MAXIM MAX17498A, MAX17498B, MAX17498C User Manual
EVALUATION KIT AVAILABLE
19-6043; Rev 1; 3/12
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 lockout (UVLO) thresholds optimized for universal offline (85V
AC to 265V AC) applications, while the MAX17498B/
MAX17498C support UVLO thresholds suitable to lowvoltage DC-DC applications.
The switching frequency of the MAX17498A/MAX17498C
flyback converters is 250kHz, while that of the MAX17498B
flyback/boost converter is 500kHz. These frequencies
allow the use of tiny magnetic and filter components,
resulting in compact, cost-effective power supplies. 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 implementation
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 MAX17498B supports a maximum duty cycle of 92% and provides programmable
slope compensation to allow optimization of control-loop
performance. The MAX17498A/MAX17498C support a
maximum duty cycle of 49%, and have fixed internal slope
compensation for optimum 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 regulation. An SS pin allows programmable soft-start time for the
flyback/boost converter. Hiccup-mode overcurrent protection 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 appears at end of data sheet.
Typical Application Circuits appears at end of data sheet.
Benefits and Features
S Peak Current-Mode Flyback/Boost 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
Hiccup-Mode Overcurrent Protection
Thermal Shutdown with Hysteresis
S Robust Protection Features
Flyback/Boost Programmable Current Limit
Input Overvoltage Protection
S Optimized Loop Performance
Programmable Slope Compensation for
Flyback /Boost Maximizes Obtainable Phase
Margin
S High Efficiency
175mI, 65V Rated n-Channel MOSFET Offers
Typical Efficiency Greater Than 80%
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 related parts and recommended products to use with this part,
refer to www.maxim-ic.com/MAX17498A.related.
_________________________________________________________________ Maxim Integrated Products 1
For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642,
or visit Maxim’s website at www.maxim-ic.com.
MAX17498A/MAX17498B/MAX17498C
AC-DC and DC-DC Peak Current-Mode Converters
for Flyback/Boost Applications
ABSOLUTE MAXIMUM RATINGS
IN to SGND ............................................................-0.3V to +40V
EN/UVLO to SGND ......................................... -0.3V to IN + 0.3V
OVI to SGND .............................................. -0.3V to VCC + 0.3V
VCC to SGND .......................................................... -0.3V to +6V
SS, LIM, EA-, EA+, COMP, SLOPE,
REF to SGND ........................................ -0.3V to (VCC + 0.3V)
LX to SGND ........................................................... -0.3V to +70V
PGOOD to SGND .................................................... -0.3V to +6V
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute
maximum rating conditions for extended periods may affect device reliability.
ELECTRICAL CHARACTERISTICS
(VIN = +15V, V
values are at TA = +25°C.) (Note 1)
INPUT SUPPLY (VIN)
IN Voltage Range (VIN)
IN Supply Startup Current Under
UVLO
IN Supply Current (IIN)
IN Boostrap UVLO Rising
Threshold
IN Bootstrap UVLO Falling
Threshold
IN Clamp Voltage EN/UVLO = SGND, IIN = 1mA (MAX17498A) (Note 2) 31 33.5 36 V
LINEAR REGULATOR (VCC)
VCC Output Voltage Range 6V < VIN < 29V, 0mA < I
VCC Dropout Voltage VIN = 4.5V, I
VCC Current Limit VCC = 0V, VIN = 6V 50 100 mA
ENABLE (EN/UVLO)
EN/UVLO Threshold
EN/UVLO Input Leakage Current
EN/UVLO
PARAMETER CONDITIONS MIN TYP MAX UNITS
= +2V, COMP = open, CIN = 1µF, C
MAX17498A 4.5 29
MAX17498B/MAX17498C 4.5 36
I
INSTARTUP
Switching, fSW = 250kHz (MAX17498A/MAX17498C) 1.8 3
Switching, fSW = 500kHz (MAX17498B) 2 3.25
