1
dc1735Af
DEMO MANUAL DC1735A
DESCRIPTION
OPERATING PRINCIPLE
LTC3226EUD
2-Cell Supercap Charger With
Backup PowerPath Controller
Demonstration circuit DC1735A is a 2-cell supercap
charger with a backup PowerPath™ controller, featuring
the LTC
®
3226. It includes a charge-pump supercapacitor
charger with programmable output voltage, a low drop-
out regulator and a power-fail comparator for switching
between normal and backup modes. The constant-input
current supercapacitor charger is designed to charge two
supercapacitors in series to a resistor programmable out-
put voltage from a 2.5V to 5.3V input supply. The charger
input current limit is programmable by an external resistor
up to 315mA. The internal backup LDO is powered from
The LTC3226 is a 2-cell series supercapacitor charger
designed to back up a Li-ion battery or any system rail in
the range of 2.5V to 5.3V. Its four principle circuit com-
ponents are:
1. Dual (1×/2×) charge pump with an integrated balancer
and a voltage clamp
2. LDO to supply the load current from the charge stored
on the supercapacitors
3. Ideal diode controller to control the gate of the external
MOSFET between VIN and VOUT
4. PFI comparator to decide whether to activate the charge
pump to charge the supercapacitor stack or to activate
the LDO to supply the load when VIN falls below an
externally programmed value.
the supercapacitors and provides up to 2A peak output
current with an adjustable output voltage. When the input
supply falls below the resistor programma-ble power-fail
threshold, the LTC3226 automatically enters a backup state
in which the supercapacitors power the output through
the LDO. The LTC3226 is available in a 16-lead, 3mm ×
3mm QFN surface mount package with an exposed pad.
Design files for this circuit board are available at
http://www.linear.com/demo
The LTC3226 has two modes of operation: normal and
backup. If VIN is above an externally programmable PFI
threshold voltage, the part is in normal mode and power
flows from VIN to VOUT through the external MOSFET while
the internal charge pump chargers the supercapacitor
stack (see Figure 1). If VIN is below the PFI threshold, the
part is in backup mode (see Figure 2). In this mode, the
internal charge pump is turned off and the LDO is turned
on to supply the load current from the stored charge on
the supercapacitor stack.
The device includes three open-drain, output status sig-
nals: CAPGOOD, PFO and RST. The CAPGOOD pin is an
open-drain N-channel MOSFET transistor controlled by a
comparator that monitors the voltage on the supercapaci-
L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks and
PowerPath is a trademark of Linear Technology Corporation. All other trademarks are the
property of their respective owners.
PERFORMANCE SUMMARY
Specifications are at TA = 25°C
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
VIN Input Voltage Range 2.5 5.5 V
IVIN(ILIM) Input Current Limit RPROG = 33.3k 315 mA
VSTACK Supercap Stack Output Voltage RCP1 = 3.83M, RCP2 = 1.21M 5.3 5.5 V
VMID Supercap Midpoint Voltage 2.65 2.75 V
2
dc1735Af
DEMO MANUAL DC1735A
Figure 2. Normal-to-Backup Mode Switchover
tor stack. This pin is pulled to ground until the CPO pin
voltage rises within 7.5% of the programmed value. Once
the CPO pin is above this threshold, the CAPGOOD pin
goes high impedance. The output of the PFI comparator
also drives the gate of an open-drain N-channel MOSFET
to report the status via the PFO pin. In normal mode the
PFO pin is high impedance, but in backup mode the pin
is pulled down to ground. The LTC3226 contains a RESET
comparator which monitors VOUT under all operating
modes via the RST_FB pin and reports the status via an
open-drain NMPS transistor on the RST pin. At any time,
if VOUT falls below 7.5% from its programmed value, it
pulls the RST pin low almost instantaneously.
However, on the rising edge, the comparator waits 290ms
after VOUT crosses the threshold voltage before making
the RST high impedance.
