Datasheet
SYNC
AGND
LM5026
R
T
=
1
F x 167 x 10
-12
RES
SS
OUTA
0V
2.5V
#1.4V
5.0V
t1 t2 t3
Current Limit
Detected
50 PA
1 PA
LM5026
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SNVS363D –AUGUST 2005–REVISED APRIL 2013
sequences will occur.
2. Hiccup only: The timer can be configured for immediate activation of a hiccup sequence upon detection of
an overload by leaving the RES pin open circuit.
3. Delayed Hiccup: The most common configuration as previously described, is a programmed interval of
cycle-by-cycle limiting before initiating a hiccup mode restart. The advantage of this configuration is short
term overload conditions will not cause a hiccup mode restart, however during extended overload conditions
the average dissipation of the power converter will be very low.
4. Externally Controlled Hiccup: The RES pin can also be used as an input. By externally driving the pin to a
level greater than the 2.5V hiccup threshold, the controller will be forced into the delayed restart sequence. If
the RES pin is used as an input, the driving source should be current limited to less than 5 mA. For example,
the external trigger for a delayed restart sequence could come an over-temperature protection circuit.
Figure 23. Hiccup Over-Load Restart Timing
Oscillator and Sync Capability
The LM5026 oscillator frequency is set by the external resistance connected between the RT pin and ground
(AGND). To set a desired oscillator frequency (F) the necessary value of total R
T
resistance can be calculated
from:
(5)
The R
T
resistor(s) should be located very close to the device and connected directly to the pins of the IC (RT and
AGND).
The SYNC pin can be used to synchronize the internal oscillator to an external clock. An open drain output is the
recommended interface between the external clock to the LM5026 SYNC pin as illustrated in Figure 24. The
clock pulse width must be greater than 15 ns. The external clock frequency must be a higher than the free
running frequency set by the R
T
resistance.
Figure 24. Sync from External Clock
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