Maxim MAX5021EUT, MAX5022EUT, MAX5021EPA, MAX5021EUA, MAX5022EPA Schematic [ru]

...
General Description
The MAX5021/MAX5022 current-mode PWM controllers contain all the control circuitry required for the design of wide input voltage range isolated power supplies. These devices are well suited for use in universal input (85VAC to 265VAC) off-line or telecom (-36VDC to
-72VDC) power supplies.
-40°C to +85°C temperature range.
Applications
Universal Off-Line Power Supplies
Standby Power Supplies
Isolated Power Supplies
Isolated Telecom Power Supplies
Mobile Phone Chargers
Features
Available in a Tiny 6-Pin SOT23 Package
50µA Typical Startup Current
1.2mA Typical Operating Current
Large UVLO Hysteresis of 14V
Fixed Switching Frequency of 262kHz ±12%
50% Maximum Duty Cycle Limit (MAX5021)
75% Maximum Duty Cycle Limit (MAX5022)
60ns Cycle-by-Cycle Current-Limit Response
Time
MAX5021/MAX5022
Current-Mode PWM Controllers for Isolated
Power Supplies
________________________________________________________________ Maxim Integrated Products 1
Pin Configuration
Ordering Information
MAX5021 MAX5022
V
OUT
V
SUPPLY
OPTO NDRV
CS
V
CC
V
IN
GND
Typical Operating Circuit
19-2066; Rev 1; 9/01
EVALUATION KIT AVAILABLE
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.
WARNING: The MAX5021/MAX5022 are designed to work with high voltages. Exercise caution!
MAX
PART
MAX5021EUT 50% -40°C to +85°C 6 SOT23-6 AASQ
MAX5021EUA 50% -40°C to +85°C 8 µMAX MAX5021EPA 50% -40°C to +85°C 8 PDIP MAX5022EUT 75% -40°C to +85°C 6 SOT23-6 AASR MAX5022EUA 75% -40°C to +85°C 8 µMAX MAX5022EPA 75% -40°C to +85°C 8 PDIP
DUTY
CYCLE
TEMP.
RANGE
PIN­ PACKAGE
TOP
MARK
TOP VIEW
16OPTO
CS
GND
NDRV
MAX5021
2
MAX5022
34
SOT23
1
OPTO
2
5 V
IN
IN
V
CC
V
CC
3
4
PDIP/µMAX
MAX5021 MAX5022
87CS
6
5
GNDV
NDRV
N.C.N.C.
MAX5021/MAX5022
Current-Mode PWM Controllers for Isolated Power Supplies
2 _______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS
(VIN= +11V to +28V, VCS= 0, OPTO is unconnected, 10nF bypass capacitors at VINand VCC, NDRV unconnected, TA= -40°C to +85°C, unless otherwise noted. Typical values are at V
IN
= +12V, TA= +25°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
V
CC
to GND............................................................-0.3V to +13V
NDRV to GND.............................................-0.3V to (V
CC
+ 0.3V)
CS, OPTO to GND ....................................................-0.3V to +6V
NDRV Short-Circuit to GND........................................Continuous
Continuous Power Dissipation (T
A
= +70°C)
6-Pin SOT23 (derate 8.7mW/°C above +70°C).............696mW
8-Pin µMAX (derate 4.5mW/°C above +70°C) ..............362mW
8-Pin PDIP (derate 9.1mW/°C above +70°C)................727mW
Operating Temperature Range ...........................-40°C to +85°C
Storage Temperature Range .............................-55°C to +150°C
Lead Temperature (soldering 10s) ..................................+300°C
)
)
)
UNDERVOLTAGE LOCKOUT/STARTUP
CURRENT-LIMIT COMPARATOR
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
Undervoltage Lockout Wakeup Level
Undervoltage Lockout Shutdown Level
VIN Supply Current at Startup I
VIN Range V
Undervoltage Lockout Propagation Delay
INTERNAL SUPPLY
VCC Regulator Set Point V
VIN Supply Current after Startup I
GATE DRIVER
Driver Output Impedance
Driver Peak Sink Current I
Driver Peak Source Current I
PWM COMPARATOR
Comparator Offset Voltage VO
CS Input Bias Current I
Propagation Delay from Comparator Input to NDRV
Minimum On-Time T
Current-Limit Trip Threshold V
Current-Limit Propagation Delay from Comparator Input to NDRV
V
V
