TSM9938

TSM9938DS r1p0

Page 9

RTFDS

previously mentioned with large values of RSENSE.

4) Circuit Efficiency and Power Dissipation

IR losses in RSENSE can be large especially at high

load currents. It is important to select the smallest,

usable RSENSE value to minimize power dissipation

and to keep the physical size of RSENSE small. If

the external RSENSE is allowed to dissipate

significant power, then its inherent temperature

coefficient may alter its design center value, thereby

reducing load current measurement accuracy.

Precisely because the TSM9938’s input stage was

designed to exhibit a very low input offset voltage,

small RSENSE values can be used to reduce power

dissipation and minimize local hot spots on the pcb.

5) RSENSE Kelvin Connections

load currents, parasitic pcb track resistance should

be minimized. Kelvin-sense pcb connections

between RSENSE and the TSM9938’s RS+ and RS-

terminals are strongly recommended. The drawing in

Figure 1 illustrates the connections between the

current-sense amplifier and the current-sense

resistor. The pcb layout should be balanced and

symmetrical to minimize wiring-induced errors. In

addition, the pcb layout for RSENSE should include

good thermal management techniques for optimal

RSENSE power dissipation.

Optional Output Filter Capacitor

If the TSM9938 is part of a signal acquisition system

where its OUT terminal is connected to the input of

an ADC with an internal, switched-capacitor track-

and-hold circuit, the internal track-and-

hold’s

A 22nF to 100nF good-quality ceramic capacitor

from the OUT terminal to GND should be used to

during the sample interval. Using a capacitor on the

OUT terminal will also reduce the TSM9938’s small-

signal bandwidth as well as band-limiting amplifier

noise.

Using the TSM9938 in Bidirectional Load Current

Applications

In many battery-powered systems, it is oftentimes

necessary to monitor a battery’s discharge and

charge currents. To perform this function, a

bidirectional current-sense amplifier is required. The

circuit illustrated in Figure 2 shows how two

TSM9938s can be configured as a bidirectional

current-sense amplifier. As shown in the figure, the

Figure 1: Making PCB Connections to the Sense

Resistor (drawing is not to scale).

Figure 2: Using Two TSM9938s for Bidirectional Load Current Detection