L5983TR STMicroelectronics, L5983TR Datasheet - Page 27

• Manufacturer Part Number: L5983TR
• Description: IC REG SW 1.5A STEPDOWN 8-VFQFPN
• Manufacturer: STMicroelectronics
• Type: Step-Down (Buck)r

Specifications of L5983TR

• Internal Switch(s): Yes
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Voltage - Output: 0.6 ~ 18 V
• Current - Output: 1.5A
• Frequency - Switching: 250kHz ~ 1MHz
• Voltage - Input: 2.9 ~ 18 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 8-VFQFN, 8-VFQFPN
• Power - Output: 1.5W
• For Use With: 497-6386 - BOARD EVAL FOR L5983
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: 497-6860-2; L5983TR

L5983
5.5
Thermal considerations
The thermal design is important to prevent the thermal shutdown of the device if junction
temperature goes above 150 °C. The three different sources of losses within the device are:
Equation 26
where D is the duty cycle of the application and the maximum R
Note that the duty cycle is theoretically given by the ratio between V
it is quite higher to compensate the losses of the regulator. So the conduction losses
increase compared with the ideal case.
Equation 27
where T
and the current flowing into it during turn on and turn off phases, as shown in
is the equivalent switching time.
For this device the typical value for the equivalent switching time is 50 ns.
Equation 28
where I
The junction temperature T
Equation 29
where T
Rth
calculated as the parallel of many paths of heat conduction from the junction to the ambient.
JA
a)
b)
c)
is the equivalent thermal resistance junction to ambient of the device; it can be
Q
A
RISE
is the quiescent current. (I
conduction losses due to the not negligible R
equal to:
switching losses due to power MOSFET turn on and off; these can be calculated
as:
Quiescent current losses, calculated as:
is the ambient temperature and P
and T
P
SW
FALL
=
V
are the overlap times of the voltage across the power switch (V
IN
⋅
I
J
OUT
can be calculated as:
Doc ID 13005 Rev 7
⋅
P
(
------------------------------------------ - Fsw
T
ON
T
RISE
Q
J
= 2.4 mA).
=
=
P
+
2
R
T
Q
T
DS on
A
FALL
+
=
TOT
(
Rth
V
)
IN
)
is the sum of the power losses just seen.
⋅
⋅
JA
(
⋅
I
I
OUT
Q
⋅
P
TOT
)
=
DS(on)
2
⋅
V
D
IN
⋅
of the power switch; these are
I
OUT
DS(on)
⋅
Application information
OUT
T
SW
is 220 mΩ.
and V
⋅
F
SW
Figure
IN
, but actually
16. T
DS
27/43
SW
)