LP87702 datasheet(82/99 Pages) TI

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9.2.2.1.6 Supply Filtering Components

The VANA input is used to supply analog and digital circuits in the device. See Table 9-8 recommended

components from for VANA input supply filtering.

Table 9-8. Recommended Supply Filtering Components

MANUFACTURER

PART NUMBER

VALUE

CASE SIZE

DIMENSIONS L×W×H

(mm)

VOLTAGE RATING

Murata

GCM188R71C104KA37D

100 nF (10%)

0603

1.6 × 0.8 × 0.8

16 V

Murata

GCM155R71C104KA55D

100 nF (10%)

0402

1.0 × 0.5 × 0.5

16 V

9.2.3 Current Limit vs Maximum Output Current

The current limit must be set high enough to account for the inductor ripple current on top of the maximum

output current for the buck converters and boost. The forward current limit for the buck converters is set by

BUCK0_ILIM, BUCK1_ILIM and for boost it is set by BOOST_ILIM.

For the buck converter the inductor current ripple can be calculated using Equation 1 and Equation 2:

OUT

IN(max)

u K

(1)

IN(max)

OUT

)

(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.

ILIM_FWD_SET_OTP (1.5...4.5 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

Figure 9-2. Current Limit vs Maximum Output Current

LP87702-Q1

SNVSAL1C – DECEMBER 2017 – REVISED JUNE 2021

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