Lineage Power AN04-005 Margining and voltage programming Datasheet

Application Note
2 September 2008
PDF: margin-volt_prog_an.pdf
Application Guidelines for Non-Isolated Converters
AN04-005: Margining and Voltage Programming
Introduction
The Austin LynxTM, Lynx II, TLynx and Naos Raptor
series of non-isolated modules all have the ability to
adjust their output voltage by interfacing through the Trim
pin. In addition to the output voltage set function, two
other types of output voltage adjustment are frequently
used. The first is margining, where the output voltage is
adjusted a fixed percentage (typically ±5 or 10%) off the
nominal during system level test. This adjustment is
generally used for checking the operational margin of
circuits and thereby assuring the robustness of the
application. The second is voltage programming where
an external voltage is provided to either provide more
accurate adjustment of the output voltage of the module
or to implement a margining-like function. This
application note describes circuits and provides design
guidelines for implementing margining or voltage
programming.
To understand how margining or voltage programming
are done, it is beneficial to understand the circuit used to
scale down the output voltage in the Austin Lynx and
Lynx II series of modules. Figure 1 shows a portion of the
output voltage divider and feedback circuitry that is used
in all Lynx and Lynx II series modules (except the fixedoutput voltage 5/3.3V and 12V input Lynx modules –
these come in different output voltage versions and do
not have an wide-output voltage adjust capability). The
output voltage is scaled down by a divider consisting of
resistors R1 and R2. The mid point of the divider is
connected to the inverting input of the op-amp which is
used to process the error voltage between the internal
reference voltage Vref (0.7V) and the divider midpoint
voltage. The voltage control loop of the module regulates
the output voltage so as to maintain the voltage at the
mid point of the divider equal to the reference voltage.
The trim pin is connected through a 1KΩ resistor to the
mid point of the divider. By connecting an external
resistor between the Trim pin and GND, the divider ratio
is changed thus allowing adjustment of the output
voltage. In both margining and voltage programming, the
output voltage is adjusted by in essence effecting a
change in the scaling between the output and voltage
divider mid point voltages.
In the TLynx and Naos Raptor series of modules, a
simpler circuit is used to divide down the voltage as
shown in Fig. 2. However, the same functionality is
obtained is obtained through the TRIM pin.
TLynx or
Naos Raptor Module
PWM
Controller
R1
-
AMP
Trim
+
Austin Lynx or
Lynx II Series Module
Vout
VREF
PWM
Controller
R1
AMP
Trim
+
R2
VREF
R1
2K
10K
2K
2K
VREF
0.6V
0.591V
0.591V
0.6V
Fig. 2. Circuit diagram of the output voltage divider
and feedback circuitry used in the TLynx and Naos
Raptor series of modules.
GND
R1
R2
R3
VREF
30.1K
402K
1K
0.7V
15K
200K
1K
0.7V
1.5K
Open
100
0.8V
Fig. 1. Circuit diagram of the output voltage divider
and feedback circuitry used in the Austin Lynx and
Lynx II series of modules (except fixed-output 5/3.3V
in Austin Lynx and 12V in Austin Lynx modules).
LINEAGE POWER
GND
3.3Vin TLynx
12Vin TLynx
3A/6A/10A/20A Naos Raptor
40A/50A/60A Naos Raptor
R3
-
5Vin Austin Lynx or
Lynx II
12Vin Austin Lynx
or Lynx II
Austin MegaLynx
Vout
Implementing Margining
Margining is implemented by essentially changing the
divider by small amounts to obtain the desired margining
voltages. One method to accomplish this is shown in Fig.
3. This scheme connects a pre-determined resistor with a
small FET in series between the trim pin and ground (to
margin up or slightly increase the output voltage), and a
similar FET+resistor combination in series between TRIM
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Application Guidelines for Non-Isolated Converters
Application Note
September 2, 2008
AN04-005: Margining and Voltage Programming
and Vout to margin down (or slightly decrease the output
voltage). Under normal operation, both FETs are kept off.
