DC826B - Demo Manual

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 826B-A/B
PUSH BUTTON ON/OFF CONTROLLER
LTC2950-2/LTC2951-2
DESCRIPTION
Demonstration Circuits 826B-A and 826B-B feature the
LTC2950-2 and the LTC2951-2 respectively, which are
low power, wide input voltage range, Push Button
On/Off Controllers. A push button 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 DC826B-A/DC826B-B.
JP1 and JP2 on the DC826B-A provide the selection of
timing options for the /PB on and off times. For the
DC826B-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. DC826B-A/DC826B-B accepts an input voltage range of 2.7V to 26.4V or a 9V battery for
portable demonstration and evaluation.
Design files for this circuit board are available. Call the LTC factory.
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.
QUICK START PROCEDURE
Demonstration circuit 826B-A/826B-B is easy to set up
to evaluate the performance of the LTC2950-2/LTC29512:
1.
Place jumpers in the following positions:
2.
Connect the input power supply of 2.7V to 26.4V
across VIN and GND or a 9V battery to the battery
connector.
3.
Push and hold the push button once to turn on the
green LED.
4.
Push and hold the push button again to turn off the
green LED.
JP1 0.033uF
JP2 0.033uF
JP3 UNTIE
Table 1. LTC2950/2951 Selection Guide (typical timing values, Cap. Adjust = 212ms on DC826B-A/ DC826B-B)
PART
ENABLE
ONT
OFFT
KILLT
DEMO BOARD
LTC2950-1
EN
32ms + Cap. Adjust*
32ms + Cap. Adjust*
1000ms
N/A
LTC2590-2
/EN
32ms + Cap. Adjust*
32ms + Cap. Adjust*
1000ms
DC826B-A
LTC2951-1
EN
128ms
32ms + Cap. Adjust*
128ms + Cap. Adjust*
N/A
LTC2951-2
/EN
128ms
32ms + Cap. Adjust*
128ms + Cap. Adjust*
DC826B-B
*The additional Cap. Adjust time is selected by an external capacitor. The DC826B-A and DC826B-B adjust times have been pre-selected with a 0.033uF capacitor to provide an
additional 212ms. The additional time is calculated with the following equations as shown in the LTC2950/LTC2951 data sheets:
CONT = 1.56E-4 [µF/ms] • (tONT – 1ms)
COFFT = 1.56E-4 [µF/ms] • (tOFFT – 1ms)
CKILLT = 1.56e-4 [µF/ms] • (t/KILL, OFF DELAY, ADDITIONAL – 1ms)
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 826B-A/B
PUSH BUTTON ON/OFF CONTROLLER
OPERATING PRINCIPLES
The duration that /PB must be shorted to ground in
order to turn on/off the DC/DC converter is independently programmed (LTC2950-2) by two external capacitors C1 and C2 and selected on the DC826B-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 DC826B-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
force a turn off.
The RC (RRPP and CRPP) at VIN on the DC826 provides
reverse polarity protection to the LTC2950-2/LTC29512. If power is connected in an application such that
the polarities 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 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 pullup 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 DC826B-A
/DC826B-B will be pulled up to an external supply,
LEDs D1 and D2 should be removed.)
Figure 1. DC826B-A/DC826B-B Example Setup
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 826B-A/B
PUSH BUTTON ON/OFF CONTROLLER
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