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PDF LTC1159 Data sheet ( Hoja de datos )
| Número de pieza | LTC1159 | |
| Descripción | High Efficiency Synchronous Step-Down Switching Regulators | |
| Fabricantes | Linear Technology | |
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LTC1159
LTC1159-3.3/LTC1159-5
High Efficiency Synchronous
Step-Down Switching Regulators
FEATURES
s Operation from 4V to 40V Input Voltage
s Ultrahigh Efficiency: Up to 95%
s 20µA Supply Current in Shutdown
s High Efficiency Maintained Over Wide Current Range
s Current Mode Operation for Excellent Line and Load
Transient Response
s Very Low Dropout Operation: 100% Duty Cycle
s Short-Circuit Protection
s Synchronous FET Switching for High Efficiency
s Adaptive Non-Overlap Gate Drives
s Available in SSOP and SO Packages
U
APPLICATIO S
s Step-Down and Inverting Regulators
s Notebook and Palmtop Computers
s Portable Instruments
s Battery-Operated Digital Devices
s Industrial Power Distribution
s Avionics Systems
s Telecom Power Supplies
DESCRIPTIO
The LTC®1159 series is a family of synchronous step-down
switching regulator controllers featuring automatic Burst
ModeTM operation to maintain high efficiencies at low
output currents. These devices drive external complemen-
tary power MOSFETs at switching frequencies up to 250kHz
using a constant off-time current-mode architecture.
A separate pin and on-board switch allow the MOSFET
driver power to be derived from the regulated output
voltage providing significant efficiency improvement when
operating at high input voltages. The constant off-time
current-mode architecture maintains constant ripple cur-
rent in the inductor and provides excellent line and load
transient response. The output current level is user pro-
grammable via an external current sense resistor.
The LTC1159 automatically switches to power saving
Burst Mode operation when load current drops below
approximately 15% of maximum current. Standby current
is only 300µA while still regulating the output and shut-
down current is a low 20µA.
, LTC and LT are registered trademarks of Linear Technology Corporation.
Burst Mode is a trademark of Linear Technology Corporation.
TYPICAL APPLICATIO
+
3.3µF
0.15µF
VIN
CAP P-GATE
VCC
VCC P-DRIVE
EXTVCC
LTC1159-5
0V = NORMAL
>2V = SHUTDOWN
3300pF
1k
CT
300pF
SHDN1
SHDN2
ITH
CT
S-GND
SENSE +
SENSE –
N-GATE
P-GND
VIN
1N4148
0.1µF
Si9435DY
+ CIN
100µF
100V
D1
MBRS140T3
L*
33µH
RSENSE
1 0.05Ω 2
34
VOUT
5V/2A
0.01µF
Si9410DY
+ COUT
220µF
LTC1159 • F01
*COILTRONICS CTX33-4-MP
Figure 1. High Efficiency Step-Down Regulator
LTC1159-5 Efficiency
100
FIGURE 1 CIRCUIT
VIN = 10V
90
VIN = 20V
80
70
60
0.02
0.2
LOAD CURRENT (A)
2
LTC1159 • TA01
1
1 page  
TYPICAL PERFOR A CE CHARACTERISTICS
LTC1159
LTC1159-3.3/LTC1159-5
EXTVCC Switch Drop
600
500
400
300
200
100
0
0 5 10 15 20
SWITCH CURRENT (mA)
LTC1159 • TPC07
Off-Time vs VOUT
80
70
60
50
40
30
20
10
0
0
LTC1159-3.3
LTC1159-5
1234
OUTPUT VOLTAGE (V)
5
LTC1159 • TPC08
Current Sense Threshold Voltage
160
140 MAXIMUM
THRESHOLD
120
100
80
60
40 MINIMUM
THRESHOLD
20
0
0 20 40 60 80 100
TEMPERATURE (°C)
LTC1159 • TPC09
PI FU CTIO S
VIN: Main Supply Input Pin.
SGND: Small-Signal Ground. Must be routed separately
from other grounds to the (–) terminal of COUT.
PGND: Driver Power Grounds. Connect to source of N-
channel MOSFET and the (–) terminal of CIN.
VCC: Outputs of internal 4.5V linear regulator, EXTVCC
switch, and supply inputs for driver and control circuits.
The driver and control circuits are powered from the higher
of the 4.5V regulator or EXTVCC voltage. Must be closely
decoupled to power ground.
CT: External capacitor CT from this pin to ground sets the
operating frequency. (The frequency is also dependent on
the ratio VOUT/VIN.)
ITH: Gain Amplifier Decoupling Point. The current com-
parator threshold increases with the ITH pin voltage.
VFB: For the LTC1159 adjustable version, the VFB pin
receives the feedback voltage from an external resistive
divider used to set the output voltage.
SENSE–: Connects to internal resistive divider which sets
the output voltage in fixed output versions. The SENSE– pin
is also the (–) input of the current comparator.
SENSE+: The (+) Input for the Current Comparator. A built-
in offset between the SENSE+ and SENSE– pins, in conjunc-
tion with RSENSE, sets the current trip threshold.
N-Gate: High Current Drive for the Bottom N-Channel
MOSFET. The N-Gate pin swings from ground to VCC.
P-Gate: Level-Shifted Gate Drive Signal for the Top
P-Channel MOSFET. The voltage swing at the P-gate pin is
from VIN to VIN – VCC.
P-Drive: High Current Gate Drive for the Top P-Channel
MOSFET. The P-drive pin(s) swing(s) from VCC to ground.
CAP: Charge Compensation Pin. A capacitor to VCC pro-
vides charge required by the P-gate level-shift capacitor
during supply transitions. The charge compensation ca-
pacitor must be larger than the gate drive capacitor.
SHDN1: This pin shuts down the control circuitry only (VCC
is not affected). Taking SHDN1 pin high turns off the
control circuitry and holds both MOSFETs off. This pin
must be at ground potential for normal operation.
SHDN2: Master Shutdown Pin. Taking SHDN2 high shuts
down VCC and all control circuitry.
5
5 Page 
LTC1159
LTC1159-3.3/LTC1159-5
APPLICATIO S I FOR ATIO
discharged bypass capacitors are effectively put in parallel
with COUT, causing a rapid drop in VOUT. No regulator can
deliver enough current to prevent this problem if the load
switch resistance is low and it is driven quickly. The only
solution is to limit the rise time of the switch drive so that
the load rise time is limited to approximately 25 • CLOAD.
Thus a 10µF capacitor would require a 250µs rise time,
limiting the charging current to about 200mA.
Line Transient Response
The LTC1159 has better than 60dB line rejection and is
generally impervious to large positive or negative line
voltage transients. However, one rarely occurring condi-
tion can cause the output voltage to overshoot if the proper
precautions are not observed. This condition is a negative
VIN transition of several volts followed within 100µs by a
positive transition of greater than 0.5V/µs slew rate.
The reason this condition rarely occurs is because it takes
tens of amps to slew the regulator input capacitor at this
rate! The solution is to add a diode between the cap and VIN
pins of the LTC1159 as shown in several of the typical
application circuits. If you think your system could have
this problem, add the diode. Note that in surface mount
applications it can be combined with the P-gate diode by
using a low cost common cathode dual diode.
EXTVCC Pin Connection
The LTC1159 contains an internal PNP switch connected
between the EXTVCC and VCC pins. The switch closes and
supplies the VCC power whenever the EXTVCC pin is higher
in voltage than the 4.5V internal regulator. This allows the
VIN
VIN
P-GATE
P-DRIVE
LTC1159-3.3
N-GATE
P-GND
EXTVCC
+
CIN
BAT85
P-CH
L
1:1 •
+
1µF
1 RSENSE 2
•3
4
N-CH
+
COUT
VOUT
LTC1159 • F05a
MOSFET driver and control power to be derived from the
output during normal operation and from the internal
regulator when the output is out of regulation (start-up,
short circuit).
Significant efficiency gains can be realized by powering VCC
from the output, since the VIN current resulting from the
driver and control currents will be scaled by a factor of
(Duty Cycle)/(Efficiency). For 5V regulators this simply
means connecting the EXTVCC pin directly to VOUT. How-
ever, for 3.3V and other low voltage regulators, additional
circuitry is required to derive VCC power from the output.
The following list summarizes the four possible connec-
tions for EXTVCC:
1. EXTVCC Left Open. This will cause VCC to be powered
only from the internal 4.5V regulator resulting in reduced
MOSFET gate drive levels and an efficiency penalty of up to
10% at high input voltages.
2. EXTVCC Connected Directly to VOUT. This is the normal
connection for a 5V regulator and provides the highest
efficiency.
3. EXTVCC Connected to an Output-Derived Boost Net-
work. For 3.3V and other low voltage regulators, efficiency
gains can still be realized by connecting EXTVCC to an
output-derived voltage which has been boosted to greater
than 4.5V. This can be done either with the inductive boost
winding shown in Figure 5a or the capacitive charge pump
shown in Figure 5b. The charge pump has the advantage of
simple magnetics and generally provides the highest effi-
ciency at the expense of a slightly higher parts count.
VIN
VIN
P-GATE
P-DRIVE
LTC1159-3.3
N-GATE
P-GND
EXTVCC +
+
P-CH
CIN
L
RSENSE
N-CH
VN2222LL
BAT85
+
BAT85 0.22µF
BAT85
1µF
LTC1159 • F05b
VOUT
COUT
Figure 5a. Inductive Boost Circuit for EXTVCC
Figure 5b. Capacitive Charge Pump for EXTVCC
11
11 Page | ||
| Páginas | Total 20 Páginas | |
| PDF Descargar | [ Datasheet LTC1159.PDF ] | |
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