General Description
The MAX17499/MAX17500 current-mode PWM con-
trollers contain all the control circuitry required for the
design of wide-input-voltage isolated and nonisolated
power supplies. The MAX17499 is well suited for low
input voltage (9.5V DC to 24V DC) power supplies. The
MAX17500 is well suited for universal input (rectified
85V AC to 265V AC) or telecom (-36V DC to -72V DC)
power supplies.
The ICs contain an internal error amplifier that regulates
the tertiary winding output voltage that is used in prima-
ry-side-regulated isolated power supplies. Primary-side
regulation eliminates the need for an optocoupler. An
input undervoltage lockout (UVLO) is provided for pro-
gramming the input-supply start voltage and to ensure
proper operation during brownout conditions. An open-
drain UVLO flag output, with 210μs internal delay,
allows the sequencing of a secondary-side controller.
The input-supply start voltage is externally programma-
ble with a voltage-divider. A UVLO/EN input is used to
shut down the devices. Internal digital soft-start elimi-
nates output voltage overshoot.
The MAX17500 has an internal bootstrap UVLO with
large hysteresis that requires a minimum 23.6V for start-
up. The MAX17499 does not have the internal bootstrap
UVLO and can be biased directly from a minimum volt-
age of 9.5V.
The switching frequency for the ICs is programmable
with an external resistor. The MAX17499A/MAX17500A
provide a 50% maximum duty-cycle limit, while the
MAX17499B/MAX17500B provide a 75% maximum
duty-cycle limit. These devices are available in 10-pin
μMAX®packages and are rated for operation over the
-40°C to +125°C temperature range.
Features
oCurrent-Mode Control
oProgrammable Switching Frequency Up to 625kHz
oAccurate UVLO Threshold (1%)
oOpen-Drain UVLO Flag Output with Internal Delay
o36V to 72V Telecom Voltage Range
oUniversal Offline Input Voltage Range
Rectified 85V AC to 265V AC (MAX17500)
o9.5V to 24V Input (MAX17499)
oDigital Soft-Start
oInternal Bootstrap UVLO with Large Hysteresis
(MAX17500)
oInternal Error Amplifier with 1.5% Accurate
Reference
o50µA (typ) Startup Supply Current
o50% Maximum Duty-Cycle Limit
(MAX17499A/MAX17500A)
o75% Maximum Duty-Cycle Limit
(MAX17499B/MAX17500B)
o60ns Cycle-by-Cycle Current-Limit Propagation
Delay
oAvailable in Tiny 10-Pin µMAX Packages
Applications
1/2, 1/4, and 1/8 Brick Power Modules
High-Efficiency, Isolated Telecom Power
Supplies
Networking/Servers
Isolated Keep-Alive Power Supplies
12V Boost and SEPIC Regulators
Isolated and Nonisolated High-Brightness LED
Power Supplies
Industrial Power Conversion
MAX17499/MAX17500
Current-Mode PWM Controllers with
Programmable Switching Frequency
________________________________________________________________
Maxim Integrated Products
1
Ordering Information
19-5485; Rev 1; 7/11
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.
Warning: The ICs are designed to work with high voltages. Exercise caution.
+
Denotes a lead(Pb)-free/RoHS-compliant package.
EVALUATION KIT
AVAILABLE
Selector Guide appears at end of data sheet.
PART DMAX (%) STARTUP VOLTAGE (V) TEMP RANGE PIN-PACKAGE
MAX17499AAUB+ 50 9.5 -40°C to +125°C 10 μMAX
MAX17499BAUB+ 75 9.5 -40°C to +125°C 10 μMAX
MAX17500AAUB+ 50 22 -40°C to +125°C 10 μMAX
MAX17500BAUB+ 75 22 -40°C to +125°C 10 μMAX
μMAX is a registered trademark of Maxim Integrated Products, Inc.
MAX17499/MAX17500
Current-Mode PWM Controllers with
Programmable Switching Frequency
2 _______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS
(VIN = +12V (for MAX17500, bring VIN up to 23.6V for startup), 10nF bypass capacitors at IN and VCC, R12 = 15kΩ(MAX17499A/
MAX17500A), R12 = 7.5kΩ(MAX17499B/MAX17500B), R15 = 1kΩ, C6 = 100nF (see the
Typical Application Circuit
), NDRV = open,
VUVLO/EN = +1.4V, VFB = +1.0V, COMP = open, VCS = 0V, TA= -40°C to +125°C, unless otherwise noted. Typical values are at TA=
+25°C.) (Note 1)
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.
