LTC3714_15 Datasheet, PDF (11/28 Pages) Linear Technology – Intel Compatible, Wide Operating Range, Step-Down Controller with Internal Op Amp

LTC3714
Operation
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⁺ pin to the output, the OPOUT pin
to the V_OSENSE pin and an external resistor R1 between
the OP^– and OPOUT pins, the op amp is hooked up as
a unity-gain feedback amplifier. Resistors R2 and R3,
together with series switches, can then be placed on the
OP^– pin to 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
connecting OPOUT to V_OSENSE and using OP ⁺ and OP^– for
differential sensing across the output capacitor as shown
in Figure 2c.
INTV_CC/EXTV_CC Power
Power for the top and bottom MOSFET drivers and most of
the internal controller circuitry is derived from the INTV_CC
pin. The top MOSFET driver is powered from a floating
bootstrap capacitor C_B. This capacitor is recharged from
INTV_CC through an external Schottky diode D_B when
the top MOSFET is turned off. When the EXTV_CC pin is
grounded, an internal 5V low dropout regulator supplies
the INTV_CC power from V_IN. If EXTV_CC rises above 4.7V,
the internal regulator is turned off, and an internal switch
connects EXTV_CC to INTV_CC. This allows a high efficiency
source connected to EXTV_CC, such as an external 5V sup-
ply or a secondary output from the converter, to provide
the INTV_CC power. Voltages up to 7V can be applied to
EXTV_CC for additional gate drive. If the input voltage is
low and INTV_CC drops below 3.5V, 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.
V_OUT
OP⁺
17
OP^– 16
15 OPV_IN
+
OPOUT
18
–
R1
V_OSENSE
23
R2
SLEEP
MODE
OFFSET
R3
BATTERY
MODE
OFFSET
Figure 2a
VID DAC
V_FB
22
BATTERY
MODE
OFFSET
V_OUT
R1
OP⁺
17
R2
OP^– 16
R2
3714 F02b
R3
SLEEP
MODE
OFFSET
15 OPV_IN
+
VID DAC
18 23
–
V_FB
22
R1
3714 F02b
Figure 2b
R
V_OUT+
R
R
V_OUT–
OP⁺
17
OP^– 16
15 OPV_IN
+
OPOUT V_OSENSE
18
23
–
R
Figure 2c
3714 F02c
3714f
11