LTC2950ITS8-1#PBF Linear Technology, LTC2950ITS8-1#PBF Datasheet - Page 9

• Manufacturer Part Number: LTC2950ITS8-1#PBF
• Manufacturer: Linear Technology

Specifications of LTC2950ITS8-1#PBF

• Operating Temperature (max): 85C
• Operating Temperature (min): -40C
• Pin Count: 8
• Mounting: Surface Mount
• Package Type: TSOT-23
• Case Length: 2.9mm
• Screening Level: Industrial
• Lead Free Status / RoHS Status: Compliant

APPLICATIONS INFORMATION
Description
The LTC2950 is a low power (6μA), wide input voltage range
(2.7V to 26.4V), push button on/off controller that can interface
to a μP and a power supply. The turn-on and turn-off debounce
times are extendable using optional external capacitors. A
simple interface (INT output, KILL input) allows a system to
power on and power off in a controlled manner.
Turn On
When power is fi rst applied to the LTC2950, the part ini-
tializes the output pins. Any DC/DC converters connected
to the EN/EN pin will therefore be held off. To assert the
enable output, PB must be held low for a minimum of
32ms (t
debounce time via an optional capacitor connected to the
ONT pin (t
ditional time that PB must be held low before asserting the
enable output. C
Once the enable output is asserted, any DC/DC converters
connected to this pin are turned on. The KILL input from the
μP is ignored during a succeeding 512ms blanking time (t
ON BLANK). This blanking time represents the maximum
time required to power up the DC/DC converter and the μP .
If KILL is not brought high during this 512ms time window,
the enable output is released. The assumption is that 512ms
is suffi cient time for the system to power up.
Turn Off
To initiate a power off sequence, PB must be held low for a
minimum of 32ms (t
time may be added via an optional capacitor connected to
the OFFT pin (t
additional time that PB must be held low to initiate a power
off sequence. C
Once PB has been validly pressed, INT is switched low. This
alerts the μP to perform its power down and housekeeping
tasks. The power down time given to the μP is 1024ms.
C
C
ONT
OFFT
DB, ON
= 1.56E-4 [μF/ms] • (t
= 1.56E-4 [μF/ms] • (t
ONT
). The LTC2950 provides additional turn on
). The following equation describes the ad-
OFFT
OFFT
ONT
). The following equation describes the
DB, OFF
is the OFFT external capacitor:
is the ONT external capacitor:
). Additional turn off debounce
ONT
OFFT
– 1ms)
– 1ms)
KILL
,
Note that the KILL input can be pulled low (thereby releasing the
enable output) at any time after t
Simplifi ed Power On/Off Sequence
Figure 1 shows a simplifi ed LTC2950-1 power on and power
off sequence. A high to low transition on PB (t
the power on sequence. This diagram does not show any
bounce on PB. In order to assert the enable output, the
PB pin must stay low continuously (PB high resets timers)
for a time controlled by the default 32ms and the external
ONT capacitor (t
512ms blanking timer is started. This blanking timer is
designed to give suffi cient time for the DC/DC converter
to reach its fi nal voltage, and to allow the μP enough time
to perform power on tasks.
The KILL pin must be pulled high within 512ms of the
EN pin going high. Failure to do so results in the EN
pin going low 512ms after it went high. (EN = low, see
Figure 2). Note that the LTC2950 does not sample KILL and
PB until after the 512ms internal timer has expired. The rea-
son PB is ignored is to ensure that the system is not forced
off while powering on. Once the 512ms timer expires (t
the release of the PB pin is then debounced with an internal
32ms timer. The system has now properly powered on and
the LTC2950 monitors PB and KILL (for a turnoff command)
while consuming only 6μA of supply current.
A high to low transition on PB (t
sequence. PB must stay low continuously (PB high resets
debounce timer) for a period controlled by the default 32ms
and the external OFFT capacitor (t
of the OFFT timing (t
that EN will be switched low in 1024ms. Once a system has
fi nished performing its power down operations, it can set
KILL low (t
the internal 1024ms timer. The release of the PB pin is then
debounced with an internal 32ms timer.
The system is now in its reset state: where the LTC2950
is in low power mode (6μA). PB is monitored for a high
to low transition.
7
) and thus immediately set EN low), terminating
LTC2950-1/LTC2950-2
2
–t
1
6
). Once EN goes high (t
), an interrupt (INT) is set, signifying
KILL
5
6
) initiates the power off
–t
, ON BLANK period.
5
). At the completion
2
), an internal
1
) initiates
295012fc
9
4
),