PTB48600A Datasheet, PDF (5/10 Pages) Texas Instruments – 85 W Dual Complementary-Output DC/DC Converter for DSL

Application Notes
Not Recommended for New Designs
PTB48600
Adjusting the Output Voltages of the
PTB48600 Series of DC/DC Converters
The PTB48600 DC/DC converter produces a balanced
pair of complementary output voltages. They are identi-
fied +V_O and -V_O, respectively. The magnitude of both
output voltages can be adjusted together as a pair, higher
or lower. The adjustment method uses a single external
resistor. ¹ The value of the resistor determines the adjust-
ment magnitude, and its placement determines whether
the magnitude is increased or decreased. The resistor
values can be calculated using the appropriate formula
(see below). The formula constants are given in Table 1-1.
The placement of each resistor is as follows.
Adjust Up: To increase the magnitude of both output
voltages, place a resistor R₁ between ±V_O Adj (pin 7) and
the -V_O (pin 8) voltage rail; see Figure 1-1(a).
Figure 1-1a
Calculation of Resistor Adjust Values
The value of the adjust resistor is calculated using one of
the following equations. Use the equation for R1 to adjust
up, or (R2) to adjust down.
R1 [Adjust Up]
=
V_R R_O
– R_S kΩ
2 (V_A – V_O )
(R2) [Adjust Down] = R_o (2 V_A – V_R ) – R_S kΩ
2 (V_O – V_A )
Where: V_O = Magitude of the original ±V_O
V_A = Magnitude of the adjusted voltage
V_R = The reference voltage from Table 1-1
R_O = The resistance value in Table 1-1
R_S = The series resistance from Table 1-1
PTB48600
5
+V_O
+VO
7
±VO Adj
6
COM
8
–VO
R1
Adjust Up
–V_O
Table 1-1
ADJUSTMENT RANGE AND FORMULA PARAMETERS
Series Pt. No.
PTB48600A
V_O (nom)
V_A (min)
V_A (max)
V_R
R_O (kΩ)
R_S (kΩ)
5V
3.31 V
6V
2.495 V
7.5
9.09
Adjust Down: To decrease the magnitude of both output
voltages, add a resistor (R2), between ±V_O Adj (pin 7)
and the +V_O (pin 5) voltage rail; see Figure 1-1(b).
Figure 1-1b
PTB48600
5
+VO
+VO
(R2)
Adj Down
7
±VO Adj
6
COM
8
–VO
–VO
Notes:
1. A 0.05-W rated resistor may be used. The tolerance
should be 1%, with a temperature stability of 100 ppm/°C or
better. Place the resistor in either the R1 or (R2)
location, as close to the converter as possible.
2. Never connect capacitors to the ±V_O Adj pin. Capacitance
added to this pin can affect the stability of the regulated
output.
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