DEMO MANUAL
DC826C-A/DC826C-B
LTC2950-2/LTC2951-2
Pushbutton On/Off Controller
DESCRIPTION
Demonstration circuits 826C-A and 826C-B feature the
LTC
®
2950-2
and the
LTC2951-2
respectively, which are
low power, wide input voltage range, pushbutton on/off
controllers. A pushbutton switch shorts the
PB
pin to
ground which in turn sets the
EN
pin low (see Note 1).
Shorting
PB
to ground a second time subsequently resets
the
EN
pin high. The
EN
pin is used to connect to a DC/
DC converter shutdown to control the turn on and off of
the circuit, simulated with a green LED on the DC826C-A/
DC826C-B.
JP1 and JP2 on the DC826C-A provide the selection
of timing options for the
PB
on and off times. For the
DC826C-B, JP1 selects
KILL
times while JP2 selects off
times. JP3 ties and unties
KILL
to
INT
for immediate or
delayed turn off. The
INT
status is shown with a red LED.
DC826C-A/DC826C-B accepts an input voltage range of
2.7V to 26.4V or a 9V battery for portable demonstration
and evaluation.
Note 1:
The inversion of
EN
of the LTC2950-2/LTC2951-2
is found in the LTC2950-1/LTC2951-1. Table 1 provides
an IC selection guide.
Design files for this circuit board are available at
http://www.linear.com/demo/DC826C
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.
IC SELECTION GUIDE
Table 1. LTC2950/LTC2951 Selection Guide (Typical Timing Values, Cap. Adjust = 212ms on DC826C-A/DC826C-B)
PART
LTC2950-1
LTC2950-2
LTC2951-1
LTC2951-2
ENABLE ONT
EN
EN
EN
EN
32ms + Cap. Adjust*
32ms + Cap. Adjust*
128ms
128ms
OFFT
32ms + Cap. Adjust*
32ms + Cap. Adjust*
32ms + Cap. Adjust*
32ms + Cap. Adjust*
KILLT
1000ms
1000ms
128ms + Cap. Adjust*
128ms + Cap. Adjust*
DEMO BOARD
N/A
DC826C-A
N/A
DC826C-B
*The additional Cap. Adjust time is selected by an external capacitor. The DC826C-A and DC826C-B adjust times have been pre-selected with a 0.033μF
capacitor to provide an additional 212ms. The additional time is calculated with the following equations as shown in the LTC2950/LTC2951 data sheets:
C
ONT
= 1.56e-4 [μF/ms] • (t
ONT
– 1ms)
C
OFFT
= 1.56e-4 [μF/ms] • (t
OFFT
– 1ms)
C
KILLT
= 1.56e-4 [μF/ms] • (t
KILL
,
OFF DELAY, ADDITIONAL
– 1ms)
dc826cf
1
DEMO MANUAL
DC826C-A/DC826C-B
QUICK START PROCEDURE
Demonstration circuit 826C-A/826C-B is easy to set up to
evaluate the performance of the LTC2950-2/LTC2951-2:
1. Place jumpers in the following positions:
JP1:
0.033μF
JP2:
0.033μF
JP3:
UNTIE
2. Connect the input power supply of 2.7V to 26.4V across
V
IN
and GND or a 9V battery to the battery connector.
3. Push and hold the pushbutton once to turn on the green
LED.
4. Push and hold the pushbutton again to turn off the
green LED.
OPERATING PRINCIPLES
The duration that
PB
must be shorted to ground in order
to turn on/off the DC/DC converter is independently pro-
grammed (LTC2950-2) by two external capacitors C1 and
C2 and selected on the DC826C-A with jumper JP1 and
JP2. The status of the
EN
pin, and simulation of the turn
on/off of a DC/DC converter, is displayed with green LED
D2 on the board.