STARTVIN
T
T
R
ON(LOW
R
ON(HIGH
SOURCE
T
ON(MIN
UVR
UVF
UVR
UVF
CCSP
SINK
PWM
T
VIN rising 22 24 26 V
VIN falling 9.3 10 10.9 V
IN
VIN steps up from +9V to +26V 5
VIN steps down from +26V to +9V 1
VIN = +11V to +28V, sourcing 1µA to 5mA from V
VIN = +28V, OPTO connected to GND 0.9 2.43
IN
VIN = +28V, OPTO unconnected (Note 2) 0.4
Measured at NDRV sinking 5mA 10 20
Measured at NDRV sourcing 5mA 20 40
PWMVOPTO
CS
25mV overdrive 60 ns
CS
25mV overdrive 60 ns
CL
= +22V 50 85 µA
CC
- V
CS
11 28 V
7.0 10.5 V
250 mA
150 mA
600 750 900 mV
-2 +2 µA
150 ns
540 600 660 mV
µs
mA
MAX5021/MAX5022
Current-Mode PWM Controllers for Isolated
Power Supplies
_______________________________________________________________________________________ 3
ELECTRICAL CHARACTERISTICS (continued)
(VIN= +11V to +28V, VCS= 0, OPTO is unconnected, 10nF bypass capacitors at VINand VCC, NDRV unconnected, TA= -40°C to +85°C, unless otherwise noted. Typical values are at V
IN
= +12V, TA= +25°C, unless otherwise noted.) (Note 1)
Note 1: All devices are 100% tested at T
A
= +25°C. All limits over temperature are guaranteed by characterization.
Note 2: This minimum current after startup is a safeguard that prevents the V
IN
pin voltage from rising in the event
that OPTO and NDRV become unconnected.
Typical Operating Characteristics
(VIN= 15V, TA = +25°C, unless otherwise noted.)
23.9
24.0
24.1
24.2
24.3
UNDERVOLTAGE LOCKOUT
vs. TEMPERATURE
MAX5021/22 toc01
TEMPERATURE (°C)
UNDERVOLTAGE LOCKOUT (V)
-40 20 40-20 0 60 80
VIN RISING
9.8
9.9
10.0
10.1
10.2
UNDERVOLTAGE LOCKOUT
vs. TEMPERATURE
MAX5021/22 toc02
TEMPERATURE (°C)
UNDERVOLTAGE LOCKOUT (V)
-40 20 40-20 0 60 80
VIN FALLING
47
48
49
50
51
52
53
-40 -20 0 20 40 60 80
STARTUP CURRENT
vs. TEMPERATURE
MAX5021/22 toc03
TEMPERATURE (°C)
STARTUP CURRENT (µA)
VIN = 23.0V
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
OSCILLATOR
Switching Frequency f
Maximum Duty Cycle D
SW
MAX
MAX5021 50 51
MAX5022 75 76
OPTO INPUT
OPTO Pullup Voltage V
OPTO Pullup Resistance R
OPTO
OPTO
OPTO sourcing 10µA 5.5 V
230 262 290 kHz
4.5 6.2 7.9 k
%
MAX5021/MAX5022
Current-Mode PWM Controllers for Isolated Power Supplies
4 _______________________________________________________________________________________
Typical Operating Characteristics (continued)
(VIN= 15V, TA = +25°C, unless otherwise noted.)
1.40
1.45
1.50
1.55
1.60
SUPPLY CURRENT
vs. TEMPERATURE
MAX5021/22 toc04
TEMPERATURE (°C)
SUPPLY CURRENT (mA)
-40 20 40-20 0 60 80
VIN = 28.0V V
OPTO
= VCS = 0
9.00
9.03
9.09
9.06
9.12
9.15
-40 0-20 20 40 60 80
MAXIMUM VCC
vs. TEMPERATURE
MAX5021/22 toc05
TEMPERATURE (°C)
MAXIMUM V
CC
(V)
VIN = 28.0V V
CS
= 0
OPTO = UNCONNECTED
7.70
7.90
7.80
8.10
8.00
8.20
8.30
-40 20 40-20 0 60 80
MINIMUM VCC
vs. TEMPERATURE
MAX5021/22 toc06
TEMPERATURE (°C)
MINIMUM V
CC
(V)
VIN = 10.8V 5mA LOAD ON V
CC
VCS = 0 OPTO = UNCONNECTED
570
590
580
610
600
630
620
640
-40 0 20-20 40 60 80
CURRENT SENSE THRESHOLD
vs. TEMPERATURE
MAX5021/22 toc07
TEMPERATURE (°C)
CURRENT SENSE THRESHOLD (mV)
+3σ
-3σ
MEAN
TOTAL NUMBER OF DEVICES = 50
0
5
15
10
20
25
540 580560 620
640 660
CURRENT SENSE
THRESHOLD
MAX5021/22 toc08
CURRENT SENSE THRESHOLD (mV)
FREQUENCY (%)
TOTAL NUMBER OF DEVICES = 200
600
245
255
250
265
260
275
270
280
-40 0 20-20 40 60 80
OSCILLATOR FREQUENCY
vs. TEMPERATURE
MAX5021/22 toc09
TEMPERATURE (°C)
OSCILLATOR FREQUENCY (kHz)
TOTAL NUMBER OF DEVICES = 50
+3σ
-3σ
MEAN
0
5
15
10
20
25
230 250240 260 270 280 290
OSCILLATOR FREQUENCY
MAX5021/22 toc10
OSCILLATOR FREQUENCY (kHz)
FREQUENCY (%)
TOTAL NUMBER OF DEVICES = 200
50
55
65
60
70
75
-40 0-20 20 40 60 80
CURRENT SENSE DELAY
