参数资料
型号: PT6641L
厂商: TEXAS INSTRUMENTS INC
元件分类: 稳压器
英文描述: SWITCHING REGULATOR, 600 kHz SWITCHING FREQ-MAX, PSMA14
封装: SIP-14
文件页数: 12/18页
文件大小: 412K
代理商: PT6641L
Application Notes
For technical support and more information, see inside back cover or visit www.ti.com/powertrends
PT6640 Series
Adjusting the Output Voltage of the PT6640 24W
Positive to Negative ISR Series
The negative output voltage of the Power Trends
PT6640 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 gives the allowable ad-
justment range for each model in the series as V
a (min)
and V
a (max).
Adjust Up:
An increase in the negative output
voltage is obtained by adding a resistor R2, between pin
14 (V
o adjust) and pins 7-10 (-Vout).
Adjust Down:
Adding a resistor (R1), between pin 14
(V
o adjust) and pins 11-13 (GND), decreases the output
voltage magnitude.
Refer to Figure 1 and Table 2 for both the placement and
value of the required resistor, either (R1) or R2 as appro-
priate.
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 pin. Any capacitance added to
the V
o adjust pin will affect the stability of the ISR.
3. If the Remote Sense feature is being used, connecting the
resistor (R1) between pin 14 (V
o adjust) and pin 1 (Remote
Sense) can benefit load regulation.
4. The maximum allowed input voltage (V
in) will change as
V
out is adjusted. The difference between the input voltage
(V
in) and the output voltage (Vout) must not exceed 30V or
10
× V
out, whichever is less. Use one of the following
formulas to determine the maximum allowed input voltage
for the PT6640.
V
out greater than 2.73V,
V
in(max)
= 30 –
V
out
Vdc
For example, if V
out = -12V,
V
in(max)
= 30 –
-12 = 18Vdc
V
out less than 2.73V,
V
in(max)
= 10
× V
out
Vdc
The values of (R1) [adjust down], and R2 [adjust up], can
also be calculated using the following formulas.
Ro (Vo – 1.25)(Va – 1.25)
(R1)
=
1.25 (Vo – Va)
– Rs
k
Ro (Vo – 1.25)
– Rs
k
R2
=
Va - Vo
Where: V
o
= Original V
out (magnitude)
V
a
= Adjusted V
out (magnitude)
R
o
= The resistance value in Table 1
R
s
= The series resistance from Table 1
Figure 1
Table 1
PT6640 ADJUSTMENT AND FORMULA PARAMETERS
Series Pt #
PT6646
PT6641
PT6642
PT6644
PT6643
PT6645
Vo (nom)
–2.5V
–3.3V
–5.0V
–9.0V
–12.0V
–15.0V
Va (min)
–1.8V
–2.2V
–3.0V
–6.0V
–9.0V
–10.0V
Va (max)
–4.3V
–4.7V
–6.5V
–10.2V
–13.6V
–17.0V
Ro (k
)
4.99
4.22
2.49
2.0
Rs (k
)
2.49
4.99
12.7
C
in
560
F
+
C
out
330
F
+
(R1)
|-V
o | Down
R2
|-V
o | Up
V
out
COM
+V
in
L
O
A
D
PT6640
7,8,9,10
14
11,12,13
4,5,6
+V in
V out
GND
V
o(adj)
SNS(+)
1
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