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General Description
The MAX5052/MAX5053 current-mode PWM controllers
contain all the control circuitry required for the design of
wide-input-voltage isolated and nonisolated power
supplies. The MAX5052 is well suited for universal input
(rectified 85VAC to 265VAC) or telecom (-36VDC to
-72VDC) power supplies. The MAX5053 is well suited for
low-input-voltage (10.8VDC to 24VDC) power supplies.
The MAX5052/MAX5053 contain an internal error amplifier that regulates the tertiary winding output voltage.
This implements a primary-side regulated, isolated
power supply, eliminating the need for an optocoupler.
An input undervoltage lockout (UVLO) is provided for
programming the input-supply start voltage and to
ensure proper operation during brownout conditions.
The input-supply start voltage is externally programmable with a voltage-divider. To shutdown the device, the
UVLO pin is pulled low. Internal digital soft-start
reduces output voltage overshoot. The internal thermal
shutdown circuit protects the device in the event the
junction temperature exceeds +130°C.
The MAX5052 has an internal bootstrap UVLO with
large hysteresis that requires a minimum voltage of
23.6V for startup. The MAX5053 does not have the
internal bootstrap UVLO and can be biased directly
from a minimum voltage of 10.8V.
The 262kHz switching frequency is internally trimmed to
±12% accuracy; this allows the optimization of the
magnetic and filter components resulting in compact,
cost-effective power supplies. The MAX5052A/
MAX5053A are offered with a 50% maximum duty-cycle
limit. The MAX5052B/MAX5053B are offered with a 75%
maximum duty-cycle limit. These devices are available
in 8-pin µMAX packages and operate over the -40°C to
+85°C temperature range.
Applications
Features
♦ Available in a Tiny 8-Pin µMAX Package
♦ Current-Mode Control
♦ 50W Output Power
♦ Universal Offline Input Voltage Range
Rectified 85VAC to 265VAC (MAX5052)
♦ VINDirectly Driven from 10.8V to 24V Input
(MAX5053)
♦ Digital Soft-Start
♦ Programmable Input Startup Voltage
♦ Internal Bootstrap UVLO with Large Hysteresis
(MAX5052)
♦ Internal Error Amplifier with 1% Accurate
Reference
♦ Thermal Shutdown
♦ 45µA (typ) Startup Supply Current
♦ 1.4mA (typ) Operating Supply Current
♦ Fixed Switching Frequency of 262kHz ±12%
♦ 50% Maximum Duty-Cycle Limit
(MAX5052A/MAX5053A)
♦ 75% Maximum Duty-Cycle Limit
(MAX5052B/MAX5053B)
♦ 60ns Cycle-by-Cycle Current-Limit Response Time
MAX5052/MAX5053
Current-Mode PWM Controllers with an Error
Amplifier for Isolated/Nonisolated Power Supplies
________________________________________________________________ Maxim Integrated Products 1
Ordering Information
19-2590; Rev 1; 11/03
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at
1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.
Functional Diagram/Typical Operating Circuit/Selector
Guide appear at end of data sheet.
PART TEMP RANGE PIN-PACKAGE
MAX5052AEUA -40°C to +85°C 8 µMAX
MAX5052BEUA -40°C to +85°C 8 µMAX
MAX5053AEUA -40°C to +85°C 8 µMAX
MAX5053BEUA -40°C to +85°C 8 µMAX
NDRV
GNDCS
1
2
87V
IN
V
CC
FB
COMP
UVLO/EN
µMAX
TOP VIEW
3
4
6
5
MAX5052
MAX5053
Pin Configuration
Warning: The MAX5052/MAX5053 are designed to work with
high voltages. Exercise caution.
Universal Input AC
Power Supplies
Isolated Telecom Power
Supplies
Networking Systems
Computer Systems/
Servers
Industrial Power
Conversion
Isolated Keep-Alive
Circuits
12V Boost Regulators
12V SEPIC Regulators
EVALUATION KIT
AVAILABLE
MAX5052/MAX5053
Current-Mode PWM Controllers with an Error
Amplifier for Isolated/Nonisolated Power Supplies
2 _______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS
(VIN= +12V (for MAX5052, VINmust first be brought up to 23.6V for startup), 10nF bypass capacitors at VINand VCC, C
NDRV
= 0,
V
UVLO
= +1.4V, VFB= +1.0V, V
COMP
= floating, VCS= 0V, typical values are measured at TA= +25°C, TA= -40°C to + 85°C, unless
otherwise noted.) (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.