vs. TEMPERATURE
MAX5021/22 toc11
TEMPERATURE (°C)
CURRENT SENSE DELAY (ns)
0
2
1
4
3
5
6
-40 20 40-20 0 60 80
UNDERVOLTAGE LOCKOUT DELAY vs. TEMPERATURE
MAX5021/22 toc12
TEMPERATURE (°C)
UNDERVOLTAGE LOCKOUT DELAY (µs)
VIN RISING
VIN FALLING
Detailed Description
The MAX5021/MAX5022 are current-mode PWM con­trollers that have been specifically designed for use in isolated power supplies. An undervoltage lockout cir­cuit (UVLO) with a large hysteresis (14V) along with very low startup and operating current result in high­efficiency, universal input power supplies. Both devices can be used in power supplies capable of operating from a universal 85VAC to 265VAC line or the telecom voltage range of -36VDC to -72VDC.
Power supplies designed with these devices use a high-value startup resistor, RS, (series combination of R1and R2) that charges a reservoir capacitor, C2 (see Figure 1). During this initial period while the voltage is less than the UVLO start threshold, the IC typically con­sumes only 50µA of quiescent current. This low startup current and the large UVLO hysteresis combined with the use of a ceramic capacitor C2 keeps the power dis­sipation in RSto less than 1/4W even at the high end of the universal AC input voltage (265VAC).
The MAX5021/MAX5022 include a cycle-by-cycle cur­rent limit which turns off the gate drive to the external MOSFET during an overcurrent condition. If the output on the secondary side of transformer T1 is shorted, the tertiary winding voltage will drop below the 10V thresh­old causing the UVLO circuit to turn off the gate drive to the external power MOSFET, thus re-initiating the start­up sequence.
Startup
Figure 2 shows the voltages on VINand VCCduring startup. Initially, both VINand VCCare 0V. After the line voltage is applied, C2 charges through the startup resistor, RS, to an intermediate voltage at which point the internal reference and regulator begin charging C3 (see Figure 1). The bias current consumed by the device during this period is only 50µA; the remaining input current charges C2 and C3. Charging of C3 stops when the VCCvoltage reaches approximately 9.5V, while the voltage across C2 continues rising until it reaches the wakeup level of 24V. Once VINexceeds the UVLO threshold, NDRV begins switching the MOSFET, transferring energy to the secondary and ter­tiary outputs. If the voltage on the tertiary output builds to higher than 10V (UVLO lower threshold), then startup has been accomplished and sustained operation will commence.
If VINdrops below 10V before startup is complete, then the IC goes back into UVLO. In this case, increase the value of C2 and/or use a MOSFET with a lower gate­charge requirement.
Startup Time Considerations
The VINbypass capacitor C2 supplies current immediate­ly after wakeup. The size of C2 will determine the number of cycles available for startup. Large values for C2 will increase the startup time, but will also supply more gate charge, allowing for more cycles after wakeup. If the value of C2 is too small, VINwill drop below 10V because
MAX5021/MAX5022
Current-Mode PWM Controllers for Isolated
Power Supplies
_______________________________________________________________________________________ 5
Pin Description
PIN
SOT23
18CS
2 7 GND Power-Supply Ground
3 6 NDRV External N-Channel MOSFET Gate Connection
43V
52V
6 1 OPTO
4, 5 N.C. No Connection. Do not make connections to these pins.
PDIP
µMAX
NAME FUNCTION
C ur r ent S ense C onnecti on for P WM Reg ul ati on and Over cur r ent P r otecti on. The cur r ent- l i m i t com p ar ator thr eshol d i s i nter nal l y set to 0.6V .
