|
|
PDF LTC3717 Data sheet ( Hoja de datos )
| Número de pieza | LTC3717 | |
| Descripción | Wide Operating Range / No RSENSE Step-Down Controller for DDR/QDR Memory Termination | |
| Fabricantes | Linear | |
| Logotipo |  |
|
Hay una vista previa y un enlace de descarga de LTC3717 (archivo pdf) en la parte inferior de esta página. Total 20 Páginas | ||
|
No Preview Available !
LTC3717
Wide Operating Range,
No RSENSETM Step-Down Controller
for DDR/QDR Memory Termination
FEATURES
s VOUT = 1/2 VIN (Supply Splitter)
s Adjustable and Symmetrical Sink/Source
Current Limit up to 20A
s ±0.65% Output Voltage Accuracy
s Up to 97% Efficiency
s No Sense Resistor Required
s Ultrafast Transient Response
s True Current Mode Control
s 2% to 90% Duty Cycle at 200kHz
s tON(MIN) ≤ 100ns
s Stable with Ceramic COUT
s Dual N-Channel MOSFET Synchronous Drive
s Power Good Output Voltage Monitor
s Wide VCC Range: 4V to 36V
s Adjustable Switching Frequency up to 1.5MHz
s Output Overvoltage Protection
s Optional Short-Circuit Shutdown Timer
s Available in a 16U-Pin Narrow SSOP Package
APPLICATIO S
s Bus Termination: DDR and QDR Memory, SSTL,
HSTL, ...
s Notebook Computers, Desktop Servers
s Tracking Power Supply
DESCRIPTIO
The LTC®3717 is a synchronous step-down switching
regulator controller for double data rate (DDR) and Quad
Data RateTM (QDRTM) memory termination. The controller
uses a valley current control architecture to deliver very
low duty cycles without requiring a sense resistor. Oper-
ating frequency is selected by an external resistor and is
compensated for variations in VIN.
Forced continuous operation reduces noise and RF inter-
ference. Output voltage is internally set to half of VREF,
which is user programmable.
Fault protection is provided by an output overvoltage
comparator and optional short-circuit shutdown timer.
Soft-start capability for supply sequencing is accom-
plished using an external timing capacitor. The regulator
current limit level is symmetrical and user programmable.
Wide supply range allows operation from 4V to 36V at the
VCC input.
, LTC and LT are registered trademarks of Linear Technology Corporation.
No RSENSE is a trademark of Linear Technology Corporation.
QDR RAMs and Quad Data Rate RAMs comprise a new family of products developed by Cypress
Semiconductor, Hitachi, IDT, Micron Technology, Inc. and Samsung.
TYPICAL APPLICATIO
VCC
5V TO 28V
1µF
VCC ION
VREF
CC
470pF
CSS
0.1µF
RC
20k
RUN/SS TG
SW
ITH BOOST
LTC3717
SGND INTVCC
BG
PGOOD PGND
RON
715k
VDD = 2.5V
CB 0.22µF
DB
CMDSH-3
+
CVCC
4.7µF
M1
Si7840DP
M2
Si7840DP
VFB
D2
B320A
VIN
+
2.5V TO 5.5V
CIN
150µF
6.3V
×2
VOUT
1.25V
L1
0.68µH
+
COUT ±10A
180µF
4V
×2
D1
B320A
3717 F01a
Figure 1. High Efficiency DDR Memory Termination Supply
Efficiency vs Load Current
100
90
80
70
60
50
40
30
20
10
0
0
VIN = 5V
VIN = 2.5V
VOUT = 1.25V
2 4 6 8 10 12 14
LOAD CURRENT (A)
3717 F01b
sn3717 3717fs
1
1 page  
TYPICAL PERFOR A CE CHARACTERISTICS
LTC3717
INTVCC Load Regulation
0
–0.1
–0.2
–0.3
–0.4
–0.5
0
10 20 30 40
INTVCC LOAD CURRENT (mA)
50
3717 G14
RUN/SS Latchoff Thresholds
vs Temperature
3
2
PULL-DOWN CURRENT
1
0
PULL-UP CURRENT
–1
–2
–50 –25
0 25 50 75
TEMPERATURE (°C)
100 125
3717 G15
RUN/SS Latchoff Thresholds
vs Temperature
5.0
4.5
LATCHOFF ENABLE
4.0
3.5
LATCHOFF THRESHOLD
3.0
–50 –25
0 25 50 75
TEMPERATURE (°C)
100 125
3717 G16
Undervoltage Lockout Threshold
vs Temperature
4.0
3.5
3.0
2.5
2.0
–50 –25
0 25 50 75
TEMPERATURE (C)
100 125
3717 G17
Maximum Current Sense Threshold
vs VRNG Voltage
300
250
200
150
100
50
0
0.50 0.75 1.00 1.25 1.50
VRNG (V)
1.75 2.00
3717 G18
Maximum Current Sense Threshold
vs RUN/SS Voltage, VRNG = 1V
160
140
120
100
80
60
40
20
0
2.0 2.2 2.4 2.6 2.8 3.0 3.2 3.4 3.6
RUN/SS (V)
3717 G19
Maximum Current Sense Threshold
vs Temperature, VRNG = 1V
180
160
140
120
100
80
60
40
20
0
–50 –30 –10 10 30 50 70 90 110 130
TEMPERATURE (°C)
3717 G20
Error Amplifier gm
vs Temperature
1.50
1.40
1.30
1.20
1.10
1.00
0.90
0.80
0.70
–50 –30 –10 10 30 50 70 90 110 130
TEMPERATURE (°C)
3717 G21
sn3717 3717fs
5
5 Page 
LTC3717
APPLICATIO S I FOR ATIO
current ratings from capacitor manufacturers are often
based on only 2000 hours of life which makes it advisable
to derate the capacitor.