OPERATING PRINCIPLE
VOLTAGE (V) 1V/DIV
dc1735A F01
TIME (5 SECONDS/DIV)
CPO
VIN
VMID
1x
MODE
2x
MODE RPROG = 33.2k
CSC = 1.2F
6
5
4
3
2
1
–1
0
TIME (SECONDS)
0
VOLTAGE (V)
3
4
5
1.6
dc1735A F02
2
1
–1 0.4 0.8 1.2
CPO
2.0
0
6
VOUT
VIN
CSC = 1.2F
COUT = 47μF
ILOAD = 2A
PFO (2V/DIV)
BACKUP
MODE
(LDO IN
REGULATION)
BACKUP MODE
(LDO IN
DROPOUT)
QUICK START PROCEDURE
Refer to Figure 3 for the proper measurement equipment
setup and jumper settings, and follow the procedure below.
NOTE. When measuring the input or output voltage ripple,
care must be taken to avoid a long ground lead on the
oscilloscope probe. Measure the input or output voltage
ripple by touching the probe tip directly across the VIN
or VOUT and GND terminals. See Figure 4 for the proper
scope probe technique.
1. Initial jumper, power supply and load settings:
JP1 = EN Power Supply = OFF
JP2 = 110mA Load = Off
JP3 = 110mA Pulse Generator = OFF
2. Connect the power supply to the VIN terminals, turn
the power supply on, and increase the voltage to 2V
while monitoring the input current. If the input current
is less than 5mA, increase the voltage until the point at
which PFO goes high. Verify that VIN is between 3.53V
and 3.65V, the input current is approximately 320mA,
the output voltage is approximately equal to the input
voltage and the voltage on the CPO pin is rising.
3. Monitor the voltage on CPO and CAPGOOD. Verify that
CAPGOOD goes high when CPO is at 4.6V and that CPO
charges between 4.83V and 5.23V. Verify that VMID is
one-half of CPO. Verify that RST is high.
Figure 1. Charge Profile with Equal Value Supercapacitors
3
dc1735Af
DEMO MANUAL DC1735A
QUICK START PROCEDURE
Figure 3. Proper Measurement Equipment Setup for DC1735A
Figure 4. Measuring Input or Output Ripple
GND
VIN
dc1735a F04
4. Turn on the load and increase the current to 2A. Verify
that VOUT is within 50mV of VIN.
5. Decrease the power supply to 3V and quickly observe
that VOUT is between 3.12V and 3.47V, PFI is low, RST
is high and the voltage on CPO is falling. Increase VIN
to 3.6V and verify that the voltage on CPO starts to
rise again. Let the voltage on CPO rise beyond where
CAPGOOD goes high.
6. Turn off the power supply and observe that VOUT remains
between 3.12V and 3.47V for greater than 700ms, and
that VOUT then falls, tracking CPO until VOUT reaches
2.4V. Verify that RST is low.
7. Disconnect the power supply from the VIN terminals, turn
down the voltage to 0V and connect the power supply
between the CPO and ground terminals. Slowly increase
the voltage to 5V and verify that VOUT is between 3.12V
and 3.47V. Increase the load on VOUT to 1A. Set up the
pulse generator for an output voltage peak of 10V, a pulse
with 1ms pulse width and a period of 20ms. Connect
the pulse generator to the pulse generator terminals and
observe the transient response on the VOUT terminals.
Verify that the negative transition of VOUT is less than
75mV and that it recovers within 100μs.
