MAX5052BEUA [MAXIM]
SMPS Controller ; SMPS控制器\n
| 型号： | MAX5052BEUA |
| 厂家： | 
MAXIM INTEGRATED PRODUCTS |
| 描述： | SMPS Controller
|
| 文件： | 总13页 (文件大小：321K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
19-2590; Rev 0; 10/02
Current-Mode PWM Controllers with an Error
Amplifier for Isolated/Nonisolated Power Supplies
General Description
Features
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.
ꢀ Available in a Tiny 8-Pin µMAX Package
ꢀ Current-Mode Control
ꢀ 50W Output Power
ꢀ Universal Offline Input Voltage Range
Rectified 85VAC to 265VAC (MAX5052)
ꢀ V Directly Driven from 10.8V to 24V Input
IN
The MAX5052/MAX5053 contain an internal error ampli-
fier 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 programma-
ble 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.
(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%
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.
ꢀ 50% Maximum Duty-Cycle Limit
(MAX5052A/MAX5053A)
ꢀ 75% Maximum Duty-Cycle Limit
(MAX5052B/MAX5053B)
The 262kHz switching frequency is internally trimmed to
12ꢀ accuracyꢁ this allows the optimization of the
magnetic and filter components resulting in compact,
cost-effective power supplies. The MAX5052A/
MAX5053A are offered with a 50ꢀ maximum duty-cycle
limit. The MAX5052B/MAX5053B are offered with a 75ꢀ
maximum duty-cycle limit. These devices are available
in 8-pin µMAX packages and operate over the -40°C to
+85°C temperature range.
ꢀ 60ns Cycle-by-Cycle Current-Limit Response Time
Ordering Information
PART
TEMP RANGE
-40°C to +85°C
-40°C to +85°C
-40°C to +85°C
-40°C to +85°C
PIN-PACKAGE
8 µMAX
MAX5052AEUA
MAX5052BEUA
MAX5053AEUA
MAX5053BEUA
8 µMAX
8 µMAX
8 µMAX
Warning: The MAX5052/MAX5053 are designed to work with
high voltages. Exercise caution.
Applications
Universal Input AC
Power Supplies
Industrial Power
Conversion
Pin Configuration
Isolated Telecom Power
Supplies
Isolated Keep-Alive
Circuits
TOP VIEW
Networking Systems
12V Boost Regulators
12V SEPIC Regulators
UVLO/EN
FB
1
2
3
4
8
7
6
5
V
V
IN
Computer Systems/
Servers
CC
MAX5052
MAX5053
COMP
CS
NDRV
GND
Functional Diagram/Typical Operating Circuit/Selector
Guide appear at end of data sheet.
µMAX
________________________________________________________________ Maxim Integrated Products
1
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.
Current-Mode PWM Controllers with an Error
Amplifier for Isolated/Nonisolated Power Supplies
ABSOLUTE MAXIMUM RATINGS
V
V
to GND .............................................................-0.3V to +30V
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
IN
CC
to GND............................................................-0.3V to +13V
FB, COMP, UVLO, CS to GND .................................-0.3V to +6V
NDRV to GND.............................................-0.3V to (V + 0.3V)
CC
Continuous Power Dissipation (T = +70°C)
A
8-Pin µMAX (derate 4.5mW/°C above +70°C)..............362mW
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
(V = +12V (for MAX5052, V must first be brought up to 23.6V for startup), 10nF bypass capacitors at V and V , C
= 0,
IN
IN
IN
CC
NDRV
V
UVLO
= +1.4V, V = +1.0V, V
= floating, V = 0V, typical values are measured at T = +25°C, T = -40°C to + 85°C, unless
COMP CS A A
FB
otherwise noted.) (Note 1)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
UNDERVOLTAGE LOCKOUT/STARTUP
Bootstrap UVLO Wake-Up Level
