LT3473/LT3473A
Micropower 1A Boost
Converter with Schottky
and Output Disconnect
FEATURES
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■
DESCRIPTIO
■
■
■
■
■
■
■
■
■
■
■
■
■
Tiny Solution Size
Low Quiescent Current:
150µA in Active Mode (V
IN
= 3.6V, V
OUT
= 15V,
No Load)
1µA in Shutdown Mode
Internal 1A, 36V Switch
Integrated Schottky Diode
Integrated PNP Output Disconnect
Internal Reference Override Pin
PGOOD Pin
25V at 80mA from 3.6V Input
Auxiliary NPNs for Intermediate
Bias Voltages (LT3473A)
Automatic Burst Mode
®
Operation at Light Load
Constant Switching Frequency: 1.2MHz
Thermal Shutdown
Input Range: 2.2V to 16V
Low Profile (3mm
×
3mm) DFN Package (LT3473)
Low Profile (4mm
×
3mm) DFN Package (LT3473A)
The LT
®
3473/LT3473A are micropower step-up DC/DC
converters with integrated Schottky diode and output
disconnect circuitry in low profile DFN packages. The
small package size, high level of integration and the use of
tiny SMT components yield a solution size of less than
50mm
2
. The internal 1A switch allows the device to deliver
25V at up to 80mA from a Li-Ion cell, while automatic Burst
Mode operation maintains efficiency at light load. An
auxiliary reference input (CTRL) allows the user to over-
ride the internal 1.25V feedback reference with any lower
value, allowing full control of the output voltage during
operation. A PGOOD pin sinks current when the output
voltage reaches 90% of final value.
The LT3473A includes two NPN transistors for generating
intermediate bias voltages from the output and is offered
in a 12-lead (4mm
×
3mm) DFN package. The LT3473
does not include these NPNs and is offered in an 8-lead
(3mm
×
3mm) package.
The rugged 36V switch and output disconnect circuitry
allow outputs up to 34V to be easily generated in a simple
boost topology.
, LTC and LT are registered trademarks of Linear Technology Corporation.
Burst Mode is a registered trademark of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
APPLICATIO S
■
■
OLED Bias
CCD Bias
TYPICAL APPLICATIO
PGOOD
CTRL
V
IN
3V TO 4.2V
6.8µH
SW
V
IN
SHDN
4.7µF
GND
LT3473
Conversion Efficiency and Power Loss vs Output Current
80
V
OUT
25V
2.2µF 80mA
V
IN
= 3.6V
V
OUT
= 15V
OUT
75
EFFICIENCY (%)
70
CAP
2M
FB
100k
3473 TA01a
65
0.47µF
60
55
0.1
U
500
400
POWER LOSS (mW)
U
U
300
200
100
10
1
OUTPUT CURRENT (mA)
0
100
3473 TA01b
3473f
1
LT3473/LT3473A
ABSOLUTE
AXI U
RATI GS
(Note 1)
CTRL Voltage .......................................................... 10V
NB1, NB2 Voltage ................................................... 36V
NE1, NE2 Voltage ................................................... 36V
Maximum Junction Temperature ......................... 125°C
Operating Temperature Range (Note 2) .. – 40°C to 85°C
Storage Temperature Range ................ – 65°C to 125°C
V
IN
Voltage ............................................................. 16V
SHDN Voltage .......................................................... 16V
SW Voltage ............................................................. 36V
PGOOD Voltage ...................................................... 36V
CAP Voltage ............................................................ 36V
OUT Voltage ........................................................... 36V
FB Voltage .............................................................. 10V
PACKAGE/ORDER I FOR ATIO
TOP VIEW
CAP 1
OUT 2
CTRL 3
FB 4
9
8
7
6
5
SW
V
IN
SHDN
PGOOD
ORDER PART
NUMBER
LT3473EDD
DD PACKAGE
8-LEAD (3mm
×
3mm) PLASTIC DFN
T
JMAX
= 125°C,
θ
JA
= 43°C/ W
EXPOSED PAD (PIN 9) IS GND
MUST BE SOLDERED TO PCB (NOTE 3)
DD PART MARKING
LBJJ
Consult LTC Marketing for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS
The
●
denotes specifications which apply over the full operating temperature range, otherwise specifications are T
A
= 25°C.
V
IN
= 3V, SHDN = 3V, CTRL = 2V, unless otherwise specified.