VINto GND .............................................................-0.3V to +30V
VCCto GND............................................................-0.3V to +13V
FB, COMP, UVLO, CS to GND .................................-0.3V to +6V
NDRV to GND.............................................-0.3V to (VCC+ 0.3V)
Continuous Power Dissipation (TA= +70°C)
8-Pin µMAX (derate 4.5mW/°C above +70°C) ..............362mW
Operating Temperature Range ...........................-40°C to +85°C
Storage Temperature Range ............................-65°C to +150°C
Junction Temperature......................................................+150°C
Lead Temperature (soldering, 10s) .................................+300°C
PARAMETER
CONDITIONS
UNITS
UNDERVOLTAGE LOCKOUT/STARTUP
Bootstrap UVLO Wake-Up Level
V
SUVR
VIN rising (MAX5052 only)
V
Bootstrap UVLO Shutdown Level
V
SUVF
VIN falling (MAX5052 only)
V
UVLO/EN Wake-Up Threshold V
ULR2
UVLO/EN rising
V
UVLO/EN Shutdown Threshold V
ULF2
UVLO/EN falling
V
UVLO/EN Input Current I
UVLO
TJ = +125°C 25 nA
UVLO/EN Hysteresis 50 mV
VIN Supply Current In
Undervoltage Lockout
I
START
VIN = +19V, for MAX5052 only when in
bootstrap UVLO
45 90 µA
VIN Range V
IN
24 V
t
EXTR
UVLO/EN steps up from +1.1V to +1.4V 12
UVLO/EN Propagation Delay
t
EXTF
UVLO/EN steps down from +1.4V to +1.1V 1.8
µs
t
BUVR
VIN steps up from +9V to +24V 5
Bootstrap UVLO Propagation
Delay
t
BUVF
VIN steps down from +24V to +9V 1
µs
INTERNAL SUPPLY
VCC Regulator Set Point V
CCSP
VIN = +10.8V to +24V, sinking 1µA to 20mA
from V
CC
7
V
VIN Supply Current After Startup I
IN
VIN = +24V 1.4 2.5 mA
Shutdown Supply Current UVLO/EN = low 90 µA
GATE DRIVER
)
Measured at NDRV sinking, 100mA 2 4
Driver Output Impedance
)
Measured at NDRV sourcing, 20mA 4 12
Ω
Driver Peak Sink Current 1A
Driver Peak Source Current
A
PWM COMPARATOR
Comparator Offset Voltage
V
COMP
- V
CS
V
CS Input Bias Current I
CS
VCS = 0V -2 +2 µA
Comparator Propagation Delay t
PWM
VCS = +0.1V 60 ns
Minimum On-Time
)
ns
SYMBOL
MIN TYP MAX
R
ON(LOW
R
ON(HIGH
VO
PWM
t
ON(MIN
19.68 21.6 23.60
9.05 9.74 10.43
1.188 1.28 1.371
1.168 1.23 1.291
10.8
0.65
1.15 1.38 1.70
150
10.5
MAX5052/MAX5053
Current-Mode PWM Controllers with an Error
Amplifier for Isolated/Nonisolated Power Supplies
_______________________________________________________________________________________ 3
Note 1: All devices are 100% tested at TA= +85°C. All limits over temperature are guaranteed by characterization.
Note 2: V
REF
is measured with FB connected to the COMP pin (see Functional Diagram).
Note 3: The MAX5052 is intended for use in universal input power supplies. The internal clamp circuit is used to prevent the boot-
strap capacitor (C1 in Figure 1) from charging to a voltage beyond the absolute maximum rating of the device when
EN/UVLO is low. The maximum current to V
IN
(hence to clamp) when UVLO is low (device in shutdown) must be externally
limited to 2mA, max. Clamp currents higher than 2mA may result in clamp voltage higher than 30V, thus exceeding the
absolute maximum rating for V
IN
. For the MAX5053, do not exceed the 24V maximum operating voltage of the device.
