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MAX5014 Schematic ( PDF Datasheet ) - Maxim Integrated

Teilenummer MAX5014
Beschreibung Current-Mode PWM Controllers
Hersteller Maxim Integrated
Logo Maxim Integrated Logo 




Gesamt 14 Seiten
MAX5014 Datasheet, Funktion
19-2082; Rev 0; 7/01
EVAALVUAAILTAIOBNLEKIT
Current-Mode PWM Controllers with Integrated
Startup Circuit for Isolated Power Supplies
General Description
The MAX5014/MAX5015 integrate all the building
blocks necessary for implementing DC-DC fixed-fre-
quency isolated power supplies. These devices are
current-mode controllers with an integrated high-volt-
age startup circuit suitable for isolated telecom/industri-
al voltage range power supplies. Current-mode control
with leading-edge blanking simplifies control-loop
design and internal ramp compensation circuitry stabi-
lizes the current loop when operating at duty cycles
above 50% (MAX5014). The MAX5014 allows 85%
operating duty cycle and could be used to implement
flyback converters, whereas the MAX5015 limits the
operating duty cycle to less than 50% and can be used
in single-ended forward converters. A high-voltage
startup circuit allows these devices to draw power
directly from the 18V to 110V input supply during start-
up. The switching frequency is internally trimmed to
275kHz ±10%, thus reducing magnetics and filter com-
ponent costs.
The MAX5014/MAX5015 are available in 8-pin SO
packages. An evaluation kit (MAX5015EVKIT) is also
available.
Warning: The MAX5014/MAX5015 are designed to
operate with high voltages. Exercise caution.
Applications
Telecom Power Supplies
Industrial Power Supplies
Networking Power Supplies
Isolated Power Supplies
TOP VIEW
Pin Configuration
Features
o Wide Input Range: (18V to 110V) or (13V to 36V)
o Current-Mode Control
o Leading-Edge Blanking
o Internally Trimmed 275kHz ±10% Oscillator
o Low External Component Count
o Soft-Start
o High-Voltage Startup Circuit
o Pulse-by-Pulse Current Limiting
o Thermal Shutdown
o SO-8 Package
Ordering Information
PART
TEMP. RANGE
MAX5014CSA*
0°C to +70°C
MAX5014ESA*
-40°C to +85°C
MAX5015CSA*
0°C to +70°C
MAX5015ESA*
-40°C to +85°C
*See Selector Guide at end of data sheet.
PIN-PACKAGE
8-SO
8-SO
8-SO
8-SO
Typical Operating Circuit
VIN
VDD
V+
NDRV
MAX5015
CS
SS_SHDN
GND
VCC
VOUT
V+ 1
VDD 2
OPTO 3
SS_SHDN 4
MAX5014/
MAX5015
8 VCC
7 NDRV
6 GND
5 CS
OPTO
OPTOCOUPLER
8-SO
________________________________________________________________ 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.






