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DEMO MANUAL DC1956A
Description
LT3905
Boost DC/DC Converter with
APD Current Monitor
Demonstration circuit 1956A features the LT
®
3905, a boost
DC/DC Converter with APD current monitor that comes in
a 3mm × 3mm QFN package. This demo board is designed
to convert a 2.7V to 12V input to a 50V output at 2mA. The
LT3905 is equipped with indicators for monitoring APD
current, overload, and loss-of-signal (LOS) conditions,
which can easily be changed with their respective resis-
tors. In addition, the output voltage can be adjusted via the
CTRL pin. DC1956A is designed for 1MHz operation but
can also be programmed for 2MHz by moving jumper JP2.
For measuring fast transient response, use the installed
Fast Monitor Response Circuit on the bottom of the demo
board and install 0Ω resistors at R14 and R20. Also, remove
R11 and any other capacitances or probes across the APD
node. The transient response should be measured at the
TIA turret. For further information, read the APD Current
Monitor Transient Response section in the data sheet.
The internal LOS_MON comparator hysteresis is 20mV on
the rising edge of the LOS_MON voltage. For additional
hysteresis, use R6, R7, R15, and R21 as stated in the Loss
of Signal Hysteresis section in the data sheet.
L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear
Technology Corporation. All other trademarks are the property of their respective owners.
performance summary
The LT3905 data sheet gives a complete description of
the part, operation, and application information. The data
sheet must be read in conjunction with this Quick Start
Guide for the DC1956A.
Design files for this circuit board are available at
http://www.linear.com/demo/DC1956A
Specifications are at TA = 25°C
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
VIN Input Supply Range 2.7 12 V
VOUT Output Voltage Range VIN = 3.3V, IAPD = 1mA 48 50 52 V
fSW Switching Frequency JP2: 1MHz 0.9 1 1.1 MHz
ILOS Loss-of-Signal APD Current R10 = 1MΩ 12.5 µA
ILIM APD Current Limit R8 = 12.4kΩ 2 mA
VMON/IAPD MON Voltage to APD Current Ratio R11 = 4.99kΩ 1 mV/µA
IAPD (mA)
0
INPUT CURRENT (mA)
20
60
100
40
80
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DC1956A F01
20 0.5 1.5
VAPD = 50V
VIN = 3.3V
VIN = 5V
Figure 1. DC1956A Input Current vs APD Current
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DEMO MANUAL DC1956A
Quick start proceDure
Demonstration circuit 1956 is easy to set up to evaluate
the performance of the LT3905. Refer to Figure 2 for
proper measurement equipment setup and follow the
procedure below:
NOTE. When measuring the output voltage ripple, connect
a BNC cable from the oscilloscope to J1. Make sure there
are no other cables connected to the APD node.
1. Place jumpers in the following positions:
JP1: Run
JP2: 1MHz
2. With power off, connect the input power supply to VIN
and GND.
3. Turn on the power at the input.
NOTE: Make sure that the input voltage does not exceed
16V.
4. Connect a 50K resistor from APD to GND and check for
the proper output voltage. VOUT = APD = 48V to 52V.
NOTE: If there is no output, temporarily disconnect the
load to make sure that the load is not set too high.
5. Once the proper output voltages are established, adjust
the loads within the operating range and observe the
output voltage regulation, ripple voltage, efficiency and
other parameters.
