LTC3813 datasheet(21/32 Pages) LINER

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LTC3813

3813fb

Using the INTVCC 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 VIN or VOUT. Deriving the 10V supply from VIN is more

efﬁcient, however deriving it from VOUT has the advantage

of maintaining regulation of VOUT when VIN 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 VIN 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

INTVCC and DRVCC pins. The internal regulators are

disabled by shorting NDRV and EXTVCC to INTVCC.

2. Figure 9b. If VIN(MAX) > 14V, an external NMOS con-

nected to the NDRV pin can be used to generate 10V

from VIN. VIN(MIN) must be > 6.2V + RNDRV • 40μA + VT

to keep INTVCC above the UV threshold and the BVDSS

of the external NMOS must be chosen to be greater

than VIN(MAX). The EXTVCC regulator is disabled by

grounding the EXTVCC pin.

3. Figure 9c. If the VIN(MAX) < 14.7V and VIN is allowed to

fall below 6.2V without disrupting the boost converter

operation, use this conﬁguration. The INTVCC supply

is derived from VIN until the VOUT > 6.7V. Once INTVCC

is derived from VOUT, VIN can fall below the 6V UV

threshold without losing regulation of VOUT. Note that

in this conﬁguration, VIN must be > 7V at least long

enough to start up the LTC3813 and charge VOUT >

6.7V. Also, since VOUT is connected to the EXTVCC pin,

this conﬁguration is limited to VOUT < 15V.

4. Figure 9d. Similar to conﬁguration 3 except that VOUT

is allowed to be >15V since VOUT is connected to an

external NMOS with appropriately rated BVDSS. VIN has

same start-up requirement as 3.

Figure 9. Four Possible Ways to Generate INTVCC Supply

APPLICATIONS INFORMATION

VOUT ≤ 15V

(a) 6.2V to 14V

Supply Available

(b) INTVCC from VIN,

VIN > 14V

VOUT ≤ 15V

(d) INTVCC from VOUT,

VOUT > 15V

3813 F09

NDRV

EXTVCC

INTVCC

VIN < 14.7V

10V

NDRV

EXTVCC

INTVCC

LTC3813

VIN

10V

NDRV

RNDRV

EXTVCC

INTVCC

VOUT

10V

RNDRV

LTC3813

–

6.2V to

14V

NDRV

EXTVCC

INTVCC

LTC3813

VIN < 14.7V

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