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PDF LTC2920-2 Data sheet ( Hoja de datos )
| Número de pieza | LTC2920-2 | |
| Descripción | Single/Dual Power Supply Margining Controller | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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FEATURES
■ Margin Voltage Precision <0.4%
■ 400:1 Current Programming Range
■ Symmetric/Asymmetric High and Low Voltage
Margining
■ Single Control Pin per Supply—High, Float, Low
■ Single Current Setting Resistor per Supply
■ Wide VCC Compliance 2.3V < VCC < 6V
■ Wide Output Compliance
0.6V < VMARGIN < (VCC – 0.6V)
■ Single in 5-Pin ThinSOTTM (LTC2920-1)
■ Dual in 8-Pin MSOP (LTC2920-2)
U
APPLICATIO S
■ Automated PCB Production Testing
■ Automated Preventative Maintenance Testing
■ DC/DC Converter Module Margining
LTC2920-1w/wLwT.DCataS2he9et42U.c0om-2
Single/Dual Power Supply
Margining Controller
DESCRIPTIO
The LTC®2920 allows power supplies and power supply
module output voltages to be precisely adjusted both up
and down for automated PCB testing. The power supply
output voltage is changed by sourcing or sinking current
into the feedback node or voltage adjust pin of the power
supply. This allows a system to test the correct operation
of electrical components at the upper and/or lower power
supply voltage limits specified for a given design (Power
Supply “Margining”).
The LTC2920 uses a single resistor to set the voltage
margining current. The margining current is adjustable
over a 400:1 range. Precision margin currents can be
supplied to within 0.6V of ground or VCC.
The LTC2920-1 is a single margining controller. The
LTC2920-2 has two independently controllable margining
channels. Each channel has its own control pin and current
setting resistor. The LTC2920-2 can be used to symmetri-
cally margin two power supplies, or asymmetrically mar-
gin a single power supply.
Both the LTC2920-1 and LTC2920-2 feature a trimmed on-
board voltage reference. Typical power supply margining
accuracy is better than 0.4%.
, LTC and LT are registered trademarks of Linear Technology Corporation.
ThinSOT is a trademark of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
TYPICAL APPLICATIO
+
33μF
–48V
3.3V Quarter Brick with ±5% Voltage Margining
1
+VIN
5
+VOUT
POWER ONE
I5S013ZE-A
+
TRIM
2
–VIN
–VOUT 6
7
150Ω
3.3V
AT 4A
0.1μF
2μF
VCC IN1
IM1 LTC2920-1
GND RS1
SYSTEM
CONTROLLER
THREE-STATE
RSET1
10k
1%
2920-1/2 TA01
5%
NOM
–5%
LOGIC HI
LOGIC FLOAT
LOGIC LOW
+VOUT
IN1
1ms/DIV
2920-1/2 TA01a
292012fa
1
1 page  
LTC2920-1w/wLwT.DCataS2he9et42U.c0om-2
TYPICAL PERFOR A CE CHARACTERISTICS
ICC vs IMARGIN High Range
Sourcing Current
5.0
4.5
4.0
2 CHANNELS
3.5
3.0
2.5
2.0
1 CHANNEL
1.5
1.0
0.5
0
0 0.5 1 1.5 2 2.5
IMARGIN (mA)
2920-1/2 G01
ICC vs IMARGIN Low Range
Sourcing Current
1800
1600
1400
2 CHANNELS
1200
1000
800
1 CHANNEL
600
400
200
0
0 20 40 60 80 100 120 140 160 180
IMARGIN (μA)
2920-1/2 G02
IMARGIN Error vs VMARGIN
5.0
4.5 VCC = 5V
HIGH RANGE
4.0
3.5
3.0
2.5
2.0
1.5
(mA)
0.15
0.3
0.5
1
2
1.0
0.5
0
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5
VMARGIN (V)
2920-1/2 G03
IMARGIN Error vs VMARGIN
5.0
4.5 VCC = 2.5V
HIGH RANGE
4.0
3.5
3.0
2.5
2.0
1.5
(mA)
0.15
0.3
0.5
1
2
1.0
0.5
0
0 0.5 1 1.5 2 2.5
VMARGIN (V)
2920-1/2 G04
IMARGIN Error vs VMARGIN
6
(μA)
55
20
4
50
3 100
166.7
2
1
VCC = 5V
LOW RANGE
0
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5
VMARGIN (V)
2920-1/2 G05
IMARGIN Error vs VMARGIN
6
(μA)
55
20
4
50
3 100
166.7
2
1
VCC = 2.5V
LOW RANGE
0
0 0.5
1
1.5
VMARGIN (V)
2 2.5
2920-1/2 G06
IMARGIN Rise Time
HIGH
RANGE
SOURCE
VIN(DELAYON)
ENDS
100%
0% LOW
RANGE
RSET = 20k
HIGH
RANGE
1μs/DIV
SINK
100%
2920-1/2 G07
IMARGIN Fall Time
SOURCE
100%
VIN(DELAYOFF)
ENDS
RSET = 20k
LOW RANGE
HIGH RANGE
0%
LOW RANGE
HIGH RANGE
100%
SINK
100ns/DIV
2920-1/2 G08
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5 Page 
LTC2920-1w/wLwT.DCataS2he9et42U.c0om-2
APPLICATIO S I FOR ATIO
the IMACCURACY specification. If VT does not fall within this
range, the LTC2920 cannot be used for this application.
