LT1933
600mA, 500kHz Step-Down
Switching Regulator
in SOT-23
FEATURES
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DESCRIPTIO
Wide Input Range: 3.6V to 36V
5V at 600mA from 16V to 36V Input
3.3V at 600mA from 12V to 36V Input
5V at 500mA from 6.3V to 36V Input
3.3V at 500mA from 4.5V to 36V Input
Fixed Frequency 500kHz Operation
Uses Tiny Capacitors and Inductors
Soft-Start
Internally Compensated
Low Shutdown Current: <2µA
Output Adjustable Down to 1.25V
Low Profile (1mm) SOT-23 (ThinSOT™) Package
The LT
®
1933 is a current mode PWM step-down DC/DC
converter with an internal 0.75A power switch, packaged
in a tiny 6-lead SOT-23. The wide input range of 3.6V to
36V makes the LT1933 suitable for regulating power from
a wide variety of sources, including unregulated wall
transformers, 24V industrial supplies and automotive
batteries. Its high operating frequency allows the use of
tiny, low cost inductors and ceramic capacitors, resulting
in low, predictable output ripple.
Cycle-by-cycle current limit provides protection against
shorted outputs, and soft-start eliminates input current
surge during start up. The low current (<2µA) shutdown
provides output disconnect, enabling easy power man-
agement in battery-powered systems.
, LTC and LT are registered trademarks of Linear Technology Corporation.
ThinSOT is a trademark of Linear Technology Corporation.
APPLICATIO S
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Automotive Battery Regulation
Industrial Control Supplies
Wall Transformer Regulation
Distributed Supply Regulation
Battery-Powered Equipment
TYPICAL APPLICATIO
3.3V Step-Down Converter
1N4148
V
IN
4.5V TO 36V
V
IN
BOOST
LT1933
OFF ON
SHDN
GND
SW
FB
16.5k
2.2µF
10k
22µF
MBRM140
0.1µF
90
95
V
IN
= 12V
22µH
EFFICIENCY (%)
V
OUT
3.3V/500mA
85
V
OUT
= 3.3V
80
75
70
65
0
100
200
300
400
LOAD CURRENT (mA)
500
600
1933 TA01a
U
Efficiency
V
OUT
= 5V
1933 TA01b
U
U
1933f
1
LT1933
ABSOLUTE
(Note 1)
AXI U
RATI GS
PACKAGE/ORDER I FOR ATIO
ORDER PART
NUMBER
TOP VIEW
BOOST 1
GND 2
FB 3
6 SW
5 V
IN
4 SHDN
Input Voltage (V
IN
) ....................................– 0.4V to 36V
BOOST Pin Voltage .................................................. 43V
BOOST Pin Above SW Pin ....................................... 20V
SHDN Pin ..................................................– 0.4V to 36V
FB Voltage ...................................................– 0.4V to 6V
Operating Temperature Range (Note 2)
LT1933E ................................................. – 40°C to 85°C
LT1933I ................................................ – 40°C to 125°C
Maximum Junction Temperature .......................... 125°C
Storage Temperature Range ................. – 65°C to 150°C
Lead Temperature (Soldering, 10 sec).................. 300°C
LT1933ES6
LT1933IS6
S6 PART MARKING
LTAGN
LTAGP
S6 PACKAGE
6-LEAD PLASTIC TSOT-23
T
JMAX
= 125°C,
θ
JA
= 165°C/ W,
θ
JC
= 102°C/ W
Consult factory for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS
The
●
denotes specifications which apply over the full operating temperature range, otherwise specifications are at T
A
= 25°C.
V
IN
= 12V, V
BOOST
= 17V, unless otherwise noted. (Note 2)
PARAMETER
Undervoltage Lockout
Feedback Voltage
FB Pin Bias Current
Quiescent Current
Quiescent Current in Shutdown
Reference Line Regulation
Switching Frequency
Maximum Duty Cycle
Switch Current Limit
Switch V
CESAT
Switch Leakage Current
Minimum Boost Voltage Above Switch
BOOST Pin Current
SHDN Input Voltage High
SHDN Input Voltage Low
SHDN Bias Current
V
SHDN
= 2.3V (Note 5)
V
SHDN
= 0V
34
0.01
I
SW
= 400mA
I
SW
= 400mA
2.3
0.3
50
0.1
1.9
18
(Note 3)
I
SW
= 400mA
V
FB
= Measured V
REF
+ 10mV (Note 4)
Not Switching
V
SHDN
= 0V
V
IN
= 5V to 36V
V
FB
= 1.1V
V
FB
= 0V
●
●
●
CONDITIONS
MIN
1.225
TYP
3.35
1.245
40
1.6
0.01
0.01
MAX
3.6
1.265
120
2.5
2
600
UNITS
V
V
nA
mA
µA
%/V
kHz
kHz
%
A
400
88
0.75
500
55
94
1.05
370
500
2
2.3
25
Note 1:
Absolute Maximum Ratings are those values beyond which the life
of the device may be impaired.
Note 2:
The LT1933E is guaranteed to meet performance specifications
from 0°C to 70°C. Specifications over the –40°C to 85°C operating
temperature range are assured by design, characterization and correlation
with statistical process controls. The LT1933I specifications are
guaranteed over the –40°C to 125°C temperature range.
Note 3:
Current limit guaranteed by design and/or correlation to static test.
Slope compensation reduces current limit at higher duty cycle.
Note 4:
Current flows out of pin.
Note 5:
Current flows into pin.
