MAXIM MAX5068BAUE

19-3176; Rev 1; 7/04
High-Frequency, Current-Mode PWM Controller
with Accurate Programmable Oscillator
The MAX5068 is a high-frequency, current-mode,
pulse-width modulation (PWM) controller that integrates
all the building blocks necessary for implementing ACDC or DC-DC fixed-frequency power supplies. Isolated
or nonisolated power supplies are easily constructed
using either primary- or secondary-side regulation.
Current-mode control with leading-edge blanking simplifies control-loop design, and a programmable internal slope-compensation circuit stabilizes the current
loop when operating at duty cycles above 50%. The
MAX5068A/B limit the maximum duty cycle to 50% for
use in single-ended forward converters. The
MAX5068C/D/E/F allow duty cycles up to 75%. The
MAX5068 features an accurate externally programmable oscillator that simplifies system design.
An input undervoltage lockout (UVLO) programs the
input-supply startup voltage and ensures proper operation during brownout conditions.
A single external resistor programs the output switching
frequency from 12.5kHz to 1.25MHz. The MAX5068A/
B/C/E provide a SYNC input for synchronization to an
external clock. The maximum FET-driver duty cycle is
50% for the MAX5068A/B and 75% for the MAX5068C/
D/E/F. Programmable hiccup current limit provides
additional protection under severe faults.
The MAX5068 is specified over the -40°C to +125°C
automotive temperature range and is available in a
16-pin thermally enhanced TSSOP-EP package. Refer to
the MAX5069 data sheet for dual FET-driver applications.
Warning: The MAX5068 is designed to work with high
voltages. Exercise caution.
Features
♦ Current-Mode Control with 47µA (typ) Startup
Current
♦ Resistor-Programmable ±4.5% Accurate
Switching Frequency:
25kHz to 1.25MHz (MAX5068A/B)
12.5kHz to 625kHz (MAX5068C/D/E/F)
♦ Rectified 85VAC to 265VAC or 36VDC to 72VDC
Input (MAX5068A/C/D)
♦ Input Directly Driven from 10.8V to 24V
(MAX5068B/E/F)
♦ Frequency Synchronization Input
(MAX5068A/B/C/E)
♦ Programmable Dead Time and Slope
Compensation
♦ Programmable Startup Voltage (UVLO)
♦ Programmable UVLO Hysteresis
(MAX5068A/B/D/F)
♦ Integrating Fault Protection (Hiccup)
♦ -40°C to +125°C Automotive Temperature Range
♦ 16-Pin Thermally Enhanced TSSOP-EP Package
Ordering Information
TEMP RANGE
PIN-PACKAGE
MAX5068AAUE
PART
-40°C to +125°C
16 TSSOP-EP*
MAX5068BAUE
-40°C to +125°C
16 TSSOP-EP*
MAX5068CAUE
-40°C to +125°C
16 TSSOP-EP*
MAX5068DAUE
-40°C to +125°C
16 TSSOP-EP*
MAX5068EAUE
-40°C to +125°C
16 TSSOP-EP*
-40°C to +125°C
16 TSSOP-EP*
MAX5068FAUE
*EP = Exposed pad.
Pin Configurations
Applications
Universal-Input AC Power Supplies
Isolated Telecom Power Supplies
TOP VIEW
RT 1
Networking System Power Supplies
SYNC 2
Server Power Supplies
HYST 3
Industrial Power Conversion
Selector Guide appears at end of data sheet.
DT 4
16 REG5
15 IN
14 VCC
MAX5068A/B
13 NDRV
UVLO/EN 5
12 AGND
FB 6
11 PGND
COMP 7
10 AGND
FLTINT 8
9
CS
TSSOP-EP
Pin Configurations continued at end of data sheet.
________________________________________________________________ Maxim Integrated Products
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.
1
MAX5068
General Description
MAX5068
High-Frequency, Current-Mode PWM Controller
with Accurate Programmable Oscillator
ABSOLUTE MAXIMUM RATINGS
IN to PGND ............................................................-0.3V to +30V
IN to AGND.............................................................-0.3V to +30V
VCC to PGND..........................................................-0.3V to +13V
VCC to AGND..........................................................-0.3V to +13V
FB, COMP, CS, HYST, SYNC, REG5 to AGND ........-0.3V to +6V
UVLO/EN, RT, DT, SCOMP, FLTINT to AGND .........-0.3V to +6V
NDRV to PGND...........................................-0.3V to (VCC + 0.3V)
AGND to PGND .....................................................-0.3V to +0.3V
Continuous Power Dissipation
16-Pin TSSOP-EP (derate 21.3mW/°C above +70°C) ...1702mW
Operating Temperature Range..........................-40°C to +125°C
Maximum Junction Temperature .....................................+150°C
Storage Temperature Range .............................-60°C to +150°C
Lead Temperature (soldering, 10s) .................................+300°C
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.
