LTC3714 Linear, LTC3714 Datasheet - Page 11

• Manufacturer Part Number: LTC3714
• Description: Wide Operating Range / Step-Down Controller with Internal Op Amp
• Manufacturer: Linear

OPERATIO
Internal Op Amp
The internal op amp allows the user to program accurate
offsets to the output voltage during power saving modes.
By connecting the OP
the V
OP
gain feedback amplifier. Resistors R2 and R3, together
with series switches, can then be placed on the OP
allow negative offsets to be switched onto the output
voltage (see Figures 2a and 2b). The accuracy of the offset
will depend on the matching of the external resistors R1 to
R2 and R3.*
For applications that require less accurate output offsets,
or none at all, the user can use the internal op amp for true
differential remote sensing of the output voltage by con-
necting OPOUT to V
differential sensing across the output capacitor as shown
in Figure 2c.
V
–
OUT
OP
and OPOUT pins, the op amp is hooked up as a unity-
OSENSE
–
OP
17
16
+
OFFSET
pin and an external resistor R1 between the
SLEEP
MODE
+
–
15
U
OPV
R2
OSENSE
+
IN
pin to the output, the OPOUT pin to
Figure 2a
OPOUT
18
BATTERY
R1
OFFSET
MODE
and using OP
V
OSENSE
23
R3
V
V
OUT
OUT
+
–
VID DAC
+
R
R
and OP
R
V
22
3714 F02b
FB
–
OP
pin to
–
–
OP
17
16
for
+
Figure 2c
BATTERY
OFFSET
MODE
+
–
INTV
Power for the top and bottom MOSFET drivers and most
of the internal controller circuitry is derived from the
INTV
floating bootstrap capacitor C
charged from INTV
D
pin is grounded, an internal 5V low dropout regulator
supplies the INTV
above 4.7V, the internal regulator is turned off, and an
internal switch connects EXTV
a high efficiency source connected to EXTV
external 5V supply or a secondary output from the
converter, to provide the INTV
7V can be applied to EXTV
the input voltage is low and INTV
undervoltage lockout circuitry prevents the power
switches from turning on.
*An alternate configuration, shown in Figure 2b, can be used to program
offsets as well. Either configuration can be used, depending upon the logic
of control signals. If offsets are not required, the op amp can be used to
remotely sense the output voltage, proving true differential sense.
R
B
15
when the top MOSFET is turned off. When the EXTV
OPV
R1
R2
CC
OFFSET
CC
SLEEP
MODE
V
IN
OUT
/EXTV
pin. The top MOSFET driver is powered from a
OPOUT V
R2
18
OP
R3
–
CC
OP
17
16
OSENSE
+
Power
23
3714 F02c
CC
CC
+
–
Figure 2b
through an external Schottky diode
power from V
R1
15
OPV
CC
IN
for additional gate drive. If
CC
CC
B
. This capacitor is re-
18
to INTV
power. Voltages up to
CC
IN
drops below 3.5V,
23
. If EXTV
LTC3714
CC
CC
VID DAC
. This allows
, such as an
CC
11
V
22
3714 F02b
FB
rises
3714f
CC