LT8602 datasheet(12/38 Pages) LINER

12 / 38 page

LT8603

8603f

For more information www.linear.com/LT8603

PIN FUNCTIONS

PG1, PG2, PG3 (Pins 1, 10, 40): Power Good Indicators

for Channels 1, 2 and 3, respectively. These pins are open-

drain outputs that pull down until the associated FB pin is

within ±8% of the target regulation voltage.

GND (Pins 2, 8, 13, 35, 38, Exposed Pad 41): Ground.

All ground pins and the exposed pad must be soldered

to PCB ground. See the Applications Information section

for PCB layout recommendations.

SW1 (Pin 3): High Voltage Converter 1 Switch Node. This

is the output of the internal power switches for Channel 1.

BST1, BST2 (Pins 4, 5): Boost Voltage for High Voltage

Converters. These pins provide the drive voltage required

by the internal power MOSFETs. A capacitor should be

connected from BST to the associated SW pin.

SW2 (Pins 6, 7): High Voltage Converter 2 Switch Node.

This is the output of the internal power switches for

Channel 2. These pins should be soldered to the same

PCB trace for even current distribution.

BIAS (Pin 9): Alternate Power Source for INTVCC and

INTVCC4 Regulators. If BIAS > 3.1V for INTVCC or > 4.6V

for INTVCC4 the internal regulators will draw their power

from BIAS. This will reduce the on-chip power dissipation

during full frequency operation and reduce the effective

no-load sleep current at the input.

PG4 (Pin 11): Power Good Indicator Channel 4. This pin

is an open-drain output that pulls low until the Channel

4 feedback voltage is greater than 92% of its reference

voltage.

FSEL4A, FSEL4B (Pins 12, 17): Boost Converter

Frequency Select and RUN Control. These pins are logic

inputs. When both pins are low, the boost controller is

shut down. The boost controller switching frequency is

controlled using these pins according to Table 2 in the

Applications Information section.

GATE4 (Pin 15): External MOSFET Gate Drive Output.

This pin switches from GND to VINTVCC4 to turn on the

low side power MOSFET in the BOOST converter. See

the Applications Information section for information on

MOSFET selection.

INTVCC4 (Pin 16): Internal Boost Regulator Output. Do

not load the INTVCC4 pin with external circuitry. INTVCC4

is 4.6V when BIAS < 4.6V, 5V when BIAS > 5V, and equal

to BIAS when BIAS is between 4.6V and 5V. Decouple to

ground with a low ESR 4.7µF capacitor.

ISP4, ISN4 (Pins 19, 18): Boost Controller Current Sense

Inputs. Connect a current sense resistor of appropriate

value between these pins with ISP4 connected to the

input supply and ISN4 to the application inductor. See

the Applications Information section for sense resistor

selection details.

TRKSS1, TRKSS2 (Pins 21, 20): Track/Soft-Start Inputs

for the High Voltage Converters. When this pin is below

1V, the converter regulates the FB pin to the TRKSS volt-

age instead of the internal reference. The TRKSS pin has a

2.4μA pull-up current. Connect a capacitor between either

of these pins to ground to program a soft-start time for

the associated channel.

EN/UVLO (Pin 22): Enable/Undervoltage Lockout Input.

The LT8603 is in low power shutdown when this pin is

below 0.4V. Between 0.4V and 1.1V, the part will turn on

the internal reference. A precision threshold at 1.2V (ris-

ing) enables the switching regulators. The precision

threshold allows the EN/UVLO pin to be used as an input

undervoltage lockout by connecting to resistor divider

between VIN and GND. When the EN/UVLO voltage is

between 0.4V and 1.2V, the LT8603 input current will

depend on the mode selected, the VIN voltage and EN/

UVLO voltage.

VIN (Pin 23): Power Supply to Internal Functions. This

pin provides power to the LT8603 internal circuitry. This

pin must reach 4V for the boost converter to complete its

internal soft-start delay of 1ms.

FB4 (Pin 24): Feedback Input Pin for the Boost Converter.

The converter regulates FB4 to 0.8V.

FB1, FB2 (Pins 26, 25): Feedback Input Pins for the

High Voltage Converters. The converters regulate the

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