ADGM1304JCPZ-R2 datasheet(26/34 Pages) AD

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ADGM1304

Data Sheet

Rev. G | Page 26 of 34

Hardware Reset

The digital portion of the ADGM1304 goes through an

initialization phase during VDD power up. To hardware reset the

ADGM1304, power cycle the VDD input. After power-up or a

hardware reset, ensure there is a minimum of 10 µs before any

SPI command is issued. Ensure that VDD does not drop out

during the 10 µs initialization phase because it may result in

incorrect operation of the ADGM1304.

Internal Error Status

When an internal error is detected in the device, the internal

error is flagged by the INTERNAL_ERROR bits (Bits[7:6]) of

the SWITCH_DATA register (Register 0x20), as shown in

Table 10. An internal error results from an error in the

configuration of the device at power up.

INTERNAL OSCILLATOR FEEDTHROUGH

The ADGM1304 has an internal oscillator running at a nominal

10 MHz. This oscillator drives the charge pump circuitry that

provides the actuation voltage for each of the switch gate elec-

trodes. Although this oscillator is very low power, the 10 MHz

signal is coupled to the switch and can be considered a noise

spur on the switch channels. The magnitude of this feedthrough

noise spur is specified in Table 1 and is typically −123 dBm or

−146 dBm/Hz when one switch is on. When all four switches

are simultaneously on, the feedthrough goes up to −120 dBm.

VDD level and temperature changes affect the frequency of the

noise spur. For the maximum and minimum frequency range

over temperature and voltage supply range, see Table 1.

INTERNAL OSCILLATOR FEEDTHROUGH

MITIGATION

In normal operation, the 80 V actuation voltage is supplied by

the driver IC. Setting the EXTD_EN pin (Pin 7) low enables the

built in 10 MHz oscillator. This setting enables the charge

pump circuitry to generate the 80 V required for MEMS switch

actuation. The internal oscillator is a source of noise which

couples through to the RF ports. The magnitude of this

feedthrough noise spur is specified in Table 1 and is typically

−123 dBm or −146 dBm/Hz when one switch is on. The

internal oscillator feedthrough can be eliminated by setting the

EXTD_EN pin high, which disables the internal oscillator and

charge pump circuitry. When the internal oscillator and charge

pump circuitry is disabled, the VCP pin (Pin 24) must be driven

with 80 V dc (VCPEXT) from an external voltage supply, as

outlined in Table 5, required for MEMS switch actuation. The

switch can still be controlled via the digital logic interface pins

or via SPI interface pins

LOW POWER MODE

Setting the EXTD_EN pin high shuts down the internal

oscillator. The ADGM1304 enters low power quiescent state,

drawing only 50 µA maximum supply current. When the

internal oscillator and charge pump circuitry is disabled, the

VCP pin (Pin 24) must be driven with 80 V dc (VCPEXT) from an

external voltage supply, as outlined in Table 5, required for

MEMS switch actuation. The switch can still be controlled via

the digital logic interface pins or via SPI interface.

TYPICAL OPERATING CIRCUIT

Figure 54 shows the typical operating circuit for the

ADGM1304 as used in the EVAL-ADGM1304SDZ. A 47 pF

(100 V rated) external capacitor is required on the VCP pin as a

holding capacitor for the 80 V gate drive voltage. The VDD pin is

connected to a 3.3 V supply. However, VDD can operate from

3.0 V to 3.6 V. RFGND is separated from AGND internally in

the device.

It is recommended to connect RFGND to AGND using one

large pad on the PCB to short together EP1 and EP2. Figure 54

shows the ADGM1304 configured to use the internal oscillator

as the reference to the driver IC control circuit.

Alternatively, set Pin 7 (EXTD_EN) high and apply 80 V dc

directly to Pin 24 to disable the internal oscillator and eliminate

all oscillator feedthrough. The switches can then be controlled

normally via the logic control interface (Pin 1 to Pin 4) or via

the SPI interface.

To avoid any floating nodes, connect a 10 MΩ shunt resistor to

RFGND on all RFx pins (RF1 to RF4, and RFC), as shown in

Figure 54. See the Floating Node section for more information.

An example of a 10 MΩ resistor that can be used with the

MEMS switch is the Multicomp MCRE000262. The

MCRE000262 is tested with the switch and has very small

(negligible) impact on the RF performance of the MEMS

switch.

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