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HCS412SN Datasheet(PDF) 7 Page - Microchip Technology |
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HCS412SN Datasheet(HTML) 7 Page - Microchip Technology |
7 / 44 page © 2002 Microchip Technology Inc. Preliminary DS41099C-page 7 HCS412 TABLE 2-2: OSCILLATOR CALIBRATION VALUE (OSCT) FIGURE 2-7: HCS412 NORMALIZED RFTE VERSUS TEMP 2.2.6 LOW VOLTAGE DETECTOR The HCS412’s battery voltage detector detects when the supply voltage drops below a predetermined value. The value is selected by the Low Voltage Trip Point Select (VLOWSEL) configuration option. The low voltage detector result is included in encoder transmissions (VLOW) allowing the receiver to indicate when the transmitter battery is low (Figure 3-2). The HCS412 indicates a low battery condition by changing the LED operation (Figure 3-9). FIGURE 2-8: TYPICAL VOLTAGE TRIP POINTS TABLE 2-3: VLOWSEL OPTIONS TABLE 2-4: VLOW STATUS BIT 2.2.7 THE S2/RFEN/LC1 PIN The S2/RFEN/LC1 pin may be used as a button input, RF enable output or as an interface to the LF antenna. Select between LC1 antenna interface and S2/RFEN functionality with the button/transponder select (S2LC) configuration option (Table 2-2). 2.2.7.1 S2 BUTTON INPUT CONSIDERATIONS The S2/RFEN/LC1 pin defaults to LF antenna output LC1 when the HCS412 is first connected to the supply voltage (i.e., battery replacement). The configuration register controlling the pin’s function is loaded on the first device activation after battery replacement. A desired S2 input state is therefore enabled only after the first activation of either S0, S1 or LC0. The transponder bias circuitry switches off and the internal pull-down resistor is enabled when the S2/ RFEN/LC1 pin reaches button input configuration. There will be an extra delay the first activation after connecting to the supply voltage while the HCS412 retrieves the configuration word and configures the pins accordingly. OSCT3:0 Description 0111b Slowest Oscillator Setting (long TE) +: 0011b 0010b 0001b : Slower (longer TE) : 0000b Nominal Setting 1111b 1110b 1101b : Faster (shorter TE) : -: 1000b Fastest Oscillator Setting (short TE) 0.94 1.10 1.08 1.06 1.04 1.02 1.00 0.98 0.96 0.92 0.90 RFTE RFTE VDD LEGEND = 2.0V = 3.0V = 6.0V NORMALIZED Temperature °C -50 -40 -30 -20 -10 0 10 20 30 40 50 60 70 80 90 Note: Values are for calibrated oscillator. RFTE VLOWSEL Nominal Trip Point Description 0 2.2V for 3V battery applications 1 4.4V for 6V battery applications VLOW Description 0VDD is above selected trip voltage 1VDD is below selected trip voltage VLOW Volts (V) -40 050 85 2.0 1.6 1.8 2.2 2.4 2.6 Temp (°C) VLOW sel = 0 4.4 4.0 4.2 3.8 4.6 4.8 5.0 VLOW sel = 1 2.8 Nominal VLOW trip point |
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