For price, delivery, and to place orders, please contact Hittite Microwave Corporation:
20 Alpha Road, Chelmsford, MA 01824 Phone: 978-250-3343 Fax: 978-250-3373
Order On-line at www.hittite.com
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HMC920LP5E
v07.1013
ACTIVE BIAS CONTROLLER
Vdd Under-Voltage Alarm
The HMC920LP5E provides a low Vdd indicator signal (VddALM pin#31) when the Vdd supply voltage is lower than
an user adjustable threshold value. VddALM pin pulled down to GND when the Vdd voltage is lower than the adjusted
VddTHR value. To adjust the Vdd under-voltage alarm threshold set R6 (the resistance from VddCHK to AGND)
according to the relation provided in (6).
Power-up and Enable Sequencing
To ensure the safety of the external amplifier the HMC920LP5E provides a certain power-up sequence for enabling
active bias control loop. During start-up VDRAIN is kept at GND while VGATE is taken to the most negative supply
available (VGATE=VNEG). This ensures that external amplifier is completely turned-off before VDRAIN is applied.
When EN signal is received VDRAIN is applied and the active bias loop is enabled. The final phase of the power-up
sequence is completed by increasing the VGATE linearly until the set IDRAIN value is achieved.
For power-down and disabling the same sequencing is applied in the reverse order.
(6)
Figure 2. Current Alarm Behavior
Daisy-Chain Operation
HMC920LP5E produces a trigger out signal (TRGOUT pin#24) when the external amplifier achieves a stable bias
current (IDRAIN). This trigger signal can be used to enable additional HMC920LP5E chips in a chain of amplifiers.
The triggering sequence can be routed in anyway, from input to output, or from output to input depending on the
use. Figure-3 presents a sample use of three HMC920LP5Es in an amplifier chain. Please note that, only one of the
HMC920LP5E is used to generate the negative voltage and the remaining HMC920LP5E is set to receive external
negative voltages (which is provided from the master HMC920LP5E). Generating negative voltage only with single
HMC920LP5E reduces the number of the components in the system, and decreases the over all current consumption
slightly, compared to each bias controller generating its own negative voltage.
To ensure proper start-up, the system enable signal should ne applied to the chip that has the negative voltage
generator.
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-
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13
88
.
0
3
150
6
VddTHR
k
R
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