ELECTRICAL CHARACTERISTICS (continued)
(VIN= +12V (for MAX5052, VINmust first be brought up to 23.6V for startup), 10nF bypass capacitors at VINand VCC, C
NDRV
= 0,
V
UVLO
= +1.4V, VFB= +1.0V, V
COMP
= floating, VCS= 0V, typical values are measured at TA= +25°C, TA= -40°C to + 85°C, unless
otherwise noted.) (Note 1)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
CURRENT-LIMIT COMPARATOR
Current-Limit Trip Threshold V
CS
320 mV
CS Input Bias Current I
CS
VCS = 0V -2 +2 µA
Propagation Delay From
Comparator Input to NDRV
t
PWM
50mV overdrive 60 ns
Switching Frequency f
SW
290 kHz
MAX505_A 50
Maximum Duty Cycle D
MAX
MAX505_B 75 76
%
VIN CLAMP VOLTAGE
VIN Clamp Voltage V
INC
2mA sink current, MAX5052 only (Note 3)
V
ERROR AMPLIFIER
Voltage Gain R
LOAD
= 100kΩ 80 dB
Unity-Gain Bandwidth R
LOAD
= 100kΩ, C
LOAD
= 200pF 2
MHz
Phase Margin R
LOAD
= 100kΩ, C
LOAD
= 200pF 65
degrees
FB Input Offset Voltage 3mV
High 2.2 3.5
COMP Pin Clamp Voltage
Low 0.4 1.1
V
Source Current 0.5 mA
Sink Current 0.5 mA
Reference Voltage V
REF
(Note 2)
V
Input Bias Current 50 nA
COMP Short-Circuit Current 8mA
THERMAL SHUTDOWN
°C
Thermal Hysteresis 25 °C
DIGITAL SOFT-START
Soft-Start Duration
clock
cycles
Reference Voltage Steps During
Soft-Start
31
steps
Reference Voltage Step 40 mV
Thermal-Shutdown Temperature 130
262 291
230 262
24.1 26.1 29.0
1.218 1.230 1.242
15,872
50.5
MAX5052/MAX5053
Current-Mode PWM Controllers with an Error
Amplifier for Isolated/Nonisolated Power Supplies
4 _______________________________________________________________________________________
Typical Operating Characteristics
(UVLO = +1.4V, VFB= +1V, V
COMP
= floating, VCS= 0V, TA= +25°C, unless otherwise noted.)
BOOTSTRAP UVLO WAKE-UP LEVEL
vs. TEMPERATURE
MAX5052 toc01
TEMPERATURE (°C)
V
IN
(V)
6040200-20
21.35
21.40
21.45
21.50
21.55
21.60
21.30
-40 80
MAX5052 VIN RISING
BOOTSTRAP UVLO SHUTDOWN LEVEL
vs. TEMPERATURE
MAX5052 toc02
TEMPERATURE (°C)
V
IN
(V)
6040200-20
9.8
9.9
10.0
10.1
9.7
-40 80
MAX5052 VIN FALLING
UVLO/EN WAKE-UP THRESHOLD
vs. TEMPERATURE
MAX5052 toc03
TEMPERATURE (°C)
UVLO/EN (V)
6040200-20
1.255
1.260
1.265
1.270
1.275
1.280
1.250
-40 80
UVLO/EN RISING
UVLO/EN SHUTDOWN THRESHOLD
vs. TEMPERATURE
MAX5052 toc04
TEMPERATURE (°C)
UVLO/EN (V)
6040200-20
1.15
1.20
1.25
1.30
1.10
-40 80
UVLO/EN FALLING
VIN SUPPLY CURRENT IN UNDERVOLTAGE
LOCKOUT vs. TEMPERATURE
MAX5052 toc05
TEMPERATURE (°C)
I
START
(µA)
6040200-20
43
44
45
46
47
48
49
50
51
52
42
-40 80
VIN = 19V
MAX5052 WHEN IN BOOTSTRAP UVLO
MAX5053 WHEN UVLO/EN IS LOW
VIN SUPPLY CURRENT AFTER STARTUP
vs. TEMPERATURE
MAX5052 toc06
TEMPERATURE (°C)
I
IN
(mA)
6040200-20
1.2
1.3
1.4
1.5
1.1
-40 80
VIN = 24V
VCC REGULATOR SET POINT
vs. TEMPERATURE
MAX5052 toc07
TEMPERATURE (°C)
V
CC
(V)
6040200-20
9.3
9.5
9.4
9.7
9.6
9.8
9.2
-40 80
VIN = 19V
NO LOAD
NDRV OUTPUT IS NOT
SWITCHING, V
FB
= 1.5V
NDRV OUTPUT IS
SWITCHING
VCC REGULATOR SET POINT
vs. TEMPERATURE
MAX5052 toc08
TEMPERATURE (°C)
V
CC
(V)
6040200-20
8.2
8.5
8.6
8.4
8.3
8.8
8.7
8.9
8.1
-40 80
VIN = 10.8V
10mA LOAD
20mA LOAD
CURRENT-LIMIT TRIP THRESHOLD
vs. TEMPERATURE
MAX5052 toc09
TEMPERATURE (°C)
CURRENT-LIMIT TRIP THRESHOLD (mV)
6040200-20
275
290
295
285
280
305
300
310
270
-40 80
+3σ
-3σ
MEAN
TOTAL NUMBER OF
DEVICES = 100
MAX5052/MAX5053
Current-Mode PWM Controllers with an Error
Amplifier for Isolated/Nonisolated Power Supplies
_______________________________________________________________________________________ 5
CURRENT-LIMIT TRIP THRESHOLD
MAX5052 toc10
CURRENT-LIMIT TRIP THRESHOLD (mV)
PERCENTAGE OF UNITS (%)
