Data Sheet

LT8350S

analog.com

Rev. A

29 of 36

The maximum steady ripple due to the voltage drop across the ESR is given by:

ΔVERS(BOOST) =

VOUT x IOUT(MAX)

VIN(MIN)

x ESR

ΔVERS(BUCK) =

VOUT x (1 -

VOUT

VIN(MIN) )

L x fSW

x ESR

Programming V

IN UVLO

A resistor divider from VIN to the EN/UVLO pin implements VIN undervoltage lockout (UVLO). The EN/UVLO enable

falling threshold is set at 1.220V with 15mV hysteresis. In addition, the EN/UVLO pin sinks 2.5µA when the voltage

on the pin is below 1.220V. This current provides user-programmable hysteresis based on the value of R1. A resistor

divider from VIN to ground can be used to program UVLO. The programmable UVLO thresholds are:

VIN(UVLO+) = 1.235V x

R1 + R2

R2

+ (2.5µA x R1)

VIN(UVLO-) = 1.220V x

R1 + R2

R2

Figure 39 shows the implementation of external shutdown control while still using the UVLO function. The NMOS

grounds the EN/UVLO pin when turned on and puts the LT8350S in shutdown with a quiescent current of less than

2µA (typical).

Figure 39. VIN Undervoltage Lockout

Programming Input or Output Current Limit

The input or output current limit is programmed by placing an appropriate value current sense resistor, RIS, in the

input or output power path. The voltage drop across RIS is Kelvin sensed by the ISP and ISN pins. The CTRL pin

should be connected to a voltage higher than 1.35V to get the full-scale 100mV (typical) threshold across the sense

resistor. The CTRL pin can be used to reduce the input or output current to zero, although relative accuracy

decreases with the decreasing sense threshold. For 0.25V ≤ VCTRL ≤ 1.15V, the current sense threshold linearly goes

up from 0mV to 90mV. For 1.15V ≤ VCTRL ≤ 1.35V, the current sense threshold smoothly transitions from the linear

function of VCTRL to the 100mV constant value. When the CTRL pin voltage, VCTRL, is less than 1.15V, the current

limit is:

IIS(MAX) =

VCTRL - 0.25V

10 x RIS

When VCTRL is higher than 1.35V, the current threshold is regulated to:

IIS(MAX) =

100mV

RIS

The CTRL pin should not be left open (tie to VREF if not used). The CTRL pin can also be used in conjunction with a

thermistor to provide overtemperature protection for the output load, or with a resistor divider to VIN to reduce

output power and switching current when VIN is low.

EN/UVLO

LT8350S

GND

R2

R1

VIN

RUN/STOP

CONTROL

(OPTIONAL)