PT6940 Datasheet, PDF (7/9 Pages) Texas Instruments – 6-A Dual Output 5-V/3.3-V Input Integrated Switching Regulator

Application Notes
PT6940 Series
Adjusting the Output Voltages of the
PT6940 Dual-Output ISRs
Each output voltage from the PT6940 series of integrated
switching regulators (ISRs) can be independently adjusted
higher or lower than the factory trimmed pre-set voltage.
The voltages, Vo₁ and Vo₂ may each be adjusted either up
or down using a single external resistor ¹. Table 1 gives the
adjustment range for both Vo₁ and Vo₂ for each model in
the series as V_a(min) and V_a(max). Note that Vo₂ must
always be lower than Vo₁ ².
Vo₁ Adjust Up: To increase the output, add a resistor R₂
between pin 2 (Vo₁ Adjust) and pins 7-12 (GND) ³.
Vo₁ Adjust Down: Add a resistor (R₁), between pin 2
(Vo₁ Adjust) and pin 3 (Vo₁ Sense).
Vo₂ Adjust Up: Add a resistor R₄ between pin 27
(Vo₂ Adjust) and pins 17–22 (GND).
Vo₂ Adjust Down: Add a resistor (R₃) between pin 27
(Vo₂ Adjust) and pin 26 (Vo₂ Sense).
Refer to Figure 1 and Table 2 for both the placement and value of
the required resistor.
The adjust up and adjust down resistor values can also be
calculated using the following formulas. Be sure to select
the correct formula parameter from Table 1 for the output
and model being adjusted.
(R₁) or (R₃) =
10 (V_a – 0.9 )
V_o – V_a
– R_s
kΩ
R₂ or R₄
=
9
V_a – V_o
– R_s
kΩ
Where: V_o = Original output voltage, (Vo₁ or Vo₂)
V_a = Adjusted output voltage
R_s = The series resistance from Table 1
Notes:
1. Use only a single 1% resistor in either the (R₁) or R₂
location to adjust Vo₁, and in the (R₃) or R₄ location to
adjust Vo₂. Place the resistor as close to the module as
possible.
2. Vo₂ must always be at least 0.3V lower than Vo₁.
3. When adjusting Vo₁ higher than the factory pre-set
output voltage the minimum input voltage must be
revised as follows.
Vo₁ =3.3V:
V_in(min) = (Vo₁ + 1)V or 4.5V, whichever is greater.
Vo₁ =2.5V:
Vo₁ =2.5V is the maximum output voltage allowed for
operation off a 3.3V input bus. If Vo₁ is adjusted above
2.5V, the input voltage must be a minimum of 4.5V.
4. Vo₁ and Vo₂ may be adjusted down to an alternative bus
voltage by making, (R₁) or (R₃) respectively, a zero ohm
link. Refer to the Table 1 footnotes for guidance.
5. Never connect capacitors to either the Vo₁ Adjust or
Vo₂ Adjust pins. Any capacitance added to these control
pins will affect the stability of the respective regulated
output.
Figure 1
3
26
V₁ Sns
V₂ Sns
4–6
V_IN
13–16
Vo₁
Vin
PT6940
23–25
Vo₂
7–12
V₂ Adj V₁ Adj
17–22
27 2
(R1)
(R3)
Vo₁ Sense
Vo₂ Sense
Vo ₁
Vo ₂
+
C_IN
GND
+
+
Co ₁
Co ₂
L
L
O
O
A
A
D
D
R2
R4
GND
For technical support and more information, see inside back cover or visit www.ti.com