Datasheet
600W
600W
VSP
VSON
VSON
100 A
Source
m
100 A
Sink
m
F1
F2
D12
G1
G2
C1
B1
A1b
B1b
A1
INP2
INP1
BUF
600W
600W
VSON
DVDD DGND
VSON
C2
B2
A2b
B2b
A2
INN2
INN1
BUF
VSN
Gain
Network
SerialPeripheralInterface
andControls
PGA280
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................................................................................................................................................ SBOS487A –JUNE 2009–REVISED SEPTEMBER 2009
Input Switch Network
Figure 44 shows the arrangement of the input switches. They are controlled individually via the digital SPI. The
switches B1b, B2b, A1b, and A2b are controlled automatically with the buffer (BUF) operation.
Figure 44. Input Switch Diagram
Switches A and B select the signal input. Input 1 (INP1 and INN1) provides two current sources and two switches
that connect to VSON (which is typically the analog ground). This configuration is intended for wire break
diagnosis. D12 can discharge an external capacitor or generate a starting condition.
Switches C1 and C2 are used to measure the input voltage referred to GND (VSON); for example, with A1 and
C2 closed. This scheme measures the voltage signal connected to the input pin (INP1) referred to a common
ground. The BUF output is protected against a short to VSON. See the SPI and Register Description section for
more information about switch control.
Input Amplifier, Gain Network and Buffer
The high-precision input amplifiers present very low dc error and drift as a result of a modern chopper technology
with an embedded synchronous filter that removes virtually all chopping noise. This topology reduces flicker
noise to a minimum and therefore enables the precise measurement of small dc-signals with high resolution,
accuracy, and repeatability. The chopper frequency of 250kHz is derived from an internal 1MHz clock. An
external clock can also be connected, if desired.
The gain network for the binary gain steps connects to the input amplifiers, thus providing the best possible
signal-to-noise ratio (SNR) and dc accuracy up to the highest gains. Gain is controlled by Register 0. This
register can control the gain and address for an external MUX in one byte. Selectable gains (in V/V) are : 128,
64, 32, 16, 8, 4, 2, 1, ½, ¼, and ⅛. The gain is set to 1/8V/V after device reset or power-on.
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