Bootstrap UVLO Shutdown Level
UVLO/EN Wake-Up Threshold
UVLO/EN Shutdown Threshold
UVLO/EN Input Current
V
V
V
V
rising (MAX5052 only)
falling (MAX5052 only)
19.68
9.05
21.6
9.74
1.28
1.23
25
23.60
10.43
1.371
1.291
V
V
SUVR
SUVF
ULR2
IN
IN
V
UVLO/EN rising
UVLO/EN falling
1.188
1.168
V
V
V
ULF2
I
T = +125°C
J
nA
mV
UVLO
UVLO/EN Hysteresis
50
V
Supply Current In
V
= +19V, for MAX5052 only when in
IN
IN
I
45
90
24
µA
V
START
Undervoltage Lockout
bootstrap UVLO
V
Range
V
10.8
IN
IN
t
UVLO/EN steps up from +1.1V to +1.4V
UVLO/EN steps down from +1.4V to +1.1V
12
1.8
5
EXTR
UVLO/EN Propagation Delay
µs
t
EXTF
t
V
V
steps up from +9V to +24V
BUVR
IN
IN
Bootstrap UVLO Propagation
Delay
µs
t
steps down from +24V to +9V
1
BUVF
INTERNAL SUPPLY
V
= +10.8V to +24V, sinking 1µA to 20mA
IN
V
Regulator Set Point
V
7
10.5
V
CC
CCSP
from V
CC
V
Supply Current After Startup
I
V = +24V
IN
1.4
2.5
90
mA
µA
IN
IN
Shutdown Supply Current
UVLO/EN = low
GATE DRIVER
R
Measured at NDRV sinking, 100mA
Measured at NDRV sourcing, 20mA
2
4
4
ON(LOW)
Driver Output Impedance
Ω
R
12
ON(HIGH)
Driver Peak Sink Current
Driver Peak Source Current
PWM COMPARATOR
Comparator Offset Voltage
CS Input Bias Current
1
A
A
0.65
VO
V
V
V
- V
CS
1.15
-2
1.38
1.70
+2
V
PWM
COMP
I
= 0V
µA
ns
ns
CS
CS
CS
Comparator Propagation Delay
Minimum On-Time
t
= +0.1V
60
PWM
t
150
ON(MIN)
2
_______________________________________________________________________________________
Current-Mode PWM Controllers with an Error
Amplifier for Isolated/Nonisolated Power Supplies
ELECTRICAL CHARACTERISTICS (continued)
(V = +12V (for MAX5052, V must first be brought up to 23.6V for startup), 10nF bypass capacitors at V and V , C
= 0,
IN
IN
IN
CC
NDRV
V
UVLO
= +1.4V, V = +1.0V, V
= floating, V = 0V, typical values are measured at T = +25°C, T = -40°C to + 85°C, unless
COMP CS A A
FB
otherwise noted.) (Note 1)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
CURRENT-LIMIT COMPARATOR
Current-Limit Trip Threshold
CS Input Bias Current
V
262
-2
291
320
+2
mV
µA
CS
I
V
= 0V
CS
CS
Propagation Delay From
Comparator Input to NDRV
t
50mV overdrive
60
ns
kHz
%
PWM
Switching Frequency
f
230
262
50
290
50.5
76
SW
MAX505_A
MAX505_B
Maximum Duty Cycle
D
MAX
75
V
CLAMP VOLTAGE
IN
V
Clamp Voltage
V
2mA sink current
24.1
26.1
29.0
V
IN
INC
ERROR AMPLIFIER
Voltage Gain
R
R
R
= 100kΩ
80
2
dB
MHz
LOAD
LOAD
LOAD
Unity-Gain Bandwidth
Phase Margin
= 100kΩ, C
= 100kΩ, C
= 200pF
= 200pF
LOAD
65
degrees
mV
LOAD
FB Input Offset Voltage
3
High
Low
2.2
0.4
3.5
1.1
COMP Pin Clamp Voltage
V
Source Current
0.5
mA
mA
V
Sink Current
0.5
Reference Voltage
V
(Note 2)
1.218
1.230
8
1.242
50
REF
Input Bias Current
nA
mA
COMP Short-Circuit Current
THERMAL SHUTDOWN
Thermal-Shutdown Temperature
Thermal Hysteresis
130
25
°C
°C
DIGITAL SOFT-START
clock
cycles
Soft-Start Duration
15,872
Reference Voltage Steps During
Soft-Start
31
40
steps
mV
Reference Voltage Step
Note 1: All devices are 100% tested at T = +85°C. All limits over temperature are guaranteed by characterization.
A
Note 2: V
is measured with FB connected to the COMP pin (see Functional Diagram).
REF
_______________________________________________________________________________________
3
Current-Mode PWM Controllers with an Error
Amplifier for Isolated/Nonisolated Power Supplies
Typical Operating Characteristics
(UVLO = +1.4V, V = +1V, V
= floating, V = 0V, T = +25°C, unless otherwise noted.)
