LP8733 datasheet(67/82 Pages) TI1

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ILIM_FWD_SET_OTP (1.5...4 A, 0.5-A step)

Inductor current =

Forward current

IL_AVG = IOUT

ILIM_FWD_TYP (+7.5%)

ILIM_FWD_MAX (+20%)

ILIM_FWD_MIN (-5%)

1 / fSW

IOUT_MAX < ILIM_FWD_SET_OTP ± 1 A

Minimum 1A guard band

to take current ripple,

inductor inductance

variation into account

IN(max)

OUT

)

OUT

IN(max)

u K

LP8733

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SNVSBK2 – SEPTEMBER 2019

Product Folder Links: LP8733

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8.2.1.6 Current Limit vs. Maximum Output Current

The inductor current ripple can be calculated using Equation 1 and Equation 2:

(1)

(2)

Example using Equation 1 and Equation 2:

VIN(max) = 5.5 V

VOUT = 1 V

η = 0.75

fSW = 1.8 MHz

L = 0.38 µH

then D = 0.242 and ΔIL = 1.59 A

Peak current is half of the current ripple. If ILIM_FWD_SET_OTP is 3 A, the minimum forward current limit would be

2.85 A when taking the –5% tolerance into account. In this case the difference between set peak current and

maximum load current = 0.795 A + 0.15 A = 0.945 A.

Figure 70. Current Limit vs Maximum Output Current

8.2.2 Detailed Design Procedure

The performance of the LP8733xx device depends greatly on the care taken in designing the printed circuit board

(PCB). The use of low-inductance and low serial-resistance ceramic capacitors is strongly recommended, while

proper grounding is crucial. Attention must be given to decoupling the power supplies. Decoupling capacitors

must be connected close to the device and between the power and ground pins to support high peak currents

being drawn from system power rail during turnon of the switching MOSFETs. Keep input and output traces as

short as possible, because trace inductance, resistance, and capacitance can become performance limiting

items. The separate buck regulator power pins VIN_Bx are not connected together internally. Connect the

VIN_Bx power connections together outside the package using power plane construction.

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