LT5528 datasheet(11/16 Pages) LINER

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LT5528

5528f

The RF output S22 with no LO power applied is given in

Table 4.

Table 4. RF Port Output Impedance vs Frequency for EN = High

and No LO Power Applied

Frequency

Output Impedance

S22

MHz

Mag

Angle

1000

23.7 + j8.1

0.371

157

1400

37.7 + j18.5

0.248

112

1600

47.0 + j14.3

0.149

93.6

1800

46.0 + j5.5

0.071

123

2000

39.2 + j3.7

0.127

159

2200

34.2 + j6.2

0.201

154

2400

31.0 + j9.4

0.260

147

2600

29.6 + j11.6

0.292

142

For EN = Low the S22 is given in Table 5.

Table 5. RF Port Output Impedance vs Frequency for EN = Low

Frequency

Output Impedance

S22

MHz

Mag

Angle

1000

22.8 + j7.7

0.386

158

1400

32.4 + j20.8

0.321

116

1600

42.4 + j25.1

0.274

91.7

1800

54.6 + j20.1

0.193

66.2

2000

55.3 + j6.0

0.076

45.3

2200

44.7 + j0.0

0.056

180

2400

36.0 + j1.9

0.164

171

2600

31.3 + j4.8

0.237

162

To improve S22 for lower frequencies, a shunt capacitor

can be added to the output. At higher frequencies, a shunt

inductor can improve the S22.Figure5showstheequivalent

circuit schematic of the RF output.

Note that an ESD diode is connected internally from

the RF output to ground. For strong output RF signal

levels (higher than 3dBm), this ESD diode can degrade

the linearity performance if the 50Ω termination imped-

ance is connected directly to ground. To prevent this, a

coupling capacitor can be inserted in the RF output line.

This is strongly recommended during a 1dB compression

measurement.

Enable Interface

Figure 6 shows a simpliﬁed schematic of the EN pin in-

terface. The voltage necessary to turn on the LT5528 is

1V. To disable (shut down) the chip, the Enable voltage

must be below 0.5V. If the EN pin is not connected, the

chip is disabled. This EN = Low condition is guaranteed

by the 75k on-chip pull-down resistor. It is important that

the voltage at the EN pin does not exceed VCC by more

than 0.5V. If this should occur, the supply current could

be sourced through the EN pin ESD protection diodes,

which are not designed to carry the full supply current,

and damage may result.

Figure 7. Evaluation Circuit Schematic

Figure 5. Equivalent Circuit Schematic of the RF Output

Figure 6. EN Pin Interface

OUTPUT

20pF

21pF

3nH

52.5

Ω

5528 F05

VCC

Evaluation Board

Figure 7 shows the evaluation board schematic. A good

ground connection is required for the exposed pad. If this

is not done properly, the RF performance will degrade.

75k

5528 F06

VCC

25k

BBIP

BBIM

VCC

VCC EN

5678

5528 F07

BBQM

BBQP

BOARD NUMBER: DC729A

100nF

OUT

GND

100nF

BBMI

LT5528

BBPI VCC

BBMQ GND

GND

BBPQ VCC

GND

100

Ω

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