LTC3589 datasheet(38/44 Pages) LINER

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LTC3589

3589p

THERMAL CONSIDERATIONS AND BOARD LAYOUT

Printed Circuit Board Power Dissipation

In order to ensure optimal performance and the ability

to deliver maximum output power to any regulator, it is

critical that the exposed ground pad on the backside of

the LTC3589 package be soldered to a ground plane on

the board. The exposed pad is the only GND connection

for the LTC3589. Correctly soldered to a 2500mm2 ground

plane on a double sided 1oz copper board the LTC3589

has a thermal resistance (θJA) of approximately 34°C/W.

Failure to make good thermal contact between the exposed

pad on the backside of the package and an adequately

sized ground plane will result in thermal resistances far

greater than 34°C/W.

Table 17. LTC3589 Read Only Status Register Table

REG

NAME

B[7]

B[6]

B[5]

B[4]

B[3]

B[2]

B[1]

B[0]

0x02

IRQSTAT Thermal

Limit Hard

Shut Down

Occurred

Near Thermal

Limit

Undervoltage

Hard Shut

Down

Occurred

Near

Undervoltage

Limit

PGOOD

Timeout Hard

Shutdown

Occurred

Unused

0x13

PGSTAT

LDO4 Status:

0 = VOUT Low

1 = VOUT

Good

LDO3 Status:

0 = VOUT Low

1 = VOUT

Good

LDO2 Status:

0 = VOUT Low

1 = VOUT Good

Buck_Boost

Status:

0 = VOUT Low

1 = VOUT Good

Step-Down

Switching

Regulator 3

Status:

0 = VOUT Low

1 = VOUT

Good

Step-Down

Switching

Regulator 2

Status:

0 = VOUT Low

1 = VOUT Good

Step-Down

Switching

Regulator 1

Status:

0 = VOUT Low

1 = VOUT Good

LDO1 Status:

0 = VOUT Low

1 = VOUT Good

OPERATION

To ensure the junction temperature of the LTC3589 die

does not exceed the maximum rated limit and to prevent

over temperature faults, the power output of the LTC3589

must be managed by the application. The total power dis-

sipation in the LTC3589 is approximated by summing the

power dissipation in each of the switching regulators and

the LDO regulators.

The power dissipation in a switching regulator is estimated

by:

PD(SWX) =(VOUTX •IOUTX)•

100 – Eff

100

Where VOUTX is the programmed output voltage, IOUTX

is the load current and Eff is the % efﬁciency that can

Table 16. LTC3589 Command Register Table

0x32 L2DTV1 Keep-Alive

Mode:

0 = Normal

Shutdown

1 = Keep-Alive

Unused

PGOOD

Mask:

0 = PGOOD

Low When

Slewing

1 = PGOOD

Not Changed

When

Slewing.

LDO 2 Feedback Reference Input (V1)

0001 1001

0x33 L2DTV2 LDO4 Control

MODE:

0 = LDO4

Enable with

EN_LDO34

1 = LDO4

Enable with

OVEN[6]

LDO4 Output Voltage:

00 = 2.8V

01 = 2.5V

10 = 1.8V

11 = 3.3V

LDO 2 Feedback Reference Input (V2)

0001 1001

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