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ML2731CT

PA Bias Controller

Micro Linear Corporation 

PRELIMINARY

ML2731

FUNCTIONAL DESCRIPTION

INTRODUCTION

EXTERNAL INTERFACES

The ML2731 has 3 logic inputs: PAEN, NEGEN and PDN.

These control lines are used to select the mode of

operation to be either SLEEP, STANDBY, PRETX or

TRANSMIT. (See Table 1)

PDN

1

0

NEGEN

X

1

PAEN

X

X

Mode

SLEEP

STANDBY

DESCRIPTION OF OPERATION

Voltage Regulator

The ML2731 integrates two low noise voltage regulators.

The first regulator internally powers the crystal oscillator

support circuit, negative voltage generator support circuit

and other on chip circuits.

The second regulator output (REGO) powers external

circuits. (See Figure 1) It has a nominal voltage output of

2.9V and sources up to 50mA of current. The low noise

output of this regulator makes it suitable for supplying

voltage to sensitive components such as final frequency

VCO’s. The regulator output is disabled in the SLEEP mode

and is enabled in all other modes.

0

0

1

PRETX

0

0

0

TRANSMIT

Table 1. Circuit Enable Logic

MODE CONTROL

Mode Functions

The function of the ML2731 in each mode of operation:

SLEEP

All the circuits are disabled. Current drain is typically less

than 1mA.

STANDBY

Oscillator circuits, sine and square wave outputs and 3.0V

voltage regulator output are all enabled. VPA output is

disabled as well as all other circuits.

PRETX

Oscillator circuits, sine and square wave outputs, 3.0V

voltage regulator output, and negative voltage generator

are enabled. VBIAS is set to –3.0V. VPA output is disabled

and PA bias control loop is inactive.

TRANSMIT

Crystal oscillator circuits, sine and square wave outputs,

3.0V voltage regulator, negative voltage generator, and

VPA output are enabled, and VBIAS is voltage controlled

so that the VPA current is proportional to the ICON input

voltage.

2.92

2.90

2.88

2.86

2.84

0

10

20

30

40

50

CURRENT (mA)

Figure 1. Regulator Ouput Voltage vs. Load Current (REGO)

6

PRELIMINARY DATASHEET January, 2000

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