CC
IN
Gate Drive Supply. Internally regulated down from VIN. Decouple with a 10nF or larger capacitor to GND.
IC Supply. Decouple with a 10nF or larger capacitor to GND. Connect a startup resistor
) from the input supply line to VIN. Connect to bias winding through diode rectifier.
(R
s
See Typical Operating Circuit.
Optocoupler Transistor Collector Connection. Connect emitter of optocoupler to GND. The OPTO has an internal pullup resistor with a typical value of 6.2kΩ.
MAX5021/MAX5022
NDRV did not switch enough times to build up sufficient voltage across the tertiary output to power the device. The device will go back into UVLO and will not start. Use a low-leakage ceramic or film capacitor for C2 and C3.
As a rule of thumb, off-line power supplies keep typical startup times to less than 500ms even in low-line condi­tions (85VAC input). Size the startup resistor, R
S
, to sup­ply the maximum startup bias of the IC (85µA) plus the additional current required for charging the capacitors C2 and C3 in less than 500ms. This resistor dissipates continuous power in normal operation, despite the fact that it is only used during the startup sequence. Therefore it must be chosen to provide enough current for the low-line condition as well as have an appropriate power rating for the high-line condition (265VAC). In most cases, split the value into two resistors connected in series for the required voltage of approximately 400VDC.
The typical value for C2 and C3 is 220nF. The startup resistor, RS, provides both the maximum quiescent cur­rent of 85µA and the charging current for C2 and C3. Bypass capacitor C3 charges to 9.5V and C2 charges
to 24V all within the desired time period of 500ms, for an overall average charging current of 15µA. Hence, the startup resistor must provide a total of at least 100µA. Developing 100µA from an input voltage of
Current-Mode PWM Controllers for Isolated Power Supplies
6 _______________________________________________________________________________________
Figure 1. Universal 5W Off-Line Standby Power Supply
Figure 2. VINand VCCDuring Startup
CENTRAL SEMICONDUCTOR
CBR1-D100S
L
85VAC TO
265VAC IN
N
G
AC
C1
AC
10µF 400V
OPTO
CNY17-3
0.22µF
250mA, 75V
CMPD914
C3
CENTRAL SEMICONDUCTOR
FAIRCHILD
L2
470µH
R8
1.2k
D1
V
CC
MAX5022
OPTO NDRV
U1
C9 10µF 400V
R1 360k RS = R1 + R2
R2 360k
C2
0.22µF
V
IN
CTX03-15256
480µH, 60T
D1
R11 10
8T
N1 INTERNATIONAL RECTIFIER IRFRC20
T1
ON SEMICONDUCTOR
3T
C7
1000pF
D2
3A, 40V
MBRS340T3
C4
150µF
6.3V
INSTRUMENTS
1k
OPTO
TEXAS
TLV431AIDBV
1%
R3
R10
10
0.01µF
24.9k
C5
8.06k
1%
1%
+5V OUT
C6
R4
0.1µF
R5
CS
GND
240k
R9
8200pF
C8
NOTE: ALL RESISTORS ARE 5% UNLESS OTHERWISE SPECIFIED.
R6
10
R
CS
1.78 1%
25
20
15
(V)
CC
, V
IN
10
V
5
0
0 10050 150 200
V
IN
V
CC
IC COMES OUT OF UVLO (WAKEUP)
SUPPLIED BY C2
V
IN
SUPPLIED BY TERTIARY
V
IN
WINDING (NORMAL OPERATION)
V
BYPASS CAPACITOR
CC
FULLY CHARGED
DROPS SLIGHTLY WHEN
V
CC
NDRV BEGINS SWITCHING
TIME (ms)
85VAC (corresponding to 120VDC) to the 24V wakeup level results in a resistor value of about 1M. If we assume RSvalues between 750kand 1M, then at the high-line voltage of 265VAC (corresponding to 374VDC) power dissipation will be between 140mW to 190mW. A single 1/4W resistor or a series combination of two 1/4W resistors is adequate.
Undervoltage Lockout (UVLO)
The device will attempt to start when VINexceeds the UVLO threshold of 24V. During startup, the UVLO cir­cuit keeps the CPWM comparator, ILIM comparator, oscillator, and output driver shut down to reduce cur­rent consumption (Functional Diagram). Once V
IN
reaches 24V, 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 10V, the UVLO circuit will shut down the CPWM com­parator, ILIM comparator, oscillator, and output driver returning the MAX5021/MAX5022 to the startup mode.
