MAX1830 Ver la hoja de datos (PDF) - Maxim Integrated
Número de pieza
componentes Descripción
Fabricante
MAX1830 Datasheet PDF : 13 Pages
| |||
3A, 1MHz, Low-Voltage, Step-Down Regulators with
Synchronous Rectification and Internal Switches
PIN
1, 3, 14, 16
2, 4
5
6
7
8
9
10
11
12
13, 15
NAME
LX
IN
SHDN
COMP
TOFF
FB
GND
REF
FBSEL
VCC
PGND
Pin Description
FUNCTION
Connection for the drains of the PMOS power switch and NMOS synchronous-rectifier switch.
Connect the inductor from this node to the output filter capacitor and load.
Supply Voltage Input for the internal PMOS power switch
Shutdown Control Input. Drive SHDN low to disable the reference, control circuitry, and internal
MOSFETs. Drive high or connect to VCC for normal operation.
Integrator Compensation. Connect a capacitor from COMP to VCC for integrator compensation. See
Integrator Amplifier section.
Off-Time Select Input. Sets the PMOS power switch off-time during constant-off-time operation.
Connect a resistor from TOFF to GND to adjust the PMOS switch off-time.
Feedback Input for both preset-output and adjustable-output operating modes. Connect directly to
output for fixed-voltage operation or to a resistive divider for adjustable operating modes.
Analog Ground
Reference Output. Bypass REF to GND with a 1µF capacitor.
Feedback Select Input. Selects output voltage. See Table 3 for programming instructions.
Analog Supply Voltage Input. Supplies internal analog circuitry. Bypass VCC with a 10Ω and 2.2µF
lowpass filter (Figure 1).
Power Ground. Internally connected to the internal NMOS synchronous-rectifier switch.
_______________Detailed Description
The MAX1830/MAX1831 synchronous, current-mode,
constant-off-time, PWM DC-DC converters step down
input voltages of +3V to +5.5V to preset output voltages,
or to an adjustable output voltage from +1.1V to VIN. The
MAX1830 has preset outputs +2.5V, +1.8V, and +1.5V.
The MAX1831 has preset outputs of +3.3V, +2.5V or
+1.5V. Both devices deliver up to 3A of continuous output
current. Internal switches composed of a 45mΩ PMOS
power switch and a 55mΩ NMOS synchronous rectifier
switch improve efficiency, reduce component count, and
eliminate the need for an external Schottky diode.
The MAX1830/MAX1831 optimize efficiency by operat-
ing in constant-off-time mode under heavy loads and in
Maxim’s proprietary Idle Mode under light loads. A sin-
gle resistor-programmable constant-off-time control
sets switching frequencies up to 1MHz, allowing the
user to optimize performance trade-offs in efficiency,
switching noise, component size, and cost. Under low-
dropout conditions, the device operates in a 100%
duty-cycle mode, where the PMOS switch remains con-
tinuously on. Idle Mode enhances light-load efficiency
by skipping cycles, thus reducing transition and gate-
charge losses.
When power is drawn from a regulated supply, constant-
off-time PWM architecture essentially provides constant-
frequency operation. This architecture has the inherent
advantage of quick response to line and load transients.
The MAX1830/MAX1831 current-mode, constant-off-
time PWM architecture regulates the output voltage by
changing the PMOS switch on-time relative to the con-
stant off-time. Increasing the on-time increases the
peak inductor current and the amount of energy trans-
ferred to the load per pulse.
Modes of Operation
The current through the PMOS switch determines the
mode of operation: constant-off-time mode (for load
currents greater than half the Idle Mode threshold), or
Idle Mode (for load currents less than half the Idle
Mode threshold). Current sense is achieved through a
proprietary architecture that eliminates current-sensing
I2R losses.
Constant-Off-Time Mode
Constant-off-time operation occurs when the current
through the PMOS switch is greater than the Idle Mode
threshold current (which corresponds to a load current
of half the Idle Mode threshold). In this mode, the regu-
6 _______________________________________________________________________________________
Share Link: 