IN to GND ...............................................................-0.3V to +30V
IN Clamp (internal shunt) Current .........................................5mA
VCC to GND............................................................-0.3V to +13V
FB, COMP, UVLO/EN, RT, CS to GND .....................-0.3V to +6V
UFLG to GND .........................................................-0.3V to +30V
NDRV to GND.............................................-0.3V to (VCC + 0.3V)
Continuous Power Dissipation (TA= +70°C)
10-Pin μMAX (derate 5.6mW/°C above +70°C) ........444.4mW
Operating Temperature Range .........................-40°C to +125°C
Storage Temperature Range ............................-65°C to +150°C
Junction Temperature......................................................+150°C
Lead Temperature (soldering, 10s) .................................+300°C
Soldering Temperature (reflow) .......................................+260°C
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
UVLO/STARTUP
Bootstrap UVLO Wake-Up Level VSUVR VIN rising (MAX17500 only) 19.68 21.6 23.60 V
Bootstrap UVLO Shutdown Level VSUVF VIN falling (MAX17500 only) 9.05 9.74 10.43 V
UVLO/EN Wake-Up Threshold VULR2 UVLO/EN rising 1.215 1.23 1.245 V
UVLO/EN Shutdown Threshold VULF2 UVLO/EN falling 1.14 1.17 1.20 V
UVLO/EN Input Current IUVLO VUVLO/EN ≤ 2V -50 +50 nA
UVLO/EN Hysteresis 60 mV
IN Supply Current In UVLO ISTART VIN = 19V, MAX17500 only when in
bootstrap UVLO 50 90 μA
IN Input Voltage Range VIN MAX17499 only 9.5 24.0 V
UVLO/EN steps up from 1V to 1.4V 3
UVLO/EN to UFLG Propagation
Delay (Figure 3) UVLO/EN steps down from 1.4V to 1V 0.6 μs
tEXTR UVLO/EN steps up from 1V to 1.4V 3 10 ms
UVLO/EN to NDRV Propagation
Delay (Figure 3) tEXTF UVLO/EN steps down from 1.4V to 1V 150 210 300 μs
tBUVR VIN steps up from 9V to 24V (MAX17500
only) 5
Bootstrap UVLO Propagation
Delay tBUVF VIN steps down from 24V to 9V
(MAX17500 only) 1
μs
UFLG Low Output Voltage VUFLG IUFLG = 5mA sinking 1.5 V
UFLG High Output Leakage
Current VUFLG = 25V 0.1 1 μA
INTERNAL SUPPLY
VCC Regulator Set Point VCCSP VIN = 10.8V to 24V, sinking 1μA to 20mA
from VCC 7.0 10.5 V
IN Supply Current After Startup IIN VIN = 24V 2 4 mA
Shutdown Supply Current UVLO/EN = low 50 90 μA
MAX17499/MAX17500
Current-Mode PWM Controllers with
Programmable Switching Frequency
_______________________________________________________________________________________ 3
ELECTRICAL CHARACTERISTICS (continued)
(VIN = +12V (for MAX17500, bring VIN up to 23.6V for startup), 10nF bypass capacitors at IN and VCC, R12 = 15kΩ(MAX17499A/
MAX17500A), R12 = 7.5kΩ(MAX17499B/MAX17500B), R15 = 1kΩ, C6 = 100nF (see the
Typical Application Circuit
), NDRV = open,
VUVLO/EN = +1.4V, VFB = +1.0V, COMP = open, VCS = 0V, TA= -40°C to +125°C, unless otherwise noted. Typical values are at TA=
+25°C.) (Note 1)
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
GATE DRIVER
RON
(
LOW
)
Measured at NDRV sinking 100mA 2 4
Driver Output Impedance RON
(
HIGH
)
Measured at NDRV sourcing 20mA 4 10
Ω
Driver Peak Sink Current 1A
Driver Peak Source Current 0.65 A
PWM COMPARATOR
Comparator Offset Voltage VPWM VCOMP - VCS 1.24 1.38 1.54 V
CS Input Bias Current ICS VCS = 0V -4 +4 μA
Comparator Propagation Delay tPWM Change in VCS = 0.1V 60 ns
CURRENT-LIMIT COMPARATOR
Current-Limit Trip Threshold VCS 900 1000 1100 mV
CS Input Bias Current ICS VCS = 0V -4 +4 μA
Propagation Delay from
Comparator Input to NDRV tPDCS 100mV overdrive 60 ns
IN CLAMP VOLTAGE
IN Clamp Voltage VINC 2mA sink current (Note 2) 24.1 26.1 29.0 V
ERROR AMPLIFIER
Voltage Gain RLOAD = 100kΩ80 dB
Unity-Gain Bandwidth RLOAD = 100kΩ, CLOAD = 200pF 2 MHz
Phase Margin RLOAD = 100kΩ, CLOAD = 200pF 65 D eg r ees
FB Input Offset Voltage ±1 mV
COMP High Voltage ICOMP = 0A 2.5 V
COMP Low Voltage ICOMP = 0A 1.1 V
Source Current 0.5 mA
Sink Current 0.5 mA
Reference Voltage VREF (Note 3) 1.230 V
Reference Voltage Accuracy -1.5 +1.5 %
FB Input Bias Current -50 +50 nA
COMP Short-Circuit Current 8mA
DIGITAL SOFT-START
1984 NDRV
cycles
Soft-Start Duration tSS
fSW = 350kHz 5.6 ms
Reference Voltage Steps During
Soft-Start 31 Steps
Reference Voltage Step 39.67 mV
MAX17499/MAX17500
Current-Mode PWM Controllers with
Programmable Switching Frequency
4 _______________________________________________________________________________________
Note 1: All devices are 100% tested at TA= +125°C. All limits over temperature are guaranteed by characterization.
Note 2: The MAX17500 is intended for use in universal input power supplies. The internal clamp circuit at IN is used to prevent the
bootstrap capacitor (C1 in Figure 1) from charging to a voltage beyond the absolute maximum rating of the device when
UVLO/EN is low (shutdown mode). Externally limit the maximum current to IN (hence to clamp) to 2mA maximum when
UVLO/EN is low. Clamp currents higher than 2mA may result in a clamp voltage higher than 30V, thus exceeding the
absolute maximum rating for IN. For the MAX17499, do not exceed the 24V maximum operating voltage of the device.
Note 3: VREF is measured with FB connected to COMP (see the
Functional Diagram
).
Note 4: The oscillator in the MAX17499A/MAX17500A is capable of operating up to 2500kHz. However, the NDRV switching fre-
quency is limited to operate up to 625kHz. Thus, the oscillator frequency for the MAX17499A/MAX17500A must be limited to
1250kHz (maximum).
