LTC3714_15 Datasheet, PDF (18/28 Pages) Linear Technology – Intel Compatible, Wide Operating Range, Step-Down Controller with Internal Op Amp

LTC3714
Applications Information
EXTV_CC Connection
The EXTVCC 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 follow-
ing list summarizes the possible connections for EXTV_CC:
1. EXTV_CC grounded. INTV_CC is always powered from the
internal 5V regulator.
2. EXTV_CC connected to an external supply. A high ef-
ficiency supply compatible with the MOSFET gate
drive requirements (typically 5V) can improve overall
efficiency.
3. EXTV_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.
External Gate Drive Buffers
The LTC3714 drivers are adequate for driving up to about
60nC into MOSFET switches with RMS currents of 50mA.
Applications with larger MOSFET switches or operating
at frequencies requiring greater RMS currents will benefit
from using external gate drive buffers such as the LTC1693.
Alternately, the external buffer circuit shown in Figure 6 can
be used. Note that the bipolar devices reduce the signal
swing at the MOSFET gate, and benefit from increased
EXTV_CC voltage of about 6V.
BOOST
INTV_CC
Q1
Q3
FMMT619
FMMT619
10Ω
TG
GATE
OF M1
BG
10Ω
GATE
OF M2
Q2
Q4
FMMT720
FMMT720
SW
PGND
3714 F06
Figure 6. Optional External Gate Driver
3714f
18