MAX2395 Просмотр технического описания (PDF) - Maxim Integrated

Номер в каталоге

Компоненты Описание

Список матч

MAX2395

WCDMA Quasi-Direct Modulator with VGA and PA Driver

Maxim Integrated 

WCDMA Quasi-Direct Modulator

with VGA and PA Driver

Register Definition

The MAX2395 includes three programmable, 20-bit

registers consisting of two divide registers and an oper-

ational control register. These registers are pro-

grammed from the SPI/ MICROWIRE-compatible serial

port. The 4 least significant bits (LSBs) are reserved for

the register’s address. The register bits have been

assigned to allow sharing of the 3-wire bus with the

MAX2390/MAX2391/MAX2392/MAX2401 receiver ICs.

The 16 most significant bits (MSBs) are used for regis-

ter data. Data is shifted in MSB first, followed by the 4-bit

address. When CS is low, the clock input is active and

data is shifted with the rising edge of the clock. When CS

transitions to high, the shift register is latched into the

register selected by the contents of the address bits.

Power-up defaults for the three registers are shown in

Table 2. Initialize the registers according to the charac-

terization table (Table 1).

The RFM register sets the main frequency divide ratio

for the RF PLL. The RFR register sets the reference fre-

quency divide ratio. The RF VCO frequency is deter-

mined by the following:

RF VCO frequency = fREFin  (RFM/RFR)

where fREFin is the external input reference frequency

for the MAX2395.

The operational control register (OPCTRL) controls the

state of the IC. See Table 3 for the function of each bit.

The RFR divide register includes test bits B9–B15.

These bits are used to troubleshoot the VCO and syn-

thesizer section (see Table 4). These bits are not need-

ed for normal use and should be left as the values at

power-up.

The device offers several different operation modes for

conserving power. Table 5 explains how to implement

each mode.

Shutdown and Idle Mode™

The part offers a shutdown mode and idle mode for opti-

mal power management. In shutdown mode, all functions

are turned off except the serial interface. When the part

is shut down using the OPCTRL register, the IC draws a

residual current of 60µA (typ). In idle mode, the VCO,

PLL, and serial interface remain on to minimize startup

time. The GmC filter can be software programmed to

power on or off during idle mode (see Table 5).

Applications Information

External Matching to PA

The Tx outputs are internally matched to 50Ω. The

open-collector output requires a pullup inductor to VCC.

The selection of matching in the MAX2395 Evaluation

Kit allows optimization of ACPR.

Electromagnetic Compliance

Considerations

Two major concepts should be employed to produce a

low-spur and EMC-compliant transmitter: Minimize cir-

cular current-loop area to reduce H-field radiation, and

minimize losses. To minimize circular current-loop area,

bypass as close to the device as possible and use the

distributed capacitance of a ground plane. To minimize

losses, make RF traces short.

Program only the necessary bits in any register to mini-

mize clock cycles. RC filtering can also be used to slow

the clock edges on the 3-wire interface, reducing high-

frequency spectral content. RC filtering also provides for

transient protection against IEC 802 testing by shunting

high frequencies to ground, while the series resistance

attenuates the transients for error-free operation. The

same applies to the logic-input pins (SHDN, IDLE).

High-frequency bypass capacitors are required close

to the pins with a dedicated via to ground. The pack-

age provides minimal inductance ground by using an

exposed pad under the part. Provide at least five low-

inductance vias under the pad to ground to minimize

ground inductance. Use a solid ground plane wherever

possible. Any cutout in the ground plane may act as a

slot radiator and reduce its shield effectiveness.

Layout Issues

The MAX2395 Evaluation Kit can be used as a refer-

ence for board layout. Gerber files are available upon

request at www.maxim-ic.com.

To minimize coupling between different sections of the

IC, the ideal power-supply layout is a star configuration,

which has a large decoupling capacitor at a central VCC

node. The VCC traces branch out from this node, each

going to a separate VCC node in the circuit. At the end

of each trace is a bypass capacitor with impedance to

ground less than 1Ω at the frequency of interest. This

arrangement provides local decoupling at each VCC

pin. Use at least one via per bypass capacitor.

Idle Mode is a trademark of Maxim Integrated Products, Inc.

8 _______________________________________________________________________________________

Share Link: