Digi BL1800 user manual Dcin

The linear voltage regulator is simply a fixed-voltage regulator with a ±5% voltage output tolerance as the temperature changes. The regulator has a small heat sink, which increases the maximum external input voltage. Higher external input voltages increase the voltage dropped by the regulator. The Vcc coming out of the regulator is always 5 V.

The power necessarily dissipated by the regulator can be calculated if both the external input voltage and the current drawn by the Jackrabbit board and daughterboards connected to the Jackrabbit board are known. The current provided by the high-power output drivers does not have to be included if a separate power supply is connected to K so that power does not come from Vcc.

The linear regulator maintains its output voltage to within ±5% as long as the heat sink is dissipating less than 2 W. The regulator will operate outside its specifications when the heat sink is dissipating 2 W to 3.3 W. Thermal shutdown turns the regulator off above 3.3 W. Figure C-2shows the power operating curves.

	350
	300					3.3 W
					(DCIN – 5 V)
(mA)	250					2 W
						(DCIN – 5 V)
Current	200		dropout area
						Thermal
						shutdown
	150			Regulated
			Undervoltage			Regulated
				within		outside
				specifications		specifications
	100
	50	5	10	15	20	25	30	35
					DCIN (V)

Figure C-2. 7805 Linear Regulator Power Operating Curve

The Jackrabbit operating at 14.74 MHz with no loading at the outputs typically consumes 105 mA when the programming cable is connected, and 95 mA when the programming cable is not connected. This means that DCIN can safely be from 7.5 V to 25 V. An addi- tional 50 mA is available for a daughterboard, but the voltage regulation would suffer slightly.

80 Jackrabbit (BL1800)