LP3906SQ-FXPI/NOPB National Semiconductor, LP3906SQ-FXPI/NOPB Datasheet - Page 36

• Manufacturer Part Number: LP3906SQ-FXPI/NOPB
• Description: IC REG DC-DC/LINEAR DUAL 24-LLP
• Manufacturer: National Semiconductor
• Series: PowerWise®r

Specifications of LP3906SQ-FXPI/NOPB

• Applications: Digital Cores
• Current - Supply: 60µA
• Voltage - Supply: 2.7 V ~ 5.5 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 24-WFQFN Exposed Pad
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

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High Vin-High Load Operation
Additional information is provided when the IC is operated at
extremes of Vin and regulator loads. These are described in
terms of the Junction temperature and, Buck output ripple
management.
Junction Temperature
The maximum junction temperature TJ-MAX-OP of 125ºC of
the IC package.
The following equations demonstrate junction temperature
determination, ambient temperature TA-MAX and Total chip
power must be controlled to keep TJ below this maximum:
TJ-MAX-OP = TA-MAX + (θJA) [ °C/ Watt] * (PD-MAX)
[Watts]
Total IC power dissipation PD-MAX is the sum of the individ-
ual power dissipation of the four regulators plus a minor
amount for chip overhead. Chip overhead is Bias, TSD & LDO
analog.
PD-MAX = P
[Watts].
Power dissipation of LDO1
P
Power dissipation of LDO2
P
LDO1
LDO2
= (Vin
= (Vin
LDO1
LDO2
LDO1
- Vout
- Vout
+ P
LD02
LDO1
LDO2
+ P
) * Iout
) * Iout
BUCK1
LDO1
+ P
LDO2
BUCK2
[V*A]
[V*A]
+ (0.0001A * Vin)
V
IN
LP3906 Buck Converter
vs I
LOAD
Operating Ranges
36
Power dissipation of Buck1
P
Vout
η
Power dissipation of Buck2
P
Vout
η
η is the efficiency for the specific condition taken from effi-
ciency graphs.
Buck Output Ripple Management
If Vin and ILoad increase, the output ripple associated with
the Buck Regulators also increases. The figure below shows
the safe operating area. To ensure operation in the area of
concern it is recommended that the system designer circum-
vents the output ripple issues to install schottky diodes on the
Bucks(s) that are expected to perform under these extreme
corner conditions.
(Schottky diodes are recommended to reduce the output rip-
ple if the system requirements include this shaded area of
operation. Vin > 5.2 V and Iload > 1.24 A)
1
2
Buck1
Buck2
= efficiency of buck 1
= efficiency of buck 2
Buck1
Buck2
= P
= P
* Iout
* Iout
IN
IN
– P
– P
Buck1
Buck2
OUT
OUT
20197864
* (1 -η
=
=
* (1 - η
1
) / η
2
) / η
1
2
[V*A]
[V*A]