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 9V. 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 applications that use the discontinuous flyback topology, this requires a MOS­FET rated at 600V. NDRV can source/sink 150mA/ 250mA peak current, thus select a MOSFET that will yield 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 MAX5021 inverts the Q output of the last D flip-flop to provide a duty cycle of 50% (Figure 3). The MAX5022 performs a logic NAND operation on the Q outputs of both D flip-flops to provide a duty cycle of 75%.
Optocoupler Feedback
The MAX5021/MAX5022 do not include an internal error amplifier and are recommended for use in optocoupler feedback power supplies. Isolated voltage feedback is achieved by using an optocoupler and a shunt regula­tor as shown in the Typical Operating Circuit. The out­put voltage set point accuracy is a function of the accuracy of the shunt regulator and resistor divider.
When a TLV431 shunt regulator is used for output volt­age regulation, the output voltage is set by the ratio of R4 and R5 (Figure 1). Output voltage is given by the following equation:
where V
REF
= 1.24V for the TLV431.
During normal operation, the optocoupler feedback pin (OPTO) is pulled up through a 6.2kresistor to the internal supply voltage of 5.25V. When the device is in UVLO, OPTO is disconnected from the 5.25V regulator and connected to ground (Functional Diagram). This helps initial startup by reducing the current consump­tion of the device.
Current Limit
The current limit is set by a current sense resistor, RCS, connected between the source of the MOSFET and ground. The CS input has a voltage trip level (VCS) of 600mV. 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) will quickly terminate the current ON-cycle, typically within 60ns. In most cases a small RC filter will be required to filter out the leading-edge spike on the sense waveform. Set the corner frequency at a few MHz.
Applications Information
Universal Off-Line Power Supply
Figure 1 shows the design of a 5V/1A isolated power supply capable of operating from a line voltage of 85VAC to 265VAC. This circuit is implemented in the MAX5022EVKIT.
MAX5021/MAX5022
Current-Mode PWM Controllers for Isolated
Power Supplies
_______________________________________________________________________________________ 7
Figure 3. Internal Oscillator
DQ
OSCILLATOR
1.048MHz
Q
DQ
Q
262kHz WITH 50% (MAX5021)
262kHz WITH 75% (MAX5022)
R
4
VV
=×+
OUT REF
 
1
 
R
5
V
CS
CS
=
I
PRI
R
MAX5021/MAX5022
WARNING! DANGEROUS AND LETHAL VOLTAGES ARE PRESENT IN OFF-LINE CIRCUITS! USE EXTREME CAUTION IN THE CONSTRUCTION, TESTING, AND USE OF OFF-LINE CIRCUITS.
Isolated Telecom Power Supply
Figure 4 shows a -48VDC telecom power supply capa­ble of generating an isolated +5V output.
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 SOT23 package have been placed to allow simple interfacing to the external MOSFET. The order of these pins directly corresponds to the order of a TO-220 or similar package MOSFET.
For universal AC input design all applicable safety reg­ulations must be followed. Off-line 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: 519
PROCESS: BiCMOS
Current-Mode PWM Controllers for Isolated Power Supplies
8 _______________________________________________________________________________________
Figure 4. -48VDC Input to +5V Output
T1
V
R
S
C2
OUT
V
IN
CS
-36VDC TO -72VDC IN
V
C3
CC
MAX5022
OPTO NDRV
GND
MAX5021/MAX5022
Current-Mode PWM Controllers for Isolated
Power Supplies
_______________________________________________________________________________________ 9
Functional Diagram
V
OPTO
IN
IN
REFERENCE
1.25V
GND
6.2k
0.75V
CS
VO
V
CS
0.6V
CPWM
PWM
ILIM
OSCILLATOR
262kHz*
*MAX5021: 50% MAXIMUM DUTY CYCLE
MAX5022: 75% MAXIMUM DUTY CYCLE
UVLO
24V 10V
S
R
IN
REGULATOR
REG_OK
Q
V
CC
V
L
(INTERNAL 5.25V
SUPPLY)
DRIVER
V
CC
NDRV
GND
MAX5021/MAX5022
Current-Mode PWM Controllers for Isolated Power Supplies
10 ______________________________________________________________________________________
Package Information
6LSOT.EPS
PROPRIETARY INFORMATION
TITLE:
PACKAGE OUTLINE, 8L uMAX/uSOP
21-0036
REV.DOCUMENT CONTROL NO.APPROVAL
1
J
1
MAX5021/MAX5022
Current-Mode PWM Controllers for Isolated
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 ____________________ 11
© 2001 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.
Package Information (continued)
PDIPN.EPS
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