LTC1626 데이터 시트보기 (PDF) - Linear Technology
부품명
상세내역
제조사
LTC1626 Datasheet PDF : 12 Pages
| |||
LTC1626
APPLICATIONS INFORMATION
Thermal Considerations
In a majority of applications, the LTC1626 does not
dissipate much heat due to its high efficiency. However, in
applications where the switching regulator is running at
high duty cycles or the part is in dropout with the switch
turned on continuously (DC), some thermal analysis is
required. The goal of the thermal analysis is to determine
whether the power dissipated by the regulator exceeds the
maximum junction temperature. The temperature rise is
given by:
TRISE = PD • θJA
where PD is the power dissipated by the regulator and θJA
is the thermal resistance from the junction of the die to the
ambient temperature.
The junction temperature is given by:
TJ = TRISE + TAMBIENT
As an example, consider the case when the LTC1626 is in
dropout at an input voltage of 3V with a load current of
0.5A. From the Typical Performance Characteristics graph
of Switch Resistance, the ON resistance of the P-channel
switch is 0.45Ω. Therefore, power dissipated by the
part is:
PD = I2 • RDS(ON) = 113mW
The SO package junction-to-ambient thermal resistance
θJA is 110°C/W. Therefore, the junction temperature of the
regulator when it is operating in a 25°C ambient tempera-
ture is:
TJ = (0.113 • 110) + 25 = 38°C
Remembering that the above junction temperature is
obtained from an RDS(ON) at 25°C, we might recalculate
the junction temperature based on a higher RDS(ON) since
it increases with temperature. However, we can safely
assume that the actual junction temperature will not
exceed the absolute maximum junction temperature
of 125°C.
Board Layout Considerations
When laying out the printed circuit board, the following
checklist should be used to ensure proper operation of the
LTC1626. These items are also illustrated graphically in
the layout diagram of Figure 6. Check the following in your
layout:
1. Are the signal and power grounds separated? The
LTC1626 signal ground (Pin 11) must return to the
(–) plate of COUT. The power ground (Pin 12) returns
to the anode of the Schottky diode and the (–) plate
of CIN.
2. Does the (+) plate of CIN connect to the power VIN (Pins
1, 13) as close as possible? This capacitor provides the
AC current to the internal P-channel MOSFET and its
driver.
1k CT
3900pF
VIN
BOLD LINES INDICATE
1 PWR VIN
14
SW
HIGH CURRENT PATHS
2
PWR VIN 13
VIN
LTC1626
+
D1
0.1µF
CIN
3
12
L
LBO
PGND
4
LBI
SGND 11
5
CT
6
ITH
7 SENSE–
10
SHDN
9
VFB
SENSE+ 8
SHUTDOWN
R1
+
R2
COUT
RSENSE
1000pF
VOUT
1626 F06
Figure 6. LTC1626 Layout Diagram (See Board Layout Checklist)
9
Share Link: 