Datasheet

XTR108
25
SBOS187C
www.ti.com
VOLTAGE OUTPUT MODE USING SIMPLE
CURRENT PUMP
In order for the voltage output mode of the XTR108 to
operate properly, a negative voltage needs to be applied to
the I
RET
pin (–200mV < I
RET
< –25mV). For systems without
a negative supply a charge pump is an easy way to generate
this voltage. Figure 14 shows a simple and inexpensive way
to build this charge pump using two resistors, two capaci-
tors, and two diodes (in an SOT package). The charge pump
uses the clock signal from the XTR108 SCLK pin to operate;
consequently, the XTR108 must be in continuous EEPROM
read mode (register 4, bit 0). Figure 15 shows the typical
output of this circuit (–50mV dc).
Voltage
Reference
Linearization
Circuit
Multiplexer
SDIO
SCLK
CS2
CS1
V/I-0
V/I-1
V/I-2
V/I-3
V/I-4
V/I-5
RTD
R
Z1
R
Z2
R
Z3
R
Z4
R
Z5
C
FILT
0.01µF
R
CM
15.8kΩ 12.1kΩ
R
SET
R
LIN
V
OUT
I
IN
PGA
OPA +INOPA –IN
OPA OUT
REF
IN
REF
OUT
Σ
I
REF
DAC
I
LIN
DAC
Zero
DAC
SPI and
Control Circuits
OSC
XTR108
12
Sub-Regulator
Driver
V
OUT
V
OUT
= −50mV
V
Gate
+5V
V
S
I
O
I
Q1
= 0mA
Q1
0mV
+0V
I
RET
Output
Current
Amplifier
2.5kΩ 51Ω
330pF
1nF
30kΩ
36.5kΩ
BAV99
D
SUB
−200mV < VOA+ < −25mV
FIGURE 14. Voltage Output Mode Using Simple Current Pump.
FIGURE 15. Output Waveform of Simple Current Pump.
5.0V
XTR108
SCLK
Charge
Pump
Output
−50mV