PT6705 Datasheet, PDF (3/6 Pages) Texas Instruments – 13 Amp 5V/3.3V Input Adjustable Integrated Switching Regulator

Application Notes
PT6705/6715 Series
Adjusting the Output Voltage of the PT6705 and
PT6715 Excalibur™ Converters
Both the PT6705 and PT6715 series ISRs are non-pro-
grammable versions of the PT6700 Excalibur™ family of
converters. These regulators have a fixed output voltage,
which may be adjusted higher or lower than the factory
trimmed pre-set voltage using a single external resistor. Table
1 gives the allowable adjustment range for each model 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 1 (V_o adjust) and pin 7
(–Remote Sense).
Adjust Down: Add a resistor (R1), between pin 1 (V_o adjust)
and pin 17 (+Remote Sense).
Refer to Figure 1 and Table 2 for both the placement and value
of the required resistor, either (R1) or R2 as appropriate.
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 adjust to either
GND, V_out, or the Remote Sense pins. Any
capacitance added to the V_o adjust pin will affect the
stability of the ISR.
3. If the Remote Sense feature is not being used, pin 7
must be connected to pin 8 for optimum output voltage
accuracy. Correspondingly the resistors (R1) and R2
may be then be connected from V_o Adjust to either
V_out or GND respectively.
4. The PT6705 series requires a 12V external bias voltage
in order to operate (see data sheet). An external bias
voltage is not required for the PT6715 series.
5. Adjusting the output voltage of the PT6705 and
PT6715 (3.3V models) higher than the factory pre-
trimmed output voltage may require an increase in the
minimum input voltage. These two models must
comply with the following requirements for V_in(min).
PT670x models:
V_in(min)
= (V_a + 1)V
PT671x models:
V_in(min) = (V_a + 1)V or 4.5V, whichever is greater.
Figure 1
Bias
(Req’d for PT6705)
2
Stby*
3
V _Bias
17
Sns(+)
+5V
4,5,6
V _in
PT6705/PT6715
13 16
V _out
+
C _in
GND
8 12
Vo(adj)
1
Sns(-)
7
(R1)
Adj Down
R2
Adjust
Up
+
C _out
Vo
L
O
A
D
COM
COM
The values of (R1) [adjust down], and R2 [adjust up], can
also be calculated using the following formulas.
(R1)
=
10⋅(V_a – 1.27)
(V_o – V_a)
– R_s
kΩ
R2
=
12.7
V_a - V_o
– R_s
kΩ
Where: V_o = Original output voltage
V_a = Adjusted output voltage
R_s = Series resistance value from Table 1
Table 1
PT6705/PT6715 SERIES ADJUSTMENT PARAMETERS
Series Pt #
12V Bias (4) PT6708
PT6707
PT6706
No-Bias
PT6718
PT6717
PT6716
Vo (nom)
Va (min)
Va (max)
Rs (kΩ)
1.5
1.47
1.73
49.9
1.8
1.75
2.0
49.9
2.5
2.25
2.85
33.2
PT6705
PT6715
3.3
2.75
3.75
24.9
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