ELECTRICAL CHARACTERISTICS
(VIN = +12V for the MAX5068B/E/F; VIN = +23.6V for the MAX5068A/C/D at startup, then reduces to +12V; CIN = CREG5 = 0.1µF;
CVCC = 1µF; RRT = 100kΩ; NDRV = floating; TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25°C.) (Note 1)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
UNDERVOLTAGE LOCKOUT/STARTUP
Bootstrap UVLO Wake-Up Level
VSUVR
VIN rising, MAX5068A/C/D only
19.68
21.6
23.60
V
Bootstrap UVLO Shutdown Level
VSUVF
VIN falling, MAX5068A/C/D only
9.05
9.74
10.43
V
UVLO/EN Wake-Up Threshold
VULR2
VUVLO/EN rising
1.205
1.230
1.255
UVLO/EN Shutdown Threshold
VULF2
VUVLO/EN falling
HYST FET On-Resistance
RDS(ON)_H
V
MAX5068A/B/D/F only, sinking 50mA,
VUVLO/EN = 0V
10
Ω
nA
HYST FET Leakage Current
ILEAK_H
VUVLO/EN = 2V, VHYST = 5V
3
IN Supply Current In
Undervoltage Lockout
ISTART
VIN = +19V, VUVLO/EN < VULF2
47
IN Range
V
1.18
VIN
10.8
90
µA
24.0
V
10.5
V
5.15
V
INTERNAL SUPPLIES (VCC and REG5)
VCC Regulator Set Point
VCCSP
VIN = +10.8V to +24V, VCC sourcing 1µA to 25mA
7.0
REG5 Output Voltage
VREG5
IREG5 = 0 to 1mA
4.85
REG5 Short-Circuit Current Limit
IN Supply Current After Startup
Shutdown Supply Current
IREG5_SC
IIN
5.00
18
VIN = +24V
fSW = 1.25MHz
mA
5
fSW = 100kHz
mA
2.5
IIN_SD
90
µA
GATE DRIVER (NDRV)
Driver Output Impedance
Driver Peak Output Current
ZOUT(LOW)
NDRV sinking 100mA
2
4
ZOUT(HIGH) NDRV sourcing 25mA
3
6
Sinking
1000
Sourcing
650
INDRV
Ω
mA
PWM COMPARATOR
Comparator Offset Voltage
VOS_PWM
VCOMP - VCS
Comparator Propagation Delay
tPD_PWM
VCS = 0.1V
1.30
1.60
40
2.00
ns
V
Minimum On-Time
tON(MIN)
Includes tCS_BLANK
110
ns
CURRENT-LIMIT COMPARATOR
Current-Limit Trip Threshold
2
VCS
298
314
_______________________________________________________________________________________
330
mV
High-Frequency, Current-Mode PWM Controller
with Accurate Programmable Oscillator
(VIN = +12V for the MAX5068B/E/F; VIN = +23.6V for the MAX5068A/C/D at startup, then reduces to +12V; CIN = CREG5 = 0.1µF;
CVCC = 1µF; RRT = 100kΩ; NDRV = floating; TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25°C.) (Note 1)
PARAMETER
CS Input Bias Current
CS Blanking Time
SYMBOL
IB_CS
CONDITIONS
VCS = 0V
MIN
0
tCS_BLANK
Propagation Delay from
Comparator Input to NDRV
TYP
50mV overdrive
MAX
UNITS
+2
µA
70
ns
40
ns
IN CLAMP VOLTAGE
IN Clamp Voltage
VIN_CLAMP
VIN sinking 2mA (Note 2)
24.0
26.0
29.0
V
Voltage Gain
AV
RCOMP = 100kΩ to AGND
80
dB
Unity-Gain Bandwidth
BW
RCOMP = 100kΩ to AGND,
CLOAD = 100pF to AGND
5
MHz
Phase Margin
PM
RCOMP = 100kΩ to AGND,
CLOAD = 100pF to AGND
65
degrees
ERROR AMPLIFIER (FB, COMP)
FB Input Offset Voltage
VOS_FB
COMP Clamp Voltage
VCOMP
Error-Amplifier Output Current
ICOMP
Reference Voltage
VREF
Input Bias Current
COMP Short-Circuit Current
3
High
2.6
3.8
Low
0.4
1.1
Sinking or sourcing
0.5
mV
V
mA
+25°C ≤ TA ≤ +125°C (Note 3)
1.215
1.230
1.245
-40°C ≤ TA ≤ +125°C
1.205
1.230
1.242
300
V
IB_EA
100
ICOMP_SC
12
nA
TSD
+170
°C
THYST
+25
°C
mA
THERMAL SHUTDOWN
Thermal-Shutdown Temperature
Thermal Hysteresis
OSCILLATOR SYNC INPUT (MAX5068A/B/C/E Only)
SYNC High-Level Voltage
VIH_SYNC
SYNC Low-Level Voltage
VIL_SYNC
SYNC Input Bias Current
IB_SYNC
Maximum SYNC Frequency
fSYNC
2.4
V
0.4
10
fOSC = 2.5MHz (Note 4)
V
nA
3.125
MHz
SYNC High-Level Pulse Width
tSYNC_HI
30
ns
SYNC Low-Level Pulse Width
tSYNC_LO
30
ns
DIGITAL SOFT-START
Soft-Start Duration
tSS
Reference-Voltage Step
(Note 5)
VSTEP
Reference-Voltage Steps During
Soft-Start
2047
cycles
9.7
mV
127
steps
OSCILLATOR
Internal Oscillator Frequency
Range
fOSC
fOSC = (1011 / RRT)
50
2500
kHz
_______________________________________________________________________________________
3
MAX5068
ELECTRICAL CHARACTERISTICS (continued)
MAX5068
High-Frequency, Current-Mode PWM Controller
with Accurate Programmable Oscillator
ELECTRICAL CHARACTERISTICS (continued)
(VIN = +12V for the MAX5068B/E/F; VIN = +23.6V for the MAX5068A/C/D at startup, then reduces to +12V; CIN = CREG5 = 0.1µF;
CVCC = 1µF; RRT = 100kΩ; NDRV = floating; TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25°C.) (Note 1)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
11
NDRV Switching Frequency
RT Voltage
fSW
VRT
(Note 6)
Oscillator Accuracy
TA = -40°C to +125°C
DMAX
25
1250
kHz
fSW = 1011/(4 x RRT),
MAX5068C/D/E/F
12.5
625
kHz
fOSC ≤ 500kHz
-2.5
40kΩ < RRT < 500kΩ
TA = +25°C
Maximum Duty Cycle
fSW = 10 /(2 x RRT),
MAX5068A/B
DT connected to
REG5
2.0
V
+2.5
fOSC > 500kHz
-4
+4
fOSC ≤ 500kHz
-4.5
+4.5
fOSC > 500kHz
-6
+6
MAX5068A/B
50
MAX5068C/D/E/F
75
%
%
DEAD-TIME CONTROL (DT)
Dead Time
Dead-Time Disable Voltage
Dead-Time Regulation Voltage
tDT
RDT = 24.9kΩ
60
ns
VREG5
- 0.5V
VDT_DISABLE
VDT
V
1.23
V
60
µA
INTEGRATING FAULT PROTECTION (FLTINT)
FLTINT Source Current
FLTINT Shutdown Threshold
IFLTINT
VFLTINT = 0
VFLTINT_SD VFLTINT rising
2.8
V
VFLTINT_RS VFLTINT falling
SLOPE COMPENSATION (SCOMP) MAX5068C/D/E/F Only
1.6
V
FLTINT Restart Threshold
Slope Compensation
VSLOPE
CSLOPE = 100pF, RRT = 110kΩ
15
mV/µs
Slope-Compensation Range
VSLOPER
0
90
mV/µs
Slope-Compensation Voltage
Range
VSCOMP
0
2.7
V
Note 1: The MAX5068 is 100% tested at TA = +25°C. All limits over temperature are guaranteed by design.