FB
COMP
CS
A
BOOTSTRAP UVLO WAKE-UP LEVEL
vs. TEMPERATURE
BOOTSTRAP UVLO SHUTDOWN LEVEL
vs. TEMPERATURE
UVLO/EN WAKE-UP THRESHOLD
vs. TEMPERATURE
21.60
21.55
21.50
21.45
21.40
21.35
21.30
10.1
10.0
9.9
1.280
1.275
1.270
1.265
1.260
1.255
1.250
MAX5052 V RISING
MAX5052 V FALLING
UVLO/EN RISING
IN
IN
9.8
9.7
-40
-20
0
20
40
60
80
-40
-20
0
20
40
60
80
-40
-20
0
20
40
60
80
TEMPERATURE (°C)
TEMPERATURE (°C)
TEMPERATURE (°C)
UVLO/EN SHUTDOWN THRESHOLD
vs. TEMPERATURE
V
SUPPLY CURRENT AFTER STARTUP
vs. TEMPERATURE
V
SUPPLY CURRENT IN UNDERVOLTAGE
LOCKOUT vs. TEMPERATURE
IN
IN
1.30
1.25
1.20
1.15
1.10
1.5
1.4
1.3
1.2
1.1
52
51
50
49
48
47
46
45
44
43
42
UVLO/EN FALLING
V = 24V
IN
V
= 19V
IN
MAX5052 WHEN IN BOOTSTRAP UVLO
MAX5053 WHEN UVLO/EN IS LOW
-40
-20
0
20
40
60
80
-40
-20
0
20
40
60
80
-40
-20
0
20
40
60
80
TEMPERATURE (°C)
TEMPERATURE (°C)
TEMPERATURE (°C)
V
REGULATOR SET POINT
vs. TEMPERATURE
CURRENT-LIMIT TRIP THRESHOLD
vs. TEMPERATURE
V
REGULATOR SET POINT
vs. TEMPERATURE
CC
CC
8.9
8.8
8.7
8.6
8.5
8.4
8.3
8.2
8.1
310
305
300
295
290
285
280
275
270
9.8
9.7
9.6
9.5
9.4
9.3
9.2
TOTAL NUMBER OF
DEVICES = 100
V
= 10.8V
V
= 19V
IN
IN
+3σ
NO LOAD
NDRV OUTPUT IS NOT
SWITCHING, V = 1.5V
FB
10mA LOAD
20mA LOAD
MEAN
NDRV OUTPUT IS
SWITCHING
-3σ
-40
-20
0
20
40
60
80
-40
-20
0
20
40
60
80
-40
-20
0
20
40
60
80
TEMPERATURE (°C)
TEMPERATURE (°C)
TEMPERATURE (°C)
4
_______________________________________________________________________________________
Current-Mode PWM Controllers with an Error
Amplifier for Isolated/Nonisolated Power Supplies
Typical Operating Characteristics (continued)
(UVLO = +1.4V, V = +1V, V
= floating, V = 0V, T = +25°C, unless otherwise noted.)
