For price, delivery and to place orders: Hittite Microwave Corporation, 2 Elizabeth Drive, Chelmsford, MA 01824

Phone: 978-250-3343

Fax: 978-250-3373

Order On-line at www.hittite.com

Application Support: Phone: 978-250-3343 or apps@hittite.com

14

HMC980

v00.0312

Active BiAs controller

High current

the bias current passing through the external amplifier can be adjusted with rsense, where rsense is the r10

connected from isense to GnD. Use the relation given in equation (2) to set the desired bias current through the

external amplifier.

iDrain=150/rsense (a)

(2)

vG2 voltage Adjustment

the hMC980 generates a second gate voltage (VG2). VG2 can be adjusted through a resistor divider connected to

VG2_Cont for the amplifiers which require second gate voltage. eqn. (3) gives the formula to adjust VG2

:

VG2(V)= VDD*r4/(r3+r4) - 1.3

(3)

For instance, choosing 5.1k ohm as r3 and 3.3k ohm as r4 sets VG2 voltage to 3.4V when VDD=12V. For improved

accuracy, choose resistor values below 5k ohm on r3.

self Protection Feature

Due to the small resistance of the internal switch Fet between VDD and VDrain, a large amount of current may flow

through the hMC980. hMC980 limits the maximum current to self protect itself under such fault conditions, by turning

off VDrain and VGate.

the hMC980 will remain in this protection mode until a full power-cycle or enable/disable cycle is applied.

vneG Fault Detection Feature

in depletion mode operation VneG is continuously monitored against short circuit fault to GnD. if VneG rises above

a preset value (typically -0.6V) the system and the external amplifier are disabled by pulling VDrain and VG2 to GnD

and VGate to VneG. the system will stay in this stand-by mode until short fault at VneG is fixed.

over/Under current Alarm

the hMC980 provides over and under current alarm indicator alM (pad#2) signal. the alM is pulled up to VDiG

when the iDrain current exceeds ± 6% (With the given r11, r12, and r13 values in application circuit) of iDrain

regulation target value as shown in Figure 1. the alarm threshold level is user adjustable through r11,r12, and r13

according to the following equations:

over current alM threshold = i

Under current alM threshold = i

where r12+r13 should always be equal to 5 kΩ (%1 accuracy)

threshold values possess a small built-in hysterisis. the condition of alM signal does not effect the operation of

hMC980. it is provided only for monitoring purposes.