ADMV1455BBCZ-R7 datasheet(84/141 Pages) AD

84 / 141 page

Data Sheet

ADMV1455

THEORY OF OPERATION

analog.com

Rev. 0 | 84 of 141

OVERLOAD PROTECTION

The ADMV1455 contains overload protection circuits connected to

DSA1 and the RF input LNA that allow the chip to automatically

power down when the CEN input is high and excessive RF input

power is detected. The overload protection helps prevent infrequent

excessive RF input power from causing catastrophic damage to the

ADMV1455.

Four different overload protection modes are available. Use Regis-

ter 0x108 (OVERLOAD_PROTECTION_MODE) to set the overload

protection mode.

When Register 0x108 is set to 0, automatic overload protection is

disabled. The two overload signals can be read back from Register

0x0A0 (RX_DSA1_OVERLOAD and RX_LNA_OVERLOAD). Exter-

nal appropriate action must be taken, such as powering down the

chip by using the CEN input.

When Register 0x108 is set to 1, automatic overload protection is

enabled for DSA1. When DSA1 experiences excessive RF input

power, the RX_DSA1_OVERLOAD bit is asserted high, and many

of the RF portions of the chip are powered down until the excessive

RF input power is removed.

When Register 0x108 is set to 2, automatic overload protection is

enabled for the RF input LNA. When the RF input LNA experiences

excessive RF input power, the RX_LNA_OVERLOAD bit is assert-

ed high, and many of the RF portions of the chip are powered down

until the excessive RF input power is removed.

When Register 0x108 is set to 3, automatic overload protection

is enabled for the RF input LNA with latch. When the RF input

LNA experiences excessive RF input power, the RX_LNA_OVER-

LOAD_LATCHED bit in Register 0x0A1 is asserted high, and

many of the RF portions of the chip are powered down. When

the excessive RF input power is removed, the many of the RF

portions of the chip continue to power down. To power up the

RF portions of the chip, the RX_LNA_OVERLOAD_LATCHED bit

must be cleared, which can be accomplished by setting OVER-

LOAD_PROTECTION_MODE to any other value. Ensure to set

OVERLOAD_PROTECTION_MODE back to the desired mode after

performing the clear operation.

The DSA1 threshold value is determined by Register 0x173. It

is recommended to use the 0 value, which corresponds with the

DSA1 overload protection input power threshold of approximately

13dBm.

The RF input LNA threshold value is determined by Register 0x172.

It is recommended to use the 0 value, which corresponds with the

LNA overload protection input power threshold of approximately

−6dBm.

Relationship to the Absolute Maximum Rating

The overload protection is intended for infrequent instances of

excessive RF input power. Continuous operation of the ADMV1455

with excessive RF input power is discouraged because it can

reduce chip lifetime.

Overload protection typically triggers at −6dBm for RF_IN (LNA)

and +13dBm for DSA_IN (DSA1). These levels exceed most abso-

lute maximum ratings when CEN = high.

When using automatic overload protection for the DSA1 mode or

the RF input LNA with latch mode, and excessive RF input power

has triggered the overload protection circuit, the expected chip

lifetime aligns with the absolute maximum ratings for CEN = low.

These two modes provide the highest level of protection.

When using the automatic overload protection for the RF input LNA

mode (nonlatched), and excessive RF input power has triggered

the overload protection circuit, the chip lifetime is approximately 2

hours with 0dBm applied.

Before overload protection activates, chip lifetime follows the abso-

lute maximum ratings for CEN = high. The RF input power range

between these ratings and the overload threshold is unprotected,

and continuous operation in this range is discouraged.

In systems that need to support a wide range of RF input power

levels, it may be advantageous to implement an external automatic

gain control (AGC) loop with the ADMV1455. The AGC loop could

monitor the RF input power and then make adjustments to DSAs on

the ADMV1455 to ensure chip lifetime is maintained.

For systems requiring prolonged excessive RF input power, or to

discuss possible AGC loop options, contact Analog Devices, Inc.,

Technical Support for guidance.

ADMV1455BBCZ-R7 Folha de dados(PDF) 84 Page - Analog Devices

ADMV1455BBCZ-R7 Folha de dados(HTML) 84 Page - Analog Devices

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 ...More

Folha de dados Download

Ligação URL