ADM1276-3ACPZ-RL(Rev0) View Datasheet(PDF) - Analog Devices

Part Name

Description

Manufacturer

ADM1276-3ACPZ-RL
(Rev.:Rev0)

Hot Swap Controller and Digital Power and Energy Monitoring with PMBus Interface

Analog Devices 

ADM1276

All comparisons performed by the power monitor require the

measured value to be strictly greater or less than the threshold

value.

At power-up, all threshold limits are set to either minimum

scale (for undervoltage or undercurrent conditions) or to

maximum scale (for overvoltage or overcurrent or overpower

conditions). This effectively disables the generation of any

status warnings by default; warning bits are not set in the status

registers until the user explicitly sets the threshold values.

VIN_OV_WARN_LIMIT and VIN_UV_WARN_LIMIT

Commands

The VIN_OV_WARN_LIMIT and VIN_UV_WARN_LIMIT

commands are used to set the OV and UV thresholds on the

input voltage, as measured at the SENSE+ pin.

VOUT_OV_WARN_LIMIT and VOUT_UV_WARN_LIMIT

Commands

The VOUT_OV_WARN_LIMIT and VOUT_UV_WARN_

LIMIT commands are used to set the OV and UV thresholds

on the output voltage, as measured at the VOUT pin.

IOUT_OC_WARN_LIMIT Command

The IOUT_OC_WARN_LIMIT command sets the OC

threshold for the current flowing through the sense resistor.

IOUT_WARN2_LIMIT Command

The IOUT_WARN2_LIMIT command provides a second

current warning threshold that can be programmed. The

polarity of this warning can be set to overcurrent or

undercurrent using the DEVICE_CONFIG command.

PIN_OP_WARN_LIMIT Command

The PIN_OP_WARN_LIMIT command is used to set the

overpower threshold for the power delivered to the load.

PMBus DIRECT FORMAT CONVERSION

The ADM1276 uses the PMBus direct format internally to

represent real-world quantities such as voltage, current, and

power values. A direct format number takes the form of a

2-byte, twos complement, binary integer value.

It is possible to convert in real-world quantities. Equation 1

converts from real-world quantities to PMBus direct values, and

Equation 2 converts PMBus direct format values to real-world

values.

Y = (mX + b) × 10R

(1)

X = 1/m × (Y × 10−R − b)

(2)

where:

Y is the value in PMBus direct format.

X is the real-world value.

m is the slope coefficient, a 2-byte, twos complement integer.

b is the offset, a 2-byte, twos complement integer.

R is a scaling exponent, a 1-byte, twos complement integer.

The same equations are used for voltage, current, and power

conversions, the only difference being the values of the m, b,

and R coefficients that are used.

Table 7 lists all the coefficients required for the ADM1276. The

coefficients shown are independent of the value of the external

sense resistor used in a given application. This means that an

additional calculation must be performed to take the sense

resistor value into account when converting to or from a real-

world current or power value.

The current sense voltage coefficients shown in Table 7 convert

between the voltage that appears across the sense resistor(s),

expressed in millivolts, and the direct format value that is used

by the ADM1276 as a threshold or reported as a current

measurement.

Example 1. IOUT_OC_WARN_LIMIT requires a current-limit

value expressed in direct format.

If the required current limit is 10 A, and the sense resistor is

2 mΩ, then the first step is to determine the current sense

voltage. This is simply V = IR, giving 20 mV in this case.

Using Equation 1, and expressing X, in units of millivolts

Y = ((807 × 20) + 20,475) × 10−1

Y = 3661.5 = 3662 (rounded up to integer form)

Writing a value of 3662 with the IOUT_OC_WARN_LIMIT

command sets an overcurrent warning at 10 A.

Example 2. The READ_IOUT command returns a direct format

value of 3339 representing the current flowing through a sense

resistor of 1 mΩ.

To convert this value to the current sense voltage, use Equation 2

X = 1/807 × (3339 × 101 − 20,475)

X = 16.00 mV

To convert to current in amps, use

I = V/R

where R is expressed in milliohms.

This means that when READ_IOUT returns a value of 3339,

16.00 A is flowing in the sense resistor.

Because power is equal to voltage × current, power value

conversions are affected by the value of the sense resistor in a

similar manner. The coefficients in Table 7 can be used to

convert direct format values to resistor scaled power values and

vice versa, which then need to be scaled by the resistor value.

When converting from real-world power to direct format, the

power (in watts) is multiplied by the value of the sense resistor

expressed in ohms to give the resistor scaled power value. The

resistor scaled power value can then be inserted into Equation 1

with the appropriate conversion coefficients to obtain the direct

format value.

When converting from direct format to real-world power, the

direct format value is first converted with Equation 2, and then

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