ELECTRICAL CHARACTERISTICS (continued)
(VIN = +12V (for MAX17500, bring VIN up to 23.6V for startup), 10nF bypass capacitors at IN and VCC, R12 = 15kΩ(MAX17499A/
MAX17500A), R12 = 7.5kΩ(MAX17499B/MAX17500B), R15 = 1kΩ, C6 = 100nF (see the
Typical Application Circuit
), NDRV = open,
VUVLO/EN = +1.4V, VFB = +1.0V, COMP = open, VCS = 0V, TA= -40°C to +125°C, unless otherwise noted. Typical values are at TA=
+25°C.) (Note 1)
BOOTSTRAP UVLO WAKE-UP LEVEL
vs. TEMPERATURE
MAX17499/500 toc01
TEMPERATURE (°C)
VIN (V)
603510-15
21.4
21.5
21.6
21.7
21.8
21.3
-40 85
MAX17500 VIN RISING
BOOTSTRAP UVLO SHUTDOWN LEVEL
vs. TEMPERATURE
MAX17499/500 toc02
TEMPERATURE (°C)
VIN (V)
603510-15
9.5
9.7
9.9
10.1
10.3
9.3
-40 85
MAX17500 VIN FALLING
UVLO/EN WAKE-UP THRESHOLD
vs. TEMPERATURE
MAX17499/500 toc03
TEMPERATURE (°C)
VUVLO/EN (V)
603510-15
1.226
1.228
1.230
1.232
1.234
1.236
1.224
-40 85
UVLO/EN RISING
Typical Operating Characteristics
(VUVLO/EN = +1.4V, VFB = +1V, COMP = open, VCS = 0V, TA= +25°C, unless otherwise noted.)
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
OSCILLATOR
Oscillator Frequency Range fOSC 50 2500 kHz
fOSC = 200kHz to 800kHz -10 +10
Oscillator Frequency Accuracy fOSC = 50kHz to 2500kHz -20 +20 %
MAX17499A/MAX17500A, fSW = fOSC/2 25 625
NDRV Switching Frequency
(Note 4) fSW MAX17499B/MAX17500B, fSW = fOSC/4 12.5 625.0 kHz
MAX17499A/MAX17500A 50
Maximum Duty Cycle DMAX MAX17499B/MAX17500B 75 %
MAX17499/MAX17500
Current-Mode PWM Controllers with
Programmable Switching Frequency
_______________________________________________________________________________________
5
UVLO/EN SHUTDOWN THRESHOLD
vs. TEMPERATURE
MAX17499/500 toc04
TEMPERATURE (°C)
VUVLO/EN (V)
603510-15
1.155
1.160
1.165
1.170
1.175
1.180
1.150
-40 85
UVLO/EN FALLING
VIN SUPPLY CURRENT IN UVLO
vs. TEMPERATURE
MAX17499/500 toc05
TEMPERATURE (°C)
ISTART (µA)
603510-15
50
55
60
65
45
-40 85
VIN = 19V
MAX17500 WHEN IN
BOOTSTRAP UVLO
VIN SUPPLY CURRENT AFTER
STARTUP vs. TEMPERATURE
MAX17499/500 toc06
TEMPERATURE (°C)
IIN (mA)
603510-15
1.6
1.7
1.8
1.9
2.0
1.5
-40 85
VIN = 24V
fSW = 350kHz
VCC REGULATOR SET POINT
vs. TEMPERATURE
MAX17499/500 toc07
TEMPERATURE (°C)
VCC (V)
603510-15
9.2
9.4
9.6
9.8
9.0
-40 85
VIN = 19V
NDRV NOT SWITCHING
NDRV SWITCHING
fSW = 350kHz
VCC REGULATOR SET POINT
vs. TEMPERATURE
MAX17499/500 toc08
TEMPERATURE (°C)
VCC (V)
6040-20 0 20
8.2
8.3
8.4
8.5
8.6
8.7
8.8
8.9
8.1
-40 80
10mA LOAD
VIN = 19V
20mA LOAD
CURRENT-LIMIT TRIP THRESHOLD
vs. TEMPERATURE
MAX17499/500 toc09
TEMPERATURE (°C)
CURRENT-LIMIT TRIP THRESHOLD (V)
603510-15
0.97
0.98
0.99
1.00
1.01
1.02
0.96
-40 85
-3σ
MEAN
+3σ
TOTAL NUMBER OF DEVICES = 140
CURRENT-LIMIT TRIP THRESHOLD
MAX17499/500 toc10
CURRENT-LIMIT TRIP THRESHOLD (V)
PERCENTAGE OF UNITS (%)
1.0220.993 1.0070.978
10
20
30
40
50
60
0
0.964 1.036
TOTAL NUMBER
OF DEVICES = 140
SWITCHING FREQUENCY
vs. TEMPERATURE
MAX17499/500 toc11
TEMPERATURE (°C)
SWITCHING FREQUENCY (kHz)
603510-15
330
335
340
345
350
355
325
-40 85
-3σ
MEAN
+3σ
TOTAL NUMBER OF DEVICES = 140
SWITCHING FREQUENCY
MAX17499/500 toc12
SWITCHING FREQUENCY (kHz)
PERCENTAGE OF UNITS (%)
354.0340.3 347.2333.5
10
20
30
40
50
60
0
326.7 360.8
TOTAL NUMBER
OF DEVICES = 140
Typical Operating Characteristics (continued)
(VUVLO/EN = +1.4V, VFB = +1V, COMP = open, VCS = 0V, TA= +25°C, unless otherwise noted.)
