SC1566IM-1.8TR 데이터 시트보기 (PDF) - Semtech Corporation
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SC1566IM-1.8TR Datasheet PDF : 9 Pages
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SC1566
POWER MANAGEMENT
Typical Characteristics (Cont.)
Quiescent Current vs.
Junction Temperature
700
VIN = 3.3V
690
680
670
660
650
640
630
620
610
600
-50 -25
0
25
50
75
TJ (°C)
100 125 150
Off-State Quiescent Current vs.
Junction Temperature
12
VIN = 5.5V
10
8
6
4
2
0
-50
-25
0
25
50
75
100 125 150
TJ (°C)
Applications Information
Introduction
The SC1566 is intended for applications such as
graphics cards where high current capability and very low
dropout voltage are required. It provides a very simple,
low cost solution that uses very little pcb real estate and
typically does not require a heatsink. Additional features
include an enable pin to allow for a very low power
consumption standby mode, and a fully adjustable
output (5-pin versions).
External voltage selection resistors (5-pin parts): the
use of 1% resistors, and designing for a current flow
³ 10µA is recommended to ensure a well regulated
output (thus R2 £ 120kW).
Thermal Considerations
The power dissipation in the SC1566 is approximately
equal to the product of the output current and the input
to output voltage differential:
Component Selection
PD ≈ (VIN − VOUT ) • IO
Input capacitor: a 4.7µF or 10µF ceramic capacitor is
recommended. This allows for the device being some
distance from any bulk capacitance on the rail.
Additionally, input droop due to load transients is reduced,
improving load transient response. Additional capacitance
may be added if required by the application.
Output capacitor: a minimum bulk capacitance of 22µF,
along with a 0.1µF ceramic decoupling capacitor is
recommended. Increasing the bulk capacitance will
improve the overall transient response. The use of
multiple lower value ceramic capacitors in parallel to
achieve the desired bulk capacitance will not cause
stability issues. Although designed for use with ceramic
output capacitors, the SC1566 is extremely tolerant of
output capacitor ESR values and thus will also work
comfortably with tantalum output capacitors.
The absolute worst-case dissipation is given by:
( ) PD(MAX ) = VIN (MAX ) − VOUT (MIN ) • IO (MAX ) + VIN (MAX ) • IQ (MAX )
For a typical scenario, VIN = 3.3V ± 5%, VOUT = 2.8V and
IO = 2.5A, therefore:
VIN(MAX) = 3.465V, VOUT(MIN) = 2.744V and IQ(MAX) = 1.75mA,
Thus PD(MAX) = 1.81W.
Using this figure, and assuming TA(MAX) = 85°C, we can
calculate the maximum thermal impedance allowable to
maintain TJ £ 150°C (see page 7):
ã 2001 Semtech Corp.
6
www.semtech.com
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