
TK631xxB/H/S
GC3-J025D
Page 29
12-2. Layout
Fig12-5: Layout example (TK631xxB)
GND
V
Cont
V
In
V
Out
GND
(Top View)
1
PCB Material : Glass epoxy
Size : 7mm
×8mm×0.8mm
Fig12-6: Layout example (TK631xxH)
V
Cont
V
In
V
Out
GND
(Top View)
NC
GND
PCB Material : Glass epoxy
Size : 10mm
×7mm×0.8mm
Fig12-7: Layout example (TK631xxS)
V
Cont
V
In
V
Out
GND
(Top View)
NC
GND
PCB Material : Glass epoxy
Size : 12mm
×7mm×0.8mm
Please do derating with 2.9mW/
°C at Pd=360mW(FC-4),
or with 4mW/
°C at Pd=500mW(SON2017-6/SOT23-5),
and 25
°C or more. Thermal resistance (θ
ja) is=250°C/W.
Fig12-8: Derating Curve (TK631xxB)
25
50
100
150°C
Pd(mW)
360
(85°C)
-2.9mW/°C
Fig12-9: Derating Curve (TK631xxH/S)
25
50
100
150°C
Pd(mW)
500
(85°C)
-4mW/°C
The package loss is limited at the temperature that the
internal
temperature
sensor
works
(about
150
°C).
Therefore, the package loss is assumed to be an internal
limitation. There is no heat radiation characteristic of the
package unit assumed because of its small size. Heat is
carried away from the device by being mounted on the
PCB. This value is directly effected by the material and
the copper pattern etc. of the PCB. The losses are
approximately 360mW(FC-4), or 500mW(SON2017-
6/SOT23-5). Enduring these losses becomes possible in a
lot of applications operating at 25
°C.
The overheating protection circuit operates when the
junction temperature reaches 150
°C (this happens when
the regulator is dissipating excessive power, outside
temperature is high, or heat radiation is bad). The output
current and the output voltage will drop when the
protection circuit operates. However, operation begins
again as soon as the output voltage drops and the
temperature of the chip decreases.
How to determine the thermal resistance when
mounted on PCB
The thermal resistance when mounted is expressed as
follows:
T
j=θja×Pd+Ta
T
j of IC is set around 150°C. Pd is the value when the
thermal sensor is activated.
If the ambient temperature is 25
°C, then:
150=
θ
ja×Pd+25
θ
ja=125/Pd (°C /mW)