|
|
PDF MAX747 Data sheet ( Hoja de datos )
| Número de pieza | MAX747 | |
| Descripción | High-Efficiency PWM / Step-Down P-Channel DC-DC Controller | |
| Fabricantes | Maxim Integrated | |
| Logotipo |  |
|
Hay una vista previa y un enlace de descarga de MAX747 (archivo pdf) en la parte inferior de esta página. Total 12 Páginas | ||
|
No Preview Available !
19-0171; Rev 1; 9/93
High-Efficiency PWM, Step-Down
P-Channel DC-DC Controller
_______________General Description
The MAX747 high-efficiency, high-current, step-down
controller drives external P-channel FETs. It provides
90% to 95% efficiency from a 6V supply with load
currents ranging from 50mA up to 2.5A. It uses a
pulse-width-modulating (PWM) current-mode control
scheme to provide precise output regulation and low
output noise. The MAX747’s 4V to 15V input voltage
range, a fixed 5V/adjustable (Dual-Mode™) output, and
a current limit set with an external resistor make this
device ideal for a wide range of applications.
High efficiency is maintained with light loads due to a
proprietary dual-control (Idle-Mode™) scheme that
minimizes switching losses by reducing the switching
frequency at light loads. The low 800µA quiescent
current and ultra-low 0.6µA shutdown current further
extend battery life.
External components are protected by the MAX747’s
cycle-by-cycle current limit. The MAX747 also features a
2V ±1.5% reference, a comparator for low-battery
detection or level translating, as well as soft-start and
shutdown capability.
The MAX746, discussed in a separate data sheet,
functions similarly to the MAX747, but it drives N-channel
logic level FETs on the high side.
________________________Applications
Notebook Power Supplies
Personal Digital Assistants
Battery-Operated Equipment
Cellular Phones
5V to 3.3V Green PC Applications
__________________Pin Configuration
TOP VIEW
LBI 1
SS 2
REF 3
SHDN 4
FB 5
CC 6
AV+ 7
MAX747
14 LBO
13 GND
12 V+
11 EXT
10 AGND
9 CS
8 OUT
____________________________Features
o 90% to 95% Efficiency for 50mA to 2.5A
Output Currents
o 4V to 15V Input Voltage Range
o Low 800µA Supply Current
o 0.6µA Shutdown Current
o Drives External P-Channel FETs
o Cycle-by-Cycle Current Limiting
o 2V ±1.5% Accurate Reference Output
o Adjustable Soft-Start
o Precision Comparator for Power-Fail or
Low-Battery Warning
______________Ordering Information
PART
TEMP. RANGE
MAX747CPD
0°C to +70°C
MAX747CSD
0°C to +70°C
MAX747C/D
0°C to +70°C
MAX747EPD
-40°C to +85°C
MAX747ESD
-40°C to +85°C
MAX747MJD
-55°C to +125°C
* Contact factory for dice specifications.
PIN-PACKAGE
14 Plastic DIP
14 Narrow SO
Dice*
14 Plastic DIP
14 Narrow SO
14 CERIDIP
__________Typical Operating Circuit
INPUT
6V TO 15V
100µF
V+ AV+
MAX747
ON/OFF
SHDN
CS
EXT
5OmΩ
P 5OµH
OUTPUT
5V
2.3A
LOW-BATTERY
DETECTOR
INPUT
OUT
LBI
REF LBO
SS CC FB AGND GND
0.1µF
LOW-BATTERY
DETECTOR
OUTPUT
430µF
DIP/SO
™ Dual-Mode and Idle-Mode are trademarks of Maxim Integrated Products.
________________________________________________________________ Maxim Integrated Products 1
Call toll free 1-800-998-8800 for free samples or literature.
1 page  
High-Efficiency PWM, Step-Down
P-Channel DC-DC Controller
______________________________________________________________Pin Description
PIN NAME
FUNCTION
1 LBI Input to the internal low-battery comparator. Tie to V+ or GND if not used.
2
SS
Soft-start limits start-up surge currents. On power-up, it charges the soft-start capacitor, slowly raising the
peak current limit to the level set by the sense resistor.
3
REF
2V reference output that can source 100µA for external loads. Bypass with 0.22µF. The reference is
disabled in shutdown mode.
4
SHDN
Active-high TTL/CMOS logic-level input. In shutdown mode, VOUT = 0V and the supply current is reduced
to 20µA.
5
FB
Feedback input for adjustable-output operation. Connect to GND for fixed +5V output. Use a resistor
divider network to adjust the output voltage. See the section Setting the Output Voltage.
6
CC
Compensation capacitor. AC compensation input for the error amplifier. Connect a capacitor between CC
and GND for fixed +5V output operation. See Compensation Capacitor section.
7
AV+
Quiet supply voltage for sensitive analog circuitry. A bypass capacitor is not required for AV+.
8
OUT
Output voltage sense input. Connects to internal resistor divider. Leave unconnected for adjustable output.
Bypass to AGND with a 0.1µF capacitor close to the IC.
9 CS Negative input to the current-sense amplifier. Connect the current-sense resistor (RSENSE) from V+ to CS.
10 AGND Quiet analog ground
11
EXT
Power MOSFET gate drive output that swings between V+ and GND. EXT is not protected against short
circuits to V+ or AGND.
12 V+ High-current supply voltage for the output driver
13 GND High-current ground return for the output driver
14
LBO
Low-battery output is an open-drain output that goes low when LBI is less than 2V. Connect to V+ through
a pull-up resistor. Leave floating if not used. LBO is disabled in shutdown mode.
