LTC3813 Datasheet, PDF (21/32 Pages) Linear Technology – 100V Current Mode Synchronous Step-Up Controller

LTC3813
APPLICATIONS INFORMATION
Using the INTV_CC Regulators
One, both or neither of these regulators can be used to
generate the 10V IC/driver supply depending on the circuit
requirements, available supplies, and the voltage range
of V_IN or V_OUT. Deriving the 10V 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 6.2V 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 10V
from V_IN. V_IN(MIN) must be > 6.2V + 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 6.2V without disrupting the boost converter
operation, use this configuration. The INTV_CC supply
is derived from V_IN until the V_OUT > 6.7V. Once INTV_CC
is derived from V_OUT, V_IN can fall below the 6V UV
threshold without losing regulation of V_OUT. Note that
in this configuration, V_IN must be > 7V at least long
enough to start up the LTC3813 and charge V_OUT >
6.7V. 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
+
LTC3813
EXTV_CC
(a) 6.2V to 14V
Supply Available
V_IN < 14.7V
+ _{6.2V to}
– _14V
NDRV
INTV_CC
LTC3813
+ ^10V
NDRV
INTV_CC
LTC3813
R_NDRV
+ ^10V
EXTV_CC
(b) INTV_CC from V_IN,
V_IN > 14V
V_OUT
NDRV
INTV_CC
LTC3813
R_NDRV
V_IN < 14.7V
+
10V
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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