Application Notes
PT6670 Series
Figure 1
Adjusting the Output Voltage of the PT6670
Series Boost Voltage ISR
1
The Power Trends PT6670 ISRs are a series of convert-
ers that operate from a 3.3V or 5V input bus voltage. In
each case, the output voltage can be adjusted higher or
lower than the factory trimmed pre-set voltage. Adjust-
ment requires the addition of a single external resistor.
Table 1 gives the permissible adjustment range for each
model in the series as Va(min) and Va(max) respectively.
Vsense
4,5,6
11,12,13
Vin
Vo
Vin
PT6670
Vo
GND
Vo(adj)
14
7,8,9,10
(R1)
Adj Down
L
O
A
D
+
+
Cin
Cout
R 2
Adjust Up:
To increase the output, add a resistor
Adjust
U p
R2 between pin 14 (Vo Adjust) and pins 7-10 (GND).
Adjust Down: Add a resistor (R1), between pin 14
C O M
C O M
(Vo Adjust) and pin 1 (Remote Sense).
Table 1
Refer to Figure 1 and Table 2 for both the placement and value
of the required resistor.
PT6670 ADJUSTMENT RANGE AND FORMULA PARAMETERS
Series Pt #
3.3V Bus
5.0V Bus
PT6671
PT6672
PT6675
PT6673
PT6674
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. Do not exceed the maximum advised adjustment voltage.
Doing so could over stress the part.
3. Never connect capacitors to the Vo Adjust control pin. Any
capacitance added to this pin will affect the stability of the
ISR.
V (nom)
o
5.0V
3.8V
5.5V
25.0
9.0V
8.2V
9.2V
48.75
80.6
12.0V
9.6V
Va(min)
Va(max)
12.8V
47.41
54.9
K
(V·kΩ)
(kΩ)
o
R
s
4.99
Table 2
4. In the case of the PT6671, when the output is adjusted
lower than the pre-trimmed output, the maximum input
voltage to the ISR should not exceed (V0 – 0.5)V.
PT6670 ADJUSTMENT RESISTOR VALUES
Series Pt #
3.3V Bus
5.0V Bus
PT6671
PT6672
PT6675
PT6673
PT6674
The adjust up and adjust down resistor values can also be
calculated using the following formulas. Be sure to select
the correct formula parameters from Table 1 for the model
being adjusted.
V (nom)
o
5.0V
9.0V
12.0V
Va(req’d)
3.8
Va(req’d)
8.2
(5.8)kΩ
(7.7)kΩ
(58.3)kΩ
(111.0)kΩ
(217.0)kΩ
(534.0)kΩ
3.9
8.4
4.0
(10.0kΩ
8.6
Ko (Va – 2.5)
2.5 (Vo – Va)
4.1
(12.8)kΩ
(16.3)kΩ
(20.7)kΩ
(26.7)kΩ
(35.0)kΩ
(47.5)kΩ
(68.3)kΩ
(110.0)kΩ
(235.0)kΩ
8.8
(R1)
=
– Rs kΩ
4.2
9.0
4.3
9.2
163.0kΩ
4.4
9.4
Ko
Va – Vo
4.5
9.6
(1.2)kΩ
(8.0)kΩ
R2
=
– Rs kΩ
4.6
9.8
4.7
10.0
10.2
10.4
10.6
10.8
11.0
11.2
11.4
11.6
11.8
12.0
12.2
12.4
12.6
12.8
(16.2)kΩ
(26.2)kΩ
(38.7)kΩ
(54.8)kΩ
(76.3)kΩ
(106.0)kΩ
(151.0)kΩ
(226.0)kΩ
(376.0)kΩ
(827.0)kΩ
4.8
4.9
Where:
Vo = Original output voltage
Va = Adjusted output voltage
5.0
5.1
245.0kΩ
120.0kΩ
78.3kΩ
57.5kΩ
45.0kΩ
Ko = The multiplier constant in Table 1
Rs = The series resistance from Table 1
5.2
5.3
5.4
5.5
182.0kΩ
63.3kΩ
24.1kΩ
4.4kΩ
R1 = (Blue)
R2 = Black
For technical support and more information, see inside back cover or visit www.ti.com/powertrends