LTM4600HVMPV View Datasheet(PDF) - Linear Technology
Part Name
Description
MFG CO.
'LTM4600HVMPV' PDF : 24 Pages View PDF
LTM4600HV
Applications Information
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.
RUN/SS
ON
LTM4600HV
PGND SGND
2N7002
4600hv F05
Figure 5. Enable Circuit with External Logic
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 VO rising and
falling can be implemented with different sets of resistor
values. See the LTC2923 data sheet for more details.
VIN
5V
DC/DC
Q1
3.3V
VIN
RONB
RONA
VCC GATE
ON
RAMP
FB1
LTC2923
VIN
LTM4600HV
VOSET VOUT
1.8V
49.9k
RTB1
RTA1 RTB2
RTA2
RAMPBUF STATUS
TRACK1
SDO
TRACK2
FB2
GND
VIN
VIN
LTM4600HV
VOSET VOUT
1.5V
66.5k
4600hv F06
Figure 6. Output Voltage Tracking with the LTC2923 Controller
EXTVCC Connection
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 VIN. The gate
driver current through LDO is about 18mA. The internal
LDO power dissipation can be calculated as:
PLDO_LOSS = 18mA • (VIN – 5V)
The LTM4600HV also provides an external gate driver
voltage pin EXTVCC. If there is a 5V rail in the system, it
is recommended to connect EXTVCC pin to the external
5V rail. Whenever the EXTVCC pin is above 4.7V, the in-
ternal 5V LDO is shut off and an internal 50mA P-channel
switch connects the EXTVCC to internal 5V. Internal 5V is
supplied from EXTVCC until this pin drops below 4.5V. Do
not apply more than 6V to the EXTVCC pin and ensure that
EXTVCC < VIN. The following list summaries the possible
connections for EXTVCC:
1. EXTVCC grounded. Internal 5V LDO is always powered
from the internal 5V regulator.
2. EXTVCC connected to an external supply. Internal LDO
is shut off. A high efficiency supply compatible with the
MOSFET gate drive requirements (typically 5V) can im-
prove overall efficiency. With this connection, it is always
required that the EXTVCC voltage can not be higher than
VIN pin voltage.
3. EXTVCC is recommended for VIN > 20V
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.
14
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4600hvfe
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