ADP1055ACPZ-R7 datasheet(23/140 Pages) AD

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Data Sheet

ADP1055

Rev. A | Page 23 of 140

ADCs AND TELEMETRY

Two kinds of ADCs are used in the ADP1055:



Low frequency (LF) Σ-Δ ADCs that runs at 1.56 MHz for

accurate measurement and telemetry



High frequency (HF) flash ADCs for the feedback and

control loop

Σ-Δ ADCs have a resolution of one bit and operate differently

from traditional flash ADCs. The equivalent resolution obtain-

able depends on how long the output bit stream of the Σ-Δ ADC

is sampled.

Σ-Δ ADCs also differ from Nyquist rate ADCs in that the quan-

tization noise is not uniform across the frequency spectrum. At

lower frequencies, the noise is lower, and at higher frequencies,

the noise is higher (see Figure 28).

Figure 28. Noise Performance for Nyquist Rate and Σ-Δ ADCs

The low frequency ADC runs at approximately 1.56 MHz. For a

specified bandwidth, the equivalent resolution can be calculated

as follows:

ln(1.56 MHz/BW)/ln2 = N bits

For example, at a bandwidth of 95 Hz, the equivalent

resolution/noise is

ln(1.56 MHz/95)/ln2 = 14 bits

At a bandwidth of 1.5 kHz, the equivalent resolution/noise is

ln(1.56 MHz/1.5 kHz)/ln2 = 10 bits

The ADC output information is available in the value registers

(Register 0xFE96 to Register 0xFEA3) or through the PMBus

READ_x commands, where x = VOUT, IOUT, and so on.

ADCs FOR CURRENT SENSING

The ADP1055 has two current sense inputs: CS1 and CS2±.

These inputs sense, protect, and control the primary input current

and the secondary output current information. The CS1 and

CS2± inputs can be calibrated to reduce errors due to external

components for accurate telemetry.

CS1 ADC for Primary Side Current

The CS1 pin is typically used for the monitoring and protection

of the primary side current. The primary side current is sensed

using a current transformer (CT). The input signal at the CS1 pin

is fed into the CS1 ADC for current monitoring. Figure 29 shows

the typical configuration for the current sense. The READ_IIN

command reports the average input current; this reading is

updated every 10.5 ms.

Figure 29. Current Sense 1 (CS1) Operation

CS2 ADC for Secondary Side Current

The CS2+ and CS2− pins are differential inputs used for the

monitoring and protection of the secondary side current. The

ADP1055 supports differential sensing using low-side current

sensing with two ranges for the ADC: 30 mV and 60 mV.

The low input range is used to operate in level shifting mode,

when the CS2 terminals are connected directly to the shunt

resistor (see Figure 30). In this mode, a pair of internal resistors

and current sources are used to perform the necessary level

shifting. In this mode, only low-side current sensing is possible,

and the ADC range is programmable to 30 mV or 60 mV.

Figure 30. Differential Low-Side Sensing

FREQUENCY

NYQUIST ADC

NOISE

Σ-∆ ADC

NOISE

CS1

1kΩ

10Ω

I = 100mA

I = 10A

VIN

OUTA

OUTB

OUTC

OUTD

ADC

12 BITS

VREF

FAST

OCP

1:100

CS2–

AGND

CS2 RANGES

RANGE1 = 0mV TO 30mV

RANGE2 = 0mV TO 60mV

CS2 FAST OCP

0mV TO 60mV/6 BITS

(STEP SIZE 0.952mV)

CS2 ADC

IOUT_OC_LIMIT

IOUT_UC_LIMIT

CS2 IREV LIMIT

0mV TO –30mV

(STEP SIZE 0.4762mV)

ILOAD

ADP1055

CS2+

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