310300290280270
5
10
15
20
25
30
0
260 320
TOTAL NUMBER OF
DEVICES = 200
SWITCHING FREQUENCY
vs. TEMPERATURE
MAX5052 toc11
TEMPERATURE (°C)
SWITCHING FREQUENCY (kHz)
6040200-20
245
260
265
255
250
275
270
280
240
-40 80
+3σ
-3σ
MEAN
TOTAL NUMBER OF
DEVICES = 100
SWITCHING FREQUENCY
MAX5052 toc12
SWITCHING FREQUENCY (kHz)
PERCENTAGE OF UNITS (%)
280270260250240
5
10
15
20
25
30
0
230 290
TOTAL NUMBER OF
DEVICES = 200
PROPAGATION DELAY FROM CURRENT-LIMIT
COMPARATOR INPUT TO NDRV vs. TEMPERATURE
MAX5052 toc13
TEMPERATURE (°C)
t
PWM
(ns)
6040200-20
55
60
65
70
75
50
-40 80
UVLO/EN PROPAGATION DELAY
vs. TEMPERATURE
MAX5052 toc14
TEMPERATURE (°C)
UNDERVOLTAGE LOCKOUT DELAY (µs)
6040200-20
4
3
2
1
7
6
5
13
12
11
10
9
8
14
0
-40 80
UVLO/EN RISING
UVLO/EN FALLING
REFERENCE VOLTAGE
vs. TEMPERATURE
MAX5052 toc15
TEMPERATURE (°C)
REFERENCE VOLTAGE (V)
6040200-20
1.226
1.227
1.228
1.229
1.230
1.225
-40 80
VIN = 12V
INPUT CURRENT
vs. INPUT CLAMP VOLTAGE
MAX5052 toc16
INPUT VOLTAGE (V)
INPUT CURRENT (mA)
27.525.020.0 22.515.0 17.512.5
1
2
3
4
5
6
7
8
9
10
0
10.0 30.0
INPUT CLAMP VOLTAGE
vs. TEMPERATURE
MAX5052 toc17
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 OUTPUT IMPEDANCE
vs. TEMPERATURE
MAX5052 toc18
TEMPERATURE (°C)
R
ON
(Ω)
6040200-20
1.3
1.4
1.5
1.6
1.7
1.8
1.9
2.0
2.1
2.2
1.2
-40 80
VIN = 24V
SINKING 100mA
Typical Operating Characteristics (continued)
(UVLO = +1.4V, VFB= +1V, V
COMP
= floating, VCS= 0V, TA= +25°C, unless otherwise noted.)
MAX5052/MAX5053
Detailed Description
The MAX5052/MAX5053 are current-mode PWM controllers that have been specifically designed for use in
isolated and nonisolated power-supply applications. A
bootstrap UVLO with a large hysteresis (11.9V), very
low startup current, and low operating current result in
efficient universal-input power supplies. In addition to
the internal bootstrap UVLO, these devices also offer
programmable input startup voltage programmed
through the UVLO/EN pin. This feature is useful in preventing the power supply from entering a brownout
condition, in case the input voltage drops below its
minimum value. This is important since switching power
supplies increases their input supply current as the
input voltage drops in order to keep the output power
constant. The MAX5052 is well suited for universal input
(rectified 85VAC to 265VAC) or telecom (-36VDC to
-72VDC) power supplies. The MAX5053 is well suited for
low-input-voltage (10.8VDC to 24VDC) power supplies.
Power supplies designed with the MAX5052 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
45µA of quiescent current. This low startup current and
the large bootstrap UVLO hysteresis helps to minimize
Current-Mode PWM Controllers with an Error
Amplifier for Isolated/Nonisolated Power Supplies
6 _______________________________________________________________________________________
Pin Description
NDRV OUTPUT IMPEDANCE
vs. TEMPERATURE
MAX5052 toc19
TEMPERATURE (°C)
R
ON
(Ω)
6040200-20
3.2
3.4
3.6
3.8
4.0
4.2
4.4
4.6
4.8
5.0
3.0
-40 80
VIN = 24V
SOURCING 20mA
ERROR AMP OPEN-LOOP GAIN
AND PHASE vs. FREQUENCY
MAX5052 toc20
FREQUENCY (Hz)
GAIN (dB)
10M1M10k1k 100k10 1001
-80
-60
-20
-40
0-70
20
60
40
80
100
120
-100
PHASE (DEGREES)
-150
-130
-90
-110
-50
-10
-30
10
30
50
-170
0.1 100M
GAIN
PHASE
Typical Operating Characteristics (continued)
(UVLO = +1.4V, VFB= +1V, V
COMP
= floating, VCS= 0V, TA= +25°C, unless otherwise noted.)
PIN NAME FUNCTION
1
Externally Programmable Undervoltage Lockout. UVLO programs the input start voltage. Connect UVLO to
GND to disable the device.
