ISL21400 Datasheet, PDF (10/17 Pages) Intersil Corporation – Programmable Temperature Slope Voltage Reference

ISL21400
Pin Descriptions
V_OUT
Programmable voltage output pin. Absolute voltage is
determined by device temperature and Equation 1. Drive
capability is limited to ±500μA output current and 5000pF
output capacitance.
A2, A1, A0
Hardware slave address pins that can be used to provide
several ISL21400 with a unique physical address to allow for
multiple devices off one I²C bus.
GND
This is the circuit ground pin. It is common for the V_OUT and
control signal inputs.
SDA
Serial Data Input/Output. Bidirectional pin used for serial
data transfer. As an output, it is open drain and may be
wire-ored with any number of open drain or open collector
outputs. A pullup resistor is required and the value is
dependent on the speed of the serial data bus and the
number of outputs tied together.
SCL
Serial Clock Input. Accepts a clock signal for clocking serial
data into and out of the device. The SCL line requires a
pullup resistor whose value is dependent on the speed of the
serial clock bus and the number of inputs tied together.
V_CC
Positive Power Supply. Connect to a voltage supply in the
range of 2.7V < V_CC < 5.5V, with minimum noise and ripple. For
best performance, bypass with a 0.1µF capacitor to ground.
If the A_V gain is set to 4 and V_OUT approaches 5.0V, then
V_CC must be set to >5.2V for best output performance.
Functional Description
Functional Overview
Refer to the Functional Block Diagram on page 2. The
ISL21400 provides a programmable output voltage which
combines both a temperature independent term and a
temperature dependent term. The temperature independent
term uses a bandgap voltage reference, and the
temperature dependent term uses a Proportional To
Absolute Temperature (PTAT) reference, or Temperature
Sensor. Each voltage source is scalable using two DACs via
the I²C serial bus. The resulting output voltage can vary from
0V to over 5V and has a variable, programmable
Temperature Slope (TS).
Reference Sections
Referring to the Block Diagram on page 2, the V_REF and
Temperature Sense (V_TS) outputs are summed together (Σ)
and then passed through the output gain stage (A). The
voltage output is programmable and is determined by the
following equation:
V_OUT
=
A_V
•
⎧
⎨
⎩
V_R
E
F
•
----ⁿ-----
255
+
V_TS
(_---2_-----•_----m_-----)_---–---2_---5_----5_--
255
⎫
⎬
⎭
(EQ. 1)
where
• A_V = 1, 2, 4
• V_REF = 1.200 (not temperature dependent)
• 0 ≤ n ≤ 255 (setting contained in Register 0, V_REF)
• V_TS = K(T-T₀)
• K = dV_TS/ dT = -2.1mV/C
• T = device temperature
• T₀ = +25°C
• 0 ≤ m ≤ 255 (setting contained in Register 1, TS)
See the Applications Information for ways to use Equation 1
and methods for output voltage calculations.
DACs Section
The ISL21400 contains two 8-bit DACs whose registers can
be programmed via the I²C serial bus. The DAC registers
are non-volatile such that the values are restored during the
V_CC power-up cycle of the device. One DAC (V_REF)is
dedicated to scale the bandgap voltage reference
(Temperature invariant) and the other DAC (V_TS) is
dedicated to scale the Temperature Sensor. Both of these
DACs can determine the output voltage as defined by
Equation 1 (See Register Information).
Output Gain Amplifier Section
The ISL21400 contains an output gain amplifier (A) that is
programmed via the I²C serial bus. The gain amplifier is the
last stage before the output and therefore controls the
overall gain for the device. The gain can be programmed for
1x, 2x, or 4x amplification. This gain factor is used to
program the output voltage as determined by Equation 1
(See Register Description).
There are 5 registers in the ISL21400 device, all nonvolatile
(see Table 2). All registers are accessible for reading or
writing through the I²C serial bus.
10
FN8091.0
December 14, 2006