MAX17498A 19 20.5 22
MAX17498B/MAX17498C 3.85 4.15 4.4
Rising 1.18 1.23 1.28
Falling 1.11 1.17 1.21
0V < V
, VIN < UVLO or EN/UVLO = SGND 22 36 µA
= 20mA 160 300 mV
VCC
EN/UVLO
< 1.5V, TA = +25NC
VCC
PGND to SGND .................................................... -0.3V to +0.3V
Continuous Power Dissipation (Single-Layer Board)
TQFN (derate 20.8mW/°C above +70°C)..................1700mW
Operating Temperature Range ........................ -40°C to +125°C
Storage Temperature Range ............................ -65°C to +160°C
Junction Temperature (continuous) ................................+150°C
Lead Temperature (soldering, 10s) ................................+300°C
Soldering Temperature (reflow) ......................................+260°C
= 1µF, TA = TJ = -40°C to +125°C, unless otherwise noted. Typical
V
mA
V
3.65 3.95 4.25 V
< 50mA 4.8 5 5.2 V
VCC
V
-100 0 +100 nA
_________________________________________________________________ Maxim Integrated Products 2
MAX17498A/MAX17498B/MAX17498C
AC-DC and DC-DC Peak Current-Mode Converters
for Flyback/Boost Applications
ELECTRICAL CHARACTERISTICS (continued)
(VIN = +15V, V
values are at TA = +25°C.) (Note 1)
OVERVOLTAGE PROTECTION (OVI)
OVI Threshold
OVI Masking Delay 2 µs
OVI Input Leakage Current
SWITCHING FREQUENCY AND MAXIMUM DUTY CYCLE (f
Switching Frequency
Maximum Duty Cycle
Minimum Controllable On Time t
SOFT-START (SS)
SS Set-Point Voltage 1.2 1.22 1.24 V
SS Pullup Current VSS = 400mV 9 10 11 µA
SS Peak Current-Limit-Enable
Threshold
ERROR AMPLIFIER (EA+, EA-, and COMP)
EA+ Input Bias Current
EA- Input Bias Current
Error-Amplifier Open-Loop
Voltage Gain
Error-Amplifier
Transconductance
Error-Amplifier Source Current V
Error-Amplifier Sink Current V
Current-Sense Transresistance 0.45 0.5 0.55
INTERNAL SWITCH
DMOS Switch On-Resistance
(R
DSON
DMOS Peak Current Limit LIM = 100K 1.62 1.9 2.23 A
DMOS Runaway Current Limit LIM = 100K 1.9 2.3 2.6 A
LX Leakage Current
CURRENT LIMIT (LIM)
LIM Reference Current 9 10 11 µA
Peak Switch Current Limit with
LIM Open
Runaway Switch Current Limit
with LIM Open
EN/UVLO
PARAMETER CONDITIONS MIN TYP MAX UNITS
)
= +2V, COMP = open, CIN = 1µF, C
Rising 1.18 1.23 1.28
Falling 1.11 1.17 1.21
0V < V
MAX17498A/MAX17498C 235 250 265
MAX17498B 470 500 530
MAX17498A/MAX17498C 47.5 48.75 50
MAX17498B 90 92 94
ONMIN
V
EA+
V
EA-
V
COMP
COMP
COMP
I
LX
VLX = 65V, TA = +25NC
< 1.5V, TA = +25NC
OVI
= 1.5V, TA = +25NC
= 1.5V, TA = +25NC
= 2V, V
= 2V, EA- < EA+ 80 120 210 µA
= 2V, EA- > EA+ 80 120 210 µA
= 200mA 175 380
= 1V 1.5 1.8 2.1 mS
LIM
= 1µF, TA = TJ = -40°C to +125°C, unless otherwise noted. Typical
VCC
-100 0 +100 nA
SW and DMAX
)
110 ns
1.11 1.17 1.21 V
-100 +100 nA
-100 +100 nA
90 dB
0.1 1 µA
0.39 0.45 0.54 A
0.39 0.5 0.6 A
V
kHz
%
I
mI
_________________________________________________________________ Maxim Integrated Products 3
MAX17498A/MAX17498B/MAX17498C
AC-DC and DC-DC Peak Current-Mode Converters
for Flyback/Boost Applications
ELECTRICAL CHARACTERISTICS (continued)
(VIN = +15V, V
values are at TA = +25°C.) (Note 1)
Number of Peak Current-Limit
Hits Before Hiccup Timeout
Number of Runaway CurrentLimit Hits Before Hiccup Timeout
Overcurrent Hiccup Timeout 32 ms
SLOPE COMPENSATION (SLOPE)
SLOPE Pullup Current 9 10 11 µA
SLOPE-Compensation Resistor
Range
Default SLOPE-Compensation
Ramp
POWER-GOOD SIGNAL (PGOOD)
PGOOD Output-Leakage
Current (Off State)
PGOOD Output Voltage
(On State)
PGOOD Higher Threshold EA- rising 93.5 95 96.5 %
PGOOD Lower Threshold EA- falling 90.5 92 93.5 %
PGOOD Delay After
EA- Reaches 95% Regulation
THERMAL SHUTDOWN
Thermal-Shutdown Threshold Temperature rising +160
Thermal-Shutdown Hysteresis 20
Note 1: All devices are 100% production tested at TA = +25NC. Limits over temperature are guaranteed by design.
