LTC4449 datasheet(10/48 Pages) AD

10 / 48 page

LTC7871

Rev. 0

For more information www.analog.com

PIN FUNCTIONS

RUN (Pin 27): Enable Control Input. A voltage above

1.22V turns on the IC. There is a 2µA pull-up current on

this pin. Once the RUN pin rises above the 1.22V thresh-

old, the pull-up current increases to 6µA.

VFBHIGH (Pin 7): VHIGH Voltage Sensing Error Amplifier

Noninverting Input.

VFBLOW (Pin 3): VLOW Voltage Sensing Error Amplifier

Inverting Input.

ITHHIGH/ITHLOW (Pins 6 and 4): Current Control Threshold

and Error Amplifier Compensation Point. The current com-

parator’s threshold varies with the ITH control voltage.

SS (Pin 1): Soft-Start Input. The voltage ramp rate at this

pin sets the voltage ramp rate of the regulated voltage. A

capacitor to ground accomplishes soft-start. This pin has

a 1µA pull-up current.

MODE (Pin 51): Mode Set Pin. Tying this pin to SGND

enables forced continuous mode in buck or boost modes.

Floating this pin results in burst mode in buck mode and

discontinuous mode in boost mode. Tying this pin to V5

enables discontinuous mode in buck or boost modes. The

input impedance of this pin is 90kΩ.

SYNC (Pin 52): Switching Frequency Synchronization

or Spread Spectrum Set Pin. Applying an external clock

between 60kHz to 750kHz to this pin causes the switch-

ing frequency to synchronize to the clock signal. If SYNC

is low, a resistor from the FREQ pin to SGND sets the

switching frequency. Tying this pin to V5 allows switching

frequency spread spectrum. This pin has a 250kΩ internal

resistor to ground.

FREQ (Pin 53): Frequency Set Pin. A resistor between

this pin and SGND sets the switching frequency. This pin

sources 20µA current.

DRVSET (Pin 44): The voltage setting on this pin pro-

grams the DRVCC output voltage. There are two internal

resistors, 200kΩ and 160kΩ, connecting this pin to the

V5 and SGND, respectively.

CLKOUT (Pin 50): Clock Output Pin. Use this pin to syn-

chronize multiple LTC7871 ICs. Signal swing is from V5

to ground.

V5 (Pin 9): Internal 5V Regulator Output. The control

circuits are powered from this voltage. Bypass this pin

to SGND with a minimum of 4.7µF low ESR tantalum or

ceramic capacitor.

DRVCC (Pin 46): Gate Driver Current Supply LDO Output.

The voltage on this pin can be set to 5V, 8V, or 10V by

the DRVSET pin. Bypass this pin to ground plane with a

minimum of 4.7μF low ESR tantalum or ceramic capacitor.

EXTVCC (Pin 42): External Power Input to an Internal LDO

Connected to DRVCC. This LDO supplies DRVCC power,

bypassing the internal LDO powered from VHIGH, when-

ever EXTVCC is higher than its switchover threshold. Do

not exceed 60V on this pin.

ILIM (Pin 49): Current Comparator Sense Voltage Limit

Selection Pin. The input impedance of this pin is 100kΩ.

SNSD1+/SNSD2+/SNSD3+/SNSD4+/SNSD5+/SNSD6+

(Pins 19, 20, 25, 56, 61, and 62): DC Positive Current

Sense Comparator Inputs. These inputs amplify the DC

portion of the current signal to the IC’s current compara-

tors and current sense amplifiers.

SNS1–/SNS2–/SNS3–/SNS4–/SNS5–/SNS6– (Pins 18, 21,

24, 57, 60, and 63): Negative Current Sense Comparator

Inputs. The negative input of the current comparator is

normally connected to the VLOW.

SNSA1+/SNSA2+/SNSA3+/SNSA4+/SNSA5+/SNSA6+

(Pins 17, 22, 23, 58, 59, and 64): AC Positive Current

Sense Comparator Inputs. These inputs amplify the AC

portion of the current signal to the IC’s current comparator.

VHIGH (Pin 48): Main VHIGH Supply. Bypass this pin to

ground with a capacitor (0.1μF to 1μF).

FAULT (Pin 35): Fault Indicator Output. Open-drain output

that pulls to ground during a fault condition.

PGOOD (Pin 30): Power Good Indictor Output for the

Regulated VHIGH/VLOW. Open drain logic out that is pulled

to ground when the regulated VHIGH/VLOW exceeds ±10%

regulation window, after the internal 40µS power bad

mask timer expires.

LTC4449 Datasheet(PDF) 10 Page - Analog Devices

LTC4449 Datasheet(HTML) 10 Page - Analog Devices

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48

Datasheet Download

Link URL