PT6440 Datasheet, PDF (5/8 Pages) Texas Instruments – 6-A 5-V/3.3-V Input Adjustable Integrated Switching Regulator

Application Notes
PT6440 Series
Adjusting the Output Voltage of the PT6440
Excalibur 5V/3.3V Bus Step-Down ISRs
The output voltage of the PT6440 Series ISRs may be
adjusted higher or lower than the factory trimmed pre-
set voltage with the addition of a single external resistor.
Table 1 gives the allowable adjustment range for each
model for either series as V_a (min) and V_a (max).
Adjust Up: An increase in the output voltage is obtained by
adding a resistor R₂, between V_o Adj (pin 12) and GND
(pins 5–8).
Adjust Down: Add a resistor (R₁), between V_o Adj (pin 12)
and V_out (pins 9–11).
Figure 1
+V_IN
C₁
2,3,4 _{Vin PT6440 Vo} 9,10,11
GND Vo(adj)
5–8
12
(R₁)
+
Adj Down
COM
R₂
Adjust Up
+V_O
+
C₂
COM
The values of (R₁) [adjust down], and R₂ [adjust up], can
also be calculated using the following formulas. Refer to
Figure 1 and Table 2 for both the placement and value of the
required resistor; either (R₁) or R₂ as appropriate.
(R₁)
=
R_o (V_a – 0.9)
V_o – V_a
– R_s kΩ
R₂
=
0.9 R_o
V_a – V_o
– R_s kΩ
Where:
V_o = Original output voltage
V_a = Adjusted output voltage
R_o = The resistance value from Table 1
R_s = The series resistance from Table 1
Notes:
1. Use only a single 1% resistor in either the (R₁) or R₂
location. Place the resistor as close to the ISR as possible.
2. Never connect capacitors from V_o adj to either GND or
V_out. Any capacitance added to the V_o adjust pin will affect
the stability of the ISR.
3. For each model, adjustments to the output voltage may
place additional limits on the minimum input voltage.
The revised minimum input voltage must comply with the
following requirement.
V_in(min) = (V_a + 0.5)V or as specified in the data sheet,
whichever is greater.
Table 1
ISR ADJUSTMENT RANGE AND FORMULA PARAMETERS
Series Pt. #
PT6441
PT6442
PT6443
Vo (nom)
Va (min)
Va (max)
Ro (kΩ)
Rs (kΩ)
3.3
2.88
3.5
10.0
49.9
2.5
1.97
2.95
10.0
20.0
2.0
1.64
2.45
10.0
20.0
PT6444
1.8
1.5
2.25
10.0
20.0
PT6445
1.5
1.3
1.95
10.0
20.0
PT6446
1.2
1.08
1.65
10.0
20.0
PT6447
1.0
0.97
1.45
10.2
20.0
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