Note 2: The MAX5068A/B are intended for use in universal-input power supplies. The internal clamp circuit 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. The maximum current to VIN (hence to clamp) when UVLO is low (device is in shutdown) must be externally limited to 2mA. Clamp currents higher than 2mA may result in clamp voltages higher than 30V, thus exceeding the
absolute maximum rating for VIN. For the MAX5068C/D, do not exceed the 24V maximum operating voltage of the device.
Note 3: Reference voltage (VREF) is measured with FB connected to COMP (see the Functional Diagram).
Note 4: The SYNC frequency must be at least 25% higher than the programmed oscillator frequency.
Note 5: The internal oscillator clock cycle.
Note 6: The MAX5068A/B driver switching frequency is one-half of the oscillator frequency. The MAX5068C/D/E/F driver switching
frequency is one-quarter of the oscillator frequency.
4
_______________________________________________________________________________________
High-Frequency, Current-Mode PWM Controller
with Accurate Programmable Oscillator
MAX5068A/C/D
21.5
VIN FALLING
MAX5068A/C/D
9.9
9.8
9.7
UVLO/EN RISING
1.240
UVLO/EN (V)
VIN (V)
VIN (V)
21.4
21.3
1.245
MAX5068 toc02
10.0
MAX5068 toc01
21.6
UVLO/EN WAKE-UP THRESHOLD
vs. TEMPERATURE
MAX5068 toc03
BOOTSTRAP UVLO SHUTDOWN LEVEL
vs. TEMPERATURE
BOOTSTRAP UVLO WAKE-UP LEVEL
vs. TEMPERATURE
1.235
1.230
21.2
9.6
21.1
1.225
9.5
21.0
10
35
60
85
-15
10
35
60
85
110
-40
-15
10
35
60
85
110
TEMPERATURE (°C)
TEMPERATURE (°C)
TEMPERATURE (°C)
UVLO/EN SHUTDOWN THRESHOLD
vs. TEMPERATURE
VIN SUPPLY CURRENT IN
UNDERVOLTAGE LOCKOUT vs. TEMPERATURE
VIN SUPPLY CURRENT AFTER STARTUP
vs. TEMPERATURE
60
1.18
VIN = 19V
WHEN IN BOOTSTRAP UVLO (MAX5068A/C/D)
UVLO/EN (MAX5068B/E/F) IS LOW
56
6
MAX5068 toc06
UVLO/EN FALLING
1.19
1.220
-40
110
MAX5068 toc05
1.20
-15
MAX5068 toc04
-40
VIN = 24V
fSW = 1.25MHz
5
1.16
1.15
1.14
52
IIN (mA)
ISTART (µA)
UVLO/EN (V)
1.17
4
48
3
44
2
fSW = 500kHz
fSW = 250kHz
1.13
fSW = 100kHz
1.11
40
-15
10
35
60
85
110
10
35
60
85
VCC vs. TEMPERATURE
REG5 OUTPUT VOLTAGE
vs. OUTPUT CURRENT
9.7
VIN = 19V, IIN = 10mA
VIN = 19V, IIN = 25mA
4.980
RRT = 100kΩ
4.975
9.1
110
-40
35
60
85
110
4.99
VIN = 10.8V
100µA LOAD
4.98
4.97
4.965
8.2
7.9
10
REG5 vs. TEMPERATURE
5.00
REG5 (V)
8.5
-15
TEMPERATURE (°C)
4.970
8.8
REG5 (V)
VCC (V)
-15
TEMPERATURE (°C)
10.0
9.4
-40
TEMPERATURE (°C)
MAX5068 toc07
-40
fSW = 50kHz
1
MAX5068 toc08
1.10
MAX5068 toc09
1.12
4.96
1mA LOAD
4.95
4.94
4.960
4.93
VIN = 10.8V, IIN = 10mA
7.6
VIN = 10.8V, IIN = 25mA
7.3
7.0
4.92
4.955
4.91
4.950
-40
-15
10
35
60
TEMPERATURE (°C)
85
110
4.90
0
0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
OUTPUT CURRENT (mA)
-40
-15
10
35
60
85
110
TEMPERATURE (°C)
_______________________________________________________________________________________
5
MAX5068
Typical Operating Characteristics
(VIN = +12V for the MAX5068B/E/F; VIN = +23.6V for MAX5068A/C/D at startup, then reduces to +12V; CIN = CREG5 = 0.1µF;
CVCC = 1µF; RRT = 100kΩ; NDRV = floating; VFB = 0; VCOMP = floating; VCS = 0; TA = +25°C, unless otherwise noted.)
Typical Operating Characteristics (continued)
(VIN = +12V for the MAX5068B/E/F; VIN = +23.6V for MAX5068A/C/D at startup, then reduces to +12V; CIN = CREG5 = 0.1µF;
CVCC = 1µF; RRT = 100kΩ; NDRV = floating; VFB = 0; VCOMP = floating; VCS = 0; TA = +25°C, unless otherwise noted.)