MAX17499/MAX17500
Current-Mode PWM Controllers with
Programmable Switching Frequency
6 _______________________________________________________________________________________
SWITCHING FREQUENCY
vs. TIMING RESISTOR
MAX17499/500 toc13
TIMING RESISTOR (kΩ)
SWITCHING FREQUENCY (kHz)
10010
100
10001
1000
10
MAX17499A/MAX17500A
PROPAGATION DELAY FROM
CURRENT-LIMIT COMPARATOR
INPUT TO NDRV vs. TEMPERATURE
MAX17499/500 toc14
TEMPERATURE (°C)
tPDCS (ns)
603510-15
45
50
55
60
40
-40 85
UVLO/EN-TO-NDRV PROPAGATION DELAY
vs. TEMPERATURE
MAX17499/500 toc15
TEMPERATURE (°C)
UVLO DELAY (ms)
603510-15
1
2
3
4
5
6
0
-40 85
UVLO/EN RISING
UVLO/EN FALLING
206μs
UVLO/EN-TO-UFLG PROPAGATION DELAY
vs. TEMPERATURE
MAX17499/500 toc16
TEMPERATURE (°C)
UVLO DELAY (μs)
603510-15
1
2
3
4
5
6
0
-40 85
UVLO/EN RISING
UVLO/EN FALLING
REFERENCE VOLTAGE
vs. TEMPERATURE
MAX17499/500 toc17
TEMPERATURE (°C)
REFERENCE VOLTAGE (V)
603510-15
1.229
1.230
1.231
1.232
1.228
-40 85
VIN = 12V
INPUT CURRENT
vs. IN VOLTAGE
MAX17499/500 toc18
IN VOLTAGE (V)
INPUT CURRENT (mA)
1817161514131211
1.64
1.68
1.72
1.76
1.80
1.60
10 19
UVLO/EN = 1.4V
NDRV SWITCHING AT 350kHz
INPUT CLAMP VOLTAGE
vs. TEMPERATURE
MAX17499/500 toc19
TEMPERATURE (°C)
INPUT CLAMP VOLTAGE (V)
6040200-20
25.2
25.4
25.6
25.8
26.0
26.2
26.4
26.6
26.8
27.0
25.0
-40 80
IIN = 2mA
NDRV LOW-OUTPUT IMPEDANCE
vs. TEMPERATURE
MAX17499/500 toc20
TEMPERATURE (°C)
RON (Ω)
603510-15
1.4
1.6
1.8
2.0
2.2
2.4
1.2
-40 85
VIN = 24V
SINKING 100mA
Typical Operating Characteristics (continued)
(VUVLO/EN = +1.4V, VFB = +1V, COMP = open, VCS = 0V, TA= +25°C, unless otherwise noted.)
MAX17499/MAX17500
Current-Mode PWM Controllers with
Programmable Switching Frequency
_______________________________________________________________________________________ 7
Pin Description
PIN
NAME
FUNCTION
1
UVLO/EN
Externally Programmable Undervoltage Lockout. UVLO/EN programs the input start voltage. Connect
UVLO/EN to GND to disable the device. NDRV stops switching approximately 210μs after the UVLO/EN
voltage falls below 1.17V.
2 UFLG Open-Drain Undervoltage Flag Output. UFLG is asserted low as soon as the UVLO/EN voltage falls below its
threshold.
3 FB Error-Amplifier Inverting Input
4
COMP
Error-Amplifier Output
5CS
Current-Sense Input. Current-sense connection for PWM regulation and cycle-by-cycle current limit.
Connect to the high side of the sense resistor. An RC filter may be necessary to eliminate leading-edge
spikes. Current-limit trip voltage is 1V.
6RT
Oscillator Timing Resistor Input. An RC network may be required to reduce jitter (see the Typical Application
Circuit).
NDRV HIGH-OUTPUT IMPEDANCE
vs. TEMPERATURE
MAX17499/500 toc21
TEMPERATURE (°C)
RON (Ω)
603510-15
3.4
3.8
4.2
4.6
5.0
3.0
-40 85
SOURCING 20mA
ERROR AMPLIFIER OPEN-LOOP GAIN
AND PHASE vs. FREQUENCY
FREQUENCY (Hz)
GAIN (dB)
PHASE (DEGREES)
100
-60
80
60
40
20
0
-20
-40
120
-200
80
40
0
-40
-80
-120
-160
10.1 10 100 1k 10k 100k 1M 10M 100M
MAX17499/500 toc22
GAIN
PHASE
Typical Operating Characteristics (continued)
(VUVLO/EN = +1.4V, VFB = +1V, COMP = open, VCS = 0V, TA= +25°C, unless otherwise noted.)
1
2
3
4
5
10
9
8
7
6
IN
+
VCC
NDRV
GNDCOMP
FB
UFLG
UVLO/EN
MAX17499
MAX17500
μMAX
TOP VIEW
RTCS
Pin Configuration
MAX17499/MAX17500
Detailed Description
The MAX17499/MAX17500 current-mode PWM con-
trollers are ideal for isolated and nonisolated power-
supply applications. The devices offer an accurate
input startup voltage programmable through the
UVLO/EN input. This feature prevents the power supply
from entering a brownout condition in case the input
voltage sags below its minimum value. This is important
since switching power supplies increases their input
supply current as the input voltage drops to keep the
output power constant. In addition to this externally
adjustable UVLO feature, the MAX17500 also offers a
bootstrap UVLO with a large hysteresis (11.9V) and
very low startup and operating current, which result in
an efficient universal input power supply. The switching
frequency of the devices is programmable with an
external resistor.
The MAX17500 is well suited for universal input (recti-
fied 85V AC to 265V AC) or telecom (-36V DC to
-72V DC) power supplies. The MAX17499 is well suited
for low-input-voltage (9.5V DC to 24V DC) power sup-
plies. The devices include an internal clamp at IN to
prevent the input voltage from exceeding the absolute
maximum rating (see Note 2 at the end of the
Electrical
Characteristics
table). The input is clamped when the
devices are started with a bleed resistor (R1 in Figure 1)
from a high input voltage and the UVLO/EN input is low.
The clamp can safely sink up to 2mA current.
Current-Mode PWM Controllers with
Programmable Switching Frequency
8 _______________________________________________________________________________________
8
9
10
3
2
1
UVLO/EN IN
7
4
V
CC
NDRV
GND
UFLG
FB
COMP
6
5RT
CS
T1
R3
R2
R12
R1
R4
C5
C2
C2 C1
C4
D2
D1
C6
R11
V
SUPPLY
0V
R13
R14
V
OUT
R15
Q1
MAX17500
Figure 1. Nonisolated Power Supply with Programmable Input-Supply Start Voltage
Pin Description (continued)
PIN
NAME
FUNCTION
7 GND Ground Connection
8
NDRV
External n-Channel MOSFET Gate Connection
9V
CC Gate-Drive Supply. Internally generated supply from IN. Decouple VCC with a 10nF or larger capacitor
to GND.
