LTM4600 LINER [Linear Technology], LTM4600 Datasheet - Page 13

• Manufacturer Part Number: LTM4600
• Description: 10A High Effi ciency DC/DC ?Module
• Manufacturer: LINER [Linear Technology]

APPLICATIO S I FOR ATIO
Enable
The RUN/SS pin can be driven from logic as shown in
Figure 5. This function allows the LTM4600 to be turned
on or off remotely. The ON signal can also control the
sequence of the output voltage.
Output Voltage Tracking
For the applications that require output voltage tracking,
several LTM4600 modules can be programmed by the
power supply tracking controller such as the LTC2923.
Figure 6 shows a typical schematic with LTC2923. Coin-
Figure 6. Output Voltage Tracking with the LTC2923 Controller
V
5V
IN
R
R
TB1
TA1
DC/DC
Figure 5. Enable Circuit with External Logic
R
R
R
R
ONB
ONA
TB2
TA2
ON
V
ON
RAMPBUF
TRACK1
TRACK2
CC
U
2N7002
GATE
LTC2923
Q1
GND
U
STATUS
RAMP
RUN/SS
SDO
PGND
FB1
FB2
LTM4600
3.3V
W
SGND
4600 F05
49.9k
66.5k
4600 F06
V
V
OSET
OSET
LTM4600
LTM4600
V
V
V
V
IN
IN
IN
IN
V
V
OUT
OUT
U
1.8V
1.5V
cident, ratiometric and offset tracking for V
falling can be implemented with different sets of resistor
values. See the LTC2923 data sheet for more details.
EXTV
An internal low dropout regulator produces an internal 5V
supply that powers the control circuitry and FET drivers.
Therefore, if the system does not have a 5V power rail,
the LTM4600 can be directly powered by V
driver current through LDO is about 18mA. The internal
LDO power dissipation can be calculated as:
P
The LTM4600 also provides an external gate driver volt-
age pin EXTV
recommended to connect EXTV
rail. Whenever the EXTV
5V LDO is shut off and an internal 50mA P-channel switch
connects the EXTV
from EXTV
more than 6V to the EXTV
< V
tions for EXTV
1. EXTV
from the internal 5V regulator.
2. EXTV
is shut off. A high effi ciency supply compatible with the
MOSFET gate drive requirements (typically 5V) can im-
prove overall effi ciency. With this connection, it is always
required that the EXTV
V
Discontinuous Operation and FCB Pin
The FCB pin determines whether the internal bottom
MOSFET remains on when the inductor current reverses.
There is an internal 4.75k pulling down resistor connecting
this pin to ground. The default light load operation mode
is forced continuous (PWM) current mode. This mode
provides minimum output voltage ripple.
LDO_LOSS
IN
IN
pin voltage.
. The following list summaries the possible connec-
CC
CC
CC
Connection
CC
grounded. Internal 5V LDO is always powered
connected to an external supply. Internal LDO
= 18mA • (V
until this pin drops below 4.5V. Do not apply
CC
CC
. If there is a 5V rail in the system, it is
:
CC
to internal 5V. Internal 5V is supplied
CC
IN
CC
voltage can not be higher than
– 5V)
CC
pin is above 4.7V, the internal
pin and ensure that EXTV
CC
pin to the external 5V
LTM4600
O
IN
. The gate
rising and
13
4600fa
CC