4.981
4.980
4.979
4.978
318
315
312
309
4.977
306
4.976
303
4.975
10
12
14
16
18
20
22
510
MEAN
505
500
-3σ
495
490
485
480
-15
10
35
60
85
470
-40
110
10
-15
35
60
85
TEMPERATURE (°C)
PROPAGATION DELAY FROM CS COMPARATOR
INPUT TO NDRV vs. TEMPERATURE
INPUT CURRENT
vs. INPUT CLAMP VOLTAGE
INPUT CLAMP VOLTAGE
vs. TEMPERATURE
42
40
38
36
10
8
6
4
34
MAX5068 toc15
26.6
26.4
26.2
26.0
25.8
25.6
25.2
0
-15
10
35
60
85
110
25.0
10.0 12.5 15.0 17.5 20.0 22.5 25.0 27.5 30.0
-40
10
35
60
85
110
INPUT CLAMP VOLTAGE (V)
TEMPERATURE (°C)
NDRV OUTPUT IMPEDANCE
vs. TEMPERATURE
NDRV OUTPUT IMPEDANCE
vs. TEMPERATURE
ERROR AMPLIFIER OPEN-LOOP GAIN
AND PHASE vs. FREQUENCY
2.6
3.8
VIN = 24V
SOURCING 25mA
3.6
100
80
3.4
RON (Ω)
2.2
2.0
3.2
3.0
1.8
2.8
1.6
2.6
1.4
2.4
1.2
2.2
1.0
GAIN (dB)
2.4
120
2.0
-15
10
35
60
TEMPERATURE (°C)
85
110
MAX5068 toc18
4.0
MAX5068 toc17
VIN = 24V
SINKING 100mA
-40
-15
TEMPERATURE (°C)
MAX5068 toc16
-40
-15
10
35
60
TEMPERATURE (°C)
85
110
0
-30
GAIN
-60
60
40
-90
PHASE
20
-120
0
-150
-20
-180
-40
-40
30
-210
0.1
10
1k
100k
FREQUENCY (Hz)
_______________________________________________________________________________________
10M
PHASE (DEGREES)
30
2.8
ISINK = 2mA
26.8
25.4
2
32
3.0
110
27.0
INPUT CLAMP VOLTAGE (V)
12
INPUT CURRENT (mA)
44
MAX5068 toc14
14
MAX5068 toc13
46
MAX5068 toc12
TOTAL NUMBER OF
DEVICES = 200
+3σ
TEMPERATURE (°C)
48
6
fSW = 500kHz
475
300
-40
24
515
VIN (V)
50
PROPAGATION DELAY (ns)
324
321
520
SWITCHING FREQUENCY (kHz)
4.982
REG5 (V)
327
CS TRIP THRESHOLD (mV)
4.983
MAX5068 toc11
IREG5 = 100µA
4.984
330
MAX5068 toc10
4.985
SWITCHING FREQUENCY
vs. TEMPERATURE
CS TRIP THRESHOLD
vs. TEMPERATURE
REG5 OUTPUT VOLTAGE vs. VIN
RON (Ω)
MAX5068
High-Frequency, Current-Mode PWM Controller
with Accurate Programmable Oscillator
High-Frequency, Current-Mode PWM Controller
with Accurate Programmable Oscillator
12.0
11.5
62.6
11.0
RON (Ω)
62.7
62.5
10.0
62.3
9.5
62.2
9.0
62.1
8.5
62.0
-15
10
35
60
85
110
0.01
-40
-15
10
35
60
85
110
0.03
0.1
2
1
TEMPERATURE (°C)
TEMPERATURE (°C)
RRT (MΩ)
NDRV SWITCHING FREQUENCY
vs. TEMPERATURE
NDRV SWITCHING FREQUENCY
vs. TEMPERATURE
NDRV SWITCHING FREQUENCY
vs. TEMPERATURE
50.8
50.4
50.0
49.6
49.2
48.8
fSW = 500kHz
503
502
501
500
499
498
497
1.40
1.35
MAX5068 toc24
504
NDRV SWITCHING FREQUENCY (kHz)
51.2
NDRV SWITCHING FREQUENCY (kHz)
fSW = 50kHz
MAX5068 toc23
505
MAX5068 toc22
52.0
MAX5068A/B
fSW = 1.25MHz
1.30
1.25
1.20
1.15
496
48.4
495
48.0
-15
10
35
60
85
1.10
-50
110
TEMPERATURE (°C)
-25
0
25
50
75
TEMPERATURE (°C)
125
100
DEAD TIME vs. TEMPERATURE
65
VIN = 24V
RDT = 24.9kΩ
RRT = 100kΩ
-15
10
35
60
85
110
DEAD TIME vs. RDT
200
MAX5068 toc26
70
-40
TEMPERATURE (°C)
MAX5068 toc25
180
160
140
60
TIME (ns)
-40
TIME (ns)
NDRV SWITCHING FREQUENCY (kHz)
0.1
MAX5068C/D/E/F
8.0
-40
51.6
MAX5068A/B
10.5
62.4
1
fSW (MHz)
62.8
VIN = 24V
SINKING 50mA
12.5
2
MAX5068 toc20
62.9
FLTINT CURRENT (µA)
13.0
MAX5068 toc19
63.0
NDRV SWITCHING FREQUENCY (fSW)
vs. RRT
HYST RON vs. TEMPERATURE
MAX5068 toc21
FLTINT CURRENT vs. TEMPERATURE
55
50
120
100
80
60
40
45
20
40
0
-40
-15
10
35
60
TEMPERATURE (°C)
85
110
1
10
100
RDT (kΩ)
_______________________________________________________________________________________
7
MAX5068
Typical Operating Characteristics (continued)
(VIN = +12V for the MAX5068B/E/F; VIN = +23.6V for MAX5068A/C/D at startup, then reduces to +12V; CIN = CREG5 = 0.1µF;
CVCC = 1µF; RRT = 100kΩ; NDRV = floating; VFB = 0; VCOMP = floating; VCS = 0; TA = +25°C, unless otherwise noted.)
MAX5068
High-Frequency, Current-Mode PWM Controller
with Accurate Programmable Oscillator
Pin Description
PIN
MAX5068A
MAX5068B
MAX5068C
MAX5068E
MAX5068D
MAX5068F
NAME
1
1
1
RT
2
2
—
SYNC
External-Clock Sync Input. Connect SYNC to AGND when not using an
external clock.
3
—
2
HYST
Programmable Hysteresis Input
—
3
3
SCOMP
4
4
4
DT
5
5
5
UVLO/EN
6
6
6
FB
7
7
7
COMP
Error-Amplifier Compensation Output
FLTINT
Fault-Integration Input. A capacitor connected to FLTINT charges with an
internal 60µA current source during repeated current-limit events. Switching
terminates when VFLTINT reaches 2.9V. An external resistor connected in
parallel discharges the capacitor. Switching resumes when VFLTINT drops to
1.6V.
8
8
8
8
FUNCTION
Oscillator-Timing Resistor Connection. Connect a resistor from RT to AGND
to set the internal oscillator frequency.
Slope-Compensation Capacitor Input. Connect a capacitor to AGND to set
the slope compensation.
Dead-Time Adjustment. Connect a resistor from DT to AGND to adjust NDRV
dead time. Connect to REG5 for maximum duty cycle.
Externally Programmable Undervoltage Lockout. UVLO/EN programs the
input start voltage. Drive UVLO/EN to AGND to disable the output.
Error-Amplifier Inverting Input
9
9
9
CS
10, 12
10, 12
10, 12
AGND
Current-Sense Resistor Connection
Analog Ground. Connect to PGND through a ground plane.
11
11
11
PGND
Power Ground. Connect to AGND through a ground plane.
13
13
13
NDRV
Gate-Driver Output. Connect the NDRV output to the gate of the external
N-channel FET.
14
14
14
VCC
15
15
15
IN
16
16
16
REG5
EP
EP
EP
PAD
9V Linear-Regulator Output. Decouple VCC with a minimum 1µF ceramic
capacitor to the AGND plane; also internally connected to the FET driver.
Power-Supply Input. IN provides power for all internal circuitry. Decouple IN
with a minimum 0.1µF ceramic capacitor to AGND (see the Typical
Operating Circuit).