PARAMETER
Minimum Operation Voltage
Maximum Operation Voltage
Supply Current
SHDN Voltage to Enable Chip
SHDN Voltage to Disable Chip
SHDN Pin Bias Current
FB Voltage
FB Voltage Line Regulation
FB Pin Bias Current
CTRL to FB Offset
CTRL Pin Bias Current
FB Threshold for PGOOD
PGOOD Current Capacity
3V < V
IN
< 16V
FB = 1.27V
CTRL = 0.5V
CTRL = 1V
CTRL = 2V
CTRL = 0.5V
●
●
CONDITIONS
SHDN = 3V, Not Switching
SHDN = 0V
●
●
2
U
U
W
W W
U
W
TOP VIEW
CAP
OUT
NB1
NE1
NB2
NE2
1
2
3
4
5
6
13
12 SW
11 V
IN
10 SHDN
9
8
7
PGOOD
CTRL
FB
ORDER PART
NUMBER
LT3473AEDE
DE PART MARKING
3473A
DE PACKAGE
12-LEAD (4mm
×
3mm) PLASTIC DFN
T
JMAX
= 125°C,
θ
JA
= 43°C/ W
EXPOSED PAD (PIN 13) IS GND
MUST BE SOLDERED TO PCB (NOTE 3)
MIN
2.2
TYP
MAX
16
UNITS
V
V
µA
µA
V
V
µA
V
%/V
nA
100
0.1
1.4
1
0.2
2
1.235
1.25
0.01
20
5
50
1.15
0.40
100
20
1.26
mV
nA
V
V
µA
3473f
LT3473/LT3473A
ELECTRICAL CHARACTERISTICS
The
●
denotes specifications which apply over the full operating temperature range, otherwise specifications are T
A
= 25°C.
V
IN
= 3V, SHDN = 3V, CTRL = 2V, unless otherwise specified.
PARAMETER
Switching Frequency
Maximum Duty Cycle
Switch Current Limit
Switch V
CESAT
Switch Leakage Current
Schottky Forward Drop
Schottky Leakage Current
Disconnect PNP Voltage Drop
Disconnect PNP Quiescent Current
Disconnect PNP Leakage Current
LTC3473A Only
NPN1 Voltage Drop
NPN1 Beta
NPN2 Voltage Drop
NPN2 Beta
INE1 = 1mA
INE1 = 1mA
INE2 = 1mA
INE2 = 1mA
60
Note 3:
Failure to correctly solder the Exposed Pad of the package to the
PC board will result in a thermal resistance much higher than 40°C.
60
0.8
V
0.8
V
I
SW
= 100mA
V
SW
= 5V
I
D
= 100mA
CAP = 36V, SW = 0V
I
OUT
= 100µA, CAP = 20V
I
OUT
= 50mA, CAP = 20V
CAP = 20V
SHDN = OUT = 0V, CAP = 20V
80
250
1.2
0.01
0.1
●
●
CONDITIONS
MIN
0.9
88
1.2
TYP
1.2
92
45
0.1
0.45
MAX
1.4
UNITS
MHz
%
A
mV
5
4
µA
V
µA
mV
mV
µA
µA
Note 1:
Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2:
The LT3473EDD and LT3473AEDE are 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.
TYPICAL PERFOR A CE CHARACTERISTICS
Load Regulation (Feedback Taken
from CAP)
20.20
20.00
FEEDBACK VOLTAGE (V)
V
IN
= 3.6V
CAP
VOLTAGE (V)
19.80
OUT
19.60
19.40
19.20
19.00
0
20
40
60
80
LOAD CURRENT (mA)
100
3473 G01
1.0
0.8
0.6
0.4
0.2
0
0
0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8
CTRL VOLTAGE (V)
2
PGOOD THRESHOLD VOLTAGE (V)
U W
T
A
= 25°C unless otherwise noted.
Feedback Voltage
1.4
1.2
PGOOD Threshold Voltage
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0
0
0.5
1
CTRL VOLTAGE (V)
3473 G03
1.5
2
3473 G02
3473f
3
LT3473/LT3473A
TYPICAL PERFOR A CE CHARACTERISTICS
T
A
= 25°C unless otherwise noted.
