PTB48540AAH Datasheet, PDF (7/12 Pages) Texas Instruments – 10-W Power-Over-Ethernet Isolated Power Module Assembly

Application Notes
PTB48540 Series
Not Recommended for New Designs
Adjusting the Output Voltage of the PTB48540
Figure 2-1; Adjust Resistor Placement
Series of Power Over Ethernet Modules
PTB48540
The set-point output voltage of the PTB48540 series of
PoE modules may be adjusted (trimmed) by up to ±10 %.
This is accomplished with the addition of a single exter-
3 ^+VOUT
nal resistor. For the input voltage range specified in the
data sheet, Table 2-1 gives the allowable adjustment range
for each model as V_o (min) and V_o (max).
Adjust Up: An increase in the output voltage is obtained
by adding a resistor, R₂ between pin 2 (V_out Adj), and
pin 1 (–V_out).
Adjust Down: Add a resistor (R₁), between pin 2 (V_out Adj)
and pin 3 (+V_out).
2 ^{VOUT Adj}
1 ^–VOUT
(R₁)
Adjust Dn
L
O
A
D
R₂
Adjust Up
Refer to Figure 2-1 and Table 2-2 for both the placement and
value of the required resistor, (R₁) or R₂.
The values of (R₁) [adjust down], and R₂ [adjust up], can
also be calculated using the following formulas.
(R₁)
=
56.2 (V_a – 1.225)
V_o – V_a
– R_s
kΩ
R₂
=
68.845
V_a – V_o
– R_s
kΩ
Where,
V_o = Original output voltage
V_a = Adjusted output voltage
R_s = Internal resistance (Table 2-1)
Notes:
1. Use only a single 1 % resistor in either the (R₁) or R₂
location. Place the resistor as close to the module as
possible.
2. Never connect capacitors to V_o adjust. Any capacitance
added to the V_o adjust control pin will affect the stability
of the module.
3. The output power is limited to 10 W. If the output
voltage is increased, the maximum load current must
be derated according to the following equation.
I_o(max)
= ¹⁰
V_a
In any instance, the load current must not exceed the
converter’s rated current (See Table 2-1).
Table 2-1
DC/DC CONVERTER ADJUSTMENT PARAMETERS
Series Pt #
Rated Current ³
PTB48540B
3A
PTB48540A
2A
Vo(nom)
Vo(min)
Vo(max)
Rs (kΩ)
3.3 V
2.95 V
3.65 V
187
5V
4.5 V
5.5 V
110
PTB48540C
0.85 A
12 V
10.8 V
13.2 V
49.9
Table 2-2
DC/DC CONVERTER ADJUSTMENT RESISTOR VALUES
Series Pt #
PTB48540B PTB48540A PTB48540C
Vo(nom)
Va(req’d)
2.95
3.0
3.05
3.1
3.15
3.2
3.25
3.3
3.35
3.4
3.45
3.5
3.55
3.6
3.65
•
4.5
4.6
4.7
4.8
4.9
5.0
5.1
5.2
5.3
5.4
5.5
•
10.8
11.0
11.5
12.0
12.5
13.0
13.2
3.3 V
(90.0)kΩ
(146.0)kΩ
(223.0)kΩ
(340.0)kΩ
(534.0)kΩ
(923.0)kΩ
(2090.0)kΩ
1190.0kΩ
501.0kΩ
272.0kΩ
157.0kΩ
88.4kΩ
42.5kΩ
9.7kΩ
5V
12 V
(258.0)kΩ
(364.0)kΩ
(541.0)kΩ
(895.0)kΩ
(1960.0)kΩ
578.0kΩ
234.0kΩ
119.0kΩ
62.1kΩ
27.7kΩ
(399.0)kΩ
(499.0)kΩ
(1110.0)kΩ
87.8kΩ
18.9kΩ
7.5kΩ
R₁ = (Blue)
R₂ = Black
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