5V Linear-Regulator Output. Decouple to AGND with a 0.1µF ceramic
capacitor.
Exposed Pad. Connect to GND.
_______________________________________________________________________________________
High-Frequency, Current-Mode PWM Controller
with Accurate Programmable Oscillator
The MAX5068 is a current-mode PWM controller for use
in isolated and nonisolated power-supply applications.
A bootstrap UVLO with a programmable hysteresis,
very low startup, and low operating current result in
high-efficiency universal-input power supplies. In addition to the internal bootstrap UVLO, the device also
offers programmable input startup and turn-off voltages, programmed through the UVLO/EN input. When
using the MAX5068 in the bootstrapped mode, if the
power-supply output is shorted, the tertiary winding
voltage drops below the 10V threshold, causing the
bootstrap UVLO to turn off the gate drive to the external
power MOSFET, reinitiating a startup sequence with
soft-start.
The MAX5068 includes a cycle-by-cycle current limit
that turns off the gate drive to the external MOSFET
during an overcurrent condition. The MAX5068 integrating fault protection reduces average power dissipation
during persistent fault conditions (see the Integrating
Fault Protection section).
The MAX5068 features a very accurate, wide-range,
programmable oscillator that simplifies and optimizes
the design of the magnetics. The MAX5068A/C/D are
well suited for universal-input (rectified 85V AC to
265VAC) or telecom (-36VDC to -72VDC) power supplies. The MAX5068B/E/F are well suited for low-input
voltage (10.8VDC to 24VDC) power supplies.
The MAX5068 high-frequency, universal input, offline/
telecom, current-mode PWM controller integrates all the
building blocks necessary for implementing AC-DC and
DC-DC fixed-frequency power supplies. Isolated or nonisolated power supplies are easily constructed using
either primary- or secondary-side regulation. Currentmode control with leading-edge blanking simplifies control-loop design, and an external slope-compensation
control stabilizes the current loop when operating at
duty cycles above 50% (MAX5068C/D/E/F). The
MAX5068A/B limit the maximum duty cycle to 50% for
use in single-ended forward converters. The
MAX5068C/D/E/F allow duty cycles up to 75% for use in
flyback converters.
An input undervoltage lockout (UVLO) programs the
input-supply startup voltage and ensures proper operation during brownout conditions. An external voltagedivider programs the supply startup voltage. The
MAX5068A/B/D/F feature a programmable UVLO hysteresis. The MAX5068A/C/D feature an additional internal
bootstrap UVLO with large hysteresis that requires a minimum startup voltage of 23.6V. The MAX5068B/E/F start
up from a minimum voltage of 10.8V. Internal digital softstart reduces output-voltage overshoot at startup.
A single external resistor programs the switching frequency from 12.5kHz to 1.25MHz. The MAX5068A/B/C/E
provide a SYNC input for synchronization to an external
clock. The maximum FET driver duty cycle is 50% for the
MAX5068A/B, and 75% for the MAX5068C/D/E/F.
Integrating fault protection ignores transient overcurrent
conditions for a set length of time. The length of time is
programmed by an external capacitor. The internal thermal-shutdown circuit protects the device if the junction
temperature should exceed +170°C.
Power supplies designed with the MAX5068 use a
high-value startup resistor, R1, which charges a reservoir capacitor, C1 (Figure 1). During this initial period,
while the voltage is less than the internal bootstrap
UVLO threshold, the device typically consumes only
47µA 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 (265VAC).
The MAX5068 includes a cycle-by-cycle current limit
that turns off the gate to the external MOSFET during an
overcurrent condition. When using the MAX5068A/C/D
in the bootstrap mode (if the power-supply output is
shorted), the tertiary winding voltage drops below the
9.74V bootstrap UVLO to turn off the gate to the external power MOSFET. This reinitiates a startup sequence
with soft-start.
Current-Mode Control
The MAX5068 offers a current-mode control operation
feature, such as leading-edge blanking with a dual
internal path that only blanks the sensed current signal
applied to the input of the PWM controller. The currentlimit comparator monitors CS at all times and provides
cycle-by-cycle current limit without being blanked. The
leading-edge blanking of the CS signal prevents the
PWM comparator from prematurely terminating the on
cycle. The CS signal contains a leading-edge spike
that results from the MOSFET gate charge current, and
the capacitive and diode reverse-recovery current of
the power circuit. Since this leading-edge spike is normally lower than the current-limit comparator threshold,
current limiting is provided under all conditions.
Use the MAX5068C/D/E/F in flyback applications where
wide line voltage and load-current variations are
expected. Use the MAX5068A/B for forward/flyback
converters where the maximum duty must be limited to
less than 50%.
_______________________________________________________________________________________
9
MAX5068
Detailed Description
MAX5068
High-Frequency, Current-Mode PWM Controller
with Accurate Programmable Oscillator
D1
VOUT
D2
C6
VIN
C1
R1
R8
R2
IN
NDRV
Q1
C2
FLTINT
CS
VCC
FB
R9
C3
C4
MAX5068A
RCS
R5
C5
REG5
COMP
R3
R6
RT
UVLO/EN
R4
RHYST
DT
SYNC
AGND
HYST
PGND
R7
Figure 1. Nonisolated Power Supply with Programmable Input Supply Voltage
Use the MAX5068C/D/E/F in forward converter applications with greater than 50% duty cycle. The large duty
cycle results in much lower operating primary RMS current through the MOSFET switch and, in most cases,
requires a smaller output filter capacitor. The major disadvantage to this is that the MOSFET voltage rating
must be higher. The MAX5068C/D/E/F capacitor
adjustable-slope-compensation feature allows for easy
stabilization of the inner current loop.
Undervoltage Lockout
The MAX5068 features an input voltage UVLO/EN function to enable the PWM controller before any operation
can begin. The MAX5068C/E shut down if the voltage
at UVLO/EN falls below its 1.18V threshold. The
MAX5068A/B/D/F also incorporate an UVLO hysteresis
input to set the desired turn-off voltage.
MAX5068C/E UVLO Adjustment
The MAX5068C/E have an input voltage UVLO/EN with
a 1.231V threshold. Before any operation can commence, the UVLO/EN voltage must exceed the 1.231V
threshold. The UVLO circuit keeps the PWM comparator, ILIM comparator, oscillator, and output driver shut
down to reduce current consumption (see the
Functional Diagram).
Calculate R6 in Figure 2 by using the following formula:
⎛ V
⎞
R6 = ⎜ ON − 1⎟ × R7
⎝ VULR2
⎠
where VULR2 is the UVLO/EN’s 1.231V rising threshold
and VON is the desired startup voltage. Choose an R7
value in the 20kΩ range.