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DEMO MANUAL DC1956A
Figure 2. Proper Measurement Equipment Setup
Quick start proceDure
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DEMO MANUAL DC1956A
parts List
ITEM QTY REFERENCE PART DESCRIPTION MANUFACTURER/PART NUMBER
Required Circuit Components
1 1 C1 CAP., X7R, 1µF, 25V, 10% 0805 AVX, 0805YC105KAT2A
2 1 C5 CAP., X7R, 0.22µF, 100V, 10% 1206 AVX, 12061C224KAT2A
3 1 L1 INDUCTOR, 10µH COOPER Bussmann, SD3110-100-R
4 3 R1, R4, R5 RES., CHIP, 100k, 1/10W, 1% 0603 VISHAY, CRCW0603100KFKEA
5 3 R3, R7, R10 RES., CHIP, 1M, 1/10W, 1% 0603 VISHAY, CRCW06031M00FKEA
6 1 R8 RES., CHIP, 12.4k, 1/10W, 1% 0603 VISHAY, CRCW060312K4FKEA
7 1 R11 RES., CHIP, 4.99k, 1/10W, 1% 0603 VISHAY, CRCW0603604KFKEA
8 1 R12 RES., CHIP, 634k, 1/10W, 1% 0603 VISHAY, CRCW0603634KFKEA
9 1 R13 RES., CHIP, 15.0k, 1/10W, 1% 0603 VISHAY, CRCW060315K0FKEA
10 2 R15, R16 RES., CHIP, 0, 1/10W, 1% 0603 VISHAY, CRCW0603000Z0EA
11 1 U1 I.C. LT3905EUD, 16 PIN, 3×3mm LINEAR TECH, LT3905EUD#PBF
Additional Demo Board Circuit Components
1 0 C2, C3, C4, C6 (OPT) CAP., 0603
2 0 C8 (OPT) CAP., 0805
3 1 C9 CAP., C0G, 0.5pF, 50V, 5% 0603 AVX, 06035A0R5KJAT2A
4 1 C10 CAP., X7R, 0.1µF, 16V, 10% 0603 AVX, 0603YC104KAT2A
5 2 C11, C12 CAP., X7R, 1µF, 16V, 10% 0603 AVX, 0603YC105KAT2A
6 1 Q1 TRANS., NPN 100V 2.5A MED SOT23-3 DIODES / ZETEX, ZXTN25100DFHTA
7 0 R2, R6, R9, R14, R20, R21 RES., 0603
8 2 R18, R19 RES., CHIP, 4.99k, 1/10W, 1% 0603 VISHAY, CRCW0603604KFKEA
9 1 R17 RES., CHIP, 1k, 1/10W, 1% 0603 VISHAY, CRCW06031K00FKEA
10 1 U2 I.C., LT6210CS6, TSOT23-6 LINEAR TECH, LT6210CS6#PBF
11 1 U3 I.C., LT1790BIS6-2.048, TSOT23 LINEAR TECH, LT1790BIS6-2.048
Hardware: For Demo Board Only
1 14 E1-E14 TESTPOINT, TURRET, .094" pbf MILL-MAX, 2501-2-00-80-00-00-07-0
2 2 JP1, JP2 3 PIN 0.079 SINGLE ROW HEADER SULLINS, NRPN031PAEN-RC
3 2 XJP1, XJP2 SHUNT, .079" CENTER SAMTEC, 2SN-BK-G
4 1 J1 CONN, BNC, 5 PINS CONNEX 112404
5 4 Stand-Off STAND-OFF, NYLON 0.25" KEYSTONE, 8831(SNAP ON)
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DEMO MANUAL DC1956A
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no representa-
tion that the interconnection of its circuits as described herein will not infringe on existing patent rights.
schematic Diagram
5
5
4
4
3
3
2
2
1
1
D D
C C
B B
A A
1. ALL RESISTORS ARE 0603.
ALL CAPACITORS ARE 0603.
