FEATURES
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LT3487
Boost and Inverting
Switching Regulator
for CCD Bias
DESCRIPTIO
The LT
®
3487 dual channel switching regulator generates
positive and negative outputs for biasing CCD imagers.
The device delivers up to –8V at 90mA and 15V at 45mA
from a lithium-ion cell, providing bias for many popular
CCD imagers. The boost regulator incorporates output
disconnect technology to eliminate the DC current path
from V
IN
to the output load that is present in standard
boost configurations. The 2MHz switching frequency
allows CCD solutions using tiny, low profile capacitors
and inductors and generates low noise outputs that are
easy to filter. Schottky diodes are internal and the output
voltages are set with one resistor per channel, reducing
the external component count.
Intelligent soft-start allows sequential soft-start of the two
channels with a single capacitor. The soft-start is sequenced
such that the output ramp of the negative channel begins
after the ramp of the positive channel. Internal sequencing
circuitry also disables the negative channel until the positive
channel has reached 87% of its final value, ensuring that
the sum of the two outputs is always positive.
The LT3487 is available in a 10-pin 3mm
×
3mm DFN
package.
Generates 15V at 45mA, –8V at 90mA from a
Li-Ion Cell
Output Disconnect
Sequencing: Positive Output Reaches Regulation
Before Negative Channel Begins Switching
Internal Schottky Diodes
2MHz Constant Switching Frequency
Requires Only One Resistor per Channel to Set
Output Voltages
V
IN
Range: 2.3V to 16V
Output Voltage Up to 28V
Short-Circuit Robust
Capacitor Programmable Soft-Start
Separate V
BAT
Pin Allows Separate Sources for
Power and Control Circuitry
Available in 10-Lead (3mm
×
3mm) DFN Package
APPLICATIO S
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CCD Bias
TFT LCD Bias
OLED Bias
±Rail Generation for Op Amps
, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
TYPICAL APPLICATIO
2.2µF
V
IN
3V TO 12V
1µF
DN
47pF
15µH
V
NEG
–8V
90mA
22µF
FBN
324k
RUN/SS
100nF
RUN/SS
SWN
V
IN
15µH
10µH
V
BAT
SWP
70
EFFICIENCY (%)
CAP
549k
FBP
4.7µF
100nF
65
60
55
50
V
POS
V
POS
15V
45mA
45
40
V
IN
= 3.6V
0
20
40
80
60
LOAD CURRENT (mA)
100
3487 TA01b
LT3487
GND
3487 TA01a
U
U
U
Conversion Efficiency
80
75
POS CHANNEL AT CAP
POS CHANNEL
AT V
POS
NEG CHANNEL
3487f
1
LT3487
ABSOLUTE
(Note 1)
AXI U RATI GS
PACKAGE/ORDER I FOR ATIO
TOP VIEW
CAP
SWP
V
BAT
SWN
DN
1
2
3
4
5
11
10 V
POS
9 FBP
8 RUN/SS
7 FBN
6 V
IN
V
IN
Voltage ............................................................... 16V
V
BAT
Voltage ............................................................. 16V
SWP, SWN Voltage................................................... 32V
CAP, V
POS
.................................................................30V
DN Voltage ............................................................. –32V
RUN/SS Voltage ..........................................................8V
FBP Voltage................................................................ 6V
FBN Voltage ................................................ –0.2V to 6V
Maximum Junction Temperature .......................... 125°C
Operating Temperature Range ................. –40°C to 85°C
Storage Temperature Range................... –65°C to 125°C
DD PACKAGE
10-LEAD (3mm
×
3mm) PLASTIC DFN
θ
JA
= 43°C/W,
θ
JC
= 3°C/W
EXPOSED PAD (PIN 11) IS GND, MUST BE CONNECTED TO PCB
ORDER PART NUMBER
LT3487EDD
DD PART MARKING
LBXB
Order Options
Tape and Reel: Add #TR
Lead Free: Add #PBF Lead Free Tape and Reel: Add #TRPBF
Lead Free Part Marking:
http://www.linear.com/leadfree/
Consult LTC Marketing for parts specified with wider operating temperature ranges.
