LM5026MTX/NOPB National Semiconductor, LM5026MTX/NOPB Datasheet - Page 16

• Manufacturer Part Number: LM5026MTX/NOPB
• Description: CURRENT MODE-ACTIVE RESET
• Manufacturer: National Semiconductor
• Series: PowerWise®r

Specifications of LM5026MTX/NOPB

• Pwm Type: Current Mode
• Number Of Outputs: 2
• Frequency - Max: 1MHz
• Duty Cycle: 92.5%
• Voltage - Supply: 13 V ~ 100 V
• Buck: Yes
• Boost: Yes
• Flyback: Yes
• Inverting: Yes
• Doubler: No
• Divider: No
• Cuk: No
• Isolated: Yes
• Operating Temperature: -40°C ~ 125°C
• Package / Case: 16-TSSOP
• Frequency-max: 1MHz
• For Use With: LM5026EVAL - BOARD EVALUATION LM5026
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: *LM5026MTX/NOPB; LM5026MTX; Q2535472

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OSCILLATOR (RT, SYNC)
Oscillator (RT, SYNC) The oscillator frequency is generally
selected in conjunction with the design of the system mag-
netic components along with the volume and efficiency goals
for a given power converter design. The total RT resistance
at the RT pin sets the oscillator frequency. The RT resistors
should be one of the first components placed and connected
when designing the PC board. Direct, short connections to
each side of the RT resistors (RT, DCL and AGND pins) are
recommended .
The SYNC pin can be used to synchronize the internal oscil-
lator to an external clock. An open drain output is the recom-
mended interface from the external clock to the SYNC pin.
The clock pulse width should be greater than 15 ns. The ex-
ternal clock must be a higher frequency than the free running
frequency set by the RT resistor. Multiple LM5026 devices
can be synchronized together simply by connecting the de-
vices SYNC pins together. Care should be taken to ensure
the ground potential differences between devices are mini-
mized. In this configuration all of the devices will be synchro-
nized to the highest frequency device.
VOLTAGE FEEDBACK (COMP)
The COMP pin is designed to accept the voltage loop feed-
back error signal from the regulated output via an error am-
FIGURE 14. Remote Standby and Disable Control
FIGURE 13. Basic UVLO Configuration
16
plifier and (typically) an optocoupler. In a typical configuration,
VOUT is compared to a precision reference voltage by the
error amplifier. The amplifier’s output drives the optocoupler,
which in turn drives the COMP pin. The parasitic capacitance
of the optocoupler often limits the achievable loop bandwidth
for a given power converter. The optocoupler LED and de-
tector junction capacitance produce a low frequency pole in
the voltage regulation loop. The LM5026 current controlled
optocoupler interface (COMP) previously described, greatly
increases the pole frequency associated with the optocou-
pler.
CURRENT SENSE (CS)
The CS pin receives an input signal representative of the
transformer primary current, either from a current sense
transformer
source of the primary switch
sensed current creates a ramping voltage across R1, while
the R
C
and the ground connection from the current sense trans-
former, or R1, should be a dedicated track to the AGND pin.
The current sense components must provide >0.5V at the CS
pin when an over-current condition exists.
F
should be as physically close to the LM5026 as possible,
F
/C
F
filter suppresses noise and transients. R1, R
(Figure
15) or from a resistor in series with the
20147924
(Figure
20147925
16). In both cases the
F
and