10 IN
IN Supply. Decouple with a 10nF or larger capacitor to GND. For bootstrapped operation (MAX17500),
connect a startup resistor from the input supply line to IN. Connect the bias winding supply to IN also (see
the Typical Application Circuit). For the MAX17499, connect IN directly to the 9.5V to 24V supply.
Power supplies designed with the MAX17500 use a
high-value startup resistor, R1, that charges a reservoir
capacitor, C1 (see Figure 1). During this initial period,
while the voltage is less than the internal bootstrap
UVLO threshold, the device typically consumes only
50μA of quiescent current. This low startup current and
the large bootstrap UVLO hysteresis help to minimize
the power dissipation across R1 even at the high end of
the universal AC input voltage (265V AC).
The devices include a cycle-by-cycle current limit that
turns off the gate drive to the external MOSFET when-
ever the internally set threshold of 1V is exceeded.
When using the MAX17500 in bootstrapped mode, if
the power-supply output is shorted, the tertiary winding
voltage drops below the internally set threshold caus-
ing the UVLO to turn off the gate drive to the external
power MOSFET. This reinitiates a startup sequence
with soft-start.
Current-Mode Control Loop
The advantages of current-mode control over voltage-
mode control are twofold. First, there is the feed-for-
ward characteristic brought on by the controller’s
ability to adjust for variations in the input voltage on a
cycle-by-cycle basis. Secondly, the stability require-
ments of the current-mode controller are reduced to
that of a single-pole system unlike the double pole in
voltage-mode control.
The devices use a current-mode control loop where the
output of the error amplifier (COMP) is compared to the
current-sense voltage at CS. When the current-sense
signal is lower than the noninverting input of the CPWM
comparator, the output of the CPWM comparator is low
and the switch is turned on at each clock pulse. When
the current-sense signal is higher than the inverting input
of the CPWM, the output of the CPWM comparator goes
high and the switch is turned off.
Undervoltage Lockout
The devices provide a UVLO/EN input. The threshold
for UVLO is 1.23V with 60mV hysteresis. Before any
operation can commence, the voltage on UVLO/EN has
to exceed 1.23V. The UVLO circuit keeps the CPWM
comparator, ILIM comparator, oscillator, and output dri-
ver shut down to reduce current consumption (see the
Functional Diagram
).
Use this UVLO/EN input to program the input-supply
start voltage. For example, a reasonable start voltage
for a 36V to 72V telecom range is usually 34V.
Calculate the resistor-divider values, R2 and R3 (see
Figure 1) by using the following formulas:
where IUVLO is the UVLO/EN input current (50nA max),
and VULR2 is the UVLO/EN wake-up threshold (1.23V).
VIN is the value of the input-supply voltage where the
power supply must start. The value of R3 is calculated
to minimize the voltage-drop error across R2 as a result
of the input bias current of the UVLO/EN input.
MAX17500 Bootstrap UVLO
In addition to the externally programmable UVLO func-
tion offered in both devices, the MAX17500 includes an
internal bootstrap UVLO that is very useful when
designing high-voltage power supplies (see the
Functional Diagram
). This allows the device to bootstrap
itself during initial power-up. The MAX17500 attempts to
start when VIN exceeds the bootstrap UVLO threshold
of 21.6V. During startup, the UVLO circuit keeps the
CPWM comparator, ILIM comparator, oscillator, and
output driver shut down to reduce current consumption.
Once VIN reaches 21.6V, the UVLO circuit turns on the
CPWM and ILIM comparators, the oscillator, and allows
the output driver to switch. If VIN drops below 1.17V, the
UVLO circuit shuts down the CPWM comparator, ILIM
comparator, oscillator, and output driver returning the
MAX17500 to the low-current startup mode.
Startup Operation
The MAX17499 starts up when the voltage at IN
exceeds 9.5V and the UVLO/EN input is greater than
1.23V. However, the MAX17500 requires that, in addi-
tion to meeting the specified startup conditions for the
MAX17499, the voltage at IN exceeds the bootstrap
UVLO threshold of 21.6V.
RVV
IVV
RVV
V
ULR IN
UVLO IN ULR
IN ULR
3500
2
2
2
2
≅−
=−
()
UULR
R
2
3
MAX17499/MAX17500
Current-Mode PWM Controllers with
Programmable Switching Frequency
_______________________________________________________________________________________ 9
MAX17499/MAX17500
For the MAX17500, the voltage at IN is normally derived
from a tertiary winding of the transformer. However, at
startup there is no energy being delivered through the
transformer; hence, a special bootstrap sequence is
required. Figure 2 shows the voltages at VIN and VCC
during startup. Initially, both VIN and VCC are 0V. After
the line voltage is applied, C1 charges through the
startup resistor, R1, to an intermediate voltage. At this
point, the internal regulator begins charging C2 (see
Figure 1). Only 50μA of the current supplied through R1
is used by the MAX17500; the remaining input current
charges C1 and C2. The charging of C2 stops when
the VCC voltage reaches approximately 9.5V, while the
voltage across C1 continues rising until it reaches the
wake-up level of 21.6V. Once VIN exceeds the boot-
strap UVLO threshold, NDRV begins switching the
MOSFET and transfers energy to the secondary and
tertiary outputs. If the voltage on the tertiary output
builds to higher than 9.74V (the bootstrap UVLO lower
threshold), then startup has been accomplished and
sustained operation commences. If VIN drops below
9.74V before startup is complete, the device goes back
to low-current UVLO. In this case, increase the value of
C1 to store enough energy to allow for the voltage at
the tertiary winding to build up.
