IN

OUT

S

OUT

IN

LS

max

OUT

V

V

L

F

2

V

V

I

I

˜

˜

˜

2 ms/div

Inductor Current

500mA/div

EN

RESET

VOUT

1ms/div

13

LM53602, LM53603

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SNVSAR0 – NOVEMBER 2016

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Copyright © 2016, Texas Instruments Incorporated

Feature Description (continued)

Figure 9. Typical Start-Up Waveform

8.3.3 Current Limit

The LM53603 incorporates valley current limit for normal overloads and for short-circuit protection. In addition,

the low side switch is also protected from excessive negative current when the device is in FPWM mode. Finally,

a high-side peak current limit is employed for protection of the top NMOS FET.

current that the LM53603 can supply. When the low-side switch turns on, the inductor current begins to ramp

limit, and results in Equation 1 for the maximum load current.

(1)

If the above situation persists for more than about 64 clock cycles, the device turns off both high-side and low-

hiccup time, another 64 cycles is counted and the process is repeated. If the current limit is not tripped for two

consecutive clock cycles, the counter is reset. Figure 10 shows the inductor current with a hard short on the

output. The hiccup time allows the inductor current to fall to zero, resetting the inductor volt-second balance. This

is the method used for short-circuit protection and keeps the power dissipation low during a fault. Of course the

output current is greatly reduced in this condition (see Typical Characteristics). A typical short-circuit transient

and recovery is shown in Figure 11.