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參數(shù)資料
| 型號(hào)： | 935269469115 |
| 廠商： | NXP SEMICONDUCTORS |
| 元件分類： | 固定正電壓?jiǎn)温份敵鯨DO穩(wěn)壓器 |
| 英文描述： | 4.8 V FIXED POSITIVE LDO REGULATOR, 0.2 V DROPOUT, PDSO5 |
| 封裝： | PLASTIC, MO-178, SOT-23, SOT-25, SO-5 |
| 文件頁數(shù)： | 2/17頁 |
| 文件大小： | 212K |
| 代理商： | 935269469115 |
Philips Semiconductors
Product data
SA57001-XX
Microminiature, low power consumption,
low dropout regulator
2003 Mar 20
10
APPLICATION INFORMATION
Power dissipation factors
The thermal performance of linear regulators depends on the
following parameters:
Maximum junction temperature (Tj) in °C
Maximum ambient temperature (Tamb) in °C
Power dissipation capability of the package in Watts (PD)
Junction-to-ambient thermal resistance in
°C/W
The Maximum Junction Temperature and Maximum Power
Dissipation are both determined by the manufacturer’s process and
device’s design. For the most part the ambient temperature is under
the control of the user. The Maximum Ambient Temperature
depends on the process used by the manufacturer. The package
type and manufacturer’s process determines Junction-to-Ambient
Thermal Resistance.
These parameters are related to each other as shown in the
following equation:
Tj = Tamb + ( PD × Rth(j-a) )
The term ( PD × Rth(j-a) ) represents the temperature rise from the
ambient to the internal junction of the device.
Power dissipation calculations
A regulator’s maximum power dissipation can be determined by
using the following equation:
PD(max) = VIN(max)IG + [VIN(max) – VOUT(min)] IOUT(max)
where:
VIN(max) is the maximum input voltage
IG is the maximum Ground Current at maximum output current
VOUT(min) is the minimum output voltage
IOUT(max) is the maximum output current
(VIN(max)IG) represents heat generated in the device due to internal
circuit biasing, leakage, etc. [VIN(max) – VOUT(min)] is the
input-to-output voltage drop across the device due to the IOUT(max)
current. When multiplied by IOUT(max), this represents heat
generated in the device due to the output load current. Heat
generated by the device represents lost energy (an inefficiency).
The SA57001 device should not be operated under conditions that
would cause a junction temperature of 150
°C to be generated
because the thermal shutdown protection circuit will shut down the
device at or near this temperature.
Heat dissipation factors
Heat generated within the device is removed to the surrounding
environment by radiation or conduction along several paths. In
general, radiated heat is dissipated directly into the surrounding
ambient from the chip package and leads. Conducted heat flows
through an intermediate material, such as the leads or thermal
grease, to circuit board traces and heat sinks in direct contact with
the device’s package or leads. The circuit board then radiates this
heat to the ambient. For this reason, adequate airflow over the
device and the circuit board is important.
The SOT23-5 package is too small to easily use external heat sinks
to increase the surface area and enhance the dissipation of
generated heat. Heat dissipation must depend primarily on radiated
heat into the surrounding environment and the heat flow through the
leads into the printed circuit board. Some improvement can be
realized by allowing additional exposed copper on the circuit board
near the device to serve as heat absorbers and dissipaters for the
device.
The overall thermal resistance from junction to the surrounding
ambient of the package (Rth(j-a)) is made up of three series elements
and can be thought of as the total resistance of a series electrical
circuit. These elements are:
Rth(j-c) = Thermal resistance from Junction-to-Case
Rth(c-s) = Thermal resistance from Case-to-heat Sink
Rth(s-a) = Thermal resistance from heat Sink-to-Ambient
Rth(j-a) is based primarily on the package type and the size of the
silicon chip used in the device. The composition of package
materials plays an important part. High heat conductivity materials
produce reduced Junction-to-Case resistances.
Rth(c-s) value is based on the package type, heat sink interface, and
contact area of the device to the heat sink. The use of thermal
grease or an insulator will increase the transfer of heat from the
case to the heat sink.
Rth(s-a), which is thermal resistance from heat sink to the ambient, is
based on heat sink emissivity and airflow over the heat sink to carry
the heat away. The heat sink to ambient heat flow is dependent on
the ability of the surrounding ambient media to absorb the heat.
The total Rth(j-a) thermal resistance is expressed as:
Rth(j-a) = Rth(j-c) + Rth(c-s) + Rth(s-a)
The maximum power that a given package can handle is given by:
P
D +
T
j(max) * Tamb
R
th(j
*a)
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