TPS7A39
ZHCSGP0A –JULY 2017–REVISED SEPTEMBER 2017
www.ti.com.cn
8.1.12.1 Estimating Junction Temperature
The JEDEC standard recommends the use of psi (Ψ) thermal metrics to estimate the junction temperatures of
the LDO when in-circuit on a typical PCB board application. These metrics are not strictly speaking thermal
resistances, but rather offer practical and relative means of estimating junction temperatures. These psi metrics
are determined to be significantly independent of the copper-spreading area. The key thermal metrics (ΨJT and
ΨJB) are given in the Electrical Characteristics table and are used in accordance with 公式 11.
YJT: TJ = TT + YJT ´ PD
YJB: TJ = TB + YJB ´ PD
where:
•
•
•
PD is the power dissipated as explained in 公式 9
TT is the temperature at the center-top of the device package
TB is the PCB surface temperature measured 1 mm from the device package and centered on the package
edge
(11)
8.2 Typical Applications
8.2.1 Design 1: Single-Ended to Differential Isolated Supply
TP1
OUTP
FBP
GND
EN
D2
INP
Diode1
Diode3
Diode2
Diode4
10 nF
COUTP
+5V
VINP
SN6505B
VCC
10 …F 0.1 …F
NR/SS
CLK
D1
TPS7A39
3mm x 3mm
10 nF
BUF
FBN
TP2
10 …F 0.1 …F
10 …F 0.1 …F
To
Signal
EN
10 nF
OUTN
INN
COUTN
GND
图 71. Single-Ended to Differential Isolated Supply Schematic
8.2.1.1 Design Requirements
表 9. Design Requirements
PARAMETER
Input supply
DESIGN REQUIREMENT
DESIGN RESULT
Must operate off of 5-V input
5-V input supply
Output supply
Positive output
Must have a 5-V and –5-V output
±5-V output, ±2% accuracy
Capable of sourcing 50 mA on positive output
Capable of sinking 50 mA on negative output
Must be isolated from input supply
50 mA (sourcing)
current
Negative output
current
50 mA (sinking)
Isolation from 5-V
supply
Isolated through center tapped transformer
85% efficiency when IOUTN = –50 mA and IOUTP
50 mA
=
Efficiency
Must have > 80% efficiency at 100 mA(1)
(1) |IOUTN| = IOUTP = 50 mA.
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