LTC3810EG LINER [Linear Technology], LTC3810EG Datasheet - Page 14

• Manufacturer Part Number: LTC3810EG
• Description: 100V Current Mode Synchronous Switching Regulator Controller
• Manufacturer: LINER [Linear Technology]

OPERATION
LTC3810
is < 6.7V or an external supply in the appropriate range
can be used. The LTC3810 will automatically detect which
mode is being used and operate properly.
The four possible operating modes for generating this
supply are summarized as follows (see Figure 4):
1. LTC3810 generates a 10V start-up supply from a small
2. Similar to (1) except that the external MOSFET is used
14
external SOT23 N-channel MOSFET acting as linear
regulator with drain connected to V
by the LTC3810’s internal linear regulator controller
through the NDRV pin. As soon as the output voltage
reaches 6.7V, the 10V IC/driver supply is derived from
the output through an internal low dropout regulator to
optimize effi ciency. If the output is lost due to a short,
the LTC3810 goes through repeated low duty cycle
soft-start cycles (with the drivers shut off in between)
to attempt to bring up the output without burning up
the SOT23 MOSFET. This scheme eliminates the long
start-up times associated with a conventional trickle
charger by using an external MOSFET to quickly charge
the IC/driver supply capacitors (C
for continuous IC/driver power instead of just for
Mode 3: Trickle Charge Mode
Mode 1: MOSFET for Start-Up Only
LTC3810
LTC3810
EXTV
EXTV
INTV
INTV
NDRV
NDRV
I > 270μA
CC
CC
CC
CC
IN
INTVCC
and gate controlled
Figure 4. Operating Modes for IC/Driver Supply
V
V
, C
OUT
OUT
+
+
V
V
IN
IN
DRVCC
(>6.7V)
10V
10V
).
3. Trickle charge mode provides an even simpler approach
4. Low voltage supply available. The simplest approach is if
Mode 2: MOSFET for Continuous Use
start-up. The MOSFET is sized for proper dissipation and
the driver shutdown/restart for V
This scheme is less effi cient but may be necessary if
V
by eliminating the external MOSFET. The IC/driver sup-
ply capacitors are charged through a single high valued
resistor connected to the input supply. When the INTV
voltage reaches the turn-on threshold of 12V (automati-
cally raised from 6.7V to provide extra headroom for
start-up), the drivers turn on and begin charging up the
output capacitor. When the output reaches 6.7V, IC/driver
power is derived from the output. In trickle-charge mode,
the supply capacitors must have suffi cient capacitance
such that they are not discharged below the 6V INTV
UV threshold before the output is high enough to take
over or else the power supply will not start.
a low voltage supply (between 6.2V and 14V) is available
and connected directly to the IC/driver supply pins.
OUT
< 6.7V and a boost network is not desired.
Mode 4: External Supply
LTC3810
LTC3810
EXTV
EXTV
INTV
INTV
NDRV
NDRV
I < 270μA
CC
CC
CC
CC
+
+
V
IN
+
–
10V
3810 F04
6.2V to
14V
OUT
< 6.7V is disabled.
3810fb
CC
CC