LTC3589HUJ#PBF Linear Technology, LTC3589HUJ#PBF Datasheet - Page 40

• Manufacturer Part Number: LTC3589HUJ#PBF
• Description: IC DC/DC CONV 8-OUTPUT 40QFN
• Manufacturer: Linear Technology

Specifications of LTC3589HUJ#PBF

• Applications: Handheld/Mobile Devices
• Current - Supply: 8µA
• Voltage - Supply: 2.7 V ~ 5.5 V
• Operating Temperature: -40°C ~ 150°C
• Mounting Type: Surface Mount
• Package / Case: *
• Primary Input Voltage: 5.5V
• No. Of Outputs: 8
• Output Voltage: 5V
• Output Current: 1.6A
• No. Of Pins: 40
• Operating Temperature Range: -40°C To +150°C
• Msl: MSL 1 - Unlimited
• No. Of Ldo Regulators: 3
• Rohs Compliant: Yes
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

LTC3589/LTC3589-1
OPERATION
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/LTC3589-1 package be soldered to a ground
plane on the board. The exposed pad is the only GND con-
nection for the LTC3589/LTC3589-1. Correctly soldered to
a 2500mm
board the LTC3589/LTC3589-1 has a thermal resistance
(θ
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.
To ensure the junction temperature of the LTC3589/
LTC3589-1 die does not exceed the maximum rated limit and
to prevent overtemperature faults, the power output of the
LTC3589/LTC3589-1 must be managed by the application.
The total power dissipation in the LTC3589/LTC3589-1 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 esti-
mated by:
Where V
is the load current and Eff is the % efficiency that can
be measured or looked up in an efficiency table for the
programmed output voltage.
40
JA
P
) of approximately 34°C/W. Failure to make good
D(SWX)
OUTX
2
= (V
ground plane on a double sided 1oz copper
is the programmed output voltage, I
OUTX
• I
OUTX
)•
100 – Eff
100
OUTX
The power dissipated by an LDO regulator is estimated by:
Where V
is the LDO supply voltage, and I
current. If one of the switching regulator outputs is used
as an LDO supply voltage, remember to include the LDO
supply current in the switching regulator load current for
calculating power loss.
An example using the equations above with the parameters
in Table 19 shows an application that is at the maximum
junction temperature of 125°C at an ambient temperature
of 85°C. LDO2, LDO3, and LDO4 are powered by step-
down switching regulator 2 and the buck-boost switching
regulator. The total load on those two switching regula-
tors is the sum of the application load and the LDO load.
This example is with the LDO regulators at one half rated
current and the switching regulators at three quarters
rated current.
Table 19. T
OUTPUT
LDO1_VSTB 3.8V
LDO2
LDO3
LDO4
V
V
V
V
OUT1
OUT2
OUT3
OUT4
INTERNAL JUNCTION TEMPERATURE AT 85°C AMBIENT
P
D(LDOX)
LDOX
J
Calculation Example
3.3V
3.3V
3.8V
3.8V
3.8V
3.8V
1.8V
V
= (V
IN
is the programmed output voltage, V
IN(LDOX)
1.25V
V
1.2V
1.2V
1.8V
2.5V
1.2V
1.8V
3.3V
OUT
APP LOAD
100mA
100mA
100mA
10mA
0.65A
0.75A
0.70A
1.2A
– V
LDOX
100mA
100mA
100mA
TOTAL
LDOX
LOAD
10mA
0.75A
0.75A
0.90A
1.2A
)• I
TOTAL POWER
LDOX
is the output load
80%
90%
90%
85%
EFF
1180mW
IN(LDOX)
POWER
290mW
300mW
150mW
140mW
140mW
30mW
60mW
80mW
125°C
DISS
3589fc