Datasheet

t3 =
C
SS
x 3.5V
50 PA
= 7 x 10
4
x C
SS
t2 =
C
SS
x 1.5V
1 PA
= 1.5 x 10
6
x C
SS
t1 =
C
RES
x 2.55V
20 PA
= 1.275 x 10
5
x C
RES
LM5034
CS1
OUT1
GND1
V
IN
AC1
Q1
Q2
R1
Power
Transformer
R
F
C
F
C
AC
V
PWR
LM5034
CS1
OUT1
GND1
V
IN
AC1
R1
Power
Transformer
Current
Sense
Q1
Q2
V
PWR
C
F
R
F
C
AC
LM5034
SNVS347A –FEBRUARY 2005–REVISED APRIL 2013 www.ti.com
Figure 32. Current Sense Using a Current Sense Transformer
Figure 33. Current Sense Using a Source Sense Resistor (R1)
HICCUP MODE CURRENT LIMIT RESTART
This circuit’s operation is described in the Functional Description. Also see Figure 22 and Figure 23. In the case
of continuous current limit detection at both CS pins, the time required to reach the 2.55V RES pin threshold is:
(7)
For example, if C
RES
= 0.1 µF the time t1 in Figure 23 is approximately 12.75 ms.
In the case of continuous current limit detection at one CS pin only, the time to reach the 2.55V threshold is
increased by a factor of four, or:
t1 = 5.1 x 10
5
x C
RES
(8)
The time t2 in Figure 23 is set by the capacitor at each SS pin and the internal 1 µA current source, and is equal
to:
(9)
If C
SS
= 0.1 µF t2 is ≊150 ms. Time t3 is set by the internal 50 µA current source, and is equal to:
(10)
The time t2 provides a periodic dwell time for the converter in the event of a sustained overload or short circuit.
This results in lower average input current and lower power dissipated within the circuit components. It is
recommended that the ratio of t2/(t1 + t3) be in the range of 5 to 10 to make good use of this feature.
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