|
|
PDF LTC1708-PG Data sheet ( Hoja de datos )
| Número de pieza | LTC1708-PG | |
| Descripción | Dual Adjustable 5-Bit VID High Efficiency/ 2-Phase Current Mode Synchronous Buck Regulator Controller | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
|
Hay una vista previa y un enlace de descarga de LTC1708-PG (archivo pdf) en la parte inferior de esta página. Total 30 Páginas | ||
|
No Preview Available !
Final Electrical Specifications
LTC1708-PG
Dual Adjustable 5-Bit VID
High Efficiency, 2-Phase Current Mode
Synchronous Buck Regulator Controller
FEATURES
DESCRIPTIO
February 2000
s Out-of-Phase Controllers Reduce Input Capacitance
and Power Supply Induced Noise
s OPTI-LOOPTM Compensation Minimizes COUT
s Power Good Output Monitors Both Outputs
s 5-Bit Mobile VID Control, VOUT: 0.9V to 2.0V
s Dual N-Channel MOSFET Synchronous Drive
s ±1% Output Voltage Accuracy
s DC Programmed Fixed Frequency 150kHz to 300kHz
s Wide VIN Range: 3.5V to 36V Operation
s Very Low Dropout Operation: 99% Duty Cycle
s Adjustable Soft-Start Current Ramping
s Foldback Output Current Limiting
s Latched Short-Circuit Shutdown with Defeat Option
s Output Overvoltage Protection
s Remote Output Voltage Sense
s Low Shutdown Current: 20µA
s 5V and 3.3V Standby Regulators
s Selectable Constant Frequency, Burst ModeTM and
Continuous Operation
U
APPLICATIO S
s Notebook and Palmtop Computers, PDAs
s Portable Instruments
The LTC®1708 is a dual adjustable 5-bit VID program-
mable step-down switching regulator controller that drives
all N-Channel power MOSFET stages. A constant fre-
quency current mode architecture allows adjustment of
the frequency up to 300kHz. Power loss and noise due to
the ESR of the input capacitance are minimized by oper-
ating the two main controller output stages out of phase.
OPTI-LOOP compensation allows the transient response
to be optimized over a wide range of output capacitance
and ESR values. The precision 0.8V reference is compat-
ible with future microprocessor generations, and a wide
3.5V to 30V (36V maximum) input supply range that
encompasses all battery chemistries. A power good out-
put indicates when the output voltages are within 7.5% of
their programmed value.
A RUN/SS pin for each controller provides both soft-start
and an optional timed, short-circuit shutdown. Other
protection features include: internal foldback current lim-
iting and an output overvoltage crowbar. The force con-
tinuous control pin (FCB) can be used to inhibit Burst
Mode operation or to regulate a third, flyback output.
, LTC and LT are registered trademarks of Linear Technology Corporation.
Burst Mode and OPTI-LOOP are trademarks of Linear Technology Corporation.
TYPICAL APPLICATIO
L1
1µH
D1
M1
M2
VOUT1
0.925V TO
2.00V
14.1A
RSENSE1
0.003Ω
COUT1a +
10µF
6.3V
CERAMIC
COUT1
270µF
2V
SP
×4
+
4.7µF
CB1 0.47µF
D3
VIN
TG1
VIDVCC INTVCC
TG2
BOOST1
BOOST2
SW1 SW2
LTC1708-PG
BG1 BG2
5 VID BITS
1000pF
CC1
1500pF
RC1
22k
VID0 TO VID4
PGND
SENSE1+
SENSE2+
SENSE1–
PGOOD
SENSE2–
ATTNIN
VOSENSE2
ITH1 ITH2
RUN/SS1 SGND RUN/SS2
CSS1
0.1µF
CSS2
0.1µF
1µF
D4 CERAMIC
CB2 0.1µF
M3a
M3b
CIN
10µF
50V
CERAMIC
×4 L2
2.2µH
VIN
4.75V TO 28V
D2
1000pF
CC2
220pF
RC2
15k
R3
20k
1%
R4
63.4k
1%
RSENSE2
0.01Ω
COUT
180µF
4V
SP
+
VOUT2
1.5V
4A
M1: IRF7811
M2: 1RF7809
M3a, M3b: FDS6982
L1: VISHAY 5050CE
ATTNOUT CONNECTED TO EAIN1
Figure 1. High Efficiency VID Controlled, 2-Output Step-Down Converter
1628 F01
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen-
tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
1
1 page  
TYPICAL PERFOR A CE CHARACTERISTICS
LTC1708-PG
Supply Current vs Input Voltage
and Mode (Figure 12)
1000
800
600
BOTH
CONTROLLERS ON
400
200
0
0
STANDBY
SHUTDOWN
5 10 15 20 25
INPUT VOLTAGE (V)
30 35
1708 G04
Internal 5V LDO Line Reg
5.1
ILOAD = 1mA
5.0
4.9
4.8
4.7
4.6
4.5
4.4
0
5 10 15 20 25 30 35
INPUT VOLTAGE (V)
1708 G07
Maximum Current Sense Threshold
vs VRUN/SS (Soft-Start)
80
VSENSE(CM) = 1.6V
60
40
20
0
01
2 34
VRUN/SS (V)
56
1708 G10
EXTVCC Voltage Drop
250
200
150
100
50
0
0 10 20 30 40 50
CURRENT (mA)
1708 G05
Maximum Current Sense Threshold
vs Duty Factor
75
50
25
0
0 20 40 60 80 100
DUTY FACTOR (%)
1708 G08
Maximum Current Sense Threshold
vs Sense Common Mode Voltage
80
76
72
68
64
60
0
1 2 34
COMMON MODE VOLTAGE (V)
5
1708 G11
INTVCC and EXTVCC Switch
Voltage vs Temperature
5.05
INTVCC VOLTAGE
5.00
4.95
4.90
4.85
4.80
EXTVCC SWITCHOVER THRESHOLD
4.75
4.70
– 50 – 25
0 25 50 75
TEMPERATURE (°C)
100 125
1708 G06
Maximum Current Sense Threshold
vs Percent of Nominal Output
Voltage (Foldback)
80
70
60
50
40
30
20
10
0
0 25 50 75 100
PERCENT ON NOMINAL OUTPUT VOLTAGE (%)
1708 G09
Current Sense Threshold
vs ITH Voltage
90
80
70
60
50
40
30
20
10
0
–10
–20
–30
0 0.5 1 1.5 2 2.5
VITH (V)
1708 G12
5
5 Page 
U
OPERATIO (Refer to Functional Diagram)
Frequency Setting
The FREQSET pin provides frequency adjustment of the
internal oscillator from approximately 140kHz to 310kHz.