Note 2: The MAX17498A is intended for use in universal input power supplies. The internal clamp circuit at IN is used to prevent the
EN/UVLO
PARAMETER CONDITIONS MIN TYP MAX UNITS
bootstrap capacitor from changing to a voltage beyond the absolute maximum rating of the device when EN/UVLO is low
(shutdown mode). Externally limit the maximum current to IN (hence to clamp) to 2mA (max) when EN/UVLO is low.
= +2V, COMP = open, CIN = 1µF, C
MAX17498B 30 150
SLOPE = open 60 mV/µs
V
PGOOD
I
PGOOD
= 5V, TA = +25NC
= 10mA 0 0.4 V
= 1µF, TA = TJ = -40°C to +125°C, unless otherwise noted. Typical
VCC
8 #
1 #
-1 +1 µA
4 ms
kI
NC
NC
_________________________________________________________________ Maxim Integrated Products 4
MAX17498A/MAX17498B/MAX17498C
AC-DC and DC-DC Peak Current-Mode Converters
for Flyback/Boost Applications
Typical Operating Characteristics
(VIN = +15V, V
EN/UVLO
= +2V, COMP = open, CIN = 1µF, C
BOOTSTRAP UVLO WAKE-UP LEVEL
vs. TEMPERATURE (MAX17498A)
20.26
20.24
20.22
20.20
20.18
20.16
BOOTSTRAP UVLO WAKE-UP LEVEL (V)
20.14
-40
TEMPERATURE (°C)
IN UVLO SHUTDOWN LEVEL
vs. TEMPERATURE
4.015
4.010
4.005
4.000
3.995
3.990
3.985
IN UVLO SHUTDOWN LEVEL (V)
3.980
3.975
-40
TEMPERATURE (°C)
EN/ UVLO FALLING LEVEL
vs. TEMPERATURE
1.170
120100806040200-20
120100-20 0206040 80
MAX17498 toc01
MAX17498 toc03
= 1µF, TA = TJ = -40°C to +125°C, unless otherwise noted.)
VCC
IN UVLO WAKE-UP LEVEL vs. TEMPERATURE
(MAX17498B/MAX17498C)
4.15
4.10
4.05
4.00
IN UVLO WAKE-UP LEVEL (V)
3.95
3.90
TEMPERATURE (°C)
EN/UVLO RISING LEVEL
vs. TEMPERATURE
1.235
1.230
1.225
1.220
EN/UVLO RISING LEVEL (V)
1.215
1.210
TEMPERATURE (°C)
OVI RISING LEVEL
vs. TEMPERATURE
1.225
MAX17498 toc02
120100806040200-20-40
MAX17498 toc04
120100806040200-20-40
1.165
1.160
1.155
1.150
EN/UVLO FALLING LEVEL (V)
1.145
1.140
-40
TEMPERATURE (°C)
120100806040200-20
MAX17498 toc05
1.220
1.215
OVI RISING LEVEL (V)
1.210
-40
120100806040200-20
TEMPERATURE (°C)
_________________________________________________________________ Maxim Integrated Products 5
MAX17498 toc06
MAX17498A/MAX17498B/MAX17498C
AC-DC and DC-DC Peak Current-Mode Converters
for Flyback/Boost Applications
Typical Operating Characteristics (continued)
(VIN = +15V, V
EN/UVLO
1.160
1.155
1.150
1.145
OVI FALLING LEVEL (V)
1.140
1.135
= +2V, COMP = open, CIN = 1µF, C
IN CURRENT DURING SWITCHING
2.6
2.4
2.2
2.0
OVI FALLING LEVEL
vs. TEMPERATURE
TEMPERATURE (°C)
vs. TEMPERATURE
120100806040200-20-40
MAX17498 toc07
MAX17498 toc09
= 1µF, TA = TJ = -40°C to +125°C, unless otherwise noted.)