Sleep Mode Quiescent Current
105
SLEEP MODE QUIESCENT CURRENT (µA)
SLEEP MODE QUIESCENT CURRENT (µA)
SHDN = 3V
V
IN
= 3V
100
98
96
94
92
SHDN = 1.5V
90
88
SHDN PIN CURRENT (µA)
95
90
–50
0
50
TEMPERATURE (°C)
Switch V
CE(SAT)
450
SWITCH SATURATION VOLTAGE (mV)
400
350
300
250
200
150
100
50
0
0
200
400
600
800 1000
SWITCH CURRENT (mA)
1200
49
48
47
46
45
44
43
42
–50
0
50
100
3473 G08
SCHOTTKY FORWARD CURRENT (mA)
SWITCH SATURATION VOLTAGE (mV)
Schottky Forward Voltage
550
SCHOTTKY FORWARD VOLTAGE (mV)
I
D
= 100mA
500
VOLTAGE DROP (mV)
300
250
200
150
100
50
–45°C
SWITCHING FREQUENCY (MHz)
450
400
350
300
–50
50
0
TEMPERATURE (°C)
4
U W
3473 G04
3473 G07
Sleep Mode Quiescent Current
(Not Switching)
102
100
SHDN = 3V
2.0
2.5
SHDN Pin Current
SHDN = 3V
V
IN
= 3V
1.5
1.0
0.5
100
0
2
4
12
INPUT VOLTAGE, V
IN
(V)
6
8
10
14
16
0
–50
50
0
TEMPERATURE (°C)
100
3473 G06
3473 G5
Switch Saturation Voltage
50
I
SW
= 100mA
1000
900
800
700
600
500
400
300
200
100
0
Schottky I-V Characteristic
0
TEMPERATURE (°C)
200
600
800
400
SCHOTTKY FORWARD DROP (mV)
1000
3473 G09
Output Disconnect Voltage Drop
400
350
90°C
25°C
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0
Switching Frequency
0
100
3473 G10
0
20
80
COLLECTOR CURRENT (mA)
40
60
100
3473 G11
0
5
10
15
3473 G12
INPUT VOLTAGE, V
IN
(V)
3473f
LT3473/LT3473A
TYPICAL PERFOR A CE CHARACTERISTICS
T
A
= 25°C unless otherwise noted.
Disconnect PNP Quiescent Current
DISCONNECT PNP QUIESCENT CURRENT (µA)
1.4
1.2
0.9
0.8
0.7
SHDN VOLTAGE (V)
1.0
0.8
0.6
0.4
0.2
0
0
5
10
15
20
25
30
35
40
CAP VOLTAGE (V)
3473 G13
0.5
0.4
0.3
0.2
0.1
0
0
80
20
60
40
OUTPUT CURRENT (mA)
100
3473 G14
NPN V
BE
(V)
PI FU CTIO S
(LT3473/LT3473A)
CAP (Pin 1/Pin 1):
Internal Output Voltage. This pin is the
Schottky cathode and disconnect PNP emitter. Connect
output capacitor here.
OUT (Pin 2/Pin 2):
Output of Disconnect Circuit. Bypass
this pin with capacitor to ground.
CTRL (Pin 3/Pin 8):
External Reference Pin. This pin sets
the FB voltage externally between 0V and 1.25V. Tie this
pin 1.5V or higher to use the internal 1.25V reference.
FB (Pin 4/Pin 7):
Feedback Pin. Pin voltage is regulated to
1.25V if internal reference is used or to the CTRL pin
voltage if the CTRL pin voltage is between 0V and 1.25V.
Connect the feedback resistor divider to this pin. The
output voltage is regulated to:
⎛
R2
⎞
V
OUT
=
V
REF
•
⎜
+
1
⎟
⎝
R1
⎠
PGOOD (Pin 5/Pin 9):
Power Good Output. Open collector
logic output that starts to sink current when FB reaches
within 100mV of the reference voltage.
SHDN (Pin 6/Pin 10):
Shutdown Pin. Connect to 1.4V or
higher to enable device; 0.2V or less to disable device. Also
functions as soft-start. Use RC filter as shown in Figure 4.
V
IN
(Pin 7/Pin 11):
Input Supply Pin. Must be locally
bypassed with a X5R or X7R type ceramic capacitor.
SW (Pin 8/Pin 12):
Switch Pin. Connect inductor here.
Minimize the metal trace area connected to the pin to
minimize EMI.
Exposed Pad (Pin 9/Pin 13):
Ground. Solder directly to
PCB ground plane through multiple vias under the pack-
age for optimum thermal performance.
LT3473A Only
NB1 (Pin 3):
NPN1 Base.
NE1 (Pin 4):
NPN1 Emitter.
NB2 (Pin 5):
NPN2 Base.
NE2 (Pin 6):
NPN2 Emitter.
U W
SHDN Voltage to Turn-On
Disconnect PNP
1.00
0.95
0.90
0.85
0.80
0.75
Auxiliary NPN V
BE
0.6
I
E
= 1mA
0.70
0.65
0.60
0.55
I
E
= 100µA
0.50
–50
50
0
TEMPERATURE (°C)
100
3473 G15
U
U
U
3473f
5
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