NCP45491

www.onsemi.com

5

APPLICATIONS INFORMATION

Differential Output Amplifier

A differential output amplifier provides a scaled

representation of multiple bus voltages and currents to an

external device on the DIFF_OUT_P and DIFF_OUT_N

pins. These voltages and currents are presented sequentially

(under control of the Sequence Logic block) via the

Multiplexer. The common−mode voltage of the differential

output amplifier is established by the voltage on the

CM_REF_IN pin.

Current Shunt Monitor (one of four identical instances)

The differential voltage across an external shunt resistor

implemented by an op−amp and external resistor R1. This

current is supplied to the SH_Ox pin where it is converted

back to a ground−referenced voltage by external resistor R2.

The conversion gain from differential voltage across the

shunt resistor to that ground−referred voltage on SH_Ox

capacitor may be connected across R2 in order to provide

noise filtering if required in the application. Note that bias

current for the op−amp is taken from the “load” side of the

shunt resistor so that it is included in the load current

measurement.

Current Shunt Resistors

Figure 1 are used to define the full dynamic range of the

shunt current monitoring and are user application

I

R

SHUNT

R

1

I

LOAD

(eq. 1)

resistance of R2 is found with the relationship;

R

V

SH_Ox

I

SH_Ox

(eq. 2)

maximum voltage of the SH_Ox pin shall not exceed

Bus Voltage Monitor (one of four identical instances)

An external voltage divider is used to scale the voltage on

the BS_INx pin to an appropriate full−scale range for the

differential output amplifier. Resistors R3 and R4 form a

resistor divider to define the full dynamic range of the bus

voltage monitor with;

R

4

R

V

(eq. 3)

Multiplexer Select

The multiplier selection is controlled by a single digital

input (MUX_SEL pin). The device will monitor this pin and

cycle through the different measured parameters in a fixed

sequence. The sequence will repeat cycle as shown in the

tables until either a timeout condition is detected or the

device is disabled. The MUX_SEL pin needs to be pulsed at

least once before normal MUX_SEL cycles begin. The

delay between the falling edge of the last initial MUX_SEL

pulse and the first rising edge of the normal MUX_SEL

cycle needs to be 14.75

ms > Td > 24.25 ms.

Operating Modes

There are two operating modes – stand−alone (one to four

channels) and paired operation (up to eight channels). In

paired operation, MODE_SEL is used to designate a

“Device A” and “Device B” of a pair. When paired, the

differential output amplifiers of the two devices are

expected to be “wire−or’ed” together, and the table logic

insures

that

only

one

device

will

actively

drive

DIFF_OUT_P and DIFF_OUT_N at any given time. See

description in the Auxiliary Functions section for details.

Additionally, devices can be configured to operate with a

reduced channel count. See description in the Auxiliary

Functions section for details.

Four−Channel Stand−Alone Operation

MUX_SEL Cycle

Differential Amp Output

Standby

Hi−Z

1

Channel 1 Bus Voltage

2

Channel 1 Shunt Current

3

Channel 2 Bus Voltage

4

Channel 2 Shunt Current

5

Channel 3 Bus Voltage

6

Channel 3 Shunt Current

7

Channel 4 Bus Voltage

8

Channel 4 Shunt Current

9

³1

Channel 1 Bus Voltage

10

³2

Channel 1 Shunt Current

….

Repeat cycle until reset or timeout

Six−Channel Paired Operation

MUX_SEL

Cycle

Differential Amp

Output (Device A)

Differential Amp

Output (Device B)

Standby

Hi−Z

Hi−Z

1

Ch 1 Bus Voltage

Hi−Z

2

Ch 1 Shunt Current

Hi−Z

3

Ch 2 Bus Voltage

Hi−Z

4

Ch 2 Shunt Current

Hi−Z

5

Ch 3 Bus Voltage

Hi−Z

6

Ch 3 Shunt Current

Hi−Z

7

Hi−Z

Ch 1 Bus Voltage

8

Hi−Z

Ch 1 Shunt Current

9

Hi−Z

Ch 2 Bus Voltage

10

Hi−Z

Ch 2 Shunt Current

11

Hi−Z

Ch 3 Bus Voltage

12

Hi−Z

Ch 3 Shunt Current

13

³1

Ch 1 Bus Voltage

Hi−Z

14

³2

Ch 1 Shunt Current

Hi−Z

….

Repeat cycle until re-

set or timeout

Repeat cycle until re-

set or timeout