2
U
mV
µA
V
mA
V
V
µA
µA
1933f
W
U
U
W W
W
LT1933
TYPICAL PERFOR A CE CHARACTERISTICS
Efficiency, V
OUT
= 5V
100
T
A
= 25°C
V
OUT
= 5V
V
IN
= 12V
100
90
EFFICIENCY (%)
90
V
IN
= 5V
V
IN
= 12V
V
IN
= 24V
SWITCH CURRENT LIMIT (mA)
EFFICIENCY (%)
80
V
IN
= 24V
70
D1 = MBRM140
L1 = Toko D53LCB 33µH
0
100
300
400
LOAD CURRENT (mA)
200
500
600
60
Maximum Load Current
800
T
A
= 25°C
V
OUT
= 5V
800
L = 22µH
600
L = 15µH
500
SWITCH VOLTAGE (mV)
LOAD CURRENT (mA)
LOAD CURRENT (mA)
700
L = 33µH
600
L = 22µH
500
400
0
5
15
20
10
INPUT VOLTAGE (V)
Feedback Voltage
1.260
1.255
FEEDBACK VOLTAGE (V)
3.6
1.250
1.245
1.240
3.2
1.235
1.230
–50 –25
3.0
–50 –25
SWITCHING FREQUENCY (kHz)
UVLO (V)
0
25
50
75
TEMPERATURE (°C)
U W
1933 G01
Efficiency, V
OUT
= 3.3V
T
A
= 25°C
V
OUT
= 3.3V
Switch Current Limit
1200
1000
800
600
400
200
0
T
A
= 25°C
TYPICAL
MINIMUM
80
70
D1 = MBRM140
L1 = Toko D53LCB 22µH
0
100
300
400
LOAD CURRENT (mA)
200
500
600
60
0
20
60
40
DUTY CYCLE (%)
80
100
1933 G03
1933 G02
Maximum Load Current
T
A
= 25°C
V
OUT
= 3.3V
Switch Voltage Drop
600
500
700
T
A
= 25°C
400
T
A
= 85°C
300
200
100
T
A
= –40°C
25
30
1933 G04
400
0
5
15
20
10
INPUT VOLTAGE (V)
0
25
30
1933 G05
0
0.1
0.2
0.4
0.3
SWITCH CURRENT (A)
0.5
0.6
1933 G06
Undervoltage Lockout
3.8
600
Switching Frequency
550
3.4
500
450
100
125
50
75
0
25
TEMPERATURE (°C)
100
125
400
–50 –25
50
75
0
25
TEMPERATURE (°C)
100
125
1933 G07
1933 G08
1933 G09
1933f
3
LT1933
TYPICAL PERFOR A CE CHARACTERISTICS
Frequency Foldback
700
600
T
A
= 25°C
1.4
1.2
SWITCHING FREQUENCY (kHz)
SWITCH CURRENT LIMIT (A)
SHDN PIN CURRENT (µA)
500
400
300
200
100
0
0.0
0.5
1.0
FB PIN VOLTAGE (V)
1.5
1933 G10
Typical Minimum Input Voltage
8
V
OUT
= 5V
T
A
= 25°C
L = 33µH
TO START
INPUT VOLTAGE (V)
7
TO START
5.0
4.5
4.0
3.5
TO RUN
SWITCH CURRENT LIMIT (A)
INPUT VOLTAGE (V)
6
TO RUN
5
4
1
10
100
LOAD CURRENT (mA)
1933 G13
Operating Waveforms
V
SW
10V/DIV
I
L
200mA/DIV
V
OUT
10mV/DIV
V
IN
= 12V, V
OUT
= 3.3V, I
OUT
= 400mA,
L = 22µH, C
OUT
= 22µF
4
U W
Soft-Start
T
A
= 25°C
DC = 30%
200
SHDN Pin Current
T
A
= 25°C
1.0
0.8
0.6
0.4
0.2
0
0
1
2
3
SHDN PIN VOLTAGE (V)
4
1933 G11
150
100
50
0
0
4
8
12
SHDN PIN VOLTAGE (V)
16
1933 G12
Typical Minimum Input Voltage
6.0
5.5
V
OUT
= 3.3V
T
A
= 25°C
L = 22µH
1.4
1.2
1.0
0.8
0.6
0.4
0.2
Switch Current Limit
3.0
1
10
100
LOAD CURRENT (mA)
1933 G14
0
–50 –25
0
25
50
75
TEMPERATURE (°C)
100
125
1933 G15
Operating Waveforms,
Discontinuous Mode
V
SW
10V/DIV
I
L
200mA/DIV
V
OUT
10mV/DIV
1933 G16
V
IN
= 12V, V
OUT
= 3.3V, I
OUT
= 20mA,
L = 22µH, C
OUT
= 22µF
1933 G16
1933f
LT1933
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 LT1933 and the circuit components. Return the feed-
back divider to this pin.
FB (Pin 3):
The LT1933 regulates its feedback pin to
1.245V. Connect the feedback resistor divider tap to this
pin. Set the output voltage according to V
OUT
= 1.245V
(1 + R1/R2). A good value for R2 is 10k.
SHDN (Pin 4):
The SHDN pin is used to put the LT1933 in
shutdown mode. Tie to ground to shut down the LT1933.
Tie to 2.3V or more for normal operation. If the shutdown
feature is not used, tie this pin to the V
IN
pin. SHDN also
provides a soft-start function; see the Applications Infor-
mation section.
V
IN
(Pin 5):
The V
IN
pin supplies current to the LT1933’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
V
IN
C2
5
V
IN
INT REG
AND
UVLO
ON OFF
R3
4
C4
SHDN
W
U
U
U
SLOPE
COMP
Σ
R
S
Q
BOOST
D2
1
C3
Q
DRIVER
Q1
SW
L1
6
D1
V
C
C1
V
OUT
OSC
FREQUENCY
FOLDBACK
g
m
1.245V
2
GND
R2
3
FB
R1
1933 BD
1933f
5
单片机
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