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LTC2956IMS-1#TRPBF

P1-P3P4-P6P7-P9P10-P12P13-P15P16-P18P19-P21P22-P24P25-P27P28-P28
LTC2956
16
2956fa
For more information www.linear.com/LTC2956
OPERATION
Push Button Debounce and PBOUT
The PB input is debounced by an internal timer. This de-
bounced signal is available at the PBOUT open drain output,
and it can be used to interrupt the system for software
purposes such as choosing an option from a menu. The
initial PBOUT pulse in Awake state typically has a width
of at least t
PBOUT_FIRST
(128ms typical) which allows the
system sufficient time to respond just after powering up
(see Figure 11). Subsequent PBOUT pulses have a width
of at least t
PD_DB
(32ms typical). Note that if the system’s
microcontroller toggles SLEEP during t
PBOUT_FIRST
, the
LTC2956 will enter the Sleep state and release PBOUT
high without waiting for t
PBOUT_FIRST
to complete.
Figure 9. Pulling the SLEEP Input High to Enter Awake State
Figure 10. Prolonged Awake State
TONMAX
EN
STATE
t
PERIOD
TIMER
SLEEP
2956 F09
SLEEPAWAKE SLEEP AWAKE
RESTART
t
SLEEP_MIN
t
SLEEP_MIN
t
AWAKE_MIN
IGNOREDIGNORED
TONMAX
EN
SLEEP
STATE
t
PERIOD
TIMER
2956 F10
SLEEP
STOP
SLEEPAWAKE
PROLONGED TURN-ON TIME NORMAL TURN-ON TIME
SLEEP AWAKE AWAKE
t
PERIOD
t
PERIOD
t
PERIOD
DELAY DUE
TO t
SLEEP_MIN
t
SLEEP_MIN
t
SLEEP_MIN
LTC2956
17
2956fa
For more information www.linear.com/LTC2956
OPERATION
APPLICATIONS INFORMATION
Figure 11. PBOUT Echoing Debounced PB
HELD IN
RESET BY PB
HELD IN
RESET BY PB
HELD IN
RESET BY PB
IGNOREDIGNORED
TONMAX
TLONG
EN
PB
PBOUT
OFFALERT
STATE
SLEEP
2956 F11
STOP
0V
START
STOP
START
STOP
START
SLEEP SLEEPAWAKE
t
LONG
t
AWAKE_MIN
32ms
>32ms >32ms
32ms 32ms 32ms 32ms
IGNORED
t
PBOUT_FIRST
Configuration
Configuring the LTC2956 wake-up timer is a 3-step process.
The wake-up timer period is determined by the resistor to
ground at the PERIOD pin and the resistive divider at the
RANGE pin. Then the minimum time required for a long
push button press that forces the wake-up timer into the
SHUTDOWN mode is determined by another resistive
divider at the LONG pin. Finally, the maximum awake time
(t
ONMAX
) is set with a capacitor to GND at the ONMAX pin.
The LTC2956 biases and samples the voltages or current
at these pins once every 66s while in RUN mode. The part
also samples these pins following power-up and when in
from Off state.
Step 1: Set t
PERIOD
with resistors at the PERIOD and
RANGE pins
The required resistance value at the PERIOD pin to set
the wake-up timer period can be determined as follows:
R
PERIOD
= 400 • t
PERIOD
/NRANGE [kΩ/s]
NRANGE is the internal clock divider and can be adjusted
through the resistive divider at the RANGE pin as shown
in Table 1. It is advisable to select an NRANGE value that
yields the largest allowable R
PERIOD
value. The LTC2956’s
oscillator can run with values of R
PERIOD
ranging from
32.4kΩ to 324kΩ.
For example, if a t
PERIOD
of 3s is desired, R
PERIOD
= 75k
and NRANGE = 16 could be used, but R
PERIOD
= 300k and
NRANGE = 4 is a better choice.
LTC2956
18
2956fa
For more information www.linear.com/LTC2956
APPLICATIONS INFORMATION
Table 1. RANGE Programming
RECOMMENDED t
PERIOD
NRANGE R
RANGE
* [kΩ]
0.25s to 0.8s 1 9.76
0.4s to 3.2s 4 17.4
1.6s to 12.8s 16 26.1
6.4s to 51.2s 64 35.7
25.6s to 3.4min 256 47.5
102s to 14min 1,024 61.9
6.8min to 55min 4,096 78.7
27min to 3.6hr 16,384 100
1.82hr to 15hr 65,536 127
7.28hr to 58hr 262,144 162
29hr to 233hr 1,048,576 210
233hr to 932hr 4,194,304 280
*R
COM
= 100kΩ
Step 2: Set required pushbutton time for shutdown with
the resistive divider at the LONG pin
The resistive divider at the LONG pin sets the t
LONG
value
and Power Up mode as shown in Table 2:
Table 2. t
LONG
Programming
t
LONG
POWER UP MODE R
LONG
* [kΩ]
0.128s SHUTDOWN 9.76
0.256s SHUTDOWN 17.4
0.512s SHUTDOWN 26.1
1.024s SHUTDOWN 35.7
2.048s SHUTDOWN 47.5
4.096s SHUTDOWN 61.9
8.192s SHUTDOWN 78.7
16.384s SHUTDOWN 100
0.128s RUN 127
0.256s RUN 162
0.512s RUN 210
1.024s RUN 280
2.048s RUN 383
4.096s RUN 576
8.192s RUN 1020
16.384s RUN Open
*R
COM
= 100kΩ
Step 3: Set maximum Awake time using capacitor at
ONMAX pin
The value of C
ONMAX
can be determined by the equation:
C
ONMAX
= t
ONMAX
• 75 [nF/s]
For example, a t
ONMAX
of 133ms requires a 10nF capacitor.
High Voltage PowerPath™ Switching
The high voltage EN open drain output of the LTC2956-2
is designed to switch on/off an external power P-channel
MOSFET. This allows a user to connect/disconnect a power
supply (or battery) to its load by toggling the PB pin.
Figure 12 shows the LTC2956-2 switching a 24V battery
application. R6 slows down the turning on of M1 so as
to limit the inrush current when needed to charge up the
capacitor at V
OUT
. R5 is optional – it helps to speed up
the turning off of M1 and also to keep M1 off when the
input voltage rise time is fast.
PB Pin in a Noisy Environment
The rugged PB pin is designed to operate in noisy en-
vironments. Transients below ground and above V
IN
will not damage the PB pin. Additionally, the PB pin can
withstand ESD HBM strikes of up to ±25kV. However, if
the pushbutton switch is located physically far from the
Figure 12. Switching 24V Battery Stack with
External P-Channel MOSFET
2956 F12
PBOUT
SLEEP
OFFALERT
ONALERT
PB
PERIOD
ONMAX
GND
12V
LEAD-ACID
BATTERIES
M1
R5*
100k
R6
100k
D1
12V
R
PERIOD
C1
100nF
C
OUT
ENV
IN
RANGE
LTC2956-2
LONG
V
OUT
C
ONMAX
100kR
LONG
R
RANGE
*R5 IS OPTIONAL
+
+
+
P1-P3P4-P6P7-P9P10-P12P13-P15P16-P18P19-P21P22-P24P25-P27P28-P28

LTC2956IMS-1#TRPBF

Mfr. #:
Buy LTC2956IMS-1#TRPBF
Manufacturer:
Analog Devices Inc.
Description:
Supervisory Circuits Wake-Up Timer w/ Pushbutton Control
Lifecycle:
New from this manufacturer.
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