After a successful startup, the MAX5068C/E shut down if
the voltage at UVLO/EN drops below its 1.18V threshold.
10
______________________________________________________________________________________
High-Frequency, Current-Mode PWM Controller
with Accurate Programmable Oscillator
MAX5068
VIN
MAX5068C/E
R6
UVLO/EN
R7
VHYST = VON - VOFF
1.23V
1.18V
VOFF
Figure 2. Setting the MAX5068C/E Undervoltage Lockout
Threshold
MAX5068A/B/D/F UVLO with
Programmable Hysteresis
In addition to programmable undervoltage lockout during startup, the MAX5068A/B/D/F incorporate a
UVLO/EN hysteresis that allows the user to set a voltage (VOFF) to disable the controller (see Figure 3).
At the beginning of the startup sequence, UVLO/EN is
below the 1.23V threshold, Q1 turns on connecting
RHYST to GND (Figure 4). Once the UVLO 1.23V threshold is crossed, Q1 turns off, resulting in the series combination of R6, RHYST, and R7, placing the MAX5068 in
normal operating condition.
Calculate the turn-on voltage (VON) by using the following formula:
VON
Figure 3. MAX5068 Hysteresis
VIN
MAX5068A/B/D/F
R6
UVLO/EN
RHYST
1.23V
1.18V
HYST
Q1
R7
⎛ V
⎞
R6 = ⎜ ON − 1⎟ × RHYST
⎝ VULR2
⎠
where VULR2 is the UVLO/EN’s 1.23V rising threshold.
Choose an RHYST value in the 20kΩ range.
The MAX5068 turns off when the MAX5068 UVLO/EN
falls below the 1.18V falling threshold. The turn-off voltage (VOFF) is then defined as:
⎛ V
⎞
R7 = R6 / ⎜ OFF − 1⎟ − RHYST
⎝ VULF2
⎠
where VULF2 is the 1.18V UVLO/EN falling threshold.
Figure 4. Setting the MAX5068A/B/D/F Turn-On/Turn-Off Voltages
Bootstrap Undervoltage Lockout
(MAX5068A/C/D Only)
In addition to the externally programmable UVLO function offered by the MAX5068, the MAX5068A/C/D feature an additional internal bootstrap UVLO for use in
high-voltage power supplies (see the Functional
Diagram). This allows the device to bootstrap itself during initial power-up. The MAX5068A/C/D start when VIN
exceeds the bootstrap UVLO threshold of 23.6V.
______________________________________________________________________________________
11
MAX5068
High-Frequency, Current-Mode PWM Controller
with Accurate Programmable Oscillator
During startup, the UVLO circuit keeps the PWM comparator, ILIM comparator, oscillator, and output driver
shut down to reduce current consumption. Once VIN
reaches 23.6V, the UVLO circuit turns on both the PWM
and ILIM comparators, as well as the oscillator, and
allows the output driver to switch. When V IN drops
below 9.7V, the UVLO circuit shuts down the PWM
comparator, ILIM comparator, oscillator, and output driver returning the MAX5068A/C/D to the startup mode.
VCC
2V/div
MAX5068
VIN PIN
5V/div
MAX5068A/C/D Startup Operation
Normally, VIN is derived from the tertiary winding of the
transformer. However, at startup there is no energy
delivered through the transformer, hence, a special
bootstrap sequence is required. Figure 5 shows the
voltages on VIN and VCC during startup. Initially, both
VIN and VCC are zero. After the input voltage is applied,
C1 charges through the startup resistor, R1, to an intermediate voltage (see Figure 1). At this point, the internal regulator begins charging C3 (see Figure 5). Only
47µA of the current supplied by R1 is used by the
MAX5068A/C/D. The remaining input current charges
C1 and C3. The charging of C3 stops when the VCC
voltage reaches approximately 9.5V. The voltage
across C1 continues rising until it reaches the wake-up
level of 23.6V. Once VIN exceeds the bootstrap UVLO
threshold, NDRV begins switching the MOSFET and
energy is transferred to the secondary and tertiary outputs. If the voltage on the tertiary output builds to higher than 9.74V (the bootstrap UVLO lower threshold),
startup ends and sustained operation commences.
If VIN drops below 9.74V before startup is complete, the
device goes back to low-current UVLO. If this occurs,
increase the value of C1 to store enough energy to
allow for the voltage at the tertiary winding to build up.
Startup Time Considerations for
Power Supplies Using the MAX5068A/C/D
The VIN bypass capacitor, C1, supplies current immediately after wakeup (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 and also
supply extra 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 that powers the device. The device goes back
into UVLO and does not start. Use low-leakage capacitors for C1 and C3.
Generally, offline power supplies keep typical startup
times to less than 500ms, even in low-line conditions
(85VAC input for universal offline applications or 36VDC
12
0V
100ms/div
Figure 5. V IN and V CC During Startup When Using the
MAX5068 in Bootstrapped Mode (Also see Figure 1)
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 C3. The
bypass capacitor, C3, must charge to 9.5V, and C1
must charge to 24V, within the desired time period of
500ms. Because of the internal soft-start time of the
MAX5068, C1 must store enough charge to deliver current to the device for at least 2047 oscillator clock
cycles. To calculate the approximate amount of capacitance required, use the following formula:
Ig = Qgtot x fSW
(IIN + Ig ) x t SS
C1 =
VHYST
where IIN is the MAX5068’s internal supply current after
startup (2.5mA typ), Qgtot is the total gate charge for
Q1, fSW is the MAX5068’s programmed switching frequency, VHYST is the bootstrap UVLO hysteresis (12V),
and tss is the internal soft-start time (2047 x 1 / fOSC).
Example: Ig = (8nC) (250kHz) ≅ 2.0mA
fOSC = 2 x 250kHz
Soft-start duration = 2047 x (1 / fOSC) = 4.1ms
C1 =
(2.5mA + 2mA) (4.1ms)
= 1.54µF
12V
Use a 2.2µF ceramic capacitor for C1.
