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PDF MAX17498B Data sheet ( Hoja de datos )
| Número de pieza | MAX17498B | |
| Descripción | (MAX17498A/B/C) AC-DC and DC-DC Peak-Current-Mode Converters | |
| Fabricantes | Maxim Integrated Products | |
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EVALUATION KIT AVAILABLE
MAX17498A/MAX17498B/MAX17498C
AC-DC and DC-DC Peak Current-Mode Converters
for Flyback/Boost Applications
General Description
The MAX17498A/MAX17498B/MAX17498C devices are
current-mode fixed-frequency flyback/boost converters
with a minimum number of external components. They
contain all the control circuitry required to design wide
input voltage isolated and nonisolated power supplies.
The MAX17498A has its rising/falling undervoltage lock-
out (UVLO) thresholds optimized for universal offline (85V
AC to 265V AC) applications, while the MAX17498B/
MAX17498C support UVLO thresholds suitable to low-
voltage DC-DC applications.
The switching frequency of the MAX17498A/MAX17498C
is 250kHz, while that of the MAX17498B is 500kHz. These
frequencies allow the use of tiny magnetic and filter com-
ponents, resulting in compact, cost-effective power sup-
plies. An EN/UVLO input allows the user to start the power
supply precisely at the desired input voltage, while also
functioning as an on/off pin. The OVI pin enables imple-
mentation of an input overvoltage-protection scheme that
ensures that the converter shuts down when the DC input
voltage exceeds the desired maximum value.
The devices incorporate a flexible error amplifier and an
accurate reference voltage (REF) to enable the end user to
regulate both positive and negative outputs. Programmable
current limit allows proper sizing and protection of the primary
switching FET. The devices support a maximum duty cycle
greater than 92% and provide programmable slope com-
pensation to allow optimization of control loop performance.
The devices provide an open-drain PGOOD pin that serves
as a power-good indicator and enters the high-impedance
state to indicate that the flyback /boost converter is in regu-
lation. An SS pin allows programmable soft-start time for the
flyback/boost converter. Hiccup-mode overcurrent pro-
tection and thermal shutdown are provided to minimize
dissipation under overcurrent and overtemperature fault
conditions. The devices are available in a space-saving,
16-pin (3mm x 3mm) TQFN package with 0.5mm lead
spacing.
Ordering Information and Typical Application Circuits
appear at end of data sheet.
For related parts and recommended products to use with this part,
refer to www.maximintegrated.com/MAX17498A.related.
Benefits and Features
S Peak Current-Mode Converter
S Current-Mode Control Provides Excellent
Transient Response
S Fixed Switching Frequency
250kHz: MAX17498A/MAX17498C
500kHz: MAX17498B
S Flexible Error Amplifier to Regulate Both Positive
and Negative Outputs
S Programmable Soft-Start to Reduce Input Inrush
Current
S Programmable Voltage or Current Soft-Start
S Power-Good Signal (PGOOD)
S Reduced Power Dissipation Under Fault
Overcurrent Protection
Thermal Shutdown with Hysteresis
S Robust Protection Features
Programmable Current Limit
Input Overvoltage Protection
S Optimized Loop Performance
Programmable Slope Compensation
S High Efficiency
Low RDSON, 175mI, 65V Rated Internal
n-Channel MOSFET
No Current-Sense Resistor
S Optional Spread Spectrum
S Space-Saving, 16-Pin (3mm x 3mm) TQFN
Package
Applications
Front-End AC-DC Power Supplies for Industrial
Applications (Isolated and Nonisolated)
Telecom Power Supplies
Wide Input Range DC Input Flyback /Boost
Industrial Power Supplies
For pricing, delivery, and ordering information, please contact Maxim Direct at
1-888-629-4642, or visit Maxim Integrated’s website at www.maximintegrated.com.
19-6043; Rev 3; 4/13
1 page  
MAX17498A/MAX17498B/MAX17498C
AC-DC and DC-DC Peak Current-Mode Converters
for Flyback/Boost Applications
Typical Operating Characteristics
(VIN = +15V, VEN/UVLO = +2V, COMP = open, CIN = 1µF, CVCC = 1µF, TA = TJ = -40°C to +125°C, unless otherwise noted.)
