¸¸

¹

·

¨¨

©

§

˜

˜

FB

OUT

B

IN

OUT

EN

Q

IN

R

V

I

K

V

V

I

I

I

2 ms/div

Iinductor, 500mA/div

2 ms/div

1ms/div

VOUT, 2V/div

Iinductor, 2A/div

5ms/div

Short Applied

Short Removed

14

LM53602, LM53603

SNVSAR0 – NOVEMBER 2016

www.ti.com

Product Folder Links: LM53602 LM53603

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Copyright © 2016, Texas Instruments Incorporated

Feature Description (continued)

Figure 10. Inductor Current Bursts in Short Circuit

Figure 11. Short-Circuit Transient and Recovery

is a cycle-by-cycle current limit and does not produce any frequency or current fold-back. It is meant to protect

the high-side MOSFET from excessive current. Under some conditions, such as high input voltage, this current

limit may trip before the low-side protection. The peak value of this current limit varies with duty-cycle.

switch is turned off until the next clock cycle. This is used to protect the low-side switch from excessive negative

the device to operate in DCM.

8.3.4 Synchronizing Input

The internal clock of the LM53603 can be synchronized to a system clock through the SYNC input. This input

recognizes a valid high level as that

≥ 1.5 V, and a valid low as that ≤ 0.4 V. The frequency synchronization

signal should be in the range of 1.9 MHz to 2.3 MHz with a duty cycle of from 10% to 90%. The internal clock is

synced to the rising edge of the external clock. If this input is not used, it should be grounded. The maximum

voltage on this input is 5.5 V; and should not be allowed to float. See the Device Functional Modes section to

determine which modes are valid for synchronizing the clock.

8.3.5 Input Supply Current

The LM53603 is designed to have very low input supply current when regulating light loads. One way this is

achieved is by powering much of the internal circuitry from the output. The BIAS pin is the input to the LDO that

powers the majority of the control circuits. By connecting the BIAS input to the output of the regulator, this current

Another advantage of the LM53603 is that the feedback divider is integrated into the device. This allows the use

of much larger resistors than can be used externally; >> 100 kΩ. This results in much lower divider current than

is possible with external resistors. Equation 2 can be used to estimate the total input supply current when the

device is regulating with no external loads. The terms of the equation are as follows:

•

•

•

•

•

K:

≈ 0.9

(2)