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Data Sheet

ADPA7008

BIASING ADPA7008 WITH THE HMC980LP4E

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Rev. 0 | 24 of 28

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 ADPA7008. 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 ADPA7008, and the option to use an external negative

voltage source.

The HMC980LP4E is also available in die form as the HMC980-Die.

VDD

CONTROL

BLOCK

PACKAGE

BASE

GND

BAND GAP

NEGATIVE

VOLTAGE

GENERATOR

GATE

CONTROL

ALM

VDD

VDRAIN

VG2_CONT

VG2

VNEG

VGATE

VDRAIN

HMC980LP4E

Figure 74. Functional Diagram of HMC980LP4E

APPLICATION CIRCUIT SETUP

Figure 75 is the schematic of an application circuit using the

HMC980LP4E to control the ADPA7008. When using an external

negative supply for VNEG, refer to the schematic in Figure 76.

In the application circuit shown in Figure 75, the ADPA7008 drain

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

equations:

VDD = VDRAIN+ IDRAIN× 0.7 Ω (1)

VDD = 5 V + (1.6 A × 0.7 Ω) = 6.12 V

where:

VDD and VDRAIN are in volts.

IDRAIN is in amperes.

R10= 150Ω×A ÷ IDRAIN

(2)

R10 = (150 Ω × A) ÷ (1.6 A) = 94 Ω

where:

R10 is in ohms.

IDRAIN is in amperes.

LIMITING VGATE FOR THE ADPA7008 VGGX

ABSOLUTE MAXIMUM RATING REQUIREMENT

When using the HMC980LP4E to control the ADPA7008, the mini-

mum voltages for VNEG and VGATE must be −1.5 V to keep the

voltages within the absolute maximum rating limit for the VGGx

pin of the ADPA7008. To set the minimum voltages, set R15 and

R16 to the values shown in Figure 75 and Figure 76. 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 75 and Figure 76.

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