____________________Getting Starting
Figure 1a shows the 5V output 11.4W standard
application circuit and Figure 1b shows the 3.3V output
7.5W standard application circuit. Most applications
will be served by these circuits. To learn more about
component selection for particular applications, refer to
the Design Procedure section. To learn more about the
operation of the MAX747, refer to the Detailed
Description.
_______________Detailed Description
The MAX747 monolithic, CMOS, step-down switch-
mode power-supply controller drives external
P-channel FETs. It uses a unique current-mode pulse-
width-modulating (PWM) control scheme that results in
high efficiency over a wide range of load currents, tight
output voltage regulation, excellent load- and line-
transient response, and low noise. Efficiency at light
loads is further enhanced by a proprietary Idle-Mode
switching control scheme that skips oscillator cycles in
order to reduce switching losses.
_______________________________________________________________________________________ 5
5 Page 
High-Efficiency PWM, Step-Down
P-Channel DC-DC Controller
Setting the Low-Battery Detector Voltage
Select R1 between 10kΩ and 1MΩ.
R2
=
R1
(VTRIP − VREF
VREF
)
Connect a pull-up resistor (e.g., 100kΩ) between LBO
and VOUT (Figure 4).
__________Applications Information
Layout Considerations
Due to high current levels and fast switching
waveforms, which radiate noise, proper MAX747 PC
board layout is essential. Protect sensitive analog
grounds by using a star ground configuration. Use an
adequate ground plane and minimize ground noise by
connecting GND, the anode of the steering Schottky
diode, the input bypass capacitor ground lead, and the
output filter capacitor ground lead to a single point
(star ground configuration). Also, minimize lead lengths
to minimize stray capacitance, trace resistance, and
radiated noise. Place bypass capacitor C3 as close as
possible to V+ and GND.
AV+ and CS are the inputs to the differential-input
current-sense amplifier. Use a Kelvin connection
across the sense resistor as shown in Figure 6. Note
that even though AV+ also functions as the supply
voltage for sensitive analog circuitry, a separate AV+
bypass capacitor should not be used. By not using a
capacitor, any noise appearing at the CS input will also
appear at the AV+ input and will appear as a common-
mode signal to the current-sense amplifier. A separate
AV+ capacitor causes the noise to appear only on one
input, and this differential noise will be amplified,
adversely affecting circuit operation.
Similarly, CC (or FB in adjustable-output operation) is a
sensitive input that should not be shorted to any node.
Avoid shorting CC when probing the circuit, as this
may damage the device.
Switching Waveforms
A region exists between CCM and DCM where the
inductor current operates in both modes, as shown in
the Idle-Mode Moderate current EXT waveform in the
Typical Operating Characteristics. As the output
voltage varies, it is fed back into CC and the duty cycle
is adjusted to compensate for this change. The switch
is considered off when VEXT ≤ the P-FET’s VGS
threshold voltage. Once the switch is off, the voltage at
EXT is pulled to V+ and the P-FET drain voltage is a
Schottky diode drop below GND. However, in this “in-
VIN
V+ AV+
RSENSE
MAX747
CS
KELVIN SENSE
CONNECTION
EXT P
L1 VOUT
Figure 6. Kelvin Connection for Current-Sense Amplifier
between” mode (due to the changing duty cycle
inherent with DCM), when the device is at maximum
duty cycle, EXT turns off at V+ - VGS. But it is not
always pulled to V+ because the switch sometimes
turns on again after a minimum off-time before EXT can
be pulled to V+. The result is short spikes that appear
on the EXT waveform in the Typical Operating
Characteristics.
AC Stability with Low
Input/Output Differentials
At low input/output differentials, the inductor current
cannot slew quickly to respond to load changes, so the
output filter capacitor must hold up the voltage as the
load transient is applied. In Figure 1a’s circuit, for
V+ = 6.5V, increase the output filter capacitor to 700µF
(Sprague 595D low-ESR capacitors) to obtain a
transient response less than 250mV with a load step
from 200mA to 2.5A. For V+ = 6V and VOUT = 5V,
increase the output filter capacitor to approximately
1000µF. As V+ increases, the device will no longer be
operating near full duty cycle with light loads, allowing
it to adjust to full duty cycle when the load transient is
applied and, in turn, allowing smaller output filter
capacitors to be used.
Dual-Mode Operation
The MAX747 is designed in either fixed-output mode
(5V-output, FB = GND) or in adjustable mode (FB = 2V)
using a resistor divider. It is not designed to be
switched from one mode to another when powered up;
however, in adjustment mode, switching between two
different resistor dividers is acceptable.
______________________________________________________________________________________ 11
11 Page | ||
| Páginas | Total 12 Páginas | |
| PDF Descargar | [ Datasheet MAX747.PDF ] | |
Hoja de datos destacado
| Número de pieza | Descripción | Fabricantes |
| MAX7400 | 8th-Order / Lowpass / Elliptic / Switched-Capacitor Filters | Maxim Integrated |
| MAX7401 | 8th-Order / Lowpass / Bessel / Switched-Capacitor Filters | Maxim Integrated |
| MAX7403 | 8th-Order / Lowpass / Elliptic / Switched-Capacitor Filters | Maxim Integrated |
| MAX7404 | 8th-Order / Lowpass / Elliptic / Switched-Capacitor Filters | Maxim Integrated |
| Número de pieza | Descripción | Fabricantes |
| SLA6805M | High Voltage 3 phase Motor Driver IC. |
 Sanken |
| SDC1742 | 12- and 14-Bit Hybrid Synchro / Resolver-to-Digital Converters. |
 Analog Devices |
|
DataSheet.es es una pagina web que funciona como un repositorio de manuales o hoja de datos de muchos de los productos más populares, |
| DataSheet.es | 2020 | Privacy Policy | Contacto | Buscar |