VCC
IN CURRENT UNDER UVLO
vs. TEMPERATURE
30
28
26
24
IN CURRENT UNDER UVLO (µA)
22
20
TEMPERATURE (°C)
LX AND PRIMARY CURRENT WAVEFORM
MAX17498 toc10
120100806040200-20-40
MAX17498 toc08
V
LX
20V/div
1.8
1.6
IN CURRENT DURING SWITCHING (mA)
1.4
-40
TEMPERATURE (°C)
EN STARTUP WAVEFORM
400µs/div
MAX17498 toc11
120100806040200-20
EN/UVLO
5V/div
V
OUT
5V/div
V
COMP
1V/div
1µs/div
EN SHUTDOWN WAVEFORM
400µs/div
MAX17498 toc12
_________________________________________________________________ Maxim Integrated Products 6
I
PRI
0.5A/div
EN/UVLO
5V/div
V
OUT
5V/div
V
COMP
1V/div
MAX17498A/MAX17498B/MAX17498C
08
AC-DC and DC-DC Peak Current-Mode Converters
for Flyback/Boost Applications
Typical Operating Characteristics (continued)
(VIN = +15V, V
EN/UVLO
= +2V, COMP = open, CIN = 1µF, C
PEAK CURRENT LIMIT (I
AT ROOM TEMPERATURE
vs. R
1800
1600
1400
1200
1000
800
600
PEAK CURRENT LIMIT (mA)
400
200
0
LIM
R
AT ROOM TEMPERATURE (kI)
LIM
TRANSIENT RESPONSE FOR 50%
LOAD STEP ON FLYBACK OUTPUT (5V)
)
LIM
706040 5020 3010
MAX17498 toc15
MAX17498 toc13
0
I
LOAD
500mA/div
= 1µF, TA = TJ = -40°C to +125°C, unless otherwise noted.)
VCC
PEAK CURRENT LIMIT AT R
= 100kI
LIM
vs. TEMPERATURE
2.00
1.99
(A)
LIM
1.98
1.97
1.96
PEAK CURRENT LIMIT AT R
1.95
1.94
-40
TEMPERATURE AT GIVEN R
SHORT-CIRCUIT PROTECTION
LIM
(°C)
MAX17498 toc16
120100806040200-20
MAX17498 toc14
V
LX
50V/div
V
OUT
500mV/div
I
PRI
2A/div
2ms/div
V
OUT
200mV/div
10ms/div
EFFICIENCY GRAPH AT 24V INPUT
BODE PLOT - (5V OUTPUT AT 24V INPUT)
BW = 8.3kHz
PM = 63°
LOG (F)
MAX17498 toc17
PHASE
36°/div
GAIN
10dB/div
100
90
80
70
60
50
40
EFFICIENCY (%)
30
20
10
0
(FLYBACK REGULATOR)
VIN = 24V
LOAD CURRENT (A)
MAX17498 toc18
1.41.20.8 1.00.4 0.60.20
_________________________________________________________________ Maxim Integrated Products 7
MAX17498A/MAX17498B/MAX17498C
AC-DC and DC-DC Peak Current-Mode Converters
for Flyback/Boost Applications
Pin Configuration
TOP VIEW
PGOOD
PGND
13
14
LX
15
16
IN
+
REF
N.C.
12 11 9
12
EN/UVLO
10
MAX17498A
MAX17498B
MAX17498C
EP (SGND)
3
CC
V
TQFN-EP
OVI N.C.
EA+
SS
8
7
COMP
EA-
6
SLOPE
5
4
LIM
Pin Description
PIN NAME FUNCTION
1 EN/UVLO
2 V
CC
3 OVI
4 LIM
5 SLOPE
6 EA-
7 COMP
8 SS Soft-Start Pin. Connect a capacitor from SS to SGND to set the soft-start time interval.
9 EA+ Noninverting Input of the Flexible Error Amplifier. Connect to SS to use 1.22V as the reference.
10, 12 N.C. No Connection
11 REF Internal 1.22V Reference Output Pin. Connect a 100pF capacitor from REF to SGND.
Enable/Undervoltage-Lockout Pin. Drive to > 1.23V to start the devices. To externally program the UVLO
threshold of the input supply, connect a resistor-divider between input supply EN/UVLO and SGND.
Linear Regulator Output. Connect input bypass capacitor of at least 1µF from VCC to SGND as close as
possible to the IC.
Overvoltage Comparator Input. Connect a resistor-divider between the input supply (OVI) and SGND to
set the input overvoltage threshold.
Current-Limit Setting Pin. Connect a resistor between LIM and SGND to set the peak-current limit for
nonisolated flyback converter. Peak-current limit defaults to 500mA if unconnected.
