LTM4600(RevA) Ver la hoja de datos (PDF) - Linear Technology
Número de pieza
componentes Descripción
Fabricante
LTM4600 Datasheet PDF : 24 Pages
| |||
LTM4600
U
OPERATIO
µModule Description
The LTM4600 is a standalone non-isolated synchronous
switching DC/DC power supply. It can deliver up to 10A of
DC output current with only bulk external input and output
capacitors. This module provides a precisely regulated
output voltage programmable via one external resistor from
0.6VDC to 5.0VDC, not to exceed 80% of the input voltage.
The input voltage range is 4.5V to 20V. A simplified block
diagram is shown in Figure 1 and the typical application
schematic is shown in Figure 17.
The LTM4600 contains an integrated LTC constant on-time
current-mode regulator, ultra-low RDS(ON) FETs with fast
switching speed and integrated Schottky diode. The typical
switching frequency is 800kHz at full load. With current
mode control and internal feedback loop compensation,
the LTM4600 module has sufficient stability margins and
good transient performance under a wide range of operat-
ing conditions and with a wide range of output capacitors,
even all ceramic output capacitors (X5R or X7R).
Current mode control provides cycle-by-cycle fast current
limit. In addition, foldback current limiting is provided in an
over-current condition while VFB drops. Also, the LTM4600
has defeatable short circuit latch off. Internal overvolt-
age and undervoltage comparators pull the open-drain
PGOOD output low if the output feedback voltage exits a
±10% window around the regulation point. Furthermore,
in an overvoltage condition, internal top FET Q1 is turned
off and bottom FET Q2 is turned on and held on until the
overvoltage condition clears.
Pulling the RUN/SS pin low forces the controller into its
shutdown state, turning off both Q1 and Q2. Releasing the
pin allows an internal 1.2µA current source to charge up
the softstart capacitor. When this voltage reaches 1.5V,
the controller turns on and begins switching.
At low load current the module works in continuous cur-
rent mode by default to achieve minimum output voltage
ripple. It can be programmed to operate in discontinuous
current mode for improved light load efficiency when the
FCB pin is pulled up above 0.8V and no higher than 6V.
The FCB pin has a 4.75k resistor to ground, so a resistor
to VIN can set the voltage on the FCB pin.
When EXTVCC pin is grounded or open, an integrated 5V
linear regulator powers the controller and MOSFET gate
drivers. If a minimum 4.7V external bias supply is ap-
plied on the EXTVCC pin, the internal regulator is turned
off, and an internal switch connects EXTVCC to the gate
driver voltage. This eliminates the linear regulator power
loss with high input voltage, reducing the thermal stress
on the controller. The maximum voltage on EXTVCC pin is
6V. The EXTVCC voltage should never be higher than the
VIN voltage. Also EXTVCC must be sequenced after VIN.
4600fa
8
Share Link: 