2FBError-Amplifier Inverting Input
3 COMP Error-Amplifier Output
4CS
Current-Sense Connection for PWM Regulation and Overcurrent Protection. Connect to high side of sense
resistor. An RC filter may be necessary to eliminate leading-edge spikes.
5 GND Power-Supply Ground
6 NDRV External N-Channel MOSFET Gate Connection
7VCCGate-Drive Supply. Internally regulated down from VIN. Decouple with a 10nF or larger capacitor to GND.
8V
IN
IC Supply. Decouple with a 10nF or larger capacitor to GND. For bootstrapped operation (MAX5052)
connect a startup resistor from the input supply line to V
IN
. Connect the bias winding supply to this point as
well (see the Typical Operating Circuit). For the MAX5053, connect V
IN
directly to 10.8V to 24V supply.
UVLO/EN
the power dissipation across R1 even at the high end of
the universal AC input voltage (265VAC).
The MAX5052/MAX5053 include a cycle-by-cycle current limit that turns off the gate drive to the external
MOSFET during an overcurrent condition. When using
the MAX5052 in the bootstrapped mode (if the powersupply output is shorted), the tertiary winding voltage
drops below the 10V threshold causing the UVLO to
turn off the gate drive to the external power MOSFET.
This reinitiates a startup sequence with soft-start.
MAX5052/MAX5053
Undervoltage Lockout
The MAX5052/MAX5053 have an input voltage
UVLO/EN pin. The threshold for this UVLO is 1.28V.
Before any operation can commence, the voltage on
this pin has to exceed 1.28V. The UVLO circuit keeps
the CPWM comparator, ILIM comparator, oscillator,
and output driver shut down to reduce current consumption (see the Functional Diagram).
Use this UVLO function to program the input-supply
start voltage. For example, a reasonable start voltage
for a 36V to 72V telecom range might be set at 34V.
Calculate the divider resistor values, R2 and R3 (see
Figure 1) by using the following formulas:
The value of R3 is calculated to minimize the voltagedrop error across R2 as a result of the input bias current of the UVLO/EN pin. V
ULR2
= 1.28V, I
UVLO
= 50nA
(max). V
IN
is the value of the input-supply voltage
where the power supply must start.
where I
UVLO
is the UVLO/EN pin input current (50nA),
and V
ULR2
is the UVLO/EN wake-up threshold.
MAX5052 Bootstrap
Undervoltage Lockout
In addition to the externally programmable UVLO function offered in both the MAX5052 and MAX5053, the
MAX5052 has an additional 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
MAX5052 attempts to start when V
IN
exceeds the boot-
strap UVLO threshold of 21.6V.
During startup, the UVLO circuit keeps the CPWM com-
parator, ILIM comparator, oscillator, and output driver
shut down to reduce current consumption. Once V
IN
reaches 21.6V, the UVLO circuit turns on both the CPWM
and ILIM comparators, as well as the oscillator, and
allows the output driver to switch. If VINdrops below
9.7V, the UVLO circuit will shut down the CPWM comparator, ILIM comparator, oscillator, and output driver
returning the MAX5052/MAX5053 to the startup mode.
MAX5052 Startup Operation
Normally VINis derived from a tertiary winding of the
transformer. However, at startup there is no energy
delivered through the transformer, hence, a special
bootstrap sequence is required. Figure 2 shows the
voltages on VINand VCCduring startup. Initially, both
VINand VCCare 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). The MAX5052 uses
only 45µA of the current supplied by R1, and the
remaining input current charges C1 and C2. The charging of C2 stops when the VCCvoltage reaches approximately 9.5V, while the voltage across C1 continues
rising until it reaches the wake-up level of 21.6V. Once
V
IN
exceeds the bootstrap 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 9.9V (the bootstrap
UVLO lower threshold), then startup has been accomplished and sustained operation commences.
R
VV
V
R
IN ULR
ULR
23
2
2
=×
−
R
VV
IVV
ULR IN
UVLO IN ULR
3
500
2
2
≅
×
×
()
−
MAX5052/MAX5053
Current-Mode PWM Controllers with an Error
Amplifier for Isolated/Nonisolated Power Supplies
_______________________________________________________________________________________ 7
Q1
T1
V
IN
V
CC
COMP
FB
GND
CS
NDRV
UVLO/EN
0V
V
SUPPLY
V
OUT
R1
C1
C2
C3
R4
R2
R3
R5
R6
C4
D1
D2
MAX5052
Figure 1. Nonisolated Power Supply with Programmable InputSupply Start Voltage
MAX5052/MAX5053
If VINdrops below 9.9V before startup is complete, the
device goes back to low-current UVLO. In this case,
increase the value of C1 in order to store enough energy
to allow for the voltage at tertiary winding to build up.
