AD5560JBCZ datasheet(36/68 Pages) AD

36 / 68 page

AD5560

Data Sheet

Rev. D | Page 36 of 68

FORCE AMPLIFIER STABILITY

There are three modes for configuring the force amplifier: safe

mode, autocompensation mode, and manual compensation mode.

Manual compensation mode has highest priority, followed by safe

mode, then autocompensation mode.

Safe Mode

Selected through Compensation Register 1 (see Table 20), this

mode guarantees stability of the force amplifier under all

conditions. Where the load is unknown, this mode is useful but

results in a slow response. This is the power-on default of the

AD5560.

Autocompensation Mode

Using this mode, the user inputs the CR and ESR values, and

the AD5560 decides the most appropriate compensation

scheme for these load conditions. The compensation chosen

is for an optimum tradeoff between ac response and stability.

Manual Compensation Mode

This mode allows access to all of the internal programmable

parameters to configure poles/zeros, which affect the dynamic

performance of the loop. These variables are outlined in

Table 12 and Table 13.

Figure 57 shows more details of the force amplifier block.

Table 12. External Variables

Name

Description

Min

Max

DUT capacitance with contributing

ESR

10 nF

160 μF

ESR in series with CR

1 mΩ

10 Ω

DUT capacitance with negligible ESR

100 pF

10 nF

Loading resistance at the DUT

~2 Ω

Infinity

Current range

±5 μA

±1.2 A

Table 13. Internal Variables

Name

Description

Min

Max

Resistor in series with CC0, which

contributes a zero.

500 Ω

1.6 MΩ

Resistor to 8 pF to contribute an

additional pole

200 Ω

1 MΩ

CC0:CC3

Capacitors to ensure

unconditional stability

100 pF

100 nF

CF0:CF4

Capacitors to optimize ac

performance into different CR, CD

4.7 nF

10 μF

gmx

Transconductance of force

amplifier input stage

40 μA/V

900 μA/V

DUTGND

FORCE

SENSE

VSENSE

–

×1

CF0

4.7nF

RZ:

500Ω TO

1.6MΩ

CF1

22nF

CF2

100nF

CF3

470nF

CF4

2.2µF

RSENSE 2

RSENSE 1

AD5560

FORCE VOLTAGE LOOP

EXTFORCE1

EXTFORCE2

100kΩ

25kΩ

20Ω

200Ω

2kΩ

20kΩ

100kΩ

6kΩ

100pF

330pF

3.3nF

CC0

CC1

CC2

CC3

FORCE

DAC

RP:

200Ω TO 1MΩ

8pF

AGND

–

Figure 57. Block Diagram of a Force Amplifier Loop

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