LT1990AIS8 Linear Technology, LT1990AIS8 Datasheet - Page 15

• Manufacturer Part Number: LT1990AIS8
• Description: IC AMP DIFF +/-250V MCRPWR 8SOIC
• Manufacturer: Linear Technology

Specifications of LT1990AIS8

• Amplifier Type: Differential
• Number Of Circuits: 1
• Output Type: Rail-to-Rail
• Slew Rate: 0.55 V/µs
• -3db Bandwidth: 105kHz
• Voltage - Input Offset: 900µV
• Current - Supply: 140µA
• Current - Output / Channel: 22mA
• Voltage - Supply, Single/dual (±): 2.7 V ~ 36 V, ±1.35 V ~ 18 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (3.9mm Width)
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Gain Bandwidth Product: -
• Current - Input Bias: -

APPLICATIO S I FOR ATIO
While the LT1990 comes from the factory with an excellent
CMRR, some precision applications with a large applied
common mode voltage may require a method to trim out
residual common mode error. This is easily accomplished
by adding series resistance to each input, +IN and –IN,
such that an adjustable resistance difference of ±1kΩ is
provided. This is most easily realized by adding a fixed
1kΩ in series with one of the inputs, and a 2kΩ trimmer in
series with the other as shown in Figure 1. The trim range
of this configuration is ±0.1% for the internal gain resistor
matching, so a much more finely resolved correction is
available using the LT1990 than is realizable with ordinary
discrete solutions. In applications where the input
common mode voltage is relatively constant and large
(perhaps at or beyond the supply range), this same
configuration can be treated as an offset adjustment.
Dual Differential-Input Arithmetic Block
The internal resistor network topology of the LT1990
allows the GAIN1 and GAIN2 pins to be used as another
differential input in addition to the normal +IN and –IN
port. This can be a very useful function for implementing
servo-loop differential error amplifiers, for example. In
this mode of operation, the output is governed by the
C1, C2, C3: TAIYO YUDEN JMK325BJ226MM-T (X7R)
L1, L2: SUMIDA CDRH6D2B-220NC
*MNA, MPA: SILICONIX Si9801
**MNB, MPB: SILICONIX Si9801
Figure 1. Optional CMRR Trim
V
V
IN
IN
100k
100k
U
20k
–
+
I
COIL
1k
2k
(i.e. ±1A FOR ±1V)
= (V
3
2
REF
+
–
IN
U
1
LT1990
+ – V
–
+
V
7
4
DD
IN
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen-
tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
LT1990
)/(10 • R
5
8
G2
G1
Figure 2. PWM-Based ±1A Electromagnet Current Controller
6
S
W
)
10k
10k
10nF
100k
100k
V
1µF
82k
10nF
DD
U
PLLLPF
R
SDSYNC
CNTRL
EAOUT
FB
AGND
SS
I
V
FAULT
V
H/C
V
LIM
SLEW
SET
THRM
TEC
LTC1923
PDRVB
NDRVB
NDRVA
PDRVA
PGND
V
TEC
TEC
V
CS
CS
I
REF
TEC
R
DD
C
T
T
+
–
+
–
following relationship:
Unlike the main inputs, the GAIN1 and GAIN2 pins are
clamped by substrate diodes and ESD structures, thus the
operating voltage range of these pins is limited to V
to V
operating input range, care must be taken to limit the input
currents to less than 10mA to prevent damage to the device.
For best results in this mode of operation the common mode
voltage of the GAIN1 and GAIN2 pins should be equal to the
REF pin voltage. Also, since the gain setting resistors associ-
ated with the GAIN1 and GAIN2 inputs are in the 10kΩ area,
low source impedances are particularly important to preserve
the precision of the LT1990.
This dual differential input mode of operation is used in the
circuit as shown in Figure 2.
This circuit is a high efficiency H-bridge driver that is PWM
modulated to provide a controlled current to an electro-
magnet coil. Since the common mode voltage of the
current sense resistor R
and the coil properties, a differential feedback is required.
In this application, it was desirable to allow the control
input to utilize the wide common mode range port (+IN and
–IN) so that constraints on input referencing are elimi-
nated. The GAIN1 and GAIN2 pins always operate within
the supply range and both ports operate with a gain of 10
to develop the loop error. The LTC1923 provides the loop
integrator and PWM functions of the servo.
V
V
O
–
REF
1µF
= 10 • (V
+ 36V. If the GAIN inputs are brought beyond the
330pF
1µF
10k
MNB**
MPA*
+IN
10µH
L1
22µF
0.1
C1
– V
V
–IN
DD
22µF
C3
S
+ V
varies with operating current
10µF
GAIN2
0.1
R
C2
22µF
10µH
S
L2
I
COIL
– V
ELECTRO-
MAGNET
COIL
MPB**
MNA*
GAIN1
LT1990
) + V
1990 F02
REF
–
15
– 0.2V
1990fb