CS A
FB
COMP
SWITCHING FREQUENCY
vs. TEMPERATURE
SWITCHING FREQUENCY
CURRENT-LIMIT TRIP THRESHOLD
280
30
25
20
15
10
5
30
25
20
15
10
5
TOTAL NUMBER OF
DEVICES = 100
TOTAL NUMBER OF
DEVICES = 200
TOTAL NUMBER OF
DEVICES = 200
+3σ
275
270
265
260
255
250
245
240
MEAN
-3σ
0
0
-40
-20
0
20
40
60
80
230
240
250
260
270
280
290
260
270
280
290
300
310
320
TEMPERATURE (°C)
SWITCHING FREQUENCY (kHz)
CURRENT-LIMIT TRIP THRESHOLD (mV)
REFERENCE VOLTAGE
vs. TEMPERATURE
PROPAGATION DELAY FROM CURRENT-LIMIT
COMPARATOR INPUT TO NDRV vs. TEMPERATURE
75
UVLO/EN PROPAGATION DELAY
vs. TEMPERATURE
1.230
1.229
1.228
1.227
1.226
1.225
14
13
12
11
10
9
8
7
6
5
V
= 12V
IN
UVLO/EN RISING
70
65
60
55
50
4
3
2
1
UVLO/EN FALLING
0
-40
-20
0
20
40
60
80
-40
-20
0
20
40
60
80
-40
-20
0
20
40
60
80
TEMPERATURE (°C)
TEMPERATURE (°C)
TEMPERATURE (°C)
INPUT CURRENT
vs. INPUT CLAMP VOLTAGE
INPUT CLAMP VOLTAGE
vs. TEMPERATURE
NDRV OUTPUT IMPEDANCE
vs. TEMPERATURE
10
9
8
7
6
5
4
3
2
1
0
27.0
26.8
26.6
26.4
26.2
26.0
25.8
25.6
25.4
25.2
25.0
2.2
2.1
2.0
1.9
1.8
1.7
1.6
1.5
1.4
1.3
1.2
I
= 2mA
V
= 24V
IN
IN
SINKING 100mA
10.0 12.5 15.0 17.5 20.0 22.5 25.0 27.5 30.0
INPUT VOLTAGE (V)
-40
-20
0
20
40
60
80
-40
-20
0
20
40
60
80
TEMPERATURE (°C)
TEMPERATURE (°C)
_______________________________________________________________________________________
5
Current-Mode PWM Controllers with an Error
Amplifier for Isolated/Nonisolated Power Supplies
Typical Operating Characteristics (continued)
(UVLO = +1.4V, V = +1V, V
= floating, V = 0V, T = +25°C, unless otherwise noted.)
CS A
FB
COMP
ERROR AMP OPEN-LOOP GAIN
AND PHASE vs. FREQUENCY
NDRV OUTPUT IMPEDANCE
vs. TEMPERATURE
MAX5052 toc20
120
100
80
50
5.0
4.8
4.6
4.4
4.2
4.0
3.8
3.6
3.4
3.2
3.0
V
= 24V
SOURCING 20mA
IN
30
10
GAIN
60
-10
-30
-50
-70
-90
-110
-130
-150
-170
40
20
0
PHASE
-20
-40
-60
-80
-100
0.1
1
10
100
1k
10k 100k 1M 10M 100M
-40
-20
0
20
40
60
80
FREQUENCY (Hz)
TEMPERATURE (°C)
Pin Description
PIN
NAME
FUNCTION
Externally Programmable Undervoltage Lockout. UVLO programs the input start voltage. Connect UVLO to
GND to disable the device.
1
UVLO/EN
2
3
FB
Error-Amplifier Inverting Input
Error-Amplifier Output
COMP
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.
4
CS
5
6
7
GND
Power-Supply Ground
NDRV
External N-Channel MOSFET Gate Connection
V
Gate-Drive Supply. Internally regulated down from V . Decouple with a 10nF or larger capacitor to GND.
IN
CC
IC Supply. Decouple with a 10nF or larger capacitor to GND. For bootstrapped operation (MAX5052)
8
V
connect a startup resistor from the input supply line to V . Connect the bias winding supply to this point as
IN
IN
well (see the Typical Operating Circuit). For the MAX5053, connect V directly to 10.8V to 24V supply.
IN
supplies increases their input supply current as the
input voltage drops in order to keep the output power
Detailed Description
The MAX5052/MAX5053 are current-mode PWM con-
trollers 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 pre-
venting the power supply from entering a brownout
condition, in case the input voltage drops below its
minimum value. This is important since switching 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
6
_______________________________________________________________________________________
Current-Mode PWM Controllers with an Error
Amplifier for Isolated/Nonisolated Power Supplies
(max). V is the value of the input-supply voltage
IN
where the power supply must start.
D1
T1
V
SUPPLY
D2
V
OUT
R5
V
− V
ULR2
IN
R2 =
× R3
R2
V
R1
C1
ULR2
C4
Q1
where I
is the UVLO/EN pin input current (50nA),
UVLO
V
V
NDRV
CS
IN
and V
is the UVLO/EN wake-up threshold.
ULR2
MAX5052
CC
C2
MAX5052 Bootstrap
Undervoltage Lockout
C3
R4
GND
R6
COMP
FB
In addition to the externally programmable UVLO func-
tion 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
UVLO/EN
R3
0V
MAX5052 attempts to start when V exceeds the boot-
IN
Figure 1. Nonisolated Power Supply with Programmable Input-
Supply Start Voltage
strap UVLO threshold of 21.6V.
