63
PGND
62
PGND
61
PGND
60
PGND
59
PGND
58
PGND
57
PGND
56
SW
55
INTV
CC
54
INTV
CC
53
SV
IN
52
SV
IN
51
SGND
50
SGND
49
PGND
1
PGND
2
PGND
3
SW
4
SW
5
SW
6
SW
7
SW
8
SW
9
SW
10
SW
11
PV
IN
V
IN
12
PV
IN
13
PV
IN
14
PV
IN
15
PV
IN
16
3610 F04
C
SEC
1µF
V
OUT2
V
OUT1
C
OUT
C
IN
IN4148
OPTIONAL EXTV
CC
CONNECTION
5V < V
OUT2
< 7V
T1
1:N
R3
+
+
•
•
+