NOTE: UNLESS OTHERWISE SPECIFIED
VIN
2.7V - 12V
EN
1MHz
2MHz
CTRL
GND
GND
ILIM
LOS
ILIM_MON
LOS_MON
MON
APD
50V / 2mA
LOAD STEP CIRCUIT
PWM
TIA
FAST MONITOR RESPONSE CIRCUIT
RUN SHDN
COPPER
BUSSMANN
SD3110-100-R
LOS ADJ
(12.5uA LOS)
(2mA Limit)
(1mV/uA)
VIN
VIN
VIN VIN
VIN
VIN
VIN
MON
MON
E5E5
E12E12
E10E10
R4
100K
R4
100K
R18 4.99K
R18 4.99K
R20
OPT
R20
OPT
E9E9
R2
OPT
R2
OPT
L1
10uH
L1
10uH
Q1
ZXTN25100DFH
Q1
ZXTN25100DFH
C1
1uF
25V
0805
C1
1uF
25V
0805
R17 1KR17 1K
R7
1M
R7
1M
R12
634K
R12
634K
E11E11
R13
15.0K
R13
15.0K
R11
4.99K
R11
4.99K
C9 0.5pF
C9 0.5pF
E4E4
V-
V+
+
-
Iset
U2
LT6210CS6
V-
V+
+
-
Iset
U2
LT6210CS6
R16
0
R16
0
E13E13
R21
OPT
R21
OPT
C10
0.1uF
C10
0.1uF
LT3905EUD
U1
LT3905EUD
U1
ILIM
1
LOS_MON
2
ILIM_MON
3
MON
4
APD 5
MONIN
6
SW
7
VOUT
8
GND 9
VIN
10
EN/UVLO
11
CTRL
12
LOS
13
LOS_ADJ
14
FB 15
FSEL
16
GND 17
C11
1uF
C11
1uF
R6
OPT
R6
OPT
E3E3
R9
OPT
R9
OPT
R14
OPT
R14
OPT
C2
OPT
C2
OPT
R5
100K
R5
100K
U3
LT1790BIS6-2.048
U3
LT1790BIS6-2.048
VIN 4
GND
2
OUT 6
GND
1
NC
3
NC
5
C3
OPT
C3
OPT
E1E1
C12
1uF
C12
1uF
JP2JP2
1
2
3
R19
4.99K
R19
4.99K
C6
OPT
C6
OPT
R8
12.4K
R8
12.4K
E6E6
R15
0
R15
0
C5
0.22uF
100V
1206
C5
0.22uF
100V
1206
E14E14
R1
100K
R1
100K
C4
OPT
C4
OPT
J1
BNC
J1
BNC
JP1JP1
1
2
3
E7E7
E2E2
R10
1M
R10
1M
R3
1M
R3
1M
E8E8
C8
OPT
0805
100V
C8
OPT
0805
100V
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dc1956afa
DEMO MANUAL DC1956A
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com
LINEAR TECHNOLOGY CORPORATION 2013
LT 0114 REV A • PRINTED IN USA
DEMONSTRATION BOARD IMPORTANT NOTICE
Linear Technology Corporation (LT C ) provides the enclosed product(s) under the following AS IS conditions:
This demonstration board (DEMO BOARD) kit being sold or provided by Linear Technology is intended for use for ENGINEERING DEVELOPMENT
OR EVALUATION PURPOSES ONLY and is not provided by LT C for commercial use. As such, the DEMO BOARD herein may not be complete
in terms of required design-, marketing-, and/or manufacturing-related protective considerations, including but not limited to product safety
measures typically found in finished commercial goods. As a prototype, this product does not fall within the scope of the European Union
directive on electromagnetic compatibility and therefore may or may not meet the technical requirements of the directive, or other regulations.
If this evaluation kit does not meet the specifications recited in the DEMO BOARD manual the kit may be returned within 30 days from the date
of delivery for a full refund. THE FOREGOING WARRANTY IS THE EXCLUSIVE WARRANTY MADE BY THE SELLER TO BUYER AND IS IN LIEU
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arising from the handling or use of the goods. Due to the open construction of the product, it is the user’s responsibility to take any and all
appropriate precautions with regard to electrostatic discharge. Also be aware that the products herein may not be regulatory compliant or
agency certified (FCC, UL, CE, etc.).
No License is granted under any patent right or other intellectual property whatsoever. LT C assumes no liability for applications assistance,
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Please read the DEMO BOARD manual prior to handling the product. Persons handling this product must have electronics training and
observe good laboratory practice standards. Common sense is encouraged.
This notice contains important safety information about temperatures and voltages. For further safety concerns, please contact a LT C applica-
tion engineer.
Mailing Address:
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1630 McCarthy Blvd.
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Copyright © 2004, Linear Technology Corporation