Startup Time Considerations For Power
Supplies Using the MAX5052
The VINbypass capacitor, C1, supplies current immediately after wake up (see Figure 1). The size of C1 and
the connection configuration of the tertiary winding
determine the number of cycles available for startup.
Large values of C1 increase the startup time but also
supply gate charge for more cycles during initial startup. If the value of C1 is too small, VINdrops below 9.9V
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.
As a rule of thumb, offline power supplies keep typical
startup times to less than 500ms even in low-line conditions (85VAC input for universal offline or 36VDC for
telecom applications). 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 60ms soft-start time of the
MAX5052, 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 IINis the MAX5052’s internal supply current after
startup (1.4mA), Q
gtot
is the total gate charge for Q1,
fSWis the MAX5052’s switching frequency (262kHz),
V
hyst
is the bootstrap UVLO hysteresis (12V) and tssis
the internal soft-start time (60ms).
For example:
Ig= (8nC) (262kHz) ≅ 2.1mA
choose 15µF standard value.
Assuming C1 > C2, calculate the value of R1 as follows:
where V
IN(MIN)
is the minimum input supply voltage for
the application (36V for telecom), V
SUVR
is the boot-
strap UVLO wake-up level (23.6V max.), I
START
is the
VINsupply current at startup (90µA, max).
For example:
choose 32kΩ standard value.
Choose a higher value for R1 than the one calculated
above if longer startup time can be tolerated in order to
minimize power loss on this resistor.
The above startup method is applicable to a circuit similar to the one shown in Figure 1. In this circuit, the tertiary
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 voltage of C1 from 22V to 10V
must be greater than the soft-start time of 60ms.
Another method for bootstrapping the power supply is to
have a separate bias winding than the one used for regulating the output voltage and to connect the bias winding so that it is in phase with the MOSFET ON time (see
Figure 3). The amount of capacitance required is much
R
VV
mA A
k1
36 12
072 90
29 6=
()()
()
+µ
()
= Ω
−
.
.
I
VF
ms
mA
C1
24 15
500
072=
()
µ
()
()
= .
R
VV
II
IN MIN SUVR
C START
11=
+
−
()
I
VC
ms
C
SUVR
1
1
500
=
×
()
C1 =
1. 4m A+ 2. 1m A
()
60ms
()
12V
()
=17.5µF
IQ f
C
IIt
V
g gtot SW
IN g SS
hyst
=×
=
+
()
()
1
Current-Mode PWM Controllers with an Error
Amplifier for Isolated/Nonisolated Power Supplies
8 _______________________________________________________________________________________
100ms/div
MAX5052
V
IN
PIN
V
CC
2V/div
0V
5V/div
Figure 2. VINand VCCDuring Startup when Using the
MAX5052 in Bootstrapped Mode (Figure 1)
smaller. However, in this mode, the input voltage range
has to be roughly 2:1. Another consideration is if the bias
winding is in phase with the output, then the power supply hiccups and soft-start under output short-circuit conditions. Whereas, this property is lost if the bias winding
is in phase with the MOSFET ON time.
Soft-Start
The MAX5052/MAX5053 soft-start feature allows the load
voltage to ramp up in a controlled manner, eliminating
output voltage overshoot. Soft-start begins after UVLO is
deasserted. The voltage applied to the noninverting
node of the amplifier ramps from 0 to 1.23V in over a
60ms soft-start timeout period. Figure 4 shows the 5V
output of the power-supply circuit in Figure 5 during
startup. Note the staircase increase of the output voltage. This is a result of the digital soft-starting technique
used. Unlike other devices, the MAX5052/MAX5053 reference voltage to the internal amplifier is soft-started;
this method results in superior control of the output voltage under heavy- and light-load conditions.
N-Channel MOSFET Switch Driver
The NDRV pin drives an external N-channel MOSFET.
The NDRV output is supplied by the internal regulator
(VCC), which is internally set to approximately 9.5V. For
the universal input voltage range, the MOSFET used
must be able to withstand the DC level of the high-line
input voltage plus the reflected voltage at the primary of
the transformer. For most offline applications that use the
discontinuous flyback topology, this requires a MOSFET
rated at 600V. NDRV can source/sink in excess of the
650mA/1000mA peak current, so select a MOSFET that
yields acceptable conduction and switching losses.
Internal Oscillator
The internal oscillator switches at 1.048MHz and is
divided down to 262kHz by two D flip-flops. The
MAX5052A/MAX5053A invert the Q output of the last D
flip-flop to provide a duty cycle of 50% (Figure 6). The
MAX5052B/MAX5053B perform a logic NAND operation on the Q outputs of both D flip-flops to provide a
duty cycle of 75%.