SENSE+
VIN+
VO+
VPS
RVT TRIM
VT
VREF –+
VIN–
RTRIM
VO–
SENSE–
ITRIM
VO–
2920-1/2 F10
Figure 10. Power Module ITRIM Model
Accuracy of Power Supply Voltages when Margining
The accuracy of margined power supply voltages depends
on several factors. Figure 11 shows the magnitude of the
errors discussed in detail below as a function of power
supply margining percentage.
In a typical feedback model (Figure 12), the delta voltage
is a function of the margin current, IMARGIN, and the
feedback resistor, RF.
VMARGIN = IMARGIN • RF
Errors in VMARGIN are directly proportional to errors in
IMARGIN and errors in RF. A 5% error in IMARGIN will cause
a 5% error in VMARGIN. In this example, a 3.3V power
supply is margined by 2.5%, or 0.0825V to 3.3825V. With
a 5% VMARGIN error, the actual margin voltage is 0.0866V
and the actual power supply voltage is 3.3866V. The error
in the expected voltage is then:
Error = ⏐1 – (3.3866/3.3825)⏐ • 100 = 0.12%
Similarly, a 1% inaccuracy in the RSET resistor would
cause only 0.024% error in the expected power supply
margined voltage. In effect, IMARGIN errors caused by the
RSET resistor or the LTC2920 are attenuated by the voltage
margining percentage.
The accuracy of the RF resistor introduces two errors in the
margined supply voltage. The first is the error in VMARGIN
(IMARGIN • RF). This error is similar in magnitude to the
errors described above and is generally quite small (0.024%
for this example). The second error is the power supply
initial set point accuracy. In this example the RF resistor
has a 1% accuracy error causing a 0.6% initial set point
error in the power supply. Because the margined power
supply voltage is the change in the voltage, VMARGIN, from
the power supply initial set point voltage, this error shows
up in the margined power supply voltage. When these two
errors are combined, the error is:
Error = ⏐1 – (3.4043/3.3825)⏐ • 100 = 0.65%
The error caused by a 1% inaccuracy in RG will be similar
since the dominate error source is the power supply initial
set point voltage.
Errors caused by RF and RG can be a major contributor to
voltage margin errors. Using 0.1% resistors for both RF
and RG is often the best choice for improving both voltage
margin accuracy and power supply initial accuracy.
0.7
0.6 1% FEEDBACK
RESISTOR INACCURACY
0.5
0.4
0.3
5% LTC2920
0.2 IMARGIN INACCURACY
1% RSET
RESISTOR
INACCURACY
0.1
0
0123456
POWER SUPPLY VOLTAGE MARGINING (%)
2920-1/2 F11
Figure 11. Sources of Power Supply Margined Voltage Errors
RSET = 20k
IMARGIN = ± 50μA
IM
LTC2920
RS
RG = 944k
RF = 1.65k
IFB = 1.27mA
–
VREF = 1.2V –+
+
VPSOUT = 3.3V
2920-1/2 F12
Figure 12. Power Supply Voltage Margin Model
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11 Page | ||
| Páginas | Total 16 Páginas | |
| PDF Descargar | [ Datasheet LTC2920-2.PDF ] | |
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