Data Sheet

ADPA7005

BIASING ADPA7005 WITH THE HMC980LP4E

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Rev. A | 19 of 24

The HMC980LP4E is an active bias controller that measures and

regulates drain current by automatically adjusting the gate voltage.

The HMC980LP4E can control the biasing of RF amplifiers with

drain voltages up to 16.5 V and currents up to 1.6 A. The control-

ler provides constant drain current biasing over temperature and

device to device variation, and properly sequences gate and drain

voltages to ensure the safe operation of the amplifier.

The HMC980LP4E offers self protection in the event of a short

circuit, as well as an internal charge pump that generates the

negative voltage required on the gate of the ADPA7005. The

HMC980LP4E also provides the option to use an external negative

voltage source. The HMC980LP4E is also available in die form as

the HMC980-DIE.

APPLICATION CIRCUIT SETUP

Figure 53 shows a schematic of an application circuit using the two

HMC980LP4E devices to control the ADPA7005. When using an

external negative supply for VNEG, refer to the schematic in

Figure 54.

Although the ADPA7005 is specified with a IDQ of 1400 mA, the

operational drain current, IDRAIN, required to achieve the maximum

output power from the ADPA7005 must be set closer to 1800 mA.

The IDRAIN current increases to approximately 1800 mA when the

RF input power is 15 dBm, the approximate input compression

point (see Figure 41). As a result, a target IDRAIN of 1800 mA is

chosen.

Two HMC980LP4E devices are needed to support current levels

at 1800 mA because a single HMC980LP4E device can support a

maximum current of 1600 mA. In the application circuit shown in

Figure 53 and Figure 54, the ADPA7005 drain voltage and drain

current are set by the following equations:

VDRAIN = VDD − IDRAIN × 0.85 Ω

where:

VDRAIN = 5 V, the drain voltage from Pin 17 and Pin 18 of the

HMC980LP4E.

VDD = 5.765 V, the supply voltage to the HMC980LP4E.

IDRAIN = 1800 mA, the constant drain current from Pin 17 and Pin

18 on the HMC980LP4E.

R10 = (150 Ω × A)/IDRAIN

R10 = (150 Ω x A)/(1.8 A) = 83 Ω

where:

R10 is in ohms.

IDRAIN is in amperes.

LIMITING VGATE AND VNEG FOR ADPA7005

VGGX ABSOLUTE MAXIMUM RATING

REQUIREMENT

When using the HMC980LP4E to control the ADPA7005, set the

minimum voltages for the VNEG and VGATE pins of the

HMC980LP4E to −1.5 V to keep these voltages within the absolute

maximum rating limits for all VGG pins of the ADPA7005. To set

the minimum voltages, use the R15 and R16 resistors shown in

Figure 53 and Figure 54. Refer to the AN‑1363 Application Note,

Meeting Biasing Requirements of Externally Biased RF/Microwave

Amplifiers with Active Bias Controllers, for more information and

calculations for R15 and R16.