MAX5052/MAX5053
Current-Mode PWM Controllers with an Error
Amplifier for Isolated/Nonisolated Power Supplies
_______________________________________________________________________________________ 9
Q1
T1
V
IN
V
CC
COMP
FB
GND
CS
NDRV
UVLO/EN
-V
IN
+V
IN
V
OUT
R1
R5
R7
R6
C1
C2
R4
R2
R3
R8
R10
C4
D1
D2
R9
MAX5052
U2
OPTO LED
U3
TL431
C3
U1
U2
OPTO TRANS
Figure 3. Secondary-Side Regulated, Isolated Power Supply
10ms/div
1V/div
0V
Figure 4. Output Voltage Soft-Start During Initial Startup for the
Circuit of Figure 5
MAX5052/MAX5053
Current-Mode PWM Controllers with an Error
Amplifier for Isolated/Nonisolated Power Supplies
10 ______________________________________________________________________________________
Internal Error Amplifier
The MAX5052/MAX5053 include an internal error amplifier that can be used to regulate the output voltage in
the case of a nonisolated power supply (see Figure 1)
Calculate the output voltage using the following equation:
where V
REF
= 1.23V. The amplifier’s noninverting input
is internally connected to a digital soft-start circuit that
gradually increases the reference voltage during startup and is applied to this pin. 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 tertiary winding output which implements a primary-side
regulated, isolated power supply (see Figure 5).
Calculate the output voltage using the following equation:
where NSis the number of secondary turns for V
OUT1
,
NTis the number of tertiary winding turns, and both V
D6
and VD1are the diode drops at the respective outputs.
V
N
N
R
R
VV V
OUT
S
T
REF D D161
1
1
2
=+
+
−
V
R
R
V
OUT REF
=+
1
5
6
IN FB_P
D8 D6
R6
33kΩ
+V
IN
+VIN
C16
15µF
35V
C1
1µF
100V
C2
1µF
100V
C12
0.22µF
R7
1.2kΩ
R12
1.2kΩ
D7
*
OPEN
5
4
3
2
1
R8*
OPEN
C10
*
OPEN
D3
*
OPEN
T1
9
7
6
10
8
C6
0.0047µF
250VAC
D1
L2
C3
68µF
6.3V
C4
22µF
6.3V
D4
C13
1µF
L1
D2
C5
47µF
25V
D5
C15
1µF
VOUT2 (+15V/0.1A)
VOUT1 (+5V/1.5A)
SGND
SGND
N1
6
5
4
1
2
3
7
8
R5
0.17Ω
1%
*COMPONENTS MARKED "OPEN" ARE OPTIONAL.
(SEE MAX5052A EV KIT DATA SHEET.)
C8
OPEN
R11
100Ω
IN
C11
0.22µF
R10
0Ω
8
6
4
5
FB_P
R1
22.6kΩ
1%
R2
2.49kΩ
1%
R9
4.3kΩ
C9
2200pF
C14
0.022µF
R3
1MΩ
1%
R4
42.2kΩ
1%
+V
IN
-VIN
SHDN
JU1
C7
0.22µF
MAX5052A
2
3
1
7
FB
COMP
UVLO/EN
V
CC
V
IN
NDRV
CS
GND
U1
Figure 5. Primary Regulated, Dual-Output, Isolated Telecom Power Supply
DQ
Q
DQ
Q
OSCILLATOR
1.048MHz
262kHz WITH 50%
(MAX5052A/MAX5053A)
262kHz WITH 75%
(MAX5052B/MAX5053B)
Figure 6. Internal Oscillator
MAX5052/MAX5053
Current-Mode PWM Controllers with an Error
Amplifier for Isolated/Nonisolated Power Supplies
______________________________________________________________________________________ 11
Current Limit
The current-sense resistor (RCS), connected between
the source of the MOSFET and ground, sets the current
limit. The CS input has a voltage-trip level (VCS) of
291mV. Use the following equation to calculate the
value of RCS:
Where I
PRI
is the peak current in the primary that flows
through the MOSFET.
When the voltage produced by this current (through the
current-sense resistor) exceeds the current-limit comparator threshold, the MOSFET driver (NDRV) quickly
terminates the current ON-cycle, typically within 60ns.
In most cases, a small RC filter is required to filter out
the leading-edge spike on the sense waveform. Set the
corner frequency at a few megahertz.
Applications Information
Primary Regulated, Isolated
Telecom Power Supply
Figure 5 shows a complete design of a dual-output power
supply with a telecom voltage range of 36V to 72V. An
important aspect of this power supply is its primary-side
regulation. This regulation, through the tertiary winding,
also acts as bias winding for the MAX5052.
In the circuit of Figure 5, cross-regulation has been
improved (tertiary and 5V outputs) by using chip inductors, L1 and L2, and R7||R2. R7||R2 presents enough
loading on the tertiary winding output to allow ±5% load
regulation on the 5V output over a load current range
from 150mA to 1.5A.