To margin up, the lower FET (Q1) would be turned on,
while to margin down the upper FET (Q2) would be
turned on. Table 1 shows a summary of the various
states and their effect on the output voltage. Another
scheme to implement margining is shown in Fig. 4,
where two FET+resistor combinations are shown
connected in parallel between the Trim and Ground pins.
For normal operation, one of the FETs (say Q1) is kept
on while the other one is kept off. To margin up, both
FETs would be on, while to margin down, both FETs
would be off. The summary of the various states and
effect on output voltage are shown in Table 2. Similar
results are obtained using either scheme.
The POL Programming Tool (free download from
www.lineagepower.com) can calculate the values of
resistors to be used with the margining schemes shown
in Fig. 3 for different POL modules.
Vo
VO
Austin Lynx or
Lynx II Series
Trim
R1
R2
Rtrim
Q1
Q2
GND
Fig. 4. Alternate circuit for implementing margining
capability in the Lynx and Lynx II series modules.
Vo
Rmargin-down
Austin Lynx or
Lynx II Series
Q2
Trim
Rmargin-up
Rtrim
Q1
GND
Fig. 3. Circuit for implementing margining capability
in the Lynx, Lynx II, TLynx and Naos Raptor series of
modules.
Table 1.
Action
Q1
Q2
Normal
OFF
OFF
Margin-up
ON
OFF
Margin-down
OFF
ON
Table 2.
Action
Q1
Q2
Normal
ON
OFF
Margin-up
ON
ON
Margin-down
OFF
OFF
LINEAGE POWER
Margining through Voltage
Programming
Another method of adjusting the output voltage of the
module is through programming using an external
voltage source. Recall that the output voltage is scaled
down by a voltage divider network, and this voltage is
then fed back to compare with a fixed reference voltage
inside the module. The Trim point represents the mid
point of this divider. By injecting an additional voltage
through a resistor into the Trim pin, the scaling between
the output voltage and the voltage at the Trim pin is
changed, effectively changing the output voltage. This
method of adjustment is referred to as voltage
programming of the module output voltage. The voltage
programming equation for the 12V input Austin Lynx and
Lynx II modules is
(Vref − Vt )⎤
⎡ Vref
Vout = Vref + 15000 × ⎢
+
200
,
000
1000 ⎥⎦
⎣
Vout = (16.075 × Vref ) − (15 × Vt )
where, Vt is the voltage at the Trim pin. This equation
shows that the output voltage is highly sensitive to
tolerances in Vref and Vt, since these terms are
multiplied by 16.075 and 15, respectively. Similar
considerations apply to the 5/3.3V in Austin Lynx and
Lynx II modules as well.
To reduce the sensitivity to tolerances in the reference
and programming voltages, a modified circuit as shown
in Fig. 4 needs to be used. The external output voltage
Vs is fed to the module's trim pin through a resistor
network to cause the change in the output voltage. When
the external voltage VS is increased, a larger current
flows through Rext and R3 into the inverting terminal of
the opamp, thereby reducing the current that flows from
Vout through resistor R1. This effectively reduces the
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Application Guidelines for Non-Isolated Converters
Application Note
September 2, 2008
AN04-005: Margining and Voltage Programming
scaling of the output voltage and results in a decrease of
Vout. The reverse occurs when VS is reduced resulting
in an increase in Vout. Table 3 shows values of various
circuit parameters for the case of the 5/3.3V input Lynx
and Lynx II series modules, while Table 4 shows a
similar set of data for the 12V input series modules.
If margining is implemented along with voltage
programming, both functions can be implemented
together by adjusting the source voltage VS to perform
the margining. Figure 5 shows a slightly modified version
of Figure 4 that can be used. Table 5 provides the values
of VS needed to margin either +/-5% or +/-10% for the
5/3.3V in Lynx and Lynx II Series modules, while Table 6
provides a similar set of data for 12V in Lynx and Lynx II
Series of modules.
