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Data Sheet

ADPA7008CHIP

Rev. 0 | Page 19 of 26

BIASING ADPA7008CHIP WITH THE HMC980LP4E

The HMC980LP4E is an active bias controller that is designed

to meet the bias requirements for enhancement mode and

depletion mode amplifiers such as the ADPA7008CHIP.

The controller 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 also offers self protection in

the event of a short circuit, an internal charge pump that

generates the negative voltage needed on the gate of the

ADPA7008CHIP, and the option to use an external negative

voltage source. Because the HMC980LP4E can deliver a

maximum current of 1.6 A and because the ADPA7008CHIP

requires a peak current of IDD = 1.7 A, two HMC980LP4E

devices must be used in parallel in this instance.

The HMC980LP4E is also available in die form as the

HMC980-Die.

ALM

VDD

VG2_CONT

PACKAGE

BASE

GND

VG2

VNEG

VGATE

VDRAIN

CONTROL

BLOCK

GATE

CONTROL

BAND GAP

NEGATIVE

VOLTAGE

GENERATOR

HMC980LP4E

Figure 58. Functional Diagram of HMC980LP4E

APPLICATION CIRCUIT SETUP

Figure 59 shows an application circuit using the HMC980LP4E

to control the ADPA7008CHIP. When using an external

negative supply for VNEG, refer to the schematic in Figure 60.

In the application circuit shown in Figure 59, the ADPA7008CHIP

drain voltage, VDRAIN, and drain current, IDRAIN, are set by the

following equations:

VDD = VDRAIN + (IDRAIN × 0.85 Ω)

(1)

VDD = 5 V + (0.85 A × 0.85 Ω) = 5.72 V

where:

VDD and VDRAIN are in volts.

IDRAIN is in amperes.

R10 = (150 Ω × A) ÷ (IDRAIN)

(2)

R10 = (150 Ω × A) ÷ (0.85 A) = 176 Ω

where:

R10 is in ohms.

IDRAIN is in amperes.

IDRAIN is set to 850 mA in these equations because the current is

split between two HMC980LP4E devices. Because both ISENSE

currents flow through the same resistor, the actual value used

must be half of the above value (that is, 88 Ω ).

LIMITING VGATE FOR THE ADPA7008CHIP VGGx

ABSOLUTE MAXIMUM RATING REQUIREMENT

When using the HMC980LP4E to control the ADPA7008CHIP,

the minimum voltages for VNEG and VGATE must be −1.5 V

to keep the voltages within the absolute maximum rating limit

for the VGGx pad of the ADPA7008CHIP. To set the minimum

voltages, set R15 and R16 to the values shown in Figure 59 and set

R16 to the value shown in Figure 60. Refer to the AN-1363 for

more information and calculations for R15 and R16.

The HMC980LP4E application circuits for biasing figures in

the AN-1363 are two examples of how the HMC980LP4E is

used as an active bias controller. Both application circuits

within the AN-1363 show the R5 and R7 resistors, which are

analogous to the R15 and R16 resistor shown in Figure 59 and

Figure 60.

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