LT8613 datasheet(17/24 Pages) LINER

17 / 24 page

For more information www.linear.com/LT8613

LT8613

8613f

applicaTions inForMaTion

capacitor on TR/SS enables soft starting the output to pre-

ventcurrentsurgeontheinputsupply.Duringthesoft-start

ramptheoutputvoltagewillproportionallytracktheTR/SS

pin voltage. For output tracking applications, TR/SS can

be externally driven by another voltage source. From 0V to

0.97V, the TR/SS voltage will override the internal 0.97V

reference input to the error amplifier, thus regulating the

FB pin voltage to that of TR/SS pin. When TR/SS is above

0.97V, tracking is disabled and the feedback voltage will

regulate to the internal reference voltage. The TR/SS pin

may be left floating if the function is not needed.

An active pull-down circuit is connected to the TR/SS pin

which will discharge the external soft-start capacitor in

the case of fault conditions and restart the ramp when the

faults are cleared. Fault conditions that clear the soft-start

capacitor are the EN/UV pin transitioning low, VIN voltage

falling too low, or thermal shutdown.

Output Power Good

When the LT8613’s output voltage is within the ±9%

window of the regulation point, which is a VFB voltage in

the range of 0.883V to 1.057V (typical), the output voltage

is considered good and the open-drain PG pin goes high

impedance and is typically pulled high with an external

resistor. Otherwise, the internal pull-down device will pull

the PG pin low. To prevent glitching both the upper and

lower thresholds include 1.3% of hysteresis.

The PG pin is also actively pulled low during several fault

conditions: EN/UV pin is below 1V, INTVCC has fallen too

low, VIN is too low, or thermal shutdown.

Synchronization

To select low ripple Burst Mode operation, tie the SYNC pin

below 0.4V (this can be ground or a logic low output). To

synchronizetheLT8613oscillatortoanexternalfrequency

connect a square wave (with 20% to 80% duty cycle) to

the SYNC pin. The square wave amplitude should have val-

leys that are below 0.4V and peaks above 2.4V (up to 6V).

Figure 4. LT8613 Sense Voltage vs IMON Voltage

INTVCC Regulator

Aninternallowdropout (LDO)regulatorproducesthe 3.4V

supply from VIN that powers the drivers and the internal

bias circuitry. The INTVCC can supply enough current for

the LT8613’s circuitry and must be bypassed to ground

withaminimumof1μFceramiccapacitor.Goodbypassing

is necessary to supply the high transient currents required

by the power MOSFET gate drivers. To improve efficiency

the internal LDO can also draw current from the BIAS

pin when the BIAS pin is at 3.1V or higher. Typically the

BIAS pin can be tied to the output of the LT8613, or can

be tied to an external supply of 3.3V or above. If BIAS is

connected to a supply other than VOUT, be sure to bypass

with a local ceramic capacitor. If the BIAS pin is below

3.0V, the internal LDO will consume current from VIN.

Applications with high input voltage and high switching

frequency where the internal LDO pulls current from VIN

will increase die temperature because of the higher power

dissipation across the LDO. Do not connect an external

load to the INTVCC pin.

Output Voltage Tracking and Soft-Start

The LT8613 allows the user to program its output voltage

ramp rate by means of the TR/SS pin. An internal 2.2μA

pulls up the TR/SS pin to INTVCC. Putting an external

VISP-VISN (mV)

200

400

600

800

1000

1200

8613 F04

VSYNC = 3.3V

LT8613 Datasheet(PDF) 17 Page - Linear Technology

LT8613 Datasheet(HTML) 17 Page - Linear Technology

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

Datasheet Download

Link URL