Slope Compensation Input Pin. Connect a resistor between SLOPE and SGND to set slopecompensation ramp. Connect to VCC for minimum slope compensation. See the Programming Slope
Compensation (SLOPE) section.
Inverting Input of the Flexible Error Amplifier. Connect to mid-point of resistor-divider from the positive
terminal output to SGND.
Flexible Error-Amplifier Output. Connect the frequency-compensation network between COMP and
SGND.
_________________________________________________________________ Maxim Integrated Products 8
MAX17498A/MAX17498B/MAX17498C
AC-DC and DC-DC Peak Current-Mode Converters
for Flyback/Boost Applications
Pin Description (continued)
PIN NAME FUNCTION
13 PGOOD
14 PGND Power Ground for Converter
15 LX External Transformer/Inductor Connection for the Converter
16 IN
—
EP
(SGND)
Open-Drain Output. PGOOD goes high when EA- is within 5% of the set point. PGOOD pulls low when
EA- falls below 92% of its set-point value.
Internal Linear Regulator Input. Connect IN to the input-voltage source. Bypass IN to PGND with a 1µF
(min) ceramic capacitor.
Exposed Pad. Internally connected to SGND. Connect EP to a large copper plane at SGND potential to
provide adequate thermal dissipation. Connect EP (SGND) to PGND at a single point.
Detailed Description
The MAX17498A offers a bootstrap UVLO wakeup level
of 20V with a wide hysteresis of 15V (min) optimized
for implementing an isolated and nonisolated universal
(85V AC to 265V AC) offline single-switch flyback
converter or telecom (36V to 72V) power supplies. The
MAX17498B/MAX17498C offer a UVLO wakeup level of
4.4V and are well suited for low-voltage DC-DC flyback/
boost power supplies. An internal reference (1.22V)
can be used to regulate the output down to 1.23V in
nonisolated flyback and boost applications. Additional
semi-regulated outputs, if needed, can be generated
by using additional secondary windings on the flyback
converter transformer. A flexible error amplifier and REF
allow the end-user selection between regulating positive
and negative outputs.
The devices utilize peak current-mode control and external compensation for optimizing the loop performance for
various inductors and capacitors. The devices include a
cycle-by-cycle peak current limit and eight consecutive
occurrences of current-limit event trigger hiccup mode,
that protect external components by halting switching for
a period of time (32ms). The devices also include voltage
soft-start for nonisolated designs and current soft-start
for isolated designs to allow monotonic rise of the output
voltage. The voltage or current soft-start can be selected
using the SLOPE pin. See the Block Diagram for more
information.
Input Voltage Range
The MAX17498A has different rising and falling UVLO
thresholds on the IN pin than those of the MAX17498B/
MAX17498C. The thresholds for the MAX17498A are
optimized for implementing power-supply startup
schemes typically used for offline AC-DC power supplies.
The MAX17498A is therefore well suited for operation from the rectified DC bus in AC-DC power-supply
applications typically encountered in front-end industrial
power-supply applications. As such, the MAX17498A
has no limitation on the maximum input voltage as long
as the external components are rated suitably and the
maximum operating voltages of the MAX17498A are
respected. The MAX17498A can successfully be used
in universal input-rectified (85V to 265V AC) bus applications, rectified 3-phase DC bus applications, and telecom (36V to 72V DC) applications.
The MAX17498B/MAX17498C are intended for implementing a flyback (isolated and nonisolated) and
boost converter with an on-board 65V rated n-channel
MOSFET. The IN pin of the MAX17498B/MAX17498C has
a maximum operating voltage of 36V. The MAX17498B/
MAX17498C implement rising and falling thresholds on
the IN pin that assume power-supply startup schemes,
typical of lower voltage DC-DC applications, down to an
input voltage of 4.5V DC. Therefore, flyback converters
with a 4.5V to 36V supply voltage range can be implemented with the MAX17498B/MAX17498C.
Internal Linear Regulator (VCC)
The internal functions and driver circuits are designed
to operate from a 5V Q5% power-supply voltage. The
devices have an internal linear regulator that is powered
from the IN pin and generates a 5V power rail. The output
of the linear regulator is connected to the VCC pin and
should be decoupled with a 2.2µF capacitor to ground
for stable operation. The VCC converter output supplies
the operating current for the devices. The maximum
operating voltage of the IN pin is 29V for the MAX17498A
and 36V for the MAX17498B/MAX17498C.
_________________________________________________________________ Maxim Integrated Products 9
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