PT6920 Datasheet, PDF (3/5 Pages) Texas Instruments – 5V TO 3.3V/2.5V 25 WATT DUAL OUTPUT INTEGRATED SWITCHING REGULATOR

Application Notes
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PT6920 Series
More Application Notes
Adjusting the Output Voltage of the PT6920 Dual
Output Voltage ISR
Both output voltages from the Power Trends PT6920 series
ISRs can be independantly adjusted higher or lower than their
factory trimmed pre-set voltage. In each case only a single
external resistor is required to adjust either V₁ (the voltage at
V₁out, or V₂ (the voltage at V₂out). Table 1 gives the permis-
sible adjustment range for both V₁ and V₂ for each model in the
series as V_a(min) and V_a(max). Note: V₂ must always be lower
than V₁.
V₁ Adjust Up: To increase the output, add a resistor R4 be-
tween pin 16 (V₁ Adjust) and pins 7-11 (GND).
V₁ Adjust Down: Add a resistor (R3), between pin 16
(V₁ Adjust) and pin 1 (V₁ Remote Sense).
V₂ Adjust Up: Add a resistor R2 between pin 23 (V₂ Adjust)
and pins 7-11 (GND).
V₂ Adjust Down: Add a resistor (R1) between pin 23 (V₂ Adjust)
and pin 22 (V₂ Remote Sense).
Refer to Figure 1 and Table 2 for both the placement and value
of the required resistor.
Notes:
1. The voltage at V₁out and V₂out may be adjusted
independantly.
2. V₂ must always be at least 0.2V lower than V₁.
3. If V₁ is increased above 3.3V, the minimum input voltage to
the ISR must also be increased. The minimum required
input voltage must be (V₁ + 1.2)V or 4.5V, whichever is
greater. Do not exceed 6.0V
4. Use only a single 1% resistor in either the (R3) or R4 loca-
tion to adjust V₁, and in the (R1) or R2 location to adjust V₂.
Place the resistor as close to the ISR as possible.
5. Never connect capacitors to either the V₁ Adjust or
V₂ Adjust pins. Any capacitance added to these control pins
will affect the stability of the respective regulated output.
6. To comply with the ISRs power dissipation limits, changes
made to either output voltage (V₁ or V₂) may affect the
maximum current available from both outputs. For more
information, consult the related applications note, “Deter-
mining the Maximum Output Current for the PT6920
Series Dual Output ISR.”
The adjust up and adjust down resistor values can also be calcu-
lated using the following formulae. Be sure to select the correct
formula parameter from Table 1 for the output and model being
adjusted.
(R1)/(R3)
=
R_o (V_a – 1)
V_o – V_a
– R_s
kΩ
R2/R4
=
R_o
V_a – V_o
– R_s
kΩ
Where:
Table 1
V_o = Original output voltage, (V₁ or V₂)
V_a = Adjusted output voltage
R_o = The resistance value from Table 1
R_s = The series resistance from Table 1
PT6920 ADJUSTMENT RANGE AND FORMULA PARAMETERS
Output Bus
Series Pt #
V1 out
PT6921/22
V2 out
PT6921
PT6922
Adj. Resistor
(R3)/R4
(R1)/R2
(R1)/R2
Vo(nom)
3.3V
2.5V
1.5
Va(min)
2.3V
1.8V
1.2
Va(max)
4.2V
3.0V
3.0
Ro (kΩ)
12.1
10.0
9.76
Rs (kΩ)
12.1
11.5
6.49
Figure 1
22
1
4,5,6
Vin
Vin
V₂(sns)
PT6920
V₁(sns)
V2_out
V1_out
18 - 21
12 - 15
STBY GND
Vo₂(adj) Vo₁(adj)
3
7 - 11
23
16
(R3)
C1
+
330µF
Adj Down
COM
R4
Adjust Up
Adjust V1 _out
(R1)
C2
+ _C3 +
330µF 100µF
R2
Adjust V2 _out
V2_out
V1_out
LL
OO
AA
DD
COM
Power Trends, Inc. 27715 Diehl Road, Warrenville, IL 60555 [phone] Fax: [phone] http://www.powertrends.com
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