MPQ8112/MPQ8112A

– 60V, HIGH-SIDE CURRENT-SENSE AMPLIFIER

MPQ8112/MPQ8112A Rev. 1.0

www.MonolithicPower.com

10

7/7/2020

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OPERATION

The MPQ8112 and MPQ8112A are high-side

current-sense amplifiers with a wide 2.7V to 60V

operating

input

voltage

(VCC)

range.

Their

common mode input voltage (VCM) is based on

VCC, with an operating range of 0 ≤ VCM ≤ VCC ≤

60V.

The MPQ8112 directly converts a differential

input voltage to a voltage output with built-in

internal common input resistors and a load

resistor. The MPQ8112 has a 50V/V gain.

The MPQ8112A converts the differential input

voltage to a current output. This current is

converted back to a voltage with an external load

resistor. The MPQ8112A has an adjustable gain

based on the external common input resistors

and load resistor.

Gain Setting

The sense current (ISENSE) flows through the

sense resistor (RSENSE), which generates a sense

voltage

(VSENSE).

The

high-precision

sense

amplifier built into the MPQ8112/MPQ8112A

monitors the differential voltage (VSENSE) and

dynamically adjusts the gate voltage of the

internal N-channel MOSFET (M1) to maintain an

equal

passing

current

(IRG1).

IRG1

is

then

multiplied by a gain factor (GM) in the output

stage current mirror, and finally flows through

ROUT to generate VOUT.

The MPQ8112/MPQ8112A

’s output (VOUT) can

be estimated with Equation (1):

VOUT = ISENSE x RSENSE / RG1 x GM x ROUT

(1)

Where GM is 5A/A, and RG1 and ROUT are external

resistors for the MPQ8112A. For the MPQ8112,

RG1 is instead RIN_1, and ROUT is instead RIN_OUT.

These values are

1kΩ and 10kΩ, respectively.

The total gain (AV) can be calculated with

Equation (2):

AV = VOUT / VSENSE = ROUT / RG1 x GM

(2)

The

MPQ8112A’s gain is adjustable by selecting

different

combinations

of

ROUT

/

RG1.

The

MPQ8112

’s gain is fixed to 50V/V, and set by the

internal resistors (RIN_1 and RIN_OUT).

VCC Supply

The VCC supply is the power source for the

internal input stage amplifier and output stage

current mirror circuitry. Use a bypass capacitor to

ensure stability. Apply a 0.1µF to 1µF low-ESR

ceramic capacitor between VCC and GND, as

close as possible. If the VCC power source is

noisy, additional capacitance may be required.

Common Input Voltage

The

MPQ8112/MPQ8112A

’s

common

input

ranges between 0V and VCC.

The minimum common input voltage is 0V. If the

common input voltage is below 1.2V, an internal,

dedicated compensation circuit is activated and

drives the M1 drain voltage high enough to make

the shunt current (IRG1) pass into the current

mirror. The compensation circuit can cause the

output error to rise when VCM is below 1.2V ( for

more information, see the Output Error vs. VSENSE

curves

in

the

Typical

Performance

Characteristics section on page 7).

It is recommended to ensure that the common

input voltage (VRG1) does not exceed VCC since

VRG1 is the positive input of the amplifier, which is

powered by VCC.

V5 Supply

V5 supplies the internal control block. It also

supplies the compensation circuit when the

common input voltage (VRG1 / VRG2) is low.

V5 can act like a digital control pin that turns the

current-sense amplifier on and off. If V5 is pulled

below its 1.9V lower threshold voltage, the chip

shuts down. If V5 is pulled above its 2V upper

threshold voltage, the part turns on.

In addition, if the common input voltage drops

below 1.2V, the compensation circuit is activated

and drives the M1 drain voltage high enough to

make the shunt current (IRG1) pass into the

current

mirror.

The

compensation

circuit

consumes 0.1mA to 1mA of current when it starts

to

work.

Therefore,

V5

requires

a

low-

impendence power source and a 10nF to 100nF

ceramic bypass capacitor.