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PDF LTC2922 Data sheet ( Hoja de datos )
| Número de pieza | LTC2922 | |
| Descripción | Power Supply Tracker | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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Hay una vista previa y un enlace de descarga de LTC2922 (archivo pdf) en la parte inferior de esta página. Total 20 Páginas | ||
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LTC2921/LTCw2ww9.D2at2aSheSete4U.rcioem s
Power Supply Tracker
with Input Monitors
FEATURES
DESCRIPTIO
s Tracks Multiple Supplies with MOSFET Switches
s Monitors 5 Input Voltages Including VCC
s Guaranteed Threshold Accuracy: ±1% at 0.5V
s Automatic Remote Sense Switching
s Adjustable Supply Ramp Rate
s Overvoltage Monitor
s Adjustable Electronic Circuit Breaker
s Adjustable Power-Good Delay
s Available for VCC Supply Voltages of 5V, 3.3V and 2.5V
s Available in 16-Pin Narrow SSOP (LTC2921 Series)
and 20-Pin TSSOP (LTC2922 Series)
U
APPLICATIO S
s Desktop Computers
s Plug-In Cards
s Telecom Infrastructure
s Supply Sequencing
s Instruments
The LTC®2921 and LTC2922 monitor up to five supplies
and force them to track on power-up in multiple supply
systems. Using external N-channel pass transistors, the
supplies can be ramped up at an adjustable rate. Auto-
matic remote sense switching allows the DC/DC convert-
ers to compensate for series voltage drops in the wiring.
An incorrect level on one or more of the supplies triggers
disconnect of all supplies. Tight 1% accuracy and glitch
immunity on the low 0.5V monitoring level ensure no false
error disconnects.
The LTC2921 and LTC2922 each feature an adjustable
electronic circuit breaker to protect the VCC supply against
short circuits. Capacitance at the TIMER pin programs the
delays in the monitoring sequence.
The LTC2921 includes three remote sense switches in a
16-pin narrow SSOP package, while the LTC2922 includes
five remote sense switches in a 20-pin TSSOP package.
Both parts are available for VCC supply voltages of 5V,
3.3V, and 2.5V.
, LTC and LT are registered trademarks of Linear Technology Corporation.
TYPICAL APPLICATIO
Three-Supply Tracker and Monitor (5V, 3.3V, 2.5V)
VOUT 5V SUPPLY
VFB
DC/DC
CONVERTER
100Ω
WSL1206
0.05Ω
Si2316DS
10Ω
5V
LOAD
VOUT 3.3V SUPPLY
VFB
DC/DC
CONVERTER
100Ω
Si2316DS
10Ω
3.3V
LOAD
VOUT 2.5V SUPPLY
VFB 100Ω
DC/DC
CONVERTER
Si1012R
CBRST
100k
CIRCUIT BREAKER
RESET CONTROL
243k 169k
49.9k 49.9k
Si2316DS
10Ω
VCC SENSE
V1 GATE
V2
V3 LTC2921
V4
PG
S1
S2
S3
GND
D1
D2
D3
TIMER
0.47µF
0.22µF
2.5V
LOAD
4.7k
RESET
tGATE ~ 500ms
tTIMER ~ 130ms
2921/22 TA01
Load Voltage Ramp-Up and
Power-Good Activation
2.5V SUPPLY
2V/DIV
OUTPUTS
2V/DIV
5V LOAD
3.3V LOAD
2.5V LOAD
PG
2V/DIV
5V SUPPLY AT 5V 100ms/DIV
3.3V SUPPLY AT 3.3V
2921/22 TA01b
29212fa
1
1 page  
LTC2921/LTCw2ww9.D2at2aSheSete4U.rcioem s
TYPICAL PERFOR A CE CHARACTERISTICS
Specifications are at TA = 25°C unless otherwise noted.