BOOTSTRAP UVLO WAKE-UP LEVEL
vs. TEMPERATURE (MAX17498A)
20.26
IN UVLO WAKE-UP LEVEL vs. TEMPERATURE
(MAX17498B/MAX17498C)
4.15
20.24
20.22
20.20
20.18
20.16
4.10
4.05
4.00
3.95
20.14
-40 -20
0 20 40 60 80 100 120
TEMPERATURE (°C)
IN UVLO SHUTDOWN LEVEL
vs. TEMPERATURE
4.015
4.010
4.005
4.000
3.995
3.990
3.985
3.980
3.975
-40 -20
0 20 40 60 80 100 120
TEMPERATURE (°C)
EN/UVLO FALLING LEVEL
vs. TEMPERATURE
1.170
3.90
-40 -20
0 20 40 60 80 100 120
TEMPERATURE (°C)
EN/UVLO RISING LEVEL
vs. TEMPERATURE
1.235
1.230
1.225
1.220
1.215
1.210
-40 -20
1.225
0 20 40 60 80 100 120
TEMPERATURE (°C)
OVI RISING LEVEL
vs. TEMPERATURE
1.165
1.160
1.220
1.155
1.150
1.215
1.145
1.140
-40 -20
0 20 40 60 80 100 120
TEMPERATURE (°C)
1.210
-40 -20
0 20 40 60 80 100 120
TEMPERATURE (°C)
Maxim Integrated
5
5 Page 
MAX17498A/MAX17498B/MAX17498C
AC-DC and DC-DC Peak Current-Mode Converters
for Flyback/Boost Applications
Soft-Start
The devices implement soft-start operation for the
flyback /boost converter. A capacitor connected to the
SS pin programs the soft-start period for the flyback/
boost converter. The soft-start feature reduces the input
inrush current. These devices allow the end user to select
between voltage soft-start usually preferred in nonisolat-
ed applications and current soft-start, which is useful in
isolated applications to get a monotonic rise in the output
voltage. See the Programming Soft-Start of the Flyback/
Boost Converter (SS) section.
Spread-Spectrum Factory Option
For EMI-sensitive applications, a spread-spectrum-
enabled version of the device can be requested from
the factory. The frequency-dithering feature modulates
the switching frequency by Q10% at a rate of 4kHz.
This spread-spectrum-modulation technique spreads
the energy of switching-frequency harmonics over a
wider band while reducing their peaks, helping to meet
stringent EMI goals.
Applications Information
Startup Voltage and Input Overvoltage-
Protection Setting (EN/UVLO, OVI)
The devices’ EN /UVLO pin serves as an enable /disable
input, as well as an accurate programmable input UVLO
pin. The devices do not commence startup operation
unless the EN/UVLO pin voltage exceeds 1.23V (typ).
The devices turn off if the EN/UVLO pin voltage falls
below 1.17V (typ). A resistor-divider from the input DC
bus to ground can be used to divide down and apply a
fraction of the input DC voltage (VDC) to the EN/UVLO
pin. The values of the resistor-divider can be selected
so that the EN/UVLO pin voltage exceeds the 1.23V (typ)
turn-on threshold at the desired input DC bus voltage. The
same resistor-divider can be modified with an additional
resistor (ROVI) to implement input overvoltage protection
in addition to the EN/UVLO functionality as shown in
Figure 2. When voltage at the OVI pin exceeds 1.23V (typ),
the devices stop switching and resume switching opera-
tions only if voltage at the OVI pin falls below 1.17V (typ).
For given values of startup DC input voltage (VSTART),
and input overvoltage-protection voltage (VOVI), the
resistor values for the divider can be calculated as fol-
lows, assuming a 24.9kI resistor for ROVI:
REN=
ROVI ×
VSVTOAVRI T
− 1 kΩ
where ROVI is in kI while VSTART and VOVI are in volts.
R SUM=
ROVI
+ REN×
VSTART
1.23
− 1 kΩ
where REN and ROVI are in kI. In universal AC input
applications, RSUM might need to be implemented as
equal resistors in series (RDC1, RDC2, RDC3) so that
voltage across each resistor is limited to its maximum
operation voltage.
R=DC1
R=DC2
R=DC3
R
SUM
3
kΩ
For low-voltage DC-DC applications based on the
MAX17498B/MAX17498C, a single resistor can be used
in the place of RSUM, as the voltage across it is
approximately 40V.
VDC
RDC1
RSUM RDC2
RDC3
EN/UVLO
MAX17498A
REN MAX17498B
MAX17498C
OVI
ROVI
Figure 2. Programming EN/UVLO and OVI
Maxim Integrated
11
11 Page | ||
| Páginas | Total 20 Páginas | |
| PDF Descargar | [ Datasheet MAX17498B.PDF ] | |
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