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LTC4214-1/LTC4214-2

421412f

APPLICATIO S I FOR ATIO

SUPPLY VOLTAGE

The LTC4214 requires a (VIN – VEE) voltage of 6V to 16V

to function. This can be derived from GND and –12V of a

–12V system or the 3.3V and –5.2V of a –5.2V system. The

positive supply is connected to VIN via an RC network

so that the LTC4214 can have a usable VIN during load

short or other transient events when (VIN – VEE) glitches

below 6V.

INTERNAL UNDERVOLTAGE LOCKOUT (UVLO)

A hysteretic comparator, UVLO, monitors VIN for

undervoltage. The thresholds are defined by VLKO and its

hysteresis, VLKH. When VIN rises above 5.1V (VLKO) the

chip is enabled; below 4.8V (VLKO – VLKH) it is disabled and

GATE is pulled low. The UVLO function at VIN should not

be confused with the UV/OV pins. These are completely

separate functions.

UV/OV COMPARATORS

An UV hysteretic comparator detects undervoltage condi-

tions at the UV pin, with the following thresholds:

UV low-to-high (VUVHI) = 2.25V

UV high-to-low (VUVHI – VUVHST) = 2V

An OV hysteretic comparator detects overvoltage condi-

tions at the OV pin, with the following thresholds:

OV low-to-high (VOVHI) = 3V

OV high-to-low (VOVHI – V0VHST) = 2.85V

In Figure 2, a divider (R1-R2) is used to scale the supply

voltage of 12V

±10%. Using R1 = 121k and R2 = 32.4k

gives a typical operating range of 10.7V to 13.5V. The

under and overvoltage shutdown thresholds are then 9.5V

to 14.2V. 1% divider resistors are recommended to pre-

serve threshold accuracy.

The R1-R2 divider values shown in Figure 2 set a standing

current of slightly more than 75

µA and define an imped-

ance at UV/OV of 25k

Ω. In most applications, 25kΩ

impedance coupled with 250mV UV hysteresis makes the

LTC4214 insensitive to noise. If more noise immunity is

desired, add a 1nF to 10nF filter capacitor from UV/OV

to VEE.

Separate UV and OV pins can be used for a wider

operating range such as 10V to 14V as shown in Figure 3.

Other combinations are possible with different resistor

arrangements.

Figure 3. – 12V/2A Application with Wider Input Operating Range

4214 F03

GND

VEE

VIN

SENSE

TIMER

GATE

PWRGD

DRAIN

LTC4214-1

124k

Ω

RIN

470

Ω

100nF

32.4k

3.65k

47nF

CSS

22nF

10nF

–12V

0.025

Ω

IRF7413

Ω

100k

NDS0605

1nF

CIN

0.1

µF

100

µF

GND

(SHORT PIN)

475k

RPULLDN

10k

VOUT

GND

Z1: SMAJ15A

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