t1 =

CRES x 2.55V

20 2A

= 1.275 x 10

5 x CRES

LM5032

CS1

OUT1

GND1

VIN

Q1

R1

Power

Transformer

RF

C

F

V

PWR

LM5032

CS1

OUT1

GND1

VIN

R1

Power

Transformer

Current

Sense

Q1

V

PWR

C

F

RF

LM5032

www.ti.com

SNVS344B – MARCH 2005 – REVISED DECEMBER 2014

Application Information (continued)

When the LM5032’s two controller channels are configured to provide a single high current output, COMP1 and

COMP2 are typically connected together, and to the feedback signal from the optocoupler.

8.1.7 Current Sense, CS1, CS2

Each CS pin receives an input signal representative of its transformer’s primary current, either from a current

sense transformer or from a resistor in series with the source of the primary switch, as shown in Figure 25 and

Figure 26. In both cases the sensed current creates a ramping voltage across R1, and the RF/CF filter

suppresses noise and transients. R1, RF and CF should be as physically close to the LM5032 as possible, and

the ground connection from the current sense transformer, or R1, should be a dedicated track to the appropriate

GND pin. The current sense components must provide >0.5V at the CS pin when an over-current condition

exists.

Figure 25. Current Sense Using a Current Sense Transformer

Figure 26. Current Sense Using a Source Sense Resistor (R1)

8.1.8 Hiccup Mode Current Limit Restart

This circuit’s operation is described in the Functional Description. Also see Figure 16 and Figure 17. In the case

of continuous current limit detection at both CS pins, the time required to reach the 2.55V RES pin threshold is:

(6)

For example, if CRES = 0.1 µF the time t1 in Figure 18 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

(7)

The time t2 in Figure 17 is set by the capacitor at each SS pin and the internal 1 µA current source, and is equal

to:

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