Data Sheet

ADCA3280

APPLICATIONS INFORMATION

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Rev. 0 | 17 of 18

SUPPLY VOLTAGE AND CURRENT

The ADCA3280 can operate over a range of supply voltage and

current, allowing for optimization of performance for a given DC

power target, or to operate on a range of established power supply

voltage rails.

Supply voltage variation is a straightforward way to alter the device

power consumption, and performance, as a function of the bias

voltage, can be seen for both DOCSIS 3.1 and DOCSIS 4.0 loading

in the DOCSIS 3.1 Downstream Performance section and the DOC-

SIS 4.0 Downstream Performance section, respectively. While the

ADCA3280 is designed with 24 V supply rails in mind, significant ef-

ficiency gains are possible with a lower supply voltage. The majority

of the data presented in this data sheet demonstrates operation at

21 V with little or no loss of performance compared with 24 V. For

some applications, such as those with 1.2 GHz channel loading, as

seen in the DOCSIS 3.1 Downstream Performance section, there is

no significant change in performance with bias as low as 18 V.

The ADCA3280 also offers adjustable supply current. The IADJ pin

(Pin 2) allows the user to adjust the bias current of the device. If

left floating, the current self sets to more than the nominal operating

current by 20 mA to 40 mA. The voltage at the IADJ pin can be

directly set with a supply capable of sinking current, set by using a

supply and an external resistor network, or set with a resistor direct-

ly to ground. An internal voltage reference die is used to keep the

bias current well centered as a function of process and temperature

variation. Generally, to increase IDD more than a nominal set point,

a supply must source current into the IADJ network. To decrease

IDD, the supply must sink current from the IADJ network. The typical

device current as a function of the voltage at the IADJ pin can

be seen in Figure 25. The typical device current as a function of

voltage at the IADJ node in the recommended application circuit

can be seen in Figure 26.

Figure 25. IDD vs. IADJ Voltage over VDD

Figure 26. IDD vs. Application Circuit IADJ Voltage over VDD

INTERNAL THERMAL MONITOR

The ADCA3280 has an internally mounted 10 kΩ NTC resistor that

can be used to monitor the temperature of the backside paddle of

the device. The NTC can be monitored directly through the TSEN

pin (Pin 8) with an ohmmeter, or by applying a small constant volt-

age (such as 0.1 V) or current (such as 0.01 mA) and calculating

the resulting resistance. Take care to minimize power dissipation in

the NTC because inaccuracies due to self heating or damage can

occur. Ideally, power dissipated in the thermistor must be less than

1 mW and not exceed 5 mW at any operating temperature. Figure

27 shows the relationship of the thermistor resistance measurement

to the paddle temperature of the ADCA3280.

Figure 27. TSEN Resistance vs. Temperature