sc1486aitstr Semtech Corporation, sc1486aitstr Datasheet - Page 16

• Manufacturer Part Number: sc1486aitstr
• Description: Complete Ddr1/2/3 Power Supply Controller
• Manufacturer: Semtech Corporation

Design Procedure (Cont.)
For our DDR2 VDDQ example:
I
We select the next lowest 1% resistor value: 13.3k
Thermal Considerations
The junction temperature of the device may be calculated as follows:
Where:
T
P
The power dissipation may be calculated as follows:
Where:
VCCA = chip supply voltage (V)
I
V
Q
f = switching frequency (kHz)
Inserting the following values as an example:
T
VCCA = 5V
I
V
Q
f = 300kHz (enter the higher of the two set frequencies here)
gives us:
As can be seen, the heating effects due to internal power dissipation are minor, thus requiring no special consider-
ation thermally during layout.
R
P
POWER MANAGEMENT
Application Information (Cont.)
T
T
VALLEY
VCCA
VCCA
A
A
D
JA
g
JA
g
D
g
g
J
J
ILIM
2006 Semtech Corp.
= ambient temperature (°C)
= gate drive voltage, typically 5V (V)
= 85°C
= 5V
= power dissipation in (W)
= FET gate charge, from the FET datasheet (C)
= 60nC
= thermal impedance junction to ambient from absolute maximum ratings (°C/W)
= 37°C/W
= operating current (A)
= 1100µA (data sheet maximum)
T
85
2
= 8.97A and R
A
I
VALLEY
VCCA
2
P
D
5
1
JA
1100
2 .
I
VCCA
ILIM
C
R
10
DS
10
= 13.6k
(
V
ON
6
g
10
)
Q
1
5
6
4 .
g
60
Ohms
f
10
W
9
300
10
3
70
16
98
C
SC1486A
www.semtech.com