LT8228 datasheet(21/69 Pages) AD

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LT8228

Rev. A

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PIN FUNCTIONS

needs its own pull-up resistor in series with a diode whose

anode is connected to its INTVCC pin. This diode prevents

unintentional boost mode selection when one or more

channels are disabled. Refer to the Paralleling Multiple

LT8228s in Applications Information section for more

information. Do not leave this pin open.

SYNC (Pin 23): Synchronization or Spread Spectrum

Input. Synchronize to an external clock with pulses that

have duty cycles between 5% and 95% from 80kHz to

600kHz. The high level of the clock voltage needs to be

above 1V and the low level needs to be below 0.5V. To

enable spread spectrum of the internal frequency genera-

tor, connect this pin to INTVCC. Connect this pin to ground

to disable spread spectrum. Do not leave this pin open.

FAULT (Pin 24): Fault Status Indicator. FAULT is an open-

drain logic pin which flags fault conditions (refer to the

FAULT Conditions in Applications Information section

for more information). When the FAULT pin asserts, the

LT8228 stops switching and the SS pin pulls low. Pull-up

the pin with an LED in series with a resistor to a voltage

source to provide a visual status indicator. For a sink cur-

rent of 2mA, the maximum voltage overtemperature at

the FAULT pin is 0.5V. Tie the pin to ground if not used.

REPORT (Pin 25): Diagnostic Status. This pin is an open-

drain active low output that reports the state of the inter-

nal diagnostic monitors of critical safety features through

a digital logic bit stream synchronized to the frequency

of the SYNC pin. See the Report Feature in Applications

Information section for more details on the report func-

tion. Pull-up the pin with a series resistor to a micro-

controller input logic voltage source. For a sink current

of 2mA, the maximum voltage overtemperature at the

REPORT pin is 0.5V. Tie the pin to ground if not used.

TMR (Pin 26): Timer Input for SOA Management of V1

Protection MOSFET (M1). Connect a capacitor between

this pin and ground to set the M1 turn-off and cool down

periods at excess power dissipation during output inrush

current in boost mode. In boost mode, when current regu-

lation at ISET1N is 1.4V and voltage across M1 (V1D,

DS1) exceeds 500mV, the TMR pin voltage starts to

increase. The current charging up this pin increases with

the voltage difference between V1D and DS1 pins (see

Applications Information). When the TMR reaches 1.4V,

the LT8228 shorts DG1 to DS1 to turn-off M1. Upon M1

gate off, a cool down interval commences while the TMR

pin cycles 32 times between 0.4V and 1.4V with 2μA

charge and discharge currents. When TMR crosses 0.4V

the 32nd time, the DG1 pin pulls high, turning on M1.

BG (Pin 27): Bottom Gate Drive. The BG pin drives the

gate of the low side N-channel synchronous switch

MOSFET M3. The BG voltage transitions between DRVCC

and ground.

DRVCC (Pin 28): 10V Gate Drive VCC Supply. DRVCC is

powered from BIAS. It provides power to the top gate (TG)

and bottom gate (BG) MOSFET drivers. Connect a mini-

mum bypass capacitor of 2.2µF from DRVCC to ground.

BIAS (Pin 29): DRVCC and Control Circuitry Supply. This

pin supplies the DRVCC regulator as well as the internal

control circuitry. BIAS can be connected to V1 or V2 or

an external supply. No negative voltage is allowed at the

BIAS pin. Refer to the BIAS, DRVCC, INTVCC and Power

Dissipation in Applications Information section for more

details. Connect a minimum bypass capacitor of 10µF

from BIAS to ground.

SW (Pin 30): Switch Node. This pin connects to the

source of the top side MOSFET M2 and to the drain of

the bottom side MOSFET M3. This pin also connects to

the inductor and the bootstrap capacitor CBST.

TG (Pin 31): Top Gate Drive. The TG pin drives the gate

of the high side N-channel MOSFET M2. TG draws power

from the BST pin and returns to the SW pin, providing true

floating gate drive to the high side MOSFETs.

BST (Pin 32): Top Gate Driver Boosted Supply. The BST

pin supplies power to the floating TG driver for the high

side MOSFET (M2). Connect a low ESR capacitor from the

BST pin to the SW pin. Connect a fast recovery diode from

DRVCC to BST to supply this pin. The pin voltage swings

from a diode below DRVCC up to DRVCC + V1D.

ENABLE (PIN 33): Enable Input. Pull this pin above 1.3V

typically to enable the LT8228. When this pin is pulled

below the typical threshold voltage of 1.2V, the controller

stops switching, the protection MOSFETs are turned off,

and the DRVCC and INTVCC regulators are disabled. When

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