During startup, the UVLO circuit keeps the CPWM com-
parator, ILIM comparator, oscillator, and output driver
the power dissipation across R1 even at the high end of
the universal AC input voltage (265VAC).
shut down to reduce current consumption. Once V
IN
The MAX5052/MAX5053 include a cycle-by-cycle cur-
rent 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 power-
supply 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.
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 V drops below
IN
9.7V, the UVLO circuit will shut down the CPWM com-
parator, ILIM comparator, oscillator, and output driver
returning the MAX5052/MAX5053 to the startup mode.
MAX5052 Startup Operation
Normally V is derived from a tertiary winding of the
IN
transformer. However, at startup there is no energy
delivered through the transformer, hence, a special
bootstrap sequence is required. Figure 2 shows the
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 con-
sumption (see the Functional Diagram).
voltages on V and V
during startup. Initially, both
CC
IN
V
and V
are 0V. After the line voltage is applied,
IN
CC
C1 charges through the startup resistor, R1, to an inter-
mediate 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 charg-
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:
ing of C2 stops when the V
voltage reaches approxi-
CC
mately 9.5V, while the voltage across C1 continues
rising until it reaches the wake-up level of 21.6V. Once
V
exceeds the bootstrap UVLO threshold, NDRV
IN
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 accom-
plished and sustained operation commences.
V
× V
ULR2
IN
− V
R3 ≅
500 × I
V
(
)
UVLO IN
ULR2
The value of R3 is calculated to minimize the voltage-
drop error across R2 as a result of the input bias cur-
rent of the UVLO/EN pin. V
= 1.28V, I
= 50nA
UVLO
ULR2
_______________________________________________________________________________________
7
Current-Mode PWM Controllers with an Error
Amplifier for Isolated/Nonisolated Power Supplies
where I is the MAX5052’s internal supply current after
IN
startup (1.4mA), Q
is the total gate charge for Q1,
gtot
V
CC
f
is the MAX5052’s switching frequency (262kHz),
is the bootstrap UVLO hysteresis (12V) and t is
ss
SW
2V/div
V
hyst
the internal soft-start time (60ms).
MAX5052
IN
5V/div
For example:
V
PIN
I = (8nC) (262kHz) ≅ 2.1mA
g
0V
1.4mA +2.1mA 60ms
) (
(
)
=17.5µF
C1=
12V
(
)
choose 15µF standard value.
Assuming C1 > C2, calculate the value of R1 as follows:
× C1
100ms/div
Figure 2. V and V
During Startup when Using the
CC
MAX5052 in Bootstrapped Mode (Figure 1)
IN
V
SUVR
I
=
C1
500ms
(
)
If V drops below 9.9V before startup is complete, the
IN
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.
V
− V
IN(MIN)
SUVR
R1=
I
+ I
START
C1
Startup Time Considerations For Power
Supplies Using the MAX5052
where V
is the minimum input supply voltage for
IN(MIN)
the application (36V for telecom), V
is the boot-
SUVR
The V bypass capacitor, C1, supplies current imme-
IN
strap UVLO wake-up level (23.6V max.), I
is the
START
diately 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 start-
V
IN
supply current at startup (90µA, max).
For example:
24V 15µF
(
) (
)
= 0.72mA
I
=
(
C1
500ms
up. If the value of C1 is too small, V drops below 9.9V
IN
(
)
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.
36V − 12V
)
(
)
R1=
= 29.6kΩ
0.72mA + 90µA
(
)
(
)
choose 32kΩ standard value.
As a rule of thumb, offline power supplies keep typical
startup times to less than 500ms even in low-line condi-
tions (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 cur-
rent to the device for at least this much time. To calcu-
late the approximate amount of capacitance required,
use the following formula:
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 simi-
lar 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 reg-
ulating the output voltage and to connect the bias wind-
ing so that it is in phase with the MOSFET ON time (see
Figure 3). The amount of capacitance required is much
I
= Q
× f
SW
g
gtot
IN
I
(
+ I
t
(
)
)
g
SS
C1=
V
hyst
8
_______________________________________________________________________________________
Current-Mode PWM Controllers with an Error
Amplifier for Isolated/Nonisolated Power Supplies
D1
T1
+V
IN
D2
V
OUT
R2
R1
C1
C4
Q1
U1
V
V
NDRV
CS
IN
R8
R9
C3
MAX5052
CC
U2
OPTO LED
R7
U2
R4
GND
OPTO TRANS
COMP
FB
U3
TL431
R5
UVLO/EN
R10
R3
R6
C2
-V
IN
Figure 3. Secondary-Side Regulated, Isolated Power Supply
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 sup-
ply hiccups and soft-start under output short-circuit con-
ditions. Whereas, this property is lost if the bias winding
is in phase with the MOSFET ON time.
