LTC1629 LINER [Linear Technology], LTC1629 Datasheet - Page 17

• Manufacturer Part Number: LTC1629
• Description: PolyPhase, High Efficiency, Synchronous Step-Down Switching Regulators
• Manufacturer: LINER [Linear Technology]

APPLICATIO S I FOR ATIO
source of the desired MOSFET. This enhances the MOSFET
and turns on the topside switch. The switch node voltage,
SW, rises to V
The value of the boost capacitor C
times that of the total input capacitance of the topside
MOSFET(s). The reverse breakdown of D
than V
The final arbiter when defining the best gate drive ampli-
tude level will be the input supply current. If a change is
made that decreases input current, the efficiency has
improved. If the input current does not change then the
efficiency has not changed either.
Output Voltage
The LTC1629 has a true remote voltage sense capablity.
The sensing connections should be returned from the load
back to the differential amplifier’s inputs through a com-
mon, tightly coupled pair of PC traces. The differential
amplifier rejects common mode signals capacitively or
inductively radiated into the feedback PC traces as well as
ground loop disturbances. The differential amplifier out-
put signal is divided down and compared with the internal
precision 0.8V voltage reference by the error amplifier.
The differential amplifier can be used in either of two
configurations according to the voltage applied to the
AMPMD pin. The first configuration, with the connections
illustrated in the Functional Diagram, utilizes a set of
internal precision resistors to enable precision instrumen-
tation-type measurement of the output voltage. This con-
Figure 5a. Secondary Output Loop and EXTV
OPTIONAL EXTV
5V < V
EXTV
IN(MAX).
CC
SEC
LTC1629
< 7V
IN
and the BOOST pin rises to V
CC
PGND
CONNECTION
SW1
TG1
BG1
U
V
IN
C
IN
N-CH
N-CH
U
+
1N4148
V
B
IN
needs to be 30 to 100
W
T1
6.8V
B
must be greater
CC
R
SENSE
Connection
V
IN
SEC
+
+
+ V
U
1629 F05a
INTVCC
1 F
C
V
OUT
OUT
.
figuration is activated when the AMPMD pin is tied to
ground and is the only configuration available for the
LTC1629-PG. When the AMPMD pin is tied to INTV
resistors are disconnected and the amplifier inputs are
made directly available. The amplifier can then be used as
a general purpose op amp. The amplifier has a 0V to 3V
common mode input range limitation due to the internal
switching of its inputs. The output is an NPN emitter
follower without any internal pull-down current. A DC
resistive load to ground is required in order to sink current.
The output will swing from 0V to 10V. (V
Soft-Start/Run Function
The RUN/SS pin provides three functions: 1) Run/Shut-
down, 2) soft-start and 3) a defeatable short-circuit latchoff
timer. Soft-start reduces the input power sources’ surge
currents by gradually increasing the controller’s current
limit I
extreme load transients from tripping the overcurrent
latch. A small pull-up current (>5 A) supplied to the RUN/
SS pin will prevent the overcurrent latch from operating.
The following explanation describes how the functions
operate.
An internal 1.2 A current source charges up the C
capacitor
controller is permitted to start operating. As the voltage on
RUN/SS increases from 1.5V to 3.0V, the internal current
limit is increased from 25mV/R
The output current limit ramps up slowly, taking an
additional 1.4 s/ F to reach full current. The output cur-
EXTV
TH(MAX)
Figure 5b. Capacitive Charge Pump for EXTV
CC
.
LTC1629
When the voltage on RUN/SS reaches 1.5V, the
LTC1629/LTC1629-PG
. The latchoff timer prevents very short,
PGND
SW1
BG1
TG1
V
IN
C
IN
N-CH
N-CH
+
BAT85
SENSE
V
IN
L1
VN2222LL
IN
to 75mV/R
0.22 F
R
V
SENSE
C
DIFFOUT
IN
+
+
CC
1629 F05b
BAT85
17
BAT85
C
V
CC
SENSE
OUT
+ 2V.)
OUT
, the
SS
.