For the Austin MegaLynx, TLynx and NSR series of
modules, the POL Programming tool can be used to
select external voltage source and series resistor values
for programming the module output voltage over a range.
Summary
Margining and output voltage programming are useful
features of the Lynx series of modules. Along with simple
external circuits, they allow versatile output voltage
adjustment of the module to fit various application needs.
Margining is used for checking the robustness of the
circuits, as well as ensuring the proper functionality of the
module under a noisy environment.
Voltage
programming can be used to provide a precise
adjustment of the module output voltage in demanding
applications or provide dynamic voltage adjustment when
needed.
Austin Lynx or
Lynx II Series Module
Vout
PWM
Controller
R1
R3
-
AMP
Austin Lynx or
Lynx II Series Module
+
Vout
PWM
Controller
Rg
VS
Trim
R2
Rtrim
Vref
0.7V
R1
GND
R3
-
AMP
Rext1
Rg1
VS
Trim
+
R2
Rtrim1
Vref
0.7V
Table 5.
External Source Value for Margining 5/3.3V Lynx
Series Modules
GND
Fig. 4. Recommended circuit to be used in voltage
programming of the Austin Lynx Series of modules.
Table 3.
Programming Voltage Values for 5/3.3V Lynx Modules
Output Voltage
Rext
Rtrim
Rg
Vs,nom
% Error
1.2V
8k
33.9k
73.2k
0.505
1.74 %
1.5V
3.5k
19.6k
55k
0.485
1.75 %
1.8V
2k
13k
39.2k
0.453
1.74 %
2.5V
1k
5.94k
14.5k
0.345
1.75 %
3.3V
0.6k
2.56k
1.685k
0.217
1.85 %
Table 4.
Programming Voltage Values for 12V Lynx Modules
Output Voltage
Rext
Rtrim
Rg
Vs,nom
Output
Voltage
Rtrim
Rg
Vs,nom
Vs,up
(+10%)
Vs,down
(-10%)
Vs,up
(+5%)
Vs,down
(-5%)
1.2
41.96k
124k
0.624
0.05
1.2
0.335
0.91
1.5V
23.07k
82k
0.573
0.05
1.095
0.310
0.835
1.8V
15.004k
55k
0.522
0.05
0.995
0.287
0.757
2.5V
6.947k
21.6k
0.403
0.05
0.758
0.226
0.58
3.3V
3.161k
5.6k
0.2675
0.05
0.485
0.159
0.376
Table 6.
External Source Value for Margining 12V Lynx Series
Modules
Output
Voltage
Rtrim
Rg
Vs,nom
Vs,up
(+10%)
Vs,down
(-10%)
Vs,up
(+5%)
Vs,down
(-5%)
1.2
22.464k
73.2k
0.67
0.05
1.29
0.365
0.98
1.5V
13.047k
54.9k
0.65
0.05
1.25
0.350
0.950
1.8V
9.024k
42.2k
0.63
0.05
1.20
0.345
0.918
2.5V
5.009k
26.1k
0.58
0.05
1.12
0.315
0.855
3.3V
3.122k
15.8k
0.53
0.05
1.01
0.290
0.770
5.0V
1.472k
6.04k
0.417
0.05
0.79
0.231
0.603
% Error
1.2
9.53k
22.464k
73.2k
0.385
2.4%
1.5V
6.34k
6.71k
10.0k
0.335
2.4 %
2.4 %
1.8V
6.19k
2.834k
1.58k
0.198
2.5V
2.21k
2.8k
6.19k
0.326
2.4 %
3.3V
1.47k
1.652k
3.19k
0.280
2.4 %
5.0V
0.32k
1.15k
3.19k
0.325
2.4 %
LINEAGE POWER
Fig. 5. Recommended circuit to be used in voltage
programming along with margining of the Austin
Lynx Series of modules.
3
Application Guidelines for Non-Isolated Converters
AN04-005: Margining and Voltage Programming
Application Note
September 2, 2008
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