UVLO Flag (UFLG)
The devices have an open-drain undervoltage flag out-
put (UFLG). When used with an optocoupler, the UFLG
output can serve to sequence a secondary-side con-
troller. An internal 210μs delay occurs the instant the
voltage on UVLO/EN drops below 1.17V until NDRV
stops switching. This allows for the UFLG output to
change state before the devices shut down (Figure 3).
When the voltage at the UVLO/EN is above the thresh-
old, UFLG is high impedance. When UVLO/EN is below
the threshold, UFLG goes low. UFLG is not affected by
bootstrap UVLO (MAX17500).
Current-Mode PWM Controllers with
Programmable Switching Frequency
10 ______________________________________________________________________________________
MAX17499/MAX17500 fig02
100ms/div
VCC
2V/div
VIN
5V/div
0V
Figure 2. VIN and VCC During Startup When Using the
MAX17500 in Bootstrapped Mode (Figure 1)
V
UVLO/EN
LOW LOW
HIGH-Z
V
UFLG
V
NDRV
SHUTDOWN SHUTDOWN
t
EXTR
3ms
1.23V
(±1%) 1.17V (typ)
t
EXTF
210μs
0.6μs
3μs
NDRV SWITCHING
Figure 3. UVLO/EN and UFLG Operation Timing
Soft-Start
The devices’ soft-start feature allows the output voltage
to ramp up in a controlled manner, eliminating voltage
overshoot. The devices’ reference generator that is
internally connected to the error amplifier soft-starts to
achieve superior control of the output voltage under
heavy- and light-load conditions. Soft-start begins after
UVLO is deasserted (VIN is above 21.6V for the
MAX17500, VIN is above 9.5V for the MAX17499, and
the voltage on UVLO/EN is above 1.23V). The voltage
applied to the noninverting node of the amplifier ramps
from 0 to 1.23V in 1984 NDRV switching cycles. Use the
following formula to calculate the soft-start time (tSS):
where fNDRV is the switching frequency at the NDRV
output. Figure 4 shows the soft-start regulated output of
a power supply using the MAX17500 during startup.
n-Channel MOSFET Switch Driver
The NDRV output drives an external n-channel MOSFET.
The internal regulator output (VCC), set to approximately
9V, drives NDRV. For the universal input voltage range,
the MOSFET used must withstand the DC level of the
high-line input voltage plus the reflected voltage at the
primary of the transformer. Most applications that use the
discontinuous flyback topology require a MOSFET rated
at 600V. NDRV can source/sink in excess of 650mA/
1000mA peak current; therefore, select a MOSFET that
mA yields acceptable conduction and switching losses.
Oscillator/Switching Frequency
Use an external resistor at RT to program the devices’
internal oscillator frequency between 50kHz and 2.5MHz.
The MAX17499A/MAX17500A output switching frequen-
cy is one-half the programmed oscillator frequency with a
50% duty cycle. The MAX17499B/MAX17500B output
switching frequency is one-quarter of the programmed
oscillator frequency with a 75% duty cycle.
The MAX17499A/MAX17500A and MAX17499B/
MAX17500B have programmable output switching fre-
quencies from 25kHz to 625kHz and 12.5kHz to
625kHz, respectively. Use the following formulas to
determine the appropriate value of resistor R12 (see
Figure 1) needed to generate the desired output
switching frequency (fSW) at the NDRV output:
where R12 is the resistor connected from RT to GND
(see Figure 1).
Connect an RC network in parallel with R12 as shown in
Figure 1. The RC network should consist of a 100nF
capacitor, C6, (for stability) in series with resistor R15,
which serves to further minimize jitter. Use the following
formula to determine the value of R15:
For example, if R12 is 4kΩ, R15 becomes 707Ω.
Internal Error Amplifier
The devices include an internal error amplifier to regu-
late the output voltage in the case of a nonisolated
power supply (see Figure 1). For the circuit in Figure 1,
calculate the output voltage using the following equation:
where VREF = 1.23V. The amplifier’s noninverting input
is internally connected to a digital soft-start circuit that
gradually increases the reference voltage during start-
up applied to this input. This forces the output voltage
to come up in an orderly and well-defined manner
under all load conditions.
The error amplifier may also be used to regulate the ter-
tiary winding output, which implements a primary-side-
regulated, isolated power supply (see Figure 6). For the
VR
RV
OUT REF
=+
⎛
⎝
⎜⎞
⎠
⎟
113
14
RR15 88 9 12
1
4
.=×
()
Rffor the MAX A MAX A
R
SW
12 10
217499 17500
12
10
=.
== 10
417499 17500
10
ffor the MAX B MAX B
SW
.
tf
SS NDRV
=1984
MAX17499/MAX17500
Current-Mode PWM Controllers with
Programmable Switching Frequency
______________________________________________________________________________________ 11
MAX17499/MAX17500 fig04
2ms/div
VOUT
2V/div
100mA LOAD ON/VOUT1
100mA LOAD ON/VOUT2
Figure 4. Primary-Side Output Voltage Soft-Start During Initial
Startup for the Circuit in Figure 6
MAX17499/MAX17500
circuit in Figure 6, calculate the output voltage using
the following equation:
where NSis the number of secondary winding turns, NT
is the number of tertiary winding turns, and both VD6
and VD2 are the diode drops at the respective outputs.
Current Limit
The current-sense resistor (R4 in Figure 1), connected
between the source of the MOSFET and ground, sets the
current limit. The current-limit comparator has a voltage
trip level (VCS) of 1V. Use the following equation to cal-
culate the value of R4:
where IPRI is the peak current in the primary side of the
transformer, which also flows through the MOSFET.