______________________________________________________________________________________
High-Frequency, Current-Mode PWM Controller
with Accurate Programmable Oscillator
D2
MAX5068
D1
VOUT
C7
VIN
C1
R1
R2
IN
NDRV
Q1
C2
FLTINT
R11
CS
C3
VCC
MAX5068A
RCS
FB
C4
R5
REG5
R3
COMP
C6
VCC
C5
R6
RT
C10
R4
UVLO/EN
RHYST
SYNC
AGND
R12
PS2913
DT
R9
MAX8515
HYST
PGND
R7
R8
R10
R13
Figure 6. Secondary-Side, Regulated, Isolated Power Supply
Assuming C1 > C3, calculate the value of R1 as follows:
VSUVR × C1
500ms
VIN(MIN) − 0.5 x VSUVR
IC1 =
R1 ≅
IC1 + ISTART
where V SUVR is the bootstrap UVLO wakeup level
(23.6V max), VIN(MIN) is the minimum input supply voltage for the application (36V for telecom), and ISTART is
the VIN supply current at startup (90µA, max).
Oscillator/Switching Frequency
For example:
24V x 2.2µF
= 106µA
500ms
36V − 12V
R1 ≅
= 122.4kΩ
106µA + 90µA
IC1 =
To minimize power loss on this resistor, choose a higher value for R1 than the one calculated above (if a
longer startup time can be tolerated).
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 time of C1 from 22V to
10V must be greater than the soft-start time (tSS).
Use an external resistor at RT to program the MAX5068
internal oscillator frequency from 50kHz to 2.5MHz. The
MAX5068A/B output switching frequency is one-half of
the programmed oscillator frequency with a 50% duty
cycle. The MAX5068C/D/E/F output switching frequency is one-quarter of the programmed oscillator frequency with a 75% duty cycle.
______________________________________________________________________________________
13
MAX5068
High-Frequency, Current-Mode PWM Controller
with Accurate Programmable Oscillator
Use the following formula to calculate the internal oscillator frequency:
1011
fosc =
RRT
where fOSC is the oscillator frequency and RRT is a
resistor connected from RT to AGND.
Choose the appropriate resistor at RT to calculate the
desired output switching frequency (fSW):
RRT =
1011
for the MAX5068A / B and
2fSW
RRT =
1011
for the MAX5068C / D / E / F
4fSW
The MAX5068A/B and the MAX5068C/D/E/F have programmable output switching frequencies from 25kHz to
1.25MHz and 12.5kHz to 625kHz, respectively.
Dead-Time Adjustment
The MAX5068 programmable dead-time function
(Figure 7) allows additional flexibility in optimizing magnetics design and overcoming parasitic effects. The
MAX5068A/B and the MAX5068C/D/E/F have a maximum 50% and 75% duty cycle, respectively. In many
applications, the duty cycle of the external MOSFET
may need to be slightly decreased to prevent saturation in the transformer’s primary. The dead time can be
configured from 30ns to 1 / (0.5 x fSW) when programming the MAX5068. Connect a resistor between DT and
AGND to set the desired dead time using the following
formula:
Dead time =
60
× RDT (ns)
29.4
External Synchronization
(MAX5068A/B/C/E)
The MAX5068A/B/C/E can be synchronized using an
external clock at the SYNC input. For proper frequency
synchronization, the SYNC’s input frequency must be at
least 25% higher than the MAX5068A/B/C/E programmed internal oscillator frequency. Connect SYNC
to AGND when not using an external clock.
Integrating Fault Protection
The integrating fault-protection feature allows transient
overcurrent conditions to be ignored for a programmable amount of time, giving the power supply time to
behave like a current source to the load. For example,
this can occur under load current transients when the
control loop requests maximum current to keep the output voltage from going out of regulation. Program the
fault-integration time by connecting an external suitably
sized capacitor to the FLTINT. Under sustained overcurrent faults, the voltage across this capacitor ramps
up towards the FLTINT shutdown threshold (typically
2.8V). Once the threshold is reached, the power supply
shuts down. A high-value bleed resistor connected in
parallel with the FLTINT capacitor allows it to discharge
towards the restart threshold (typically 1.6V). Once this
threshold is reached, the supply restarts with a new
soft-start cycle.
Note that cycle-by-cycle current limiting is provided at
all times by CS with a threshold of 314mV (typ). The
fault-integration circuit forces a 60µA current onto
FLTINT each time that the current-limit comparator is
tripped (see the Functional Diagram). Use the following
formula to calculate the value of the capacitor necessary for the desired shutdown time of the circuit:
I
x tSH
CFLTINT ≅ FLTINT
2.8V
where RDT is in kΩ and the dead time is in ns.
Connect DT to REG5 to remove the delay and achieve
the MAX5068 maximum duty cycles.
SYNC
MAX5068A/B/C/E
NDRV
RT
tDT
DEAD TIME
< 50%
< 50%
AGND
Figure 7. MAX5068 NDRV Dead-Time Timing Diagram
14
Figure 8. External Synchronization of the MAX5068A/B/C/E
______________________________________________________________________________________
High-Frequency, Current-Mode PWM Controller
with Accurate Programmable Oscillator
RFLTINT ≅
t RT
0.595 × CFLTINT
rent. Therefore, select a MOSFET that yields acceptable
conduction and switching losses.
Error Amplifier
The MAX5068 includes an internal error amplifier that
can regulate the output voltage in the case of a nonisolated power supply (Figure 1). Calculate the output voltage using the following equation:
R8 ⎞
⎛
VOUT = ⎜1 +
⎟ x VREF
⎝
R9 ⎠
where tRT is the desired recovery time.
Choose tRT = 10 x tSH. Typical values for tSH range from
a few hundred microseconds to a few milliseconds.
Soft-Start
The MAX5068 soft-start feature allows the load voltage
to ramp up in a controlled manner, eliminating outputvoltage 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 2047
oscillator clock cycles (soft-start timeout period). Unlike
other devices, the MAX5068 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.
Internal Regulators
Two internal linear regulators power the MAX5068 internal and external control circuits. VCC powers the external N-channel MOSFET and is internally set to
approximately 9.5V. The REG5 5V regulator has a 1mA
sourcing capability and may be used to provide power
to external circuitry. Bypass VCC and REG5 with 1µF
and 0.1µF high quality capacitors, respectively. Use
lower value ceramics in parallel to bypass other
unwanted noise signals. Bootstrapped operation
requires startup through a bleed resistor. Do not excessively load the regulators while the MAX5068 is in the
power-up mode. Overloading the outputs can cause
the MAX5068 to fail upon startup.
N-Channel MOSFET Switch Driver
NDRV 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 applications that use the discontinuous flyback
topology, a MOSFET rated at 600V is required. NDRV
can source/sink in excess of 650mA/1000mA peak cur-
where VREF = 1.23V. The amplifier’s noninverting input
internally connects to a digital soft-start reference voltage.
