ltm4600hv Linear Technology Corporation, ltm4600hv Datasheet - Page 13

• Manufacturer Part Number: ltm4600hv
• Description: 10a, 28vin High Efficiency Dc/dc ?module
• Manufacturer: Linear Technology Corporation

APPLICATIO S I FOR ATIO
Enable
The RUN/SS pin can be driven from logic as shown in Figure
5. This function allows the LTM4600HV 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 LTM4600HV modules can be programmed by the
power supply tracking controller such as the LTC2923.
Figure 6 shows a typical schematic with LTC2923. Coin-
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.
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
LTM4600HV
3.3V
W
SGND
4600hv
49.9k
66.5k
4600hv F06
V
V
F05
LTM4600HV
OSET
LTM4600HV
OSET
V
V
V
V
IN
IN
IN
IN
O
V
V
OUT
OUT
rising and
U
1.8V
1.5V
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 LTM4600HV can be directly powered by V
driver current through LDO is about 18mA. The internal
LDO power dissipation can be calculated as:
P
The LTM4600HV also provides an external gate driver
voltage pin EXTV
is recommended to connect EXTV
5V rail. Whenever the EXTV
ternal 5V LDO is shut off and an internal 50mA P-channel
switch connects the EXTV
supplied from EXTV
not apply more than 6V to the EXTV
EXTV
connections 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
3. EXTV
Discontinuous Operation and FCB Pin
The FCB pin determines whether the internal bottom
MOSFET remains on when the current reverses. There is
an internal 4.75k pull-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
pin voltage.
CC
CC
CC
CC
CC
Connection
< V
grounded. Internal 5V LDO is always powered
connected to an external supply. Internal LDO
is recommended for V
= 18mA • (V
IN
. The following list summaries the possible
CC
. If there is a 5V rail in the system, it
CC
CC
until this pin drops below 4.5V. Do
CC
IN
:
voltage can not be higher than
– 5V)
CC
CC
to internal 5V. Internal 5V is
pin is above 4.7V, the in-
LTM4600HV
IN
CC
CC
> 20V
pin and ensure that
pin to the external
IN
. The gate
13
4600hvfc