LM5166DRCT datasheet(21/53 Pages) TI1

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VIN

1.22V

Comparator

RUV1

RUV2

1.144V

HYS

RHYS

LM5166

www.ti.com

SNVSA67A – DECEMBER 2016 – REVISED DECEMBER 2016

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7.3.5 Adjustable Current Limit

The LM5166 protects the system from overload conditions using cycle-by-cycle current limiting of the peak

inductor current. The current sensed in the high-side MOSFET is compared to the current limit threshold set by

the ILIM pin (See Table 3). Current is sensed after a 120-ns leading-edge blanking time following the high-side

MOSFET turn on. The propagation delay of the current limit comparator is 80 ns, typical.

(1)

For this current limit threshold selection, the ILIM pin may also be left open instead of using a 100 kΩ

or greater resistor.

(2)

This ILIM setting enables a function that modulates the ILIM levels during the first three switching cycles

as illustrated in Figure 40.

Table 3. Current Limit Thresholds

Mode of Operation

RILIM (kΩ)

Typical IHS_LIM (mA)

Typical ILS_LIM (mA)

IOUT_MAX (mA)

COT Mode

750

415

500

≥ 100(1)

500

315

300

PFM Mode

1250

N/A

500

24.9

1250(2)

N/A

500

56.2

750

N/A

300

≥ 100(1)

500

N/A

200

Note that in PFM mode, the inductor current ramps from zero to the chosen peak threshold every switching

cycle. Consequently, the maximum output current is equal to half the peak inductor current. The output current

capability in COT mode is higher and equal to the peak current threshold minus one-half the inductor ripple

current. The ripple current is determined by the input and output voltage and the chosen inductance and

frequency.

7.3.6 Precision Enable (EN) and Hysteresis (HYS)

The precision EN input supports adjustable input undervoltage lockout (UVLO) with hysteresis programmed

independently via the HYS pin for application specific power-up and power-down requirements. EN connects to

the input of a comparator with 76-mV hysteresis. The reference input of the comparator is connected to a 1.22-V

bandgap reference. An external logic signal can be used to drive EN input to toggle the output on and off for

system sequencing or protection. The simplest way to enable operation is to connect EN directly to VIN. This

allows self-start-up of the LM5166 when VIN is within its valid operating range. However, many applications

benefit from using a resistor divider RUV1 and RUV2 as shown in Figure 42 to establish a precision UVLO level.

Adding RHYS and the connection to the HYS pin increases the voltage hysteresis as needed.

Figure 42. Input Voltage UVLO using EN and HYS

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