The selection of COUT is primarily determined by the ESR
required to minimize voltage ripple and load step
transients. The output ripple ∆VOUT is approximately
bounded by:
∆VOUT
≤
∆IL
ESR
+
1
8fC OUT
Since ∆IL increases with input voltage, the output ripple is
highest at maximum input voltage. Typically, once the ESR
requirement is satisfied, the capacitance is adequate for
filtering and has the necessary RMS current rating.
Multiple capacitors placed in parallel may be needed to
meet the ESR and RMS current handling requirements.
Dry tantalum, special polymer, aluminum electrolytic and
ceramic capacitors are all available in surface mount
packages. Special polymer capacitors offer very low ESR
but have lower capacitance density than other types.
Tantalum capacitors have the highest capacitance density
but it is important to only use types that have been surge
tested for use in switching power supplies. Aluminum
electrolytic capacitors have significantly higher ESR, but
can be used in cost-sensitive applications providing that
consideration is given to ripple current ratings and long
term reliability. Ceramic capacitors have excellent low
ESR characteristics but can have a high voltage coefficient
and audible piezoelectric effects. The high Q of ceramic
capacitors with trace inductance can also lead to signifi-
cant ringing. When used as input capacitors, care must be
taken to ensure that ringing from inrush currents and
switching does not pose an overvoltage hazard to the
power switches and controller. To dampen input voltage
transients, add a small 5µF to 50µF aluminum electrolytic
capacitor with an ESR in the range of 0.5Ω to 2Ω. High
performance through-hole capacitors may also be used,
but an additional ceramic capacitor in parallel is recom-
mended to reduce the effect of their lead inductance.
Top MOSFET Driver Supply (CB, DB)
An external bootstrap capacitor CB connected to the BOOST
pin supplies the gate drive voltage for the topside MOSFET.
This capacitor is charged through diode DB from INTVCC
when the switch node is low. When the top MOSFET turns
on, the switch node rises to VIN and the BOOST pin rises
to approximately VIN + INTVCC. The boost capacitor needs
to store about 100 times the gate charge required by the
top MOSFET. In most applications 0.1µF to 0.47µF, X5R or
X7R dielectric capacitor is adequate.
Fault Condition: Current Limit
The maximum inductor current is inherently limited in a
current mode controller by the maximum sense voltage. In
the LTC3717, the maximum sense voltage is controlled by
the voltage on the VRNG pin. With valley current control,
the maximum sense voltage and the sense resistance
determine the maximum allowed inductor valley current.
The corresponding output current limits are:
ILIMIT POSITIVE
=
VSNS(MAX)
RDS(ON) ρT
+
1
2
∆IL
ILIMIT NEGATIVE
=
VSNS(MIN)
RDS(ON) ρT
–
1
2
∆IL
The current limit value should be checked to ensure that
ILIMIT(MIN) > IOUT(MAX). The minimum value of current limit
generally occurs with the largest VIN at the highest ambi-
ent temperature, conditions that cause the largest power
loss in the converter. Note that it is important to check for
self-consistency between the assumed MOSFET junction
temperature and the resulting value of ILIMIT which heats
the MOSFET switches.
Caution should be used when setting the current limit
based upon the RDS(ON) of the MOSFETs. The maximum
current limit is determined by the minimum MOSFET on-
resistance. Data sheets typically specify nominal and
maximum values for RDS(ON), but not a minimum. A
reasonable assumption is that the minimum RDS(ON) lies
the same amount below the typical value as the maximum
lies above it. Consult the MOSFET manufacturer for further
guidelines.
Minimum Off-time and Dropout Operation
The minimum off-time tOFF(MIN) is the smallest amount of
sn3717 3717fs
11
11 Page | ||
| Páginas | Total 20 Páginas | |
| PDF Descargar | [ Datasheet LTC3717.PDF ] | |
Hoja de datos destacado
| Número de pieza | Descripción | Fabricantes |
| LTC3710 | 0.3 Four LED Clock Frequency Displays |  LITE-ON |
| LTC3710 | 0.3 Four LED Clock Frequency Displays |  Taiwan Liton |
| LTC3713 | Low Input Voltage / High Power / No RSENSE Synchronous Buck DC/DC Controller | Linear |
| LTC3714 | Wide Operating Range / Step-Down Controller with Internal Op Amp | Linear |
| Número de pieza | Descripción | Fabricantes |
| SLA6805M | High Voltage 3 phase Motor Driver IC. |
 Sanken |
| SDC1742 | 12- and 14-Bit Hybrid Synchro / Resolver-to-Digital Converters. |
 Analog Devices |
|
DataSheet.es es una pagina web que funciona como un repositorio de manuales o hoja de datos de muchos de los productos más populares, |
| DataSheet.es | 2020 | Privacy Policy | Contacto | Buscar |