Datasheet

LTC3814-5
18
38145fc
Using the INTV
CC
Regulators
One, both or neither of these regulators can be used to
generate the 5.5V IC/driver supply depending on the
circuit requirements, available supplies, and the voltage
range of V
IN
or V
OUT
. Deriving the 5.5V supply from V
IN
is more effi cient, however deriving it from V
OUT
has the
advantage of maintaining regulation of V
OUT
when V
IN
drops below the UV threshold. Four possible confi gurations
are shown in Figures 9a through 9d, and are described
as follows:
1. Figure 9a. If the V
IN
voltage or another low voltage
supply between 4.5V and 14V is available, the sim-
plest approach is to connect this supply directly to the
INTV
CC
and DRV
CC
pins. The internal regulators are
disabled by shorting NDRV and EXTV
CC
to INTV
CC
.
2. Figure 9b. If V
IN(MAX)
> 14V, an external NMOS con-
nected to the NDRV pin can be used to generate 5.5V
from V
IN
. V
IN(MIN)
must be > 4.5V + R
NDRV
• 40µA + V
T
to keep INTV
CC
above the UV threshold and the BV
DSS
of the external NMOS must be chosen to be greater
than V
IN(MAX)
. The EXTV
CC
regulator is disabled by
grounding the EXTV
CC
pin.
3. Figure 9c. If the V
IN(MAX)
< 14.7V and V
IN
is allowed to
fall below 4.2V without disrupting the boost converter
operation, use this confi guration. The INTV
CC
supply
is derived from V
IN
until the V
OUT
> 4.7V. Once INTV
CC
is derived from V
OUT
, V
IN
can fall below the 4V UV
threshold without losing regulation of V
OUT
. Note that
in this confi guration, V
IN
must be > ~5V at least long
enough to start up the LTC3814-5 and charge V
OUT
>
4.7V. Also, since V
OUT
is connected to the EXTV
CC
pin,
this confi guration is limited to V
OUT
< 15V.
4. Figure 9d. Similar to confi guration 3 except that V
OUT
is allowed to be >15V since V
OUT
is connected to an
external NMOS with appropriately rated BV
DSS
. V
IN
has
same start-up requirement as 3.
APPLICATIONS INFORMATION
Figure 9. Four Possible Ways to Generate INTV
CC
Supply
V
OUT
≤ 15V
(a) 4.2V to 14V
Supply Available
(b) INTV
CC
from V
IN
,
V
IN
> 14V
(c) INTV
CC
from V
OUT
,
V
OUT
≤ 15V
(d) INTV
CC
from V
OUT
,
V
OUT
> 15V
38145 F09
NDRV
EXTV
CC
INTV
CC
+
V
IN
< 14.7V
5.5V
NDRV
EXTV
CC
INTV
CC
LTC3814-5
V
IN
5.5V
NDRV
R
NDRV
EXTV
CC
INTV
CC
+
V
OUT
5.5V
R
NDRV
+
LTC3814-5
LTC3814-5
+
–
4.5V to
14V
NDRV
EXT
V
CC
INTV
CC
+
LTC3814-5
V
IN
< 14.7V