MAX5014 Datasheet, Funktion
Current-Mode PWM Controllers with Integrated
Startup Circuit for Isolated Power Supplies
Pin Description
PIN NAME
FUNCTION
1
V+
High-Voltage Startup Input. Connect directly to an input voltage between 18V to 110V. Connects
internally to a high-voltage linear regulator that generates VCC during startup.
VDD is the Input of the Linear Regulator that Generates VCC. For supply voltages less than 36V, VDD
2
VDD
and V+ can both be connected to the supply. For supply voltages greater than 36V, VDD receives
its power from the tertiary winding of the transformer and accepts voltages from 13V to 36V. Bypass
to GND with a 4.7µF capacitor.
3
OPTO
Optocoupler Input. The control voltage range on this input is 2V to 3V.
Soft-Start Timing Capacitor Connection. Ramp time to full current limit is approximately 0.45ms/nF.
4 SS_SHDN This pin is also the reference voltage output. Bypass with a minimum 10nF capacitor to GND. The
device goes into shutdown when VSS_SHDN is pulled below 0.25V.
Current Sense Input. Turns power switch off if VCS rises above 465mV for cycle-by-cycle current
5 CS limiting. CS is also the feedback for the current-mode controller. CS is connected to the PWM
comparator through a leading edge blanking circuit.
6
GND
Ground
7
NDRV
Gate Drive. Drives a high-voltage external N-channel power MOSFET.
Regulated IC Supply. Provides power for the entire IC. VCC is regulated from VDD during normal
8 VCC operation and from V+ during startup. Bypass VCC with a 10µF tantalum capacitor in parallel with
0.1µF ceramic capacitor to GND.
Detailed Description
Use the MAX5014/MAX5015 PWM current-mode con-
trollers to design flyback- or forward-mode power sup-
plies. Current-mode operation simplifies control-loop
design while enhancing loop stability. An internal high-
voltage startup regulator allows the device to connect
directly to the input supply without an external startup
resistor. Current from the internal regulator starts the
controller. Once the tertiary winding voltage is estab-
lished the internal regulator is switched off and bias
current for running the IC is derived from the tertiary
winding. The internal oscillator is set to 275kHz and
trimmed to ±10%. This permits the use of small mag-
netic components to minimize board space. Both the
MAX5014 and MAX5015 can be used in power sup-
plies providing multiple output voltages. A functional
diagram of the IC is shown in Figure 1. Typical applica-
tions circuits for forward and flyback topologies are
shown in Figure 2 and Figure 3, respectively.
Current-Mode Control
The MAX5014/MAX5015 offer current-mode control
operation with added features such as leading-edge
blanking with dual internal path that only blanks the
sensed current signal applied to the input of the PWM
comparator. The current limit comparator monitors the
CS pin 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 is the result of the
MOSFET gate charge current, 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 not
blanked and cycle-by-cycle current limiting is provided
under all conditions.
Use the MAX5014 in discontinuous flyback applications
where wide line voltage and load current variation is
expected. Use the MAX5015 for single transistor for-
ward converters where the maximum duty cycle must
be limited to less than 50%.
Under certain conditions it may be advantageous to
use a forward converter with greater than 50% duty
cycle. For those cases use the MAX5014. The large
duty cycle results in much lower operating primary
RMS currents through the MOSFET switch and in most
cases a smaller output filter inductor. The major disad-
vantage to this is that the MOSFET voltage rating must
be higher and that slope compensation must be provid-
ed to stabilize the inner current loop. The MAX5014
provides internal slope compensation.
6 _______________________________________________________________________________________

6 Page









MAX5014 pdf, datenblatt
Current-Mode PWM Controllers with Integrated
Startup Circuit for Isolated Power Supplies
ing equation to calculate the tertiary winding turns
ratio:
VDDMIN + 0.7
VIN_MIN
× NP
NT
VDDMAX + 0.7
VIN_MAX
× NP
where:
VDDMIN is the minimum VDD supply voltage (13V).
VDDMAX is the maximum VDD supply voltage (36V).
VIN_MIN is the minimum input voltage (36V).
VIN_MAX is the maximum input voltage (72V in this
design example).
NP is the number of turns of the primary winding.
NT is the number of turns of the tertiary winding.
13.7
36
× 14
NT
36.7
72
× 14
5.33 NT 7.14
Choose NT = 6.
6) Choose RSENSE according to the following equation:
RSENSE
NS
NP
VILIM
×1.2 × IOUTMAX
where:
VILim is the current-sense comparator trip threshold
voltage (0.465V).
NS/NP is the secondary side turns ratio (5/14 in this
example).
IOUTMAX is the maximum DC output current (10A in
this example).
RSENSE
5
0.465V
×1.2 ×10
= 109m
14
7) Choose the inductor value so that the peak ripple
current (LIR) in the inductor is between 10% and
20% of the maximum output current.
L (VOUT + VD ) × (1-DMIN)
2 × LIR × 275kHz × IOUTMAX
where VD is the output Schottky diode forward volt-
age drop (0.5V) and LIR is the ratio of inductor rip-
ple current to DC output current.
L (5.5) × (1- 0.198) = 4.01µH
0.4 × 275kHz ×10A
8) The size and ESR of the output filter capacitor deter-
mine the output ripple. Choose a capacitor with a
low ESR to yield the required ripple voltage.
Use the following equations to calculate the peak-to-
peak output ripple:
VRIPPLE = VR2IPPLE,ESR + VR2IPPLE,C
where:
VRIPPLE is the combined RMS output ripple due to
VRIPPLE,ESR, the ESR ripple, and VRIPPLE,C, the
capacitive ripple. Calculate the ESR ripple and
capacitive ripple as follows:
VRIPPLE,ESR = IRIPPLE x ESR
VRIPPLE,C = IRIPPLE/(2 x π x 275kHz x COUT)
Layout Recommendations
All connections carrying pulsed currents must be very
short, be as wide as possible, and have a ground plane
as a return path. The inductance of these connections
must be kept to a minimum due to the high di/dt of the
currents in high-frequency switching power converters.
Current loops must be analyzed in any layout pro-
posed, and the internal area kept to a minimum to
reduce radiated EMI. Ground planes must be kept as
intact as possible.
Chip Information
TRANSISTOR COUNT: 589
PROCESS: BiCMOS
12 ______________________________________________________________________________________

12 Page





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