MAX2745 查看數據表（PDF） - Maxim Integrated

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MAX2745

Single-Chip Global Positioning System Receiver Front-End

Maxim Integrated 

Single-Chip Global Positioning System

Receiver Front-End

Temperature Sensor

The MAX2745 features an on-chip temperature sensor to

facilitate system temperature compensations in conjunc-

tion with the trimmed capacitor. This circuit generates an

output voltage at TEMPOUT, which is used to approxi-

mate the temperature by the following equation:

T = TO + (VOUT - VOUT,TO)/SG

where SG is the sensor gain, TO is factory-trimmed tem-

perature, which can be any value (normally +27°C), and

VOUT is the temperature output voltage at TO. The coeffi-

cient SG in the above equation is targeted to be between

6mV/°C and 8mV/°C, depending on the temperature.

Voltage Booster

The MAX2745 integrates an internal voltage booster to

allow proper operation with supply voltages as low as

1.6V. The circuit includes two 6nF floating external

capacitors connected to VB_CS± (pins 22 and 23) and

a 1µF capacitance to VOUT (boosted voltage output,

pin 24). To reduce the output voltage ripple, use an

external LC lowpass filter, which can be built with two

inductors and one capacitor.

Applications Information

Operation with Voltage Booster

Under normal operating conditions, the recommended

power-supply voltage ranges from 2.4V to 3.6V. But

with the integrated voltage booster on-chip, the

MAX2745 can be powered from power-supply voltages

as low as 1.6V, and only requires a minimal number of

external components. This is not the most efficient

operating mode, since the power efficiency will be low-

ered to less than 50%.

As described in the Detailed Description section, to use

the voltage booster, connect 6nF floating capacitors to

VB_CS±, pins 22 and 23, and 1µF bypass capacitor to

VOUT, pin 24. Connect VOUT (pin 24) to all the power-

supply (VDD) pins and pull BST_CTRL, pin 17, high to

activate the booster. Then the MAX2745 can be pow-

ered from supply voltages ranging from 1.6V to 2.3V at

VDD_VB, pin 19, and the voltage booster output can

source up to 25mA current. It is recommended that the

voltage booster be used as a backup supply. To do

this, additional circuits including a voltage monitor and

a switch are needed. These components are inexpen-

sive and can be found in the Maxim product family.

Layout Issues

A properly designed PC board is an essential part of

any RF/microwave circuit. Use the MAX2745 EV kit as a

guide. Use controlled-impedance lines on all frequency

inputs and outputs. Use low inductance connections to

ground on all ground pins and wherever the compo-

nents are connected to ground. Place decoupling

capacitors close to all VCC connections. For proper

operation, connect the metal exposed paddle at the

back of the IC to the PC board ground plane with multi-

ple vias.

Chip Information

TRANSISTOR COUNT: 9205

PROCESS: CMOS

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