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PDF LT1934-1 Data sheet ( Hoja de datos )
| Número de pieza | LT1934-1 | |
| Descripción | Micropower Step-Down Switching Regulators in ThinSOT | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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FEATURES
s Wide Input Voltage Range: 3.2V to 34V
s Micropower Operation: IQ = 12µA
s 5V at 250mA from 6.5V to 34V Input (LT1934)
s 5V at 60mA from 6.5V to 34V Input (LT1934-1)
s 3.3V at 250mA from 4.5V to 34V Input (LT1934)
s 3.3V at 60mA from 4.5V to 34V Input (LT1934-1)
s Low Shutdown Current: <1µA
s Low VCESAT Switch: 200mV at 300mA
s Low Profile (1mm) SOT-23 (ThinSOTTM) Package
U
APPLICATIO S
s Wall Transformer Regulation
s Automotive Battery Regulation
s Standby Power for Portable Products
s Distributed Supply Regulation
s Industrial Control Supplies
LT19w3ww4.D/atLaTSh1ee9t4U3.c4om-1
Micropower Step-Down
Switching Regulators
in ThinSOT
DESCRIPTIO
The LT®1934 is a micropower step-down DC/DC con-
verter with internal 400mA power switch, packaged in a
low profile (1mm) ThinSOT. With its wide input range of
3.2V to 34V, the LT1934 can regulate a wide variety of
power sources, from 4-cell alkaline batteries and 5V logic
rails to unregulated wall transformers and lead-acid bat-
teries. Quiescent current is just 12µA and a zero current
shutdown mode disconnects the load from the input
source, simplifying power management in battery-pow-
ered systems. Burst Mode® operation and the low drop
internal power switch result in high efficiency over a broad
range of load current.
The LT1934 provides up to 300mA of output current. The
LT1934-1 has a lower current limit, allowing optimum
choice of external components when the required output
current is less than 60mA. Fast current limiting protects
the LT1934 and external components against shorted
outputs, even at 34V input.
, LTC and LT are registered trademarks of Linear Technology Corporation.
Burst Mode is a registered trademark of Linear Technology Corporation.
ThinSOT is a trademark of Linear Technology Corporation.
TYPICAL APPLICATIO
3.3V Step-Down Converter
D2
VIN
4.5V TO 34V
C2
2.2µF
ON OFF
BOOST
VIN SW
LT1934
SHDN
FB
GND
0.22µF L1
47µH
D1
10pF 1M +
604k
VOUT
3.3V
250mA
C1
100µF
C1: SANYO 4TPB100M
C2: TAIYO YUDEN GMK325BJ225MN
D1: ON SEMICONDUCTOR MBR0540
D2: CENTRAL CMDSH-3
L1: SUMIDA CDRH4D28-470
1934 TA01
100
LT1934
VIN = 12V
90
80
70
Efficiency
VOUT = 5V
VOUT = 3.3V
60
50
0.1
1 10 100
LOAD CURRENT (mA)
1934 TA02
1934f
1
1 page  
LT19w3ww4.D/atLaTSh1ee9t4U3.c4om-1
PI FU CTIO S
BOOST (Pin 1): The BOOST pin is used to provide a drive
voltage, higher than the input voltage, to the internal
bipolar NPN power switch.
GND (Pin 2): Tie the GND pin to a local ground plane below
the LT1934 and the circuit components. Return the feed-
back divider to this pin.
FB (Pin 3): The LT1934 regulates its feedback pin to 1.25V.
Connect the feedback resistor divider tap to this pin. Set
the output voltage according to VOUT = 1.25V (1 + R1/R2)
or R1 = R2 (VOUT/1.25 – 1).
SHDN (Pin 4): The SHDN pin is used to put the LT1934 in
shutdown mode. Tie to ground to shut down the LT1934.
Apply 2.3V or more for normal operation. If the shutdown
feature is not used, tie this pin to the VIN pin.
VIN (Pin 5): The VIN pin supplies current to the LT1934’s
internal regulator and to the internal power switch. This
pin must be locally bypassed.
SW (Pin 6): The SW pin is the output of the internal power
switch. Connect this pin to the inductor, catch diode and
boost capacitor.
BLOCK DIAGRA
VIN
5
VIN
+
C2
+
–
ON OFF
ON TIME
12µs DELAY
OFF TIME
1.8µs DELAY
R Q′
SQ
SHDN
4
VREF 1.25V
+
–
GND
2
FB
3
R2 R1
ENABLE
FEEDBACK
COMPARATOR
BOOST
1
SW
6
D2
C3
L1
D1
VOUT
C1
1934 BD
1934f
5
5 Page 
LT19w3ww4.D/atLaTSh1ee9t4U3.c4om-1
APPLICATIO S I FOR ATIO
Minimum Input Voltage VOUT = 3.3V
6.0
LT1934
VOUT = 3.3V
5.5 TA = 25°C
BOOST DIODE TIED TO OUTPUT
5.0
VIN TO START
4.5
4.0
VIN TO RUN
3.5
3.0
0.1
1 10 100
LOAD CURRENT (mA)
1934 G12
Minimum Input Voltage VOUT = 5V
8
LT1934
VOUT = 5V
TA = 25°C
7 BOOST DIODE TIED TO OUTPUT
VIN TO START
6
VIN TO RUN
5
VIN), then the LT1934’s internal circuitry will pull its
quiescent current through its SW pin. This is fine if your
system can tolerate a few mA in this state. If you ground
the SHDN pin, the SW pin current will drop to essentially
zero. However, if the VIN pin is grounded while the output
is held high, then parasitic diodes inside the LT1934 can
pull large currents from the output through the SW pin and
the VIN pin. Figure 4 shows a circuit that will run only when
the input voltage is present and that protects against a
shorted or reversed input.
D4
51
VIN VIN BOOST
LT1934
100k 4
6
SHDN
SW
GND FB
1M 2 3
VOUT
BACKUP
D4: MBR0530
1934 F07
Figure 4. Diode D4 Prevents a Shorted Input from Discharging
a Backup Battery Tied to the Output; It Also Protects the Circuit
from a Reversed Input. The LT1934 Runs Only When the Input
is Present
4
0.1 1
10 100
LOAD CURRENT (mA)
1934 G13
Figure 3. The Minimum Input Voltage Depends
on Output Voltage, Load Current and Boost Circuit
maximum duty cycle of the LT1934, requiring a higher
input voltage to maintain regulation.
Shorted Input Protection
If the inductor is chosen so that it won’t saturate exces-
sively, an LT1934 buck regulator will tolerate a shorted
output. There is another situation to consider in systems
where the output will be held high when the input to the
LT1934 is absent. This may occur in battery charging
applications or in battery backup systems where a battery
or some other supply is diode OR-ed with the LT1934’s
output. If the VIN pin is allowed to float and the SHDN pin
is held high (either by a logic signal or because it is tied to
PCB Layout
For proper operation and minimum EMI, care must be
taken during printed circuit board layout. Figure 5 shows
the high current paths in the buck regulator circuit. Note
that large, switched currents flow in the power switch, the
catch diode (D1) and the input capacitor (C2). The loop
formed by these components should be as small as
possible. Furthermore, the system ground should be tied
to the regulator ground in only one place; this prevents the
switched current from injecting noise into the system
ground. These components, along with the inductor and
output capacitor, should be placed on the same side of the
circuit board, and their connections should be made on
that layer. Place a local, unbroken ground plane below
these components, and tie this ground plane to system
ground at one location, ideally at the ground terminal of the
output capacitor C1. Additionally, the SW and BOOST
nodes should be kept as small as possible. Finally, keep
the FB node as small as possible so that the ground pin and
1934f
11
11 Page | ||
| Páginas | Total 20 Páginas | |
| PDF Descargar | [ Datasheet LT1934-1.PDF ] | |
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