Figure 1 shows how the
EN
is connected to the
SHDN
pin
of a DC/DC converter and how
INT
and
KILL
interfaces with
a µP or µC. An internal 500ms timer blanks (ignores) the
KILL
signal during system power up. This allows sufficient
time for the DC/DC converter and a µP to perform power
up tasks. During turn off, a power down timer provides
a delay (LTC2950-2: 1000ms, LTC2951-2: adjustable)
from interrupting the µP (INT = low) to turning off the DC/
DC converter (EN = high). This delay gives the µP time
to perform power down and housekeeping tasks. On the
DC826C-B, JP1 selects the power down timer, while JP2
is used to adjust the turn off
PB
duration. The red LED
D1 shows the state of the
INT
pin. A µP can turn off the
converter with no delay by asserting
KILL
low. By tying
KILL
to
INT
through JP3,
KILL
is forced low during the
INT
blanking time and thus forces a turn off.
The RC (R
RPP
and C
RPP
) at V
IN
on the DC826 provides
reverse polarity protection to the LTC2950-2/LTC2951-2. If
power is connected in an application such that the polari-
ties are ensured to be in the correct configuration, this RC
may be removed from the circuit.
An additional RC (RF and CF), located at the
PB
pin, acts
as a filter and is used in an application where the switch
is located far from the LTC2950-2/LTC2951-2. In such a
case, the RC would be placed next to the switch rather
than the part. If the switch is located near the LTC2950-2/
LTC2951-2, then the RC may be removed from the circuit.
An LDO (U2) is used on the DC826 to provide a pull-up
voltage of 2.6V which is well below the absolute maximum
on the
INT, EN,
and
KILL
pins for the full range of input
voltage of 2.7V to 26.4V. In an application, pull these
pins up to a voltage no higher than their rated absolute
maximum shown in the data sheet. Optional Zener diodes
(D3 – D5) can be used if the pull-up voltage exceeds the
rated absolute maximum. (If the interface pins on the
DC826C-A /DC826C-B will be pulled up to an external
supply, LEDs D1 and D2 should be removed.)
2
dc826cf
DEMO MANUAL
DC826C-A/DC826C-B
OPERATING PRINCIPLES
PUSHBUTTON
V
IN
V
IN
2.7V TO 26.4
OR
9V BATTERY
V
OUT
DC/DC
BUCK
SHDN
R1
10k
INT
KILL
µP/µC
DC826C F01
Figure 1. DC826C-A/DC826C-B Example Setup
dc826cf
3
SCHEMATIC DIAGRAM
DEMO MANUAL
DC826C-A/DC826C-B
GND
ONT/KILLT
OFFT
4
3
7
4
B
C
D
E
A
ECO REV
DATE
Jan 27, 2014
C
PRODUCTION(Replaced S1, D1 & D2)
REVISION HISTORY
APPROVED
DESCRIPTION
Dilian Reyes
4
2.6V
4
R1
100
R2
100
VIN
RRPP
1k
1
VIN
EN
KILL
D3
11V
(Opt)
1
2
3
OPEN
JP2
VIN
1
3
C2
0.033uF
0.033uF
OFFT
D4
11V
(Opt)
D5
11V
(Opt)
8
6
SEE NOTE #1
PB
INT
5
CRPP
0.1uF
50V
R3
100k
RED
TP1
VIN
2.7V-26.4V
KEYSTONE
#232
U1
LTC2950CTS8-2
D1
RED
2V
INT
D2
GRN
2V
EN
TP2
INT
TP3
EN
TP5
KILL
3
3
PB
5.1k
CF
0.1uF
50V
S1
ON/OFF
3
JP1
C1
0.033uF
TP4
RF
2
BLK
TP7
GND
ONT/KILLT
1
0.033uF
2
OPEN
INT/KILL
1
TIE
2
UNTIE
JP3
3
TP6
GND
U2
LT3014BES5
IN
NC
OUT
ADJ
GND
2
R5
100k
1%
5
4
R4
113k
1%
2.6V
2
2
C4
0.47uF
10V
CUSTOMER NOTICE
APPROVALS
PCB DES.
1
APP ENG.
Dilian Reyes
TECHNOLOGY
TITLE: SCHEMATIC
www.linear.com
NOTE 1. EN, the inverse of EN,
is available in the LTC2950-1/LTC2951-1.
