Datasheet

TPS60300, TPS60301, TPS60302, TPS60303
SINGLE-CELL TO 3.0-V/3.3-V, 20-mA DUAL OUTPUT,
HIGH-EFFICIENCY CHARGE PUMP
SLVS302A – DECEMBER 2000 – REVISED MARCH 2001
17
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
design procedure (continued)
OUT1
5
+
C
(OUT1)
1 µF
OUT2
6
C
(OUT2)
1 µF
10
PG
V
IN
3
C
IN
1 µF
1
EN
GND
9
TPS60302
7
8
C
2F
1 µF
C2+
C2–
C1+
C1–
C
1F
1 µF
4
2
C
PG
0.1 µF
ON
R1
1 MΩ
1.5 V
MSP430
Display
Amplifier Sensor
+
+
Figure 23. Application With MSP430; PG as Supply for Analog Circuits
power dissipation
As given in the data sheet, the thermal resistance of the unsoldered package is R
θJA
= 294°C/W. Soldered on
the EVM, a typical thermal resistance of R
θJA(EVM)
= 200°C/W was measured.
The thermal resistance can be calculated as follows:
R
θJA
+
T
J
–T
A
P
D
Where:
T
J
is the junction temperature.
T
A
is the ambient temperature.
P
D
is the power that needs to be dissipated by the device.
The maximum power dissipation can be calculated with the following formula:
P
D
= V
IN
× I
IN
– V
O
× I
O
= V
IN(max)
× (3 × I
O
+ I
(SUPPLY)
) – V
O
× I
O
The maximum power dissipation happens with maximum input voltage and maximum output current:
At maximum load the supply current is approximately 2 mA.
P
D
= 1.8 V × (3 × 20 mA + 2 mA) – 3.3 V × 20 mA = 46 mW.
With this maximum rating and the thermal resistance of the device on the EVM, the maximum temperature rise
above ambient temperature can be calculated:
∆T
J
= R
θJA
× P
D
= 200°C/W × 46 mW = 10°C
This means that internal dissipation increases T
J
by 10°C.
The junction temperature of the device must not exceed 125°C.
This means the IC can easily be used at ambient temperatures up to:
T
A
= T
J(max)
– ∆T
J
= 125°C – 10°C = 115°C
layout and board space
All capacitors should be soldered as close as possible to the IC. A PCB layout proposal for a two-layer board
is shown in Figure 24. Care has been taken to connect all capacitors as close as possible to the circuit to achieve
optimized output voltage ripple performance. The bottom layer is not shown in Figure 24. It only consists of a
ground-plane with a single track between the two vias that can be seen in the left part of the top layer.