PT6340 Datasheet, PDF (7/11 Pages) Texas Instruments – 6-A 12-V Input Adjustable Integrated Switching Regulator

Application Notes
PT6340 Series
Adjusting the Output Voltage of the PT6340
Excalibur 6 A, 12 V Bus Step-Down ISRs
The output voltage of the PT6340 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 accordingly 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 pin 12 (V_o adj) and pins 5-8
(GND).
Adjust Down: Add a resistor (R₁), between pin 12 (V_o adj) and
pins 9-11 (V_o).
Figure 1
+ V _IN
COM
2,3,4 _{Vin PT6340 Vo} 9,10,11
+
C₁
GND Vo(adj)
5–8 12
(R1)
Adj Down
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 – V_r)
V_o – V_a
– R_s
kΩ
R₂
=
V_r · R_o
V_a – V_o
– R_s kΩ
Where:
V_o = Original output voltage
V_a = Adjusted output voltage
V_r = Reference voltage (Table 1)
R_o = Resistance constant (Table 1)
R_s = Internal series resistance (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.
Table 1
ISR ADJUSTMENT RANGE AND FORMULA PARAMETERS
Series Pt #
PT6341
PT6342
PT6343
Vo (nom)
Va (min)
Va (max)
Vr (V)
Ro (kΩ)
Rs (kΩ)
5.0
4.0
5.5
1.27
10.0
24.9
3.3
2.8
3.8
1.27
10.0
24.9
2.5
2.2
3.0
1.27
10.0
24.9
PT6244
1.8
1.7
2.3
1.27
10.0
24.9
PT6345
1.5
1.45
2.0
1.27
10.0
24.9
PT6346
1.2
1.1
1.45
0.8
10.0
24.9
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