1
LINEAR TECHNOLOGY HAS MADE A BEST EFFORT TO DESIGN A
CIRCUIT THAT MEETS CUSTOMER-SUPPLIED SPECIFICATIONS;
HOWEVER, IT REMAINS THE CUSTOMER'S RESPONSIBILITY TO
VERIFY PROPER AND RELIABLE OPERATION IN THE ACTUAL
APPLICATION. COMPONENT SUBSTITUTION AND PRINTED
CIRCUIT BOARD LAYOUT MAY SIGNIFICANTLY AFFECT CIRCUIT
PERFORMANCE OR RELIABILITY. CONTACT LINEAR
TECHNOLOGY APPLICATIONS ENGINEERING FOR ASSISTANCE.
C:\PADS PROJECTS\826C-A\SCH\826C-A_REV1.DSN
THIS CIRCUIT IS PROPRIETARY TO LINEAR TECHNOLOGY AND
SUPPLIED FOR USE WITH LINEAR TECHNOLOGY PARTS.
SIZE
IC NO.
REV.
SCALE = NONE
B
C
D
MODIFY DATE:
E
1
SHEET
1
OF
1
A
dc826cf
A
B
C
D
E
ECO REV
DATE
Jan 27, 2014
C
PRODUCTION(Replaced S1, D1 & D2)
REVISION HISTORY
APPROVED
DESCRIPTION
Dilian Reyes
4
2.6V
4
R1
100
R2
100
SCHEMATIC DIAGRAM
VIN
RRPP
1k
1
VIN
EN
OFFT
KILL
D3
11V
(Opt)
1
2
3
OPEN
JP2
VIN
1
3
C2
0.033uF
0.033uF
OFFT
UNTIE
JP3
D4
11V
(Opt)
D5
11V
(Opt)
8
6
SEE NOTE #1
PB
GND
INT
5
CRPP
0.1uF
50V
R3
100k
RED
TP1
VIN
2.7V-26.4V
KEYSTONE
#232
U1
LTC2951CTS8-2
D1
RED
2V
INT
D2
GRN
2V
EN
TP2
INT
TP3
EN
TP5
KILL
3
3
CF
0.1uF
50V
4
3
S1
7
INT/KILL
1
TIE
2
3
BLK
TP7
GND
3
JP1
C1
0.033uF
ON/OFF
ONT/KILLT
1
0.033uF
2
OPEN
ONT/KILLT
PB
5.1k
TP4
RF
2
TP6
GND
U2
LT3014BES5
IN
NC
OUT
ADJ
GND
2
R5
100k
1%
5
4
R4
113k
1%
2.6V
2
2
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.
C4
0.47uF
10V
CUSTOMER NOTICE
APPROVALS
PCB DES.
1
APP ENG.
Dilian Reyes
TECHNOLOGY
TITLE: SCHEMATIC
www.linear.com
NOTE 1. EN, the inverse of EN,
is available in the LTC2950-1/LTC2951-1.
1
LINEAR TECHNOLOGY HAS MADE A BEST EFFORT TO DESIGN A
CIRCUIT THAT MEETS CUSTOMER-SUPPLIED SPECIFICATIONS;
HOWEVER, IT REMAINS THE CUSTOMER'S RESPONSIBILITY TO
VERIFY PROPER AND RELIABLE OPERATION IN THE ACTUAL
APPLICATION. COMPONENT SUBSTITUTION AND PRINTED
CIRCUIT BOARD LAYOUT MAY SIGNIFICANTLY AFFECT CIRCUIT
PERFORMANCE OR RELIABILITY. CONTACT LINEAR
TECHNOLOGY APPLICATIONS ENGINEERING FOR ASSISTANCE.
C:\PADS PROJECTS\826C-B\SCH\826C-B_REV1.DSN
THIS CIRCUIT IS PROPRIETARY TO LINEAR TECHNOLOGY AND
SUPPLIED FOR USE WITH LINEAR TECHNOLOGY PARTS.
SIZE
IC NO.
REV.
SCALE = NONE
C
D
MODIFY DATE:
E
1
SHEET
1
OF
1
A
B
DEMO MANUAL
DC826C-A/DC826C-B
dc826cf
5
Embedded System
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