This forces the output voltage to come up in an orderly
and well-defined manner under all load conditions.
Slope Compensation (MAX5068C/D/E/F)
The MAX5068C/D/E/F use an internal-ramp generator
for slope compensation. The internal-ramp signal resets
at the beginning of each cycle and slews at the rate
programmed by the external capacitor connected at
SCOMP and the resistor at RT. Adjust the MAX5068
slew rate up to 90mV/µs using the following equation:
SR =
165 × 10 −6
(mV / µs)
RRT × CSCOMP
where RRT is the external resistor at RT that sets the oscillator frequency and CSCOMP is the capacitor at SCOMP.
PWM Comparator
The PWM comparator uses the instantaneous current,
the error amplifier, and the slope compensation to
determine when to switch NDRV off. In normal operation, the N-channel MOSFET turns off when:
IPRIMARY x RCS > VEA – VOFFSET - VSCOMP
where IPRIMARY is the current through the N-channel
MOSFET, V EA is the output voltage of the internal
amplifier, VOFFSET is the 1.6V internal DC offset and
VSCOMP is the ramp function starting at zero and slewing at the programmed slew rate (SR). When using the
MAX5068 in a forward-converter configuration, the following conditions must be met to avoid current-loop
subharmonic oscillations:
K × RCS × VOUT
NS
×
= SR
L
NP
where K = 0.75 and NS and NP are the number of turns
on the secondary and primary side of the transformer,
respectively. L is the secondary filter inductor. When
______________________________________________________________________________________
15
MAX5068
where IFLTINT = 60µA, tSH is the desired fault-integration time during which current-limit events from the current-limit comparator are ignored. For example, a 0.1µF
capacitor gives a fault-integration time of 4.7ms.
This is an approximate formula. Some testing may be
required to fine-tune the actual value of the capacitor. To
calculate the recovery time, use the following formula:
MAX5068
High-Frequency, Current-Mode PWM Controller
with Accurate Programmable Oscillator
optimally compensated, the current loop responds to
input-voltage transients within one cycle.
Applications Information
Current Limit
Keep all PC board traces carrying switching currents
as short as possible, and minimize current loops.
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 (V CS) of
314mV. Use the following equation to calculate the
value of RCS:
RCS =
VCS
IPRI
where IPRI is the peak current in the primary that flows
through the MOSFET at full load.
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. In most cases, a small
RC filter is required to filter out the leading-edge spike
on the sense waveform. Set the corner frequency to a
few MHz above the switching frequency.
16
Layout Recommendations
For universal AC input design, follow all applicable safety regulations. Offline power supplies may require UL,
VDE, and other similar agency approvals. Contact these
agencies 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 minimize the
surface area of the heatsink as much as possible.
To achieve best performance and to avoid ground
loops, use a solid ground-plane connection.
______________________________________________________________________________________
High-Frequency, Current-Mode PWM Controller
with Accurate Programmable Oscillator
D1
VOUT
D2
C7
VIN
C1
R1
IN
R2
NDRV
Q1
C2
R11
CS
FLTINT
C3
RCS
VCC
MAX5068C
C6
FB
VCC
C4
R5
C5
REG5
COMP
R3
R6
C10
RT
UVLO/EN
R4
R12
PS2913
DT
R9
R7
MAX8515
SYNC
SCOMP
AGND
PGND
R8
R13
R10
Selector Guide
STARTUP
VOLTAGE (V)
PROGRAMMABLE
UVLO
HYSTERESIS
OSCILLATOR
SYNC
SLOPE
COMPENSATION
Yes
23.6
Yes
Yes
No
No
10.8
Yes
Yes
No
75%
Yes
23.6
No
Yes
Yes
75%
Yes
23.6
Yes
No
Yes
MAX5068E
75%
No
10.8
No
Yes
Yes
MAX5068F
75%
No
10.8
Yes
No
Yes
PART
NUMBER
MAX DUTY
CYCLE
BOOTSTRAP
UVLO
MAX5068A
50%
MAX5068B
50%
MAX5068C
MAX5068D
______________________________________________________________________________________
17
MAX5068
Typical Operating Circuit
High-Frequency, Current-Mode PWM Controller
with Accurate Programmable Oscillator
MAX5068
Functional Diagram
HYST*
BOOTSTRAP
UVLO
MAX5068
UVLO/EN
21.6V/
9.74V
UVLO
1.23V
REFERENCE
1.23V/
1.18V
IN
VIN
CLAMP
26V
IN
2.8V/
1.6V
60µA
REGULATOR
Q
FLTINT
REG_OK
R
5V
OUT
REG5
VCC
S
VCC
CURENT-LIMIT
COMPARATOR
S
314mV
5kΩ
+
CS
+
Σ
*
1.6V
Q
NDRV
R
PGND
70ns
BLANKING
AGND
PWM
COMPARATOR
OSC
DEAD
TIME
SLOPE
COMPENSATION
***SCOMP
1.23V
THERMAL
SHUTDOWN
DIGITAL
SOFT-START
ERROR
AMP
FB
*MAX5068A/B/D AND MAX5068F ONLY.
**MAX5068A/B/C AND MAX5068E ONLY.
***MAX5068C/D/E/F ONLY.
18
COMP
SYNC**
RT
DT
______________________________________________________________________________________
High-Frequency, Current-Mode PWM Controller
with Accurate Programmable Oscillator
TOP VIEW
RT 1
16 REG5
SYNC 2
15 IN
14 VCC
SCOMP 3
DT 4
MAX5068C/E
RT 1
16 REG5
HYST 2
15 IN
14 VCC
SCOMP 3
MAX5068D/F
13 NDRV
DT 4
UVLO/EN 5
12 AGND
UVLO/EN 5
12 AGND
13 NDRV
FB 6
11 PGND
FB 6
11 PGND
COMP 7
10 AGND
COMP 7
10 AGND
FLTINT 8
9
FLTINT 8
9
TSSOP-EP
CS
CS
TSSOP-EP
Chip Information
TRANSISTOR COUNT: 4,266
PROCESS: BiCMOS
______________________________________________________________________________________
19
MAX5068
Pin Configurations (continued)
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.)
TSSOP 4.4mm BODY.EPS
MAX5068
High-Frequency, Current-Mode PWM Controller
with Accurate Programmable Oscillator
PACKAGE OUTLINE, TSSOP, 4.40 MM BODY
EXPOSED PAD
21-0108
D
1
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.
20 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600
© 2004 Maxim Integrated Products
Printed USA
is a registered trademark of Maxim Integrated Products.