This input is nominally biased through an internal resistor
to the 1.19V reference, setting the oscillator frequency to
approximately 220kHz. This pin can be driven from an
external AC or DC signal source to control the instanta-
neous frequency of the oscillator.
INTVCC/EXTVCC Power
Power for the top and bottom MOSFET drivers and most
other internal circuitry is derived from the INTVCC pin.
When the EXTVCC pin is left open, an internal 5V low
dropout linear regulator supplies INTVCC power. If EXTVCC
is taken above 4.7V, the 5V regulator is turned off and an
internal switch is turned on connecting EXTVCC to INTVCC.
This allows the INTVCC power to be derived from a high
efficiency external source such as the output of the regu-
lator itself or a secondary winding, as described in the
Applications Information.
Standby Mode Pin
The STBYMD pin is a three-state input that controls
common circuitry within the IC as follows: When the
STBYMD pin is held at ground, both controller RUN/SS
pins are pulled to ground providing a single control pin to
shut down both controllers. When the pin is left open, the
internal RUN/SS currents are enabled to charge the
RUN/SS capacitor(s), allowing the turn-on of either con-
troller and activating necessary common internal biasing.
When the STBYMD pin is taken above 2V, both internal
linear regulators are turned on independent of the state on
the RUN/SS pins of the two switching regulator control-
lers, providing an output power source for “wake-up”
circuitry. Decouple the pin with a small capacitor (0.01µF)
to ground if the pin is not connected to a DC potential.
Output Overvoltage Protection
An overvoltage comparator, OV, guards against transient
overshoots (>7.5%) as well as other more serious condi-
tions that may overvoltage the output. In this case, the top
MOSFET is turned off and the bottom MOSFET is turned on
until the overvoltage condition is cleared.
LTC1708-PG
VID Control
Logic inputs VID0 to VID4 program an internal resistive
divider. The output voltage can be programmed in 50mV
and 25mV increments from 0.925V to 2.0V (see Table 1).
These logic input pins are internally pulled up to the
VIDVCC pin using separate internal series resistor/diode
paths. The diodes provide electrical isolation when the
logic pins are externally pulled up to a higher voltage
supply than VIDVCC.
Power Good (PGOOD)
The PGOOD pin is connected to an open drain of an internal
MOSFET. The MOSFET turns on when the outputs are not
both within ±7.5% of their nominal output levels as
determined by their feedback dividers. When both outputs
are within ±7.5% of their nominal values, the MOSFET is
turned off within 10µs and the pin is pulled up by an
external source
Foldback Current, Short-Circuit Detection
and Short-Circuit Latchoff
The RUN/SS capacitors are used initially to limit the inrush
current of each switching regulator. After the controller
has been started and been given adequate time to charge
up the output capacitors and provide full load current, the
RUN/SS capacitor is used in a short-circuit time-out
circuit. If the output voltage falls to less than 70% of its
nominal output voltage, the RUN/SS capacitor begins
discharging on the assumption that the output is in an
overcurrent and/or short-circuit condition. If the condition
lasts for a long enough period as determined by the size of
the RUN/SS capacitor, both controllers will be shut down
until the RUN/SS pin’s voltages are recycled. This built-in
latchoff can be overridden by providing a >5µA pull-up at
a compliance of 5V to the RUN/SS pin(s). This current
shortens the soft-start period but also prevents net dis-
charge of the RUN/SS capacitor(s) during an overcurrent
and/or short-circuit condition. Foldback current limiting is
also activated when the output voltage falls below 70% of
its nominal level whether or not the short-circuit latchoff
circuit is enabled. Even if a short is present and the short-
circuit latchoff is not enabled, a safe, low output current is
provided due to internal current foldback and actual power
11
11 Page | ||
| Páginas | Total 30 Páginas | |
| PDF Descargar | [ Datasheet LTC1708-PG.PDF ] | |
Hoja de datos destacado
| Número de pieza | Descripción | Fabricantes |
| LTC1708-PG | Dual Adjustable 5-Bit VID High Efficiency/ 2-Phase Current Mode Synchronous Buck Regulator Controller | Linear Technology |
| 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 |