ISL21400USB-EVALZ Intersil, ISL21400USB-EVALZ Datasheet - Page 15

• Manufacturer Part Number: ISL21400USB-EVALZ
• Description: EVAL BOARD FOR ISL21400
• Manufacturer: Intersil

Specifications of ISL21400USB-EVALZ

• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

In many cases a form of Equation 6 is needed which yields a
V
we get Equation 7:
EXAMPLE 1: PROGRAMMED TEMPERATURE
COMPENSATION EXAMPLE
The ISL21400 can easily compensate for known
temperature drift by programming the device for the initial
V
some simple steps. The accuracy of the final programmed
output will be limited to the data sheet specifications
(typically 1% accuracy for V
In this example, an N-Channel MOSFET gate has a
-2.8mV/°C Tempco from -10°C to +85°C. A constant bias
drain current is desired, with a target Vgs range derived from
the data sheet of 2.5V to 3.5V at +25°C.
Offset Setting: Using Equation 2 and targeting
V
Note that A
Temperature Slope Setting: Using Equation 5, which can
solve for Slope directly:
The ISL21400 device can be programmed with these
calculated parameters and perform temperature
compensation or direct control in the target circuit. If
parameters change for some reason, then the device can be
reprogrammed with new values and the circuit retested.
EXAMPLE 2. CALCULATING THE V
SLOPE
In some applications, it may be desirable to calculate what
the output voltage and temp slope are, given the
programmed register settings. Such an application could be
a closed loop system with internal calibration procedure. By
reading the registers of the ISL21400, then calculating the
V
A REF
n
V
OUT
OUT
OUT
OUT
(
OUT
=
V
A
A
m
=
OUT
TS
TS
159 decimal
9F hex
=
=
T ( )
(
setting and Tempco using standard equations and
= 3.0VDC:
change with respect to temperature. By rearranging,
DC
)
=
=
170 decimal
A9 hex
T ( )
=
=
------------------- -
4
0.333
)
=
2.50
---------- -
=
–
•
V
---------------------------- -
REF
A
2.8
4
–
OUT
(
(
A
T T
V
V
2.1
A
V
REF
•
–
V
=
=
varies from 0 to 1, so to get 2.40, A
•
A
(
•
TS
(
----------------------------------
K
0
REF
0.625
V
2 m
)
•
=
REF
•
)
A
=
255
1.20V
TS
=
) 255
A
•
=
–
V
2.50
A
=
--------- -
255
•
REF
n
–
K
OUT
15
2.8mV °C
•
)
A
TS
=
and Slope).
3.00V
⁄
,(in mV/°C )
OUT
TEMPERATURE
V
= 4.
(EQ. 7)
ISL21400
V
recorded.
For the following example, let’s determine the voltage output,
V
temperature variation (ppm) from +25°C to +85°C.
Equations 4 and 7 will be used to calculate the answers.
Given, the contents of the registers:
A
n = 178 decimal
m = 74 decimal
Using Equation 2:
Using Equation 5:
Also, to solve for overall temp slope of the output:
Note that Equation 1 can be used directly to solve for output
voltage at a given temperature, in this case +85°C:
Typical Applications Circuits
LDMOS RF Power Amplifier (RFPA). The ISL21400 is used
to set the gate bias for the LDMOS transistor in a single
stage of an RFPA. Normally this is done with a DAC or digital
potentiometer with some discrete temperature
compensation circuitry. The ISL21400 simplifies this control
and allows a full range of DC bias and tempco control.
A typical circuit can be calibrated for correct bias at room
temperature (+25°C) on power-up using a microcontroller or
direct I
increased to the highest operating range, and the
Temperature Slope setting can then be adjusted to bring the
amplifier back to correct bias. Since the Temp Slope setting
has a negligible effect on the room temperature setting, the
amplifier will be biased correctly over the operating
temperature of the unit.
V
=
=
0.8812mV °C
--------------------------------------- 10
V
V
V
V
OUT
OUT
OUT
OUT
OUT
OUT
1
0.8812mV °C
872.5mV
= 1
•
–
(DC) at +25°C, and also the change due to
T ( )
(
parameters, the system characteristics can be
(
2.1
+85°C
=
2
DC
C control. The temperature of the unit can then be
=
A
=
•
V
⁄
)
⎛
⎝
=
1 1.20
=
(
•
(
----------------------------------- -
⁄
A
) =
•
2 74
⎧
⎨
⎩
(
0.8376V
V
•
=
=
A
V
•
V
•
REF
1
•
0.8905V
255
K
⎧
⎨
⎩
•
6
) 255
1.20
V
•
•
=
–
•
REF
178
--------- -
255
A
1010ppm °C
--------- -
255
TS
n
•
⎞
⎠
) mV °C
178
--------- -
255
•
+
A
K T T
REF
+
(
⁄
– (
⁄
–
)
0.0021
0
)
(
------------------------------- -
2 m
) 85 25
•
(
255
) 255
–
–
)
⎫
⎬
⎭
(
--------------------------------- -
2 74
March 31, 2011
•
255
FN8091.3
) 255
–
⎫
⎬
⎭