参数资料
型号: LP3906SQXPPXP
厂商: NATIONAL SEMICONDUCTOR CORP
元件分类: 稳压器
英文描述: 2 A DUAL SWITCHING CONTROLLER, 2000 kHz SWITCHING FREQ-MAX, QCC24
封装: 5 X 4 MM, 0.80 MM HEIGHT, LLP-24
文件页数: 30/40页
文件大小: 4197K
代理商: LP3906SQXPPXP
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 125C 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
LDO1 + PLD02 + PBUCK1 + PBUCK2 + (0.0001A * Vin)
[Watts].
Power dissipation of LDO1
P
LDO1 = (VinLDO1- VoutLDO1) * IoutLDO1 [V*A]
Power dissipation of LDO2
P
LDO2 = (VinLDO2 - VoutLDO2) * IoutLDO2 [V*A]
Power dissipation of Buck1
P
Buck1 = PIN – POUT =
Vout
Buck1* IoutBuck1 * (1 -η
1) / η1 [V*A]
η1 = efficiency of buck 1
Power dissipation of Buck2
P
Buck2 = PIN – POUT =
Vout
Buck2 * IoutBuck2 * (1 - η
2) / η2 [V*A]
η2 = efficiency of buck 2
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)
LP3906 Buck Converter
V
IN vs ILOAD Operating Ranges
20197864
www.national.com
36
LP3906
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