PTB48510_14 Datasheet, PDF (10/18 Pages) Texas Instruments – DUAL COMPLEMENTARY-OUTPUT DC/DC CONVERTER FOR DSL

Not Recommended for New Designs
PTB48510
PTB48511
SLTS219F – FEBRUARY 2004 – REVISED MARCH 2007
APPLICATION INFORMATION
www.ti.com
ADJUSTING THE OUTPUT VOLTAGE OF THE PTB4851x SERIES OF DC/DC CONVERTERS
The PTB48510 and PTB48511 DC/DC converters produce a balanced pair of complimentary output voltages.
They are identified V_O1 and V_O2, 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 adjustment 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. 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 1}Adj (pin 7) and
the V_O2 (pin 8) voltage rail; see Figure 16.
Adjust Down: To decrease the magnitude of both output voltages, add a resistor (R₂), between V_OAdj (pin 7)
and the V_O1 (pin 5) voltage rail; see Figure 17.
PTB48510
V_O1 5
COM 6
V_OAdj 7
V_O2 8
V_O1
R₁
Adjust Up
V_O2
PTB48510
V_O1 5
V_O1
R₂
Adjust Down
V_OAdj 7
COM 6
V_O2 8
V_O2
UDG-07041
Figure 16. Adjust Up Resistor Placement
UDG-07042
Figure 17. Adjust Down Resistor Placement
ADJUST RESISTOR CALCULATION
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]
+
Vr Ro
2^ǒVa * Vo^Ǔ
*
Rs
kW
(1)
ǒ Ǔ _R2
[Adjust
Down]
+
Ro^ǒ2 Va * Vr^Ǔ
2 ^ǒVo * Va^Ǔ
*
Rs
kW
(2)
Where:
V_O = Magitude of the original V_O1 or V_O2
V_a = Magnitude of the adjusted voltage
V_r = The reference voltage from Table 1
R_O = The resistance value in Table 1
R_S = The series resistance from Table 1
10
Copyright © 2004–2007, Texas Instruments Incorporated