When the voltage produced by this current (through the
current-sense resistor) exceeds the current-limit com-
parator threshold, the MOSFET driver (NDRV) termi-
nates the current on-cycle within 60ns (typ). Use a
small RC network to filter out the leading-edge spikes
on the sensed waveform when needed. Set the corner
frequency between 2MHz and 10MHz.
Applications Information
Startup Time Considerations for Power
Supplies Using the MAX17500
The bypass capacitor at IN, C1, supplies current imme-
diately after the MAX17500 wakes up (see Figure 1).
The size of C1 and the connection configuration of the
tertiary winding determine the number of cycles avail-
able for startup. Large values of C1 increase the start-
up time but also supply gate charge for more cycles
during initial startup. If the value of C1 is too small, VIN
drops below 9.74V because NDRV does not have
enough time to switch and build up sufficient voltage
across the tertiary output, which powers the device.
The device goes back into UVLO and does not start.
Use a low-leakage capacitor for C1 and C2.
Typically, offline power supplies keep startup times to
less than 500ms even in low-line conditions (85V AC
input for universal offline or 36V DC for telecom appli-
cations). Size the startup resistor, R1, to supply both
the maximum startup bias of the device (90μA) and the
charging current for C1 and C2. The bypass capacitor,
C2, must charge to 9.5V and C1 to 24V, all within the
desired time period of 500ms. Because of the internal
soft-start time of the MAX17500 (approximately 5.6ms
when fSW = 350kHz), C1 must store enough charge to
deliver current to the device for at least this much time.
To calculate the approximate amount of capacitance
required, use the following formula:
where IIN is the MAX17500’s internal supply current
(2mA) after startup, QGTOT is the total gate charge for
Q1, fSW is the MAX17500’s switching frequency
(350kHz), VHYST is the bootstrap UVLO hysteresis
(approximately 12V), and tSS is the internal soft-start
time (5.6ms).
Example: IG= (8nC) (350kHz) ≅2.8mA
Choose a 2.2μF standard value (assuming 350kHz
switching frequency).
Assuming C1 > C2, calculate the value of R1 as follows:
where VIN(MIN) is the minimum input supply voltage for
the application (36V for telecom), VSUVR is the boot-
strap UVLO wake-up level (23.6V max), and ISTART is
the IN supply current at startup (90μA max).
For example:
Choose a 61.9kΩstandard value.
()(.)
()
.
()(
IVμF
ms mA
RV
C1
24 2 2
500 0 105
136 2
==
≅−44
0 105 90 61 5
V
mA μA k
)
(. ) ( ) .
+=Ω
IVC
ms
RVV
II
CSUVR
IN MIN SUVR
CS
1
1
1
500
1
=
≅−
+
()
()
TTART
CmA mA ms
VμF122856
12 224=+=
(.)(.)
.
IQ f
CIIt
V
GGTOTSW
IN G SS
HYST
=
=+
1()()
RV
I
CS
PRI
4=
VN
N
R
RVVV
OUT S
TREF D D
=+
⎛
⎝
⎜⎞
⎠
⎟+
⎡
⎣
⎢⎤
⎦
⎥−11
262
Current-Mode PWM Controllers with
Programmable Switching Frequency
12 ______________________________________________________________________________________
Choose a higher value for R1 than the one calculated in
the previous equation if a longer startup time can be
tolerated to minimize power loss on this resistor.
The above startup method is applicable to a circuit simi-
lar to the one shown in Figure 1. In this circuit, the ter-
tiary winding has the same phase as the output
windings. Thus, the voltage on the tertiary winding at any
given time is proportional to the output voltage and goes
through the same soft-start period as the output voltage.
The minimum discharge time of C1 from 21.6V to 9.74V
must be greater than the soft-start time of 5.6ms.
Another method for bootstrapping the power supply is
to use a bias winding that is in-phase with the MOSFET
on-time (see Figure 5). In this case, the amount of
capacitance required at IN (C1) is much smaller.
However, the input voltage cannot have a range
greater than approximately 2:1 (primary-winding volt-
age to bias-winding voltage ratio).
For hiccup-mode fault protection, make the bias wind-
ing in-phase with the output, then the power-supply hic-
cups and soft-starts under output short-circuit
conditions. The power supply does not hiccup if the
bias winding is in-phase with the MOSFET on-time.
MAX17499/MAX17500
Current-Mode PWM Controllers with
Programmable Switching Frequency
______________________________________________________________________________________ 13
V
CC
COMP
FB
GND
CS
NDRV
UVLO/EN
V
IN
R1 R2
R3
R4
D1
T1
C1
C2
R5
R6
R7
U2
OPTO
TRANS
RT
UFLG
C6
R15
R12
C4
IN
MAX17500A
U1
C3
U3
TL431
U2
OPTO LED
R9
V
OUT
R8
R10
D2
Q1
Figure 5. Secondary-Side Regulated, Isolated Power Supply
MAX17499/MAX17500
Primary-Side-Regulated,
Isolated Telecom Power Supply
Figure 6 shows a complete circuit of a dual-output
power supply with a 36V to 72V telecom voltage range.
An important aspect of this power supply is that it is pri-
mary-side regulated. The regulation through the tertiary
winding also supplies bias for the MAX17500.
In the circuit of Figure 6, cross-regulation has been
improved (tertiary and 5V outputs) by using chip induc-
tors, L1 and L2, and R7 || R12 across C12. R7 || R12
presents enough loading on the tertiary winding output
to allow ±10% load regulation on the 5V output over a
150mA to 1.5A load current range (Figure 7).