1V/div
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 volt-
age. This is a result of the digital soft-starting technique
used. Unlike other devices, the MAX5052/MAX5053 ref-
erence voltage to the internal amplifier is soft-started;
this method results in superior control of the output volt-
age under heavy- and light-load conditions.
0V
10ms/div
Figure 4. Output Voltage Soft-Start During Initial Startup for the
Circuit of Figure 5
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 opera-
tion on the Q outputs of both D flip-flops to provide a
duty cycle of 75%.
N-Channel MOSFET Switch Driver
The NDRV pin drives an external N-channel MOSFET.
The NDRV output is supplied by the internal regulator
(V ), which is internally set to approximately 9.5V. For
CC
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
_______________________________________________________________________________________
9
Current-Mode PWM Controllers with an Error
Amplifier for Isolated/Nonisolated Power Supplies
IN
FB_P
T1
D8
D6
D2
VOUT2 (+15V/0.1A)
L2
9
10
8
5
4
C5
47µF
25V
C15
1µF
C16
15µF
35V
R6
33kΩ
R7
1.2kΩ
R12
1.2kΩ
C12
0.22µF
D5
D7*
SGND
OPEN
+V
IN
VOUT1 (+5V/1.5A)
+VIN
D1
L1
3
2
1
7
6
C3
C4
C1
1µF
100V
C2
C13
1µF
C10*
OPEN
68µF
22µF
R8*
OPEN
D4
1µF
SGND
6.3V
6.3V
100V
C6
0.0047µF
D3*
250VAC
OPEN
FB_P
R1
22.6kΩ
1%
IN
2
8
FB
V
IN
C11
C9
2200pF
R2
2.49kΩ
1%
0.22µF
6
R9
5
4
8
7
4.3kΩ
N1
3
3
6
4
COMP
NDRV
CS
U1
1
2
R10
0Ω
C14
0.022µF
+V
R11
100Ω
IN
MAX5052A
1
7
UVLO/EN
C8
OPEN
R3
R5
1MΩ
1%
0.17Ω
1%
5
V
GND
CC
C7
R4
0.22µF
42.2kΩ
1%
-VIN
SHDN
*COMPONENTS MARKED "OPEN" ARE OPTIONAL.
(SEE MAX5052A EV KIT DATA SHEET.)
JU1
Figure 5. Primary Regulated, Dual-Output, Isolated Telecom Power Supply
where V
= 1.23V. The amplifier’s noninverting input
REF
is internally connected to a digital soft-start circuit that
gradually increases the reference voltage during start-
up and is applied to this pin. This forces the output volt-
age to come up in an orderly and well-defined manner
under all load conditions.
262kHz WITH 50%
D
Q
Q
D
Q
Q
(MAX5052A/MAX5053A)
OSCILLATOR
1.048MHz
262kHz WITH 75%
(MAX5052B/MAX5053B)
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 5).
Calculate the output voltage using the following equation:
Figure 6. Internal Oscillator
Internal Error Amplifier
The MAX5052/MAX5053 include an internal error ampli-
fier 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:
N
N
R1
R2
S
V
=
1 +
V
+ V
D6
− V
D1
OUT1
REF
T
R5
R6
where N is the number of secondary turns for V
T
,
S
OUT1
V
= 1 +
V
REF
OUT
N is the number of tertiary winding turns, and both V
D6
and V are the diode drops at the respective outputs.
D1
10 ______________________________________________________________________________________
Current-Mode PWM Controllers with an Error
Amplifier for Isolated/Nonisolated Power Supplies
Current Limit
Layout Recommendations
All printed circuit board traces carrying switching cur-
rents must be kept as short as possible, and the cur-
rent loops they form must be minimized. The pins of the
µMAX package have been placed to allow easy inter-
facing to the external MOSFET.
The current-sense resistor (R ), connected between
CS
the source of the MOSFET and ground, sets the current
limit. The CS input has a voltage-trip level (V ) of
CS
291mV. Use the following equation to calculate the
value of R
:
CS
V
CS
For universal AC input design, all applicable safety reg-
ulations 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.
