Datasheet

T
HICCUP
=
5 µA
C
RES
x (2.0Vx8)
10 µA
C
RES
x ((2.0Vx8) + 1.0V)
+
T
CS
=
C
RES
x 1.0V
30 PA
Q1
Q2
Q3
Q4
N
P
CS
LM5045
R
F
C
F
R
CS
VIN
AGND
Q1
Q2
Q3
Q4
V
PWR
N
P
N
S1
N
S2
R
F
C
F
R
CS
CS
LM5045
VIN
AGND
LM5045
www.ti.com SNVS699G –FEBRUARY 2011–REVISED MARCH 2013
Figure 28. Transformer Current Sense
Figure 29. Resistor Current Sense
Hiccup Mode Current Limit Restart
The operation of the hiccup mode restart circuit is explained in the FUNCTIONAL DESCRIPTION section. During
a continuous current limit condition, the RES pin is charged with 30µA current source. The restart delay time
required to reach the 1.0V threshold is given by:
(8)
This establishes the time allowed before the IC initiates a hiccup restart sequence. For example, if the
C
RES
=0.01µF, the time TCS as noted in Figure 30 below is 334µs. Once the RES pin reaches 1.0V, the 30µA
current source is turned-off and a 10µA current source is turned-on during the ramp up to 4V and a 5µA is turned
on during the ramp down to 2V. The hiccup mode off-time is given by:
(9)
With a C
RES
=0.01µF, the hiccup time is 49ms. Once the hiccup time is finished, the RES pin is pulled-low and the
SS pin is released allowing a soft-start sequence to commence. Once the SS pin reaches 1V, the PWM pulses
will commence. The hiccup mode provides a cool-down period for the power converter in the event of a
sustained overload condition thereby lowering the average input current and temperature of the power
components during such an event.
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