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PT6937A Datasheet, PDF (9/14 Pages) Texas Instruments – Internal Sequencing Short Circuit Protection 23-pin Space-Saving Package
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Application Notes
Not Recommended For New Designs
PT6935 Series
Adjusting the Output Voltage of the PT6935
Dual Output Voltage ISRs
Each output voltage from the PT6935 series of ISRs can be
independantly 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 Va(min) and Va(max).
Note that Vo2 must always be lower than Vo1 2.
Vo1 Adjust Up: To increase the output, add a resistor R4
between pin 16 (V1 Adjust) and pins 7-11 (GND) 1.
Vo1 Adjust Down: Add a resistor (R3), between pin 16
(Vo1 Adjust) and pin 1 (Vo1 Sense) 1.
Vo2 Adjust Up: Add a resistor R2 between pin 23
(Vo2 Adjust) and pins 7-11 (GND) 1.
Vo2 Adjust Down: Add a resistor (R1) between pin 23
(Vo2 Adjust) and pin 22 (Vo2 Sense) 1.
Refer to Figure 1 and Table 2 for both the placement and value of
the required resistor.
Notes:
1. Use only a single 1% resistor in either the (R3) or R4
location to adjust Vo1, and in the (R1) or R2 location to
adjust Vo2. Place the resistor as close to the ISR as
possible.
2. Vo2 must always be at least 0.2V lower than Vo1.
3. Both the Vo1 and Vo2 may be adjusted down to an
alternative bus voltage by making, (R3) or (R1)
respectively, a zero ohm link. Refer to the Table 1
footnotes for guidance.
4. Adjusting the Vo1 output voltage of either the PT6935
(2.5V/1.8V model) or PT6939 (2.5V/1.2V) higher than
the factory pre-trimmed output voltage, may increase
the minimum input voltage specified for the part. These
models must comply with the following requirements.
PT6935/PT6939:
Vin(min) =(Va + 0.6)V or 3.1V,
whichever is greater.
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.
6. Adjusting either voltage (Vo1 or Vo2) may increase the
power dissipation in the regulator, and change the
maximum current available at either output. Consult
the note on p.2 of the data sheet regarding Vo1/Vo2
loading.
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 (Va – Vr )
Vo – Va
– Rs
kΩ
(R2) or (R4)
=
10 · Vr
Va – Vo
– Rs
kΩ
Where: Vo
Va
Vr
Rs
= Original output voltage, (Vo1 or Vo2)
= Adjusted output voltage
= The reference voltage from Table 1
= The series resistance from Table 1
Figure 1
22
1
4,5,6
VIN
Vin
Vo2(sns) Vo1(sns)
Vo2
PT6935
Vo1
18 - 21
12 - 15
STBY GND
Vo2(adj) Vo1(adj)
3
7 - 11
23
16
(R3)
+
C1
Adj Down
(R1)
COM
R4 R2
Adjust Up
Adjust Vo 1
Vo2
Vo1
+
C2
+
C3
LL
OO
AA
DD
Adjust Vo 2
COM
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