R
=
CS
I
PRI
Where I
is the peak current in the primary that flows
PRI
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) 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.
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 cur-
rent often form high di/dt loops. Similarly, the heatsink
of the MOSFET presents a dv/dt source, thus the sur-
face 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 sin-
gle-system ground connection.
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.
Chip Information
TRANSISTOR COUNT: 1449
In the circuit of Figure 5, cross-regulation has been
improved (tertiary and 5V outputs) by using chip induc-
tors, 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.
PROCESS: BiCMOS
L1
D1
5V OUTPUT LOAD REGULATION
12V
15V
6.0
5.8
5.6
5.4
5.2
5.0
4.8
4.6
4.4
4.2
R2
C4
Q1
R5
V
V
NDRV
CS
IN
C1
MAX5053
CC
C2
C3
R1
GND
R6
COMP
FB
UVLO/EN
R3
4.0
0.15 0.35 0.55 0.75 0.95 1.15 1.35
0V
I
(A)
OUT
Figure 7. Output Voltage Regulation for the Figure 5 Circuit
Figure 8. 12V to 15V Out Boost Regulator
______________________________________________________________________________________ 11
Current-Mode PWM Controllers with an Error
Amplifier for Isolated/Nonisolated Power Supplies
Functional Diagram
V
IN
V
V
CC
IN
CC
V
IN
CLAMP
REGULATOR
REG_OK
26.1V
BOOTSTRAP UVLO
V
L
**
DIGITAL
SOFT-START
REFERENCE
1.23V
21.6V
9.74V
(INTERNAL 5.25V SUPPLY)
UVLO
UVLO
1.28V
1.23V
COMP
DRIVER
S
R
Q
FB
NDRV
GND
ERROR
AMP
CPWM
OSCILLATOR
262kHz*
CS
1.4V
VO
PWM
THERMAL
SHUTDOWN
V
CS
0.3V
MAX5052/MAX5053
*MAX5052A/MAX5053A: 50% MAXIMUM DUTY CYCLE,
MAX5052B/MAX5053B: 75% MAXIMUM DUTY CYCLE.
**MAX5052 ONLY.
ILIM
Typical Operating Circuit
Selector Guide
D1
BOOTSTRAP
UVLO
STARTUP
VOLTAGE
MAX DUTY
CYCLE
T1
PART
D2
C4
R7
C5
MAX5052A
MAX5052B
MAX5053A
MAX5053B
Yes
Yes
No
22V
22 V
50%
75%
50%
75%
V
SUPPLY
V
OUT
R2
R1
C1
D4
10.8V*
10.8V*
Q1
No
V
V
NDRV
CS
IN
*The MAX5053 does not have an internal bootstrap UVLO. The
MAX5053 starts operation as long as the V pin is higher than
MAX5052
CC
CC
C2
C3
7V (the guaranteed output with a V pin voltage of 10.8V) and
the UVLO/EN pin is high.
IN
R4
GND
R5
R6
COMP
FB
UVLO/EN
R3
0V
12 ______________________________________________________________________________________
Current-Mode PWM Controllers with an Error
Amplifier for Isolated/Nonisolated Power Supplies
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.)
4X S
8
8
MILLIMETERS
INCHES
DIM MIN
MAX
MAX
MIN
-
-
0.043
0.006
0.037
0.014
0.007
0.120
1.10
0.15
0.95
0.36
0.18
3.05
A
0.002
0.030
0.010
0.005
0.116
0.05
0.75
0.25
0.13
2.95
A1
A2
b
E
H
ÿ 0.50±0.1
c
D
e
0.0256 BSC
0.65 BSC
0.6±0.1
E
H
0.116
0.188
0.016
0∞
0.120
2.95
4.78
0.41
0∞
3.05
5.03
0.66
6∞
0.198
0.026
6∞
L
1
1
α
S
0.6±0.1
0.0207 BSC
0.5250 BSC
BOTTOM VIEW
D
TOP VIEW
A1
A2
A
c
α
e
L
b
SIDE VIEW
FRONT VIEW
PROPRIETARY INFORMATION
TITLE:
PACKAGE OUTLINE, 8L uMAX/uSOP
APPROVAL
DOCUMENT CONTROL NO.
REV.
1
21-0036
J
1
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
© 2002 Maxim Integrated Products
Printed USA
is a registered trademark of Maxim Integrated Products.
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