PTB48580AAH_14 Datasheet, PDF (7/14 Pages) Texas Instruments – Dual Complementary Outputs

Application Notes
Not Recommended for New Designs
PTB48580 Series
Adjusting the Output Voltages of the
PTB48580 Series of DC/DC Converters
The PTB48580 series of DC/DC converters produce a
balanced pair of complementary output voltages. They
are identified +V_O and -V_O , respectively. The magnitude
of both output voltages can be adjusted together as a
pair, higher or lower, by up to ±10% of their nominal. The
adjustment method uses a single external resistor. ¹ The
value of the resistor determines the magnitude of the
adjustment, 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 ⁽³⁾ 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
PTB48580
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.
PTB48580A
PTB48580B
V_O (nom)
V_A (min)
V_A (max) ⁽³⁾
V_R
R_O (kΩ)
R_S (kΩ)
5V
3.5 V
6V
2.495 V
7.5
9.09
12 V
6.5 V
13.4 V
2.495 V
18.2
16.9
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
PTB48580
5
+VO
+VO
(R2)
Adj Down
7
±VO Adj
6
COM
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.
3. When the output voltage is adjusted higher than the
nominal output voltage the load current must not exceed
the module’s maximum power rating of 30 W. For example,
when the PTB48580A is adjusted to ±6 V (12 V in the
single output configuration), the load current is limited to
2.5 A.
8
–VO
–VO
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