Texas Instruments Evaluation Module for TPS24711 Positive Voltage, Power-Limiting Hotswap Controller TPS24711EVM-004 TPS24711EVM-004 데이터 시트
제품 코드
TPS24711EVM-004
LIM
SENSE
SNS PL _ MIN
IN _ MAX
P
R
29.3 W
2 m
V
4.19 mV (> 3 mV)
V
14 V
-
´
´
W
=
=
=
PROG
LIM
SENSE
PROG
3125
R
=
P
+ R
therefore,
3125
R
=
= 53.15 kΩ
29.3 W
0.002 Ω
´
(
)
(
)
(
)
(
)
2
J(MAX)2
MAX
DS(on)
CA
A(MAX)
LIM
JC
2
LIM
T
I
r
R
T
P
0.8
,
R
therefore,
130 C
12 A
0.002
51 C / W
1.8 C / W
50 C
P
0.8
29.3 W
1.8 C / W
q
q
é
ù
-
´
´
+
ë
û
£
´
é
ù
° -
´
W ´
°
-
°
+
°
ê
ú
ë
û
£
´
=
°
(
)
J(MAX)
A(MAX)
DS(on)(MAX)
2
MAX
JA
DS(on)(MAX)
2
T
T
r
,
I
R
therefore,
150 C 50 C
r
13.6 m
12 A
51 C / W
q
-
=
´
° -
°
=
=
W
´
°
SLVSAL2E – JANUARY 2011 – REVISED NOVEMBER 2013
Next select the on resistance of the transistor, r
DS(on)
. The maximum on-resistance must not generate a voltage
greater then the minimum power-good threshold voltage of 140 mV. Assuming a current limit of 12 A, a
maximum r
maximum r
DS(on)
of 11.67 m
Ω is required. Also consider the effect of r
DS(on)
upon the maximum operating
temperature T
J(MAX)
of the MOSFET.
computes the value of r
DS(on)(MAX)
at a junction temperature of
T
J(MAX)
. Most manufacturers list r
DS(on)(MAX)
at 25°C and provide a derating curve from which values at other
temperatures can be derived. Compute the maximum allowable on-resistance, r
DS(on)(MAX)
, using
(6)
Taking these factors into consideration, the TI CSD16403Q5 was selected for this example. This transistor has a
V
V
GS(MAX)
rating of 16 V, a V
DS(MAX)
rating of 25 V, and a maximum r
DS(on)
of 2.8 m
Ω at room temperature. During
normal circuit operation, the MOSFET can have up to 10 A flowing through it. The power dissipation of the
MOSFET equates to 0.24 W and a 9.6°C rise in junction temperature. This is well within the data sheet limits for
the MOSFET. The power dissipated during a fault (e.g., output short) is far larger than the steady-state power.
The power handling capability of the MOSFET must be checked during fault conditions.
MOSFET equates to 0.24 W and a 9.6°C rise in junction temperature. This is well within the data sheet limits for
the MOSFET. The power dissipated during a fault (e.g., output short) is far larger than the steady-state power.
The power handling capability of the MOSFET must be checked during fault conditions.
STEP 3. Choose Power-Limit Value, P
LIM
, and R
PROG
MOSFET M
1
dissipates large amounts of power during inrush. The power limit P
LIM
of the TPS24710/11/12/13
should be set to prevent the die temperature from exceeding a short-term maximum temperature, T
J(MAX)2
. The
short-term T
J(MAX)2
could be set as high as 130°C while still leaving ample margin to the usual manufacturer’s
rating of 150°C.
is an expression for calculating P
LIM
,
(7)
where R
θJC
is the junction-to-case thermal resistance of the MOSFET, r
DS(on)
is the resistance at the maximum
operating temperature, and the factor of 0.8 represents the tolerance of the constant-power engine. For an
ambient temperature of 50°C, the calculated maximum P
ambient temperature of 50°C, the calculated maximum P
LIM
is 29.3 W. From
, a 53.6-k
Ω, 1% resistor
is selected for R
PROG
(see
(8)
V
SNS-PL_MIN
is the minimum sense voltage during power limit operation. Due to offsets of internal amplifiers,
programmed power limit (P
LIM
) accuracy degrades at low V
SNS-PL_MIN
and could cause start-up issues. To ensure
reliable operation, verify that V
SNS,PL,MIN
> 3 mV using
(9)
Copyright © 2011–2013, Texas Instruments Incorporated
23
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