Current-Mode PWM Controllers with
Programmable Switching Frequency
14 ______________________________________________________________________________________
MAX17500A
U1
+VIN
UFLG
-VIN
VOUT2
15V/100mA
5V/1.5A
SGND
VOUT1
SGND
12
1
2
3
3
2
1
4
4
678
5T1 D2
D3
OPEN
D6
D8
D1
10
D7
OPEN
R12
1.2kΩ
7
9
8
6
C6
0.0047μF
250V AC
C3
68μF
6.3V
5T
12T D5 C15
1μF
D4
L1
C13
1μF
C4
22μF
6.3V
28T
35μH
15T
5
N1 IRF7464
R7
1.2kΩ
R8
OPEN
C10
OPEN
R5
0.600Ω
1%
R15
750Ω
C16
1μF
35V
R6
33kΩ
C5
47μF
25V
L2
FB_P
IN
36V TO 72V
IN
+VIN
10
IN
NDRV
CS
GND
FB_P
RT
8
5
6
7
FB
COMP
UVLO/EN
UFLG
NOTE: MOSFET N1 = IR IRF7464.
VCC
JU1
3
4
1
2
9
+VIN
C12
15μF
35V
R14
14.3kΩ
1%
C17
OPEN
C9
100pF
C14
3900pF
R4
51.1kΩ
R3
1.37MΩ
1%
R9
75kΩ
1%
R2
2.49kΩ
1%
R1
22.6kΩ
1%
R13
10kΩ
C8
OPEN
C7
0.22μF
C11
0.22μF
C19
OPEN
C18
0.1μF
R11
100Ω
UFLG_PULL
SHDN
R10
4.7Ω
C2
1μF
100V
C1
1μF
100V
Figure 6. Primary-Side-Regulated, Dual-Output, Isolated Telecom Power Supply
5V OUTPUT LOAD REGULATION
MAX17499/MAX17500 fig07
IOUT (A)
VOUT (V)
1.351.200.30 0.45 0.60 0.900.75 1.05
4.9
5.0
5.1
5.2
5.3
5.4
5.5
5.6
4.8
0.15 1.50
NO LOAD AT 15V
OUTPUT
VIN+ = 40V
VIN- = 0V
Figure 7. Output Voltage Regulation for the Circuit in Figure 6
Figure 8 shows the 12V to 15V output boost regulator.
Layout Recommendations
Typically, there are two sources of noise emission in a
switching power supply: high di/dt loops and high
dV/dt surfaces. For example, traces that carry the drain
current often form high di/dt loops. Similarly, the
heatsink of the MOSFET presents a dV/dt source; there-
fore, minimize the surface area of the heatsink as much
as possible. Keep all PCB traces carrying switching
currents as short as possible to minimize current loops.
Use a ground plane for best results. The pins of the
μMAX package are positioned to allow easy interfacing
to the external MOSFET.
For universal AC input design, follow all applicable
safety regulations. Offline power supplies may require
UL, VDE, and other similar agency approvals. To avoid
noise coupling of signals from RT to NDRV, route traces
from RT away from NDRV.
MAX17499/MAX17500
Current-Mode PWM Controllers with
Programmable Switching Frequency
______________________________________________________________________________________ 15
V
CC
COMP
FB
GND
CS
NDRV
UVLO/EN
0V
12V
R2
R3
R1
C1
RT
UFLG
C6
R15
R12
C4
IN
MAX17499
C2
C3
R5
R6
15V
D1
Q1
L1
Figure 8. 12V to 15V Output Boost Regulator
MAX17499/MAX17500
Current-Mode PWM Controllers with
Programmable Switching Frequency
16 ______________________________________________________________________________________
8
9
10
3
2
1
UVLO/EN IN
7
4
V
CC
NDRV
GND
UFLG
FB
COMP
6
5RT
CS
T1
R3
R2
R5
R12
R1
R4
C536V TO 72V
+
-
C2
C2 C1
C4
D2
D1
C6
R11
V
OUT
R15
R6
Q1
MAX17500
Typical Application Circuit
MAX17499/MAX17500
Current-Mode PWM Controllers with
Programmable Switching Frequency
______________________________________________________________________________________ 17
Selector Guide
*
The MAX17499 does not have an internal bootstrap UVLO. The
MAX17499 starts operation as long as VIN is higher than 9.5V
and UVLO/EN is higher than 1.23V.
PART* BOOTSTRAP
UVLO
STARTUP
VOLTAGE (V)
MAX DUTY
CYCLE (%)
MAX17499A No 9.5 50
MAX17499B No 9.5 75
MAX17500A Yes 22 50
MAX17500B Yes 22 75
Chip Information
PROCESS: BiCMOS
DRIVER
FB
CS
NDRV
GND
IN
COMP
UVLO/EN
IN
CLAMP
26.1V
*MAX17500 ONLY
*
UFLG
V
CC
MAX17499
MAX17500
ERROR
AMP
CPWM
UVLO
RT
OSCILLATOR
ILIM
S
R
REG_OK
REGULATOR
(INTERNAL 5.25V
SUPPLY)
IN
V
L
V
CC
Q
1.23V
1.17V
V
CS
1V
1.4V
DIGITAL
SOFT-START
REFERENCE
1.23V
N
210μs
DELAY
BOOTSTRAP UVLO
21.6V
9.74V
Functional Diagram
Package Information
For the latest package outline information and land patterns
(footprints), go to www.maxim-ic.com/packages. Note that a
“+”, “#”, or “-” in the package code indicates RoHS status only.
Package drawings may show a different suffix character, but
the drawing pertains to the package regardless of RoHS status.
PACKAGE
TYPE
PACKAGE
CODE
OUTLINE
NO.
LAND
PATTERN NO.
10 μMAX U10+2 21-0061 90-0330
MAX17499/MAX17500
Current-Mode PWM Controllers with
Programmable Switching Frequency
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are
implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
18
____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600
© 2011 Maxim Integrated Products Maxim is a registered trademark of Maxim Integrated Products, Inc.
Revision History
REVISION
NUMBER
REVISION
DATE DESCRIPTION PAGES
CHANGED
0 9/10 Initial release —
1 7/11 Changed operating temperature from -40°C to +85°C to -40°C to +125°C 1–4