Gate Voltage vs Supply Voltage
12 GATE LOAD = 1000pF || 10MΩ
PG LOAD = 2kΩ TO VCC
11 VCC BYPASS CAP = 1µF
LTC2921
LTC2922
10
9
LTC2921-3.3
8 LTC2922-3.3
7 LTC2921-2.5
LTC2922-2.5
6
2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5
VCC (V)
2921/2 G10
GATE Pull-Up Current
vs Temperature
11.5
VGATE = VCC
11.0
10.5
10.0
9.5
9.0
8.5
–50 –30
–10 10
30
50
TEMPERATURE (°C)
70 90
2921/2 G13
Gate Voltage vs Temperature
12
11 LTC2921
LTC2922
10
LTC2921-3.3
LTC2922-3.3
9
GATE LOAD = 1000pF || 10MΩ
PG LOAD = 2kΩ TO VCC
8 VCC BYPASS CAP = 1µF
LTC2921-2.5
7 LTC2922-2.5
6
–50 –30
–10 10 30 50
TEMPERATURE (°C)
70 90
2921/2 G11
PG Voltage vs Supply Voltage
12 GATE LOAD = 1000pF || 10MΩ
PG LOAD = 1000pF || 10MΩ
11 VCC BYPASS CAP = 1µF
LTC2921
LTC2922
10
LTC2921-3.3
9 LTC2922-3.3
8
LTC2921-2.5
7 LTC2922-2.5
6
2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5
VCC (V)
2921/2 G14
Gate Voltage vs Load Current
12
LTC2921
LTC2922
10
8
LTC2921-3.3
LTC2922-3.3
6
LTC2921-2.5
LTC2922-2.5
4
GATE LOAD = 1000pF || 10MΩ
2 PG LOAD = 2kΩ TO VCC
VCC BYPASS CAP = 1µF
0
0 1 2 3 4 5 6 7 8 9 10
LOAD CURRENT (µA)
2921/2 G12
PG Pull-Up Current vs
Temperature
5.5
VPG = VCC
5.0
4.5
4.0
3.5
3.0
2.5
–50 –30
–10 10 30 50
TEMPERATURE (°C)
70 90
2921/2 G15
29212fa
5
5 Page 
LTC2921/LTCw2ww9.D2at2aSheSete4U.rcioem s
APPLICATIO S I FOR ATIO
Setting the Supply Monitor Levels
The LTC2921 and LTC2922 series both feature low 0.5V
monitoring thresholds with tight 1% accuracy. To set a
supply monitoring level tightly, design a precision ratio
resistive divider to relate the lowest valid supply voltage to
the maximum specified monitor threshold voltage. Use
resistors with 1% tolerance or better to limit the error due
to mismatch. The basic resistive divider connection for
supply monitoring is shown in Figure 5.
VOUT
VFB
GND
VSRC1
+ VQ1 – VL1
Q1
RY1 RB1
RG1
IMON
10Ω
LOAD
VV1 ±0.1µA V1
GATE
RZ1 IA1 RA1
LTC2922
GND
CGATE
DC/DC
CONVERTER
2921/22 F05
Figure 5. Basic Monitor Connection
First, divide the nominal monitor threshold voltage by an
acceptable bias current (IA1), and choose a nearby stan-
dard value for resistor RA1 (see Equation 1).
Next, calculate the bounds on the value of RB1 that
guarantee that the divided minimum supply voltage ex-
ceeds the maximum specified monitor threshold voltage,
and that the minimum specified overvoltage threshold
exceeds the divided maximum supply voltage. Use Equa-
tions 2 and 3 to calculate RB1(MAX) and RB1(MIN) from RA1,
the resistor tolerance (RTOL), the supply voltage, the
monitor threshold and overvoltage specifications, and the
monitor pin leakage current specification.
When the integrated remote sensing switch is closed, the
DC/DC converter will compensate for the IR drop from
drain to source of the external N-channel FET (VQ1(ON)) by
increasing the supply voltage by the same amount. Calcu-
late with VQ1(ON)(MAX) = 0V if the remote sense switch is
not used.
RA1
=
0.500V
IA1
(1)
RB1(MAX) =
RA1
•
1–
1+
RRTTOOLL
•
VSRC1(MIN) – 0.505V
0.505V + 0.1µA •RA1
(2)
RB1(MIN)
=
RA1
•
1+
1–
RRTTOOLL
•
VSRC1(MAX) + VQ1(ON)(MAX) – 0.665V
0.665V – 0.1µA •RA1
(3)
Choose a standard resistor value for RB1 that satisfies the
inequality of Equation 4.
RB1(MIN) ≤ RB1 ≤ RB1(MAX)
(4)
When several standard values meet the requirement,
choose the value closest to RB1(MAX) to set the tightest
monitor threshold. This also allows more headroom for
larger VQ1(ON)(MAX). Alternatively, choose the standard
value closest to RB1(MIN) to set the tightest overvoltage
threshold.
All four monitor input voltages must be between the
monitor threshold and the overvoltage threshold for the
turn-on sequence to begin. Connect unneeded monitor
input pins to any of the utilized monitor input pins.
Selecting the External N-Channel MOSFETs
The GATE pin drives the gate of external N-channel
MOSFETs above VCC to connect the supplies to the loads.
The GATE drive voltage provided by the LTC2921/LTC2922
series is best suited to logic-level and sublogic-level
power MOSFETs. To achieve the lowest switch resistance,
the VCC pin must be connected to the highest supply
voltage.
Consider the application requirements for current, turnoff
speed, on-resistance, gate-source voltage specification,
etc. Refer to the Electrical Specifications and Typical
Performance Curves to determine the GATE voltages for
given VCC voltages over the required range of conditions.
Calculate the minimum gate drive voltage for each moni-
tored supply for use in selecting the FETs. Check the
maximum GATE voltage against the FETs’ gate-source
29212fa
11
11 Page | ||
| Páginas | Total 20 Páginas | |
| PDF Descargar | [ Datasheet LTC2922.PDF ] | |
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