ltc1629-6 Linear Technology Corporation, ltc1629-6 Datasheet - Page 17

• Manufacturer Part Number: ltc1629-6
• Description: Polyphase, Synchronous Step-down Switching Regulator
• Manufacturer: Linear Technology Corporation

APPLICATIO S I FOR ATIO
Topside MOSFET Driver Supply (C
Functional Diagram)
External bootstrap capacitors C
the BOOST1 and BOOST2 pins supply the gate drive
voltages for the topside MOSFETs. Capacitor C
Functional Diagram is charged though diode D
INTV
turns on, the driver places the C
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 LTC1629-6 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
Figure 5a. Secondary Output Loop and EXTV
CC
OPTIONAL EXTV
5V < V
EXTV
IN(MAX).
when the SW pin is low. When the topside MOSFET
CC
SEC
LTC1629-6
< 7V
IN
CC
and the BOOST pin rises to V
CONNECTION
PGND
SW1
TG1
BG1
U
V
IN
C
IN
N-CH
N-CH
+
U
V
1N4148
B
B1
IN
voltage across the gate-
T1
B
6.8V
and C
needs to be 30 to 100
W
B
,D
B
R
B
) (Refer to
SENSE
B2
must be greater
CC
connected to
Connection
V
IN
SEC
+
+
+ V
U
B
1629 F05a
B
INTVCC
1 F
C
V
in the
OUT
OUT
from
.
as ground loop disturbances. The differential amplifier
output signal is divided down and compared with the
internal precision 0.6V voltage reference by the error
amplifier.
The output is an NPN emitter follower without any internal
pull-down current. A DC resistive load to ground is re-
quired 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
current thus ramps up slowly, reducing the starting surge
EXTV
TH(MAX)
Figure 5b. Capacitive Charge Pump for EXTV
CC
.
LTC1629-6
When the voltage on RUN/SS reaches 1.5V, the
IN
. The latchoff timer prevents very short,
PGND
SW1
V
BG1
TG1
V
DIFFOUT
IN
C
IN
N-CH
N-CH
+
+ 2V.)
BAT85
V
IN
L1
SENSE
VN2222LL
LTC1629-6
R
to 75mV/R
0.22 F
SENSE
+
+
CC
1629 F05b
BAT85
17
BAT85
C
V
SENSE
OUT
OUT
16296f
SS
.