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dc1735Af
DEMO MANUAL DC1735A
PARTS LIST
ITEM QTY REFERENCE PART DESCRIPTION MANUFACTURER/PART NUMBER
Required Circuit Components
1 1 C2 Cap., Chip, X5R, 4.7μF, 10%, 6.3V, 0603 Murata, GRM188R60J475KE19D
2 1 C3 Cap., Chip, X5R, 2.2μF, 20%, 10V, 0603 Murata, GRM188R61A225KE34D
3 2 C4, C5 Cap., Chip, X7R, 0.1μF, 10%, 16V, 0402 Murata, GRM155R71C104KA88D
41C6 Supercap, 1.2μF, 5.5V, 39mm × 17mm CAP-XX, HS230F
5 1 C7 Cap., Chip, X5R, 47μF, 20%, 6.3V, 1206 Murata, GRM31CR60J476ME19L
7 1 R2 Res., Chip, 210k, 1/16W, 1%, 0402 Vishay, CRCW0402210KFKED
8 1 R3 Res., Chip, 121k, 1/16W, 1%, 0402 Vishay, CRCW0402121KFKED
9 1 R7 Res., Chip, 100k, 1/16W, 1%, 0402 Vishay, CRCW0402100KFKED
10 1 R8 Res., Chip, 3.83M, 1/16W, 1%, 0402 Vishay, CRCW04023M83FKED
11 1 R9 Res., Chip, 1.21M, 1/16W, 1%, 0402 Vishay, CRCW04021M21FKED
12 1 R10 Res., Chip, 255k, 1/16W, 1%, 0402 Vishay, CRCW0402255KFKED
13 1 R11 Res., Chip, 80.6k, 1/16W, 1%, 0402 Vishay, CRCW040280K6FKED
14 1 Q1 MOSFET, –20V, 33mΩ, –5.5A, SUPERSOT-6 Fairchild, FDC604P
15 1 U1 2-Cell Supercapacitor Charger with Backup
PowerPath Controller
Linear Technology, LTC3226EUD
Additional Circuit Components
1 1 C1 Cap., SMD, OSCON, 220μF, 20%, 6.3V,
6.3mm × 6mm
Sanyo, 6VPE220M
2 0 C8 (OPT) Cap., Chip, 0402
3 1 D1 SMD, Switching Diode, SOD323 Vishay, 1N4148WS-V-GS08
4 1 R1 Res., Chip, 1M, 1/16W, 1%, 0402 Vishay, CRCW04021M00FKED
5 1 R4 Res., Chip, 10k, 1/16W, 1%, 0402 Vishay, CRCW040210K0FKED
6 3 R5, R6, R16 Res., Chip, 100k, 1/16W, 1%, 0402 Vishay, CRCW0402100KFKED
7 3 R12 to R14 Res., Chip, 475k, 1/16W, 1%, 0402 Vishay, CRCW0402475KFKED
8 1 R15 Res., Chip, 1k, 1/16W, 1%, 0402 Vishay, CRCW04021K00FKED
9 2 R17, R18 Res., Chip, 6.65Ω, 1/4W, 1%, 1206 Vishay, CRCW12066R65FKED
10 1 Q2 MOSFET, 30V, 65mΩ, 3.5A, SOT-23 Vishay, Si2306BDS
Hardware for Demo Board Only
1 4 E1, E2, E8, E9 Turret, 0.09 DIA Mill-Max, 2501-2
2 12 E3 to E7, E10 to E16 Turret, 0.061 DIA Mill-Max, 2308-2
3 3 JP1 to JP3 Header, 3 Pins, 2mm Samtec, TMM-103-02-L-S
4 3 JP1 to JP3 Shunt 2mm Samtec, 2SN-BK-G
5 4 Stand-Off, Nylon, 0.375" Tall (Snap On) Keystone, 8832 (Snap On)
5
dc1735Af
DEMO MANUAL DC1735A
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
Figure 5. Demo Circuit Schematic
ALL CAPACITORS ARE 0402, 10%
1. ALL RESISTORS ARE 0402, 1%, 1/16W
5% DUTY CYCLE
3.3V-5.5V
3.3V - 5.5V
2.0A MAX
2. INSTALL SHUNTS AS SHOWN.
NOTE: UNLESS OTHERWISE SPECIFIED
220mA
110mA
OFF
OFF
OFF
OFF
ON
ON
ON
ON
I
JP3
330mA
JP2
LIMIT
220mA
LIMIT PROGRAMMING
INPUT CURRENT
2
DEMO CIRCUIT 1735A
11
BACKUP POWER PATH CONTROLLER
N/A
LTC3226EUD
NC
JIM D.
05-16-11
2-CELL SUPERCAPACITOR CHARGER WITH
SIZE
DATE:
IC NO. REV.
SHEET OF
TITLE:
APPROVALS
PCB DES.
APP ENG.