The
●
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= 3.6V, V
BAT
= 3.6V, unless otherwise noted.
PARAMETER
Operating Voltage Range
Quiescent Current
RUN/SS Voltage Threshold (Full Current)
RUN/SS Voltage Threshold (Shutdown)
RUN/SS Pin Current
FBP (Positive Channel) Pin Voltage
FBN (Negative Channel) Pin Voltage
FBP Pin Voltage Line Regulation
FBN Pin Voltage Line Regulation
FBP Pin Bias Current
FBN Pin Bias Current
FBP Threshold (Percent of Final Value)
to Start Negative Channel
Switching Frequency
Maximum Duty Cycle
Positive Channel Switch Current Limit
Negative Channel Switch Current Limit
Positive Channel V
CESAT
Negative Channel V
CESAT
(Note 5)
(Note 5)
I
SWP
= 400mA
I
SWN
= 600mA
●
●
●
●
●
ELECTRICAL CHARACTERISTICS
CONDITIONS
RUN/SS = 3V, Not Switching
RUN/SS = 0V
(Note 3)
●
MIN
2.3
TYP
3.7
5.3
MAX
16
5
8
1.6
UNITS
V
mA
µA
V
mV
µA
V
mV
%/V
mV/V
100
1
1.19
–7
160
1.4
1.23
3
0.007
0.001
2
1.27
12
RUN/SS = 0V (Note 4)
●
●
24.4
24.4
25
25
87
25.6
25.6
90
2.15
1.85
87
750
900
2
93
920
1090
280
340
3487f
2
U
µA
µA
%
MHz
%
mA
mA
mV
mV
W
U
U
W W
W
LT3487
ELECTRICAL CHARACTERISTICS
PARAMETER
Schottky DP Forward Drop
Schottky DN Forward Drop
Disconnect PNP V
CE
Disconnect Current Limit
V
CAP
– V
BAT
to Disconnect
Disconnect Leakage
The
●
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= 3.6V, V
BAT
= 3.6V, unless otherwise noted.
CONDITIONS
I
SWP
= 400mA
I
SWN
= 600mA
I
VPOS
= 50mA
V
CAP
= 15V, V
POS
= 0V
V
BAT
= 3.6V, V
POS
= 0V, I
CAP
< 100µA
V
BAT
= 3.6V, CAP = 3.6V, V
POS
= 0V
100
MIN
TYP
1045
980
205
155
1.2
0.1
1.6
1.0
MAX
UNITS
mV
mV
mV
mA
V
µA
Note 1:
Stresses beyond those listed under Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to any Absolute
Maximum Rating condition for extended periods may affect device
reliability and lifetime.
Note 2:
The LT3487E is guaranteed to meet specified performance from
0°C to 85°C. Specifications over the –40°C to 85°C operating range are
assured by design, characterization and correlation with statistical process
controls.
Note 3:
Guaranteed by design, not directly tested.
Note 4:
Current flows out of pin.
Note 5:
Current limit guaranteed by design and/or correlation to static test.
Slope compensation reduces current limit at higher duty cycle.
