LTC3814-5_15 Datasheet, PDF (18/30 Pages) Linear Technology – 60V Current Mode Synchronous Step-Up Controller

LTC3814-5
APPLICATIONS INFORMATION
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 efficient, 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 configurations
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 configuration. 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 configuration, 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 configuration is limited to V_OUT < 15V.
4. Figure 9d. Similar to configuration 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.
V_IN
NDRV
INTV_CC
LTC3814-5
EXTV_CC
(a) 4.2V to 14V
Supply Available
NDRV
INTV_CC
LTC3814-5
+
+
–
4.5V to
14V
V_IN < 14.7V
+ ^5.5V
NDRV
INTV_CC
LTC3814-5
R_NDRV
+ ^5.5V
EXTV_CC
(b) INTV_CC from V_IN,
V_IN > 14V
V_OUT
NDRV
INTV_CC
LTC3814-5
R_NDRV
V_IN < 14.7V
+
5.5V
18
EXTV_CC
V_OUT ≤ 15V
EXTV_CC
(c) INTV_CC from V_OUT,
V_OUT ≤ 15V
(d) INTV_CC from V_OUT,
V_OUT > 15V
Figure 9. Four Possible Ways to Generate INTV_CC Supply
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