TECHNOLOGY
Fax: (408)434-0507
Milpitas, CA 95035
Phone: (408)432-1900
1630 McCarth y B lvd .
LTC Confidential-For Customer Use Only
CUSTOMER NOTICE
LINEAR TECHNOLOGY HAS MADE A BEST EFFORT TO DESIGN A
CIRCUIT THAT MEETS C US TO ME R- SUPPLIED SPECIFICATI ONS;
HOWEVER, IT REMAINS THE CUSTOMER'S RESPONSIBILITY TO
VERIFY PROPE R AND RELIABLE OPERATION IN THE ACTUAL
APPLICATION. COMPO NEN T SU BSTI TUT IO N AND PRINTED
CIRCUIT BOARD LAYOUT MAY SIGNIFICANTLY AF FEC T CI RC UI T
PERFORMANCE OR RELIABILITY . C ONTA CT L INE AR
TECHNOLOGY APPLICATIONS ENGINEERING FOR ASS IST ANC E.
THIS CIRCUIT IS PROPRIETARY TO LINEAR TECHNOLOGY AND
SCHEMATIC
SUPPLIED FOR USE WITH LINEAR TECHNOLOGY PARTS.
SCALE = NONE
www.linear.com
JIM D.PRODUCTION2 05-16-11
REVISION HISTORY
DESCRIPTION DATEAPPROVEDECO REV
PFI
PFI
VIN
VOUT
VOUT
VOUT
E5
GND
JP1
ENABLE
OFF
EN
1
3
2
E1
VIN
E11VMID
C2
4.7uF
6.3V
X5R
0603
E4
PROG
JP3
110mA
ON
OFF
1
3
2
R9
1.21MEG
E6
PULSE LOAD
R1
1.0Meg
R18
6.65
1206
0.25W
R13
475K
R15
1K
E9 GND
E12GND
R5
100K
C3
2.2uF
10V
X5R
0603
E7
GND
JP2
110mA
ON
OFF
1
3
2
R10
255K
D1
1N4148-SMD
2 1
R2
210K
R14
475K
R16
100K
R6
100K
E13 RST
C4
0.1uF
16V
X7R
R11
80.6K
R3
121K
E16GND
E14 PFO
R17
6.65
1206
0.25W
BAL
C6
1.2F
HS230F
39mm x 17mm
+
21
3
+
C1
220uf
CAP-CV-6.3X6
6.3V
R7
100K
E3
ENABLE
E15CAPGOOD
C5
0.1uF
16V
X7R
E2
GND
R12
475K
R4
10K
Q2
Si2306BDS
C8
OPT
Q1
FDC604P
3
2 4
1
5
6
U1
LTC3226EUD
1
2
3
4
5
6
78
9
10
11
12
13
1415
16
17
VOUT
PFO
PFI
LDO_FB
GATE
RST_FB
RST
EN_CHG
PROG
CPO_FB
CAPGOOD
C-
VIN
VMIDC+
CPO
GND
R8
3.83MEG
E8 VOUT
E10CPO
C7
47uF
6.3V
X5R
1206
20%
6
dc1735Af
DEMO MANUAL DC1735A
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com
© LINEAR TECHNOLOGY CORPORATION 2011
LT 0711 • PRINTED IN USA
DEMONSTRATION BOARD IMPORTANT NOTICE
Linear Technology Corporation (LTC) 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 LTC 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
OF ALL OTHER WARRANTIES, EXPRESSED, IMPLIED, OR STATUTORY, INCLUDING ANY WARRANTY OF MERCHANTABILITY OR FITNESS
FOR ANY PARTICULAR PURPOSE. EXCEPT TO THE EXTENT OF THIS INDEMNITY, NEITHER PARTY SHALL BE LIABLE TO THE OTHER FOR
ANY INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES.
The user assumes all responsibility and liability for proper and safe handling of the goods. Further, the user releases LTC from all claims
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
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No License is granted under any patent right or other intellectual property whatsoever. LTC assumes no liability for applications assistance,
customer product design, software performance, or infringement of patents or any other intellectual property rights of any kind.
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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 LTC applica-
tion engineer.
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1630 McCarthy Blvd.
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Copyright © 2004, Linear Technology Corporation
