August 27, 1998
GENERAL RELEASE SPECIFICATION
SECTION 13
CURRENT SENSE AMPLIFIER
The Current Sense Amplifier module, used in conjunction with the Analog Sub-
system, is designed to monitor charge and discharge currents in smart battery
applications.
13.1 CURRENT SENSE AMPLIFIER APPLICATION
A typical connection for the Current Sense Amplifier (CSA) block is illustrated in
Figure 13-1. With a sense resistor, R
of 0.01Ω, the voltage setup across the
SENSE
node CSA and V (ground) will vary to the current (in either charging or discharg-
SS
ing mode) as shown in Table 13-1.
Table 13-1. Voltage Across the Sense Resistor against Current
Current flowing
Voltage across the Sense Resistor, R
SENSE
10mA
1A
0.1mV
10mV
50mV
5A
R
=0.01Ω
SENSE
In this case, the CSA is required to measure a current from 10mA to 5A over the
operating temperature from 0°C to 70°C.
With the A/D in the Analog Subsystem set up for 12-bit resolution, the step size is
approximately 1.22mV (V =5V). To measure the 0.1mV for the 10mA current
DD
flow, a gain of greater than 10 is required.
The CSA module is designed with two gain settings, 10 and 30. With a 10-bit A/D,
and a gain of 30, the CSA can measure current with a typical resolution of 17mA
steps.
After amplification, the resultant signal is fed to channel 6 (MUX6) of the analog
subsystem for A/D conversion.
MC68HC05SB7
REV 2.1
CURRENT SENSE AMPLIFIER
MOTOROLA
13-1
FREESCALE [ Freescale ]
