znbg4003 Diodes, Inc., znbg4003 Datasheet - Page 5

• Manufacturer Part Number: znbg4003
• Description: 4 Stage Fet Lna Bias Controller
• Manufacturer: Diodes, Inc.

Applications Information
Above is a partial applications circuit for the ZNBG4003 showing all external components needed for biasing one of the four FET
stages available. Each bias stage is provided with a gate and drain pin. The drain pin provides a regulated 2.0V supply that
includes a drain current monitor. The drain current taken by the external FET is compared with a user selected level, generating a
signal that adjusts the gate voltage of the FET to obtain the required drain current. If for any reason, an attempt is made to draw
more than the user set drain current from the drain pin, the drain voltage will be reduced to ensure excess current is not taken.
The gate pin drivers are also current limited.
The bias stages are split up into two pairs, with the drain current of each pair set by an external R
currents of stages 1 and 3, whilst R
differing tasks such as input stages where noise can be critical and later amplifier stages where gain may be more important.
A graph showing the relationship between the value of R
datasheet.
The ZNBG4003 includes a switched capacitor DC-DC converter that is used to generate the negative supply required to bias
depletion mode FETs used in common source circuit configuration as shown above. This converter uses two external capacitors,
C
gate driver use and for external use if required (for extra discrete bias stages, mixer bias, local oscillator bias etc.). The -2.5V
supply is available from the C
If any bias stages are not required, their gate and drain pins may be left open circuit. If all bias stages associated with an R
resistor are not required, then this resistor may be omitted.
To ease PCB layout, the pinout for the ZNBG4003 includes two Vcc pins. These pins are internally connected so only one of the
pins needs to be powered for the device to function. It is probable that the extra pin will help avoid the need for trace cross-over
components or ground plane disruption from reverse side PCB links. Note that the exposed pad of the package must be either left
floating or connected to Csub.
Package Outline Dimensions
Note: Controlling dimensions are in millimetres. Approximate dimensions are provided in inches.
ZNBG4003
Document number: DS35007 Rev. 1 - 2
NB
the charge transfer capacitor and C
The package appearance may vary as shown, for further details please contact your local Diodes sales office.
Pin #1 ID
SUB
e
b
pin.
D
CAL
Z
2 sets the drain currents of stages 2 and 4. This allows the optimisation of drain currents for
SUB
E2
E
the output reservoir capacitor. The circuit provides a regulated -2.5V supply both for
L
D2
A
www.diodes.com
CAL
A1
A3
5 of 7
and I
D
is provided in the Typical Characteristics section of this
All Dimensions in mm
Dim
A1
A3
D2
E2
A
D
E
b
e
L
Z
Diodes Incorporated
QFN16 3x3
A Product Line of
0.55
0.00
0.18
2.95
1.40
2.95
1.40
0.35
Min
0.625 Typ
0.50 BSC
0.15 Typ
Max
0.65
0.05
0.28
3.05
1.60
3.05
1.60
0.45
CAL
resistor. R
CAL
1 sets the drain
ZNBG4003
© Diodes Incorporated
August 2010
CAL