Layout Recommendations
All printed circuit board traces carrying switching currents must be kept as short as possible, and the current loops they form must be minimized. The pins of the
µMAX package have been placed to allow easy interfacing to the external MOSFET.
For universal AC input design, all applicable safety regulations must be followed. Offline power supplies may
require UL, VDE, and other similar agency approvals.
These agencies can be contacted for the latest layout
and component rules.
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, thus the surface area of the heatsink must be minimized as much
as possible.
To achieve best performance, a star ground connection
is recommended to avoid ground loops. For example,
the ground returns for the power-line input filter, power
MOSFET switch, and sense resistor should be routed
separately through wide copper traces to meet at a single-system ground connection.
Chip Information
TRANSISTOR COUNT: 1449
PROCESS: BiCMOS
R
V
I
CS
CS
PRI
=
0.55 0.75 0.950.350.15
5V OUTPUT LOAD REGULATION
I
OUT
(A)
V
OUT
(V)
1.351.15
4.2
4.4
4.6
4.8
5.0
5.2
5.4
5.6
5.8
6.0
4.0
Figure 7. Output Voltage Regulation for the Figure 5 Circuit
Q1
V
IN
V
CC
COMP
FB
GND
CS
NDRV
UVLO/EN
0V
12V
15V
C1
C2
C3
R1
R2
R3
R5
R6
C4
D1
MAX5053
L1
Figure 8. 12V to 15V Out Boost Regulator
MAX5052/MAX5053
Current-Mode PWM Controllers with an Error
Amplifier for Isolated/Nonisolated Power Supplies
12 ______________________________________________________________________________________
Q1
T1
V
IN
V
CC
COMP
FB
GND
CS
NDRV
UVLO/EN
0V
V
SUPPLY
V
OUT
R1
C1
C2
C3
R4
R2
R3R6
R5
C4
D1
D2
MAX5052
R7
C5
D4
Typical Operating Circuit
Q
S
R
OSCILLATOR
262kHz*
(INTERNAL 5.25V SUPPLY)
DRIVER
FB
CS
NDRV
REFERENCE
1.23V
REGULATOR
IN
V
CC
V
CC
V
IN
V
L
21.6V
9.74V
REG_OK
GND
*MAX5052A/MAX5053A: 50% MAXIMUM DUTY CYCLE,
MAX5052B/MAX5053B: 75% MAXIMUM DUTY CYCLE.
**MAX5052 ONLY.
CPWM
ILIM
THERMAL
SHUTDOWN
DIGITAL
SOFT-START
ERROR
AMP
COMP
1.28V
1.23V
UVLO
**
BOOTSTRAP UVLO
UVLO
V
IN
CLAMP
26.1V
1.4V
VO
PWM
V
CS
0.3V
MAX5052/MAX5053
Functional Diagram
Selector Guide
PART
BOOTSTRAP
UVLO
STARTUP
MAX DUTY
CYCLE
MAX5052A Yes 22V 50%
MAX5052B Yes 22 V 75%
MAX5053A No 10.8V* 50%
MAX5053B No 10.8V* 75%
*The MAX5053 does not have an internal bootstrap UVLO. The
MAX5053 starts operation as long as the V
CC
pin is higher than
7V (the guaranteed output with a V
IN
pin voltage of 10.8V) and
the UVLO/EN pin is high.
VOLTAGE
MAX5052/MAX5053
Current-Mode PWM Controllers with an Error
Amplifier for Isolated/Nonisolated Power Supplies
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.
Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 ____________________ 13
© 2003 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.
Package Information
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information,
go to www.maxim-ic.com/packages.)
8LUMAXD.EPS
PACKAGE OUTLINE, 8L uMAX/uSOP
1
1
21-0036
J
REV.DOCUMENT CONTROL NO.APPROVAL
PROPRIETARY INFORMATION
TITLE:
MAX
0.043
0.006
0.014
0.120
0.120
0.198
0.026
0.007
0.037
0.0207 BSC
0.0256 BSC
A2
A1
c
e
b
A
L
FRONT VIEW
SIDE VIEW
E H
0.6±0.1
0.6±0.1
ÿ 0.50±0.1
1
TOP VIEW
D
8
A2
0.030
BOTTOM VIEW
1
6∞
S
b
L
H
E
D
e
c
0∞
0.010
0.116
0.116
0.188
0.016
0.005
8
4X S
INCHES
-
A1
A
MIN
0.002
0.950.75
0.5250 BSC
0.25 0.36
2.95 3.05
2.95 3.05
4.78
0.41
0.65 BSC
5.03
0.66
6∞0∞
0.13 0.18
MAX
MIN
MILLIMETERS
- 1.10
0.05 0.15
α
α
DIM
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