HCS370 Datasheet, PDF (5/36 Pages) Microchip Technology – KEELOQ Code Hopping Encoder

HCS370
2.0 DEVICE DESCRIPTION
As shown in the typical application circuits (Figure 2-1),
the HCS370 is an easy device to use. It requires only
the addition of buttons and RF circuitry for use as the
encoder in your security application. A description of
each pin is described in Table 2-1. Refer to Figure 2-3
for information on the I/O pins.
Note:
S0-S5 and SHIFT inputs have pull-down
resistors. VIN should be tied high if the
step-up regulator is not used.
TABLE 2-1: PIN DESCRIPTIONS
Name
Pin
Number
Description
S0
S1
S2
S3
S4
S5/SLEEP
SHIFT
VIN
STEP
RFEN
VSS
DATA
LED
VDD
1 Switch input S0
2 Switch input S1
3 Switch input S2
4 Switch input S3
5 Switch input S4
6 Switch input S5, or SLEEP
output
7 SHIFT input
8 Step-up regulator input
9 Step-up pulses output
10 RF enable output
11 Ground reference
12 Transmission output pin
13 Open drain output for LED
with pull-up resistor
14 Positive supply voltage
The HCS370 will normally be in a low power SLEEP
mode. When a button input is taken high, the device will
wake-up, start the step-up regulator, and go through
the button debounce delay of TDB before the button
code is latched. In addition, the device will then read
the configuration options. Depending on the configura-
tion options and the button code, the device will deter-
mine what the data and modulation format will be for
the transmission. The transmission will consist of a
stream of code words and will be transmitted TPU after
the button is pressed for as long as the buttons are held
down or until a time-out occurs. The code word format
can be either a code hopping format or a seed format.
The time-out time can be selected with the Time-out
Select (TSEL) configuration option. This option allows
the time-out to be set to 0.8s, 3.2s, 12.8s, or 25.6s.
When a time-out occurs, the device will go into SLEEP
mode to protect the battery from draining when a button
gets stuck. This option must be chosen to meet maxi-
mum transmission length regulatory limits which vary
by country.
FIGURE 2-1: TYPICAL CIRCUITS
Figure 2-1(A)
VDD
RLED
B0
S0
VDD
B1
S1
LED
RF PLL
Tx out
B2
S2
DATA
DATA IN
B3
S3
VSS
B4
S4
RFEN
ENABLE
B5
S5
STEP
VDD
SHIFT
VIN
Six Button remote with PLL control
Figure 2-1(B)
2.05-5.5V
S0
VDD
S1
LED
S2
DATA
S3
VSS
S4
RFEN
SLEEP STEP
SHIFT
VIN
330 µH
Tx out
1N4148
COUT
22 µF
6V@1 mA
33kΩ
10kΩ
2.2 kΩ
2N3904
1000 pF
Two Button remote with Step-up circuit
Note: Using SLEEP output low instead of grounding the resistor
divider reduces battery drain between transmissions
Figure 2-1(C)
VDD
Tx2
Tx1
RLED
S0
VDD
S1
LED
S2
DATA
S3
VSS
S4
RFEN
S5
SHIFT
STEP
VIN
Tx out
VDD
DUAL Transmitter remote control
2002 Microchip Technology Inc.
Preliminary
DS41111D-page 5