TYPICAL PERFOR A CE CHARACTERISTICS
Shutdown Quiescent Current
10
PERCENTAGE OF FINAL FBP VOLTAGE (%)
100
QUIESCENT CURRENT (µA)
8
4
70
2
60
0
–50 –25
50
25
0
75
TEMPERATURE (°C)
100
125
50
–50
–25
50
25
0
75
TEMPERATURE (°C)
100
125
V
FBP
(V)
6
U W
3487 G01
Positive Output to Enable Inverter
1.300
FBP Voltage
90
1.275
80
1.250
1.225
1.200
–50
–25
75
0
25
50
TEMPERATURE (°C)
100
125
3487 G02
3487 G03
3487f
3
LT3487
TYPICAL PERFOR A CE CHARACTERISTICS
FBN Voltage
10.0
7.5
5.0
V
FBN
(mV)
2.5
0
–2.5
–5.0
–7.5
–10.0
–50 –25
0
50
75
25
TEMPERATURE (°C)
100
125
24.0
–50
24.0
–50
24.5
24.5
I
FBP
(µA)
I
FBN
(µA)
25.0
25.0
25.5
25.5
26.0
Positive Channel Switch V
CE(SAT)
NEGATIVE SWITCH SATURATION VOLTAGE (mV)
POSITIVE SWITCH SATURATION VOLTAGE (mV)
500
500
POSITIVE SCHOTTKY FORWARD CURRENT (mA)
400
300
200
100
0
0
100
200
300
400
500
SWITCH CURRENT (mA)
Negative Channel Schottky I-V
Characteristic
NEGATIVE SCHOTTKY FORWARD CURRENT (mA)
800
700
600
500
400
300
200
100
0
600 650 700 750 800 850 900 950 1000
SCHOTTKY FORWARD DROP (mV)
3487 G10
V
CAP
– V
POS
(mV)
I
CAP
(mA)
4
U W
3487 G04
FBP Bias Current
26.0
FBN Bias Current
–25
75
0
25
50
TEMPERATURE (°C)
100
125
–25
75
0
25
50
TEMPERATURE (°C)
100
125
3487 G05
3487 G06
Negative Channel Switch V
CE(SAT)
600
500
400
300
200
100
Positive Channel Schottky I-V
Characteristic
400
300
200
100
0
0 100 200 300 400 500 600 700 800 900
SWITCH CURRENT (mA)
3487 G08
600
0
600 650 700 750 800 850 900 950 1000
SCHOTTKY FORWARD DROP (mV)
3487 G09
3487 G07
Output Disconnect Voltage Drop
(50mA Load)
300
140
120
250
100
80
60
40
20
100
–50
0
Maximum Disconnect Current
V
CAP
– V
POS
= 500mV
T
A
= 25°C
200
150
–25
75
0
25
50
TEMPERATURE (°C)
100
125
0
2.5
5
7.5
10
12.5
3487 G20
V
CAP
– V
BAT
(V)
3487 G11
3487f
LT3487
TYPICAL PERFOR A CE CHARACTERISTICS
Output Disconnect Current Limit
200
V
CAP
= 15V
V
BAT
= 3.6V
V
POS
= 0V
CURRENT LIMITS (mA)
1200
1150
NEG CHANNEL
1100
1050
1000
950
900
850
100
–50
–25
75
0
25
50
TEMPERATURE (°C)
100
125
800
–50 –25
0
50
75
25
TEMPERATURE (°C)
100
125
POS CHANNEL
CURRENT LIMITS (mA)
CURRENT LIMIT (mA)
175
150
125
Switch Current Limits vs RUN/SS
Voltage (at 55% Duty Cycle)
1000
NEG CHANNEL
3.0
2.5
P0S CHANNEL
600
I
RUN/SS
(µA)
2.0
1.5
1.0
200
0.5
RUN/SS PIN CURRENT (µA)
800
CURRENT LIMITS (mA)
400
0
0
250
500
750 1000
RUN/SS (mV)
UVLO Voltage
2.5
300
250
200
150
100
2.1
50
2.4
V
RUN/SS
(mV)
UVLO (V)
2.3
2.2
2.0
–50
–25
50
25
0
75
TEMPERATURE (°C)
U W
3487 G12
Switch Current Limits
1200
1000
800
Switch Current Limits
vs Duty Cycle
NEG CHANNEL
P0S CHANNEL
600
400
200
0
0
20
40
60
DUTY CYCLE (%)
80
100
3487 G14
3487 G13
RUN/SS Pin Current in Shutdown
2.0
RUN/SS Pin Current
vs V
IN
in Shutdown
1.5
1.0
0.5
1250
1500
0
–50 –25
0
50
25
75
0
TEMPERATURE (°C)
100
125
2
4
6
8
10
V
IN
(V)
12
14
16
3487 G15
3487 G16
3487 G17
RUN/SS Shutdown Threshold
100
125
0
–50 –25
50
25
75
0
TEMPERATURE (°C)
100
125
3487 G18
3487 G19
3487f
5
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