Quick Start Procedure; Operating Principles - Linear Technology DC826C-A Demo Manual

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

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.
2
2. Connect the input power supply of 2.7V to 26.4V across
V and GND or a 9V battery to the battery connector.
IN
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.
The RC (R and C ) at V
RPP RPP
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.)
on the DC826 provides
IN
dc826cf