MAX8566(2005) Ver la hoja de datos (PDF) - Maxim Integrated
Número de pieza
componentes Descripción
Fabricante
MAX8566 Datasheet PDF : 21 Pages
| |||
High-Efficiency, 10A, PWM
Internal-Switch Step-Down Regulator
Detailed Description
The MAX8566 high-efficiency, voltage-mode switching
regulator is capable of delivering up to 10A of output
current. The MAX8566 provides output voltages from
0.6V to (0.87 x VIN) from 2.3V to 3.6V input supplies,
making it ideal for on-board point-of-load applications.
The output voltage accuracy is better than ±1% over
load, line, and temperature.
The MAX8566 features a wide switching frequency
range, allowing the user to achieve all-ceramic-capaci-
tor designs and faster transient responses. The high
operating frequency minimizes the size of external
components. The MAX8566 also features a wide 2.3V
to 3.6V input voltage range, making it ideal for point-of-
load applications with both 3.3V and 2.5V input volt-
ages. The MAX8566 is available in a small (5mm x
5mm), 32-pin thin QFN package. The SYNCOUT func-
tion allows end users to operate two MAX8566s at the
same switching frequency with 180° out-of-phase oper-
ation to minimize the input ripple current, consequently
reducing the input capacitance requirements. The
REFIN function makes the MAX8566 an ideal candidate
for DDR and tracking power supplies. Using internal
low-RDS(ON) (8mΩ) n-channel MOSFETs for both high-
and low-side switches maintains high efficiency at both
heavy-load and high-switching frequencies. In addition,
the MAX8566 features a low-side-driver supply input
(LSS) to boost the efficiency with a higher driver volt-
age (3.3V) for 2.5V input applications.
The MAX8566 employs the voltage-mode control archi-
tecture with a high bandwith (> 10MHz) error amplifier.
The voltage-mode control architecture allows above
2MHz switching, reducing board area. The op-amp
voltage error amplifier works with Type 3 compensation
to fully utilize the bandwidth of the high-frequency
switching to obtain fast transient response. Adjustable
soft-start time provides flexibilities to minimize input
startup inrush current. An open-drain power-good
(PWRGD) output goes high when VFB reaches 0.54V.
Principle of Operation
The controller logic block is the central processor that
determines the duty cycle of the high-side MOSFET
under different line, load, and temperature conditions.
Under normal operation, where the current limit and
temperature protection are not triggered, the controller
logic block takes the output from the PWM comparator
and generates the driver signals for both high-side and
low-side MOSFETs. The break-before-make logic and
the timing for charging the bootstrap capacitors are
calculated by the controller logic block. The error signal
from the voltage error amplifier is compared with the
ramp signal generated by the oscillator at the PWM
comparator and thus the required PWM signal is pro-
duced. The high-side switch is turned on at the begin-
ning of the oscillator cycle and turns off when the ramp
voltage exceeds the VCOMP signal or the current-limit
threshold is exceeded. The low-side switch is then
turned on for the remainder of the oscillator cycle.
Current Limit
The internal, high-side MOSFET has a typical 15A peak
current-limit threshold. When current flowing out of LX
exceeds this limit, the high-side MOSFET turns off and
the synchronous rectifier turns on. The synchronous
rectifier remains on until the inductor current falls below
the low-side current limit. This lowers the duty cycle
and causes the output voltage to droop until the current
limit is no longer exceeded.
The MAX8566 uses a hiccup mode to prevent over-
heating during short-circuit output conditions. The
device enters hiccup mode when VFB drops below
420mV and the current limit is reached. The IC turns off
for 3.4ms and then enters soft-start. If the short-circuit
condition remains after the soft-start time, the IC shuts
down for another 3.4ms. The IC repeats this behavior
until the short-circuit condition is removed.
Soft-Start and REFIN
The MAX8566 utilizes an adjustable soft-start function
to limit inrush current during startup. An 8µA (typ) cur-
rent source charges an external capacitor connected to
SS to increase the capacitor voltage in a controlled
manner. The soft-start time is adjusted by the value of
the external capacitor from SS to GND. The required
capacitance value is determined as:
C = 8µA × tSS
0.6V
where tSS is the required soft-start time in seconds.
The MAX8566 also features an external reference input
(REFIN). The IC regulates FB to the voltage applied to
REFIN. The internal soft-start is not available when
using an external reference. A method of soft-start
when using an external reference is shown in Figure 2.
Connect REFIN to SS to use the internal 0.6V reference.
______________________________________________________________________________________ 13
Share Link: 