7
LT1237
U
S
A
O
PP
L
IC
AT
I
WU
U
I FOR ATIO
Storage Capacitor Selection
The V
+
and V
–
storage capacitors must be chosen care-
fully to insure low ripple and stable operation. The LT1237
charge pump operates in a power efficient Burst Mode
TM
operation. When storage capacitor voltage drops below a
preset threshold, the oscillator is gated on until V
+
and V
–
are boosted up to levels exceeding a second threshold.
The oscillator then turns off, and current is supplied from
the V
+
and V
–
storage capacitors.
The V
–
potential is monitored to control charge pump
operation. It is therefore important to insure lower V
+
ripple than V
–
ripple, or erratic operation of the charge
pump will result. Proper operation is insured in most
applications by choosing the V
+
filter capacitor to be at
least 5 times the V
–
filter capacitor value. If V
+
is more
heavily loaded than V
–
, a larger ratio may be needed.
The V
–
filter capacitor should be selected to obtain low
ripple when the drivers are loaded, forcing the charge
pump into continuous mode. A minimum value 0.1µF is
suggested.
Do not attempt to reduce V
–
ripple when the charge pump
is in discontinuous Burst Mode operation. The ripple in
this mode is determined by internal comparator thresh-
olds. Larger storage capacitor values increase the burst
period, and do not reduce ripple amplitude.
Power Saving Operational Modes
The LT1237 has both shutdown and driver disable operat-
ing modes. These operating modes can optimize power
consumption based upon applications needs.
The On/Off shutdown control turns off all circuitry except
for Low-Q RX5. When RX5 detects a signal, this informa-
tion can be used to wake up the system for full operation.
If more than one line must be monitored, the driver disable
mode provides a power efficient operating option. The
driver disable mode turns off the charge pump and RS232
drivers, but keeps all five receivers active. Power con-
sumption in driver disable mode is 3mA from V
CC
.
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.
Burst Mode is a trademark of Linear Technology Corporation
PACKAGE DESCRIPTIO
U
Dimensions in inches (millimeters) unless otherwise noted.
G Package
28-Lead Plastic SSOP (0.209)
(LTC DWG # 05-08-1640)
G28 SSOP 0694
0.301 – 0.311
(7.65 – 7.90)
1234
5
6
7
8 9 10 11 12 1413
0.397 – 0.407*
(10.07 – 10.33)
2526 222120 19 18
17
161523242728
0.068 – 0.078
(1.73 – 1.99)
0.002 – 0.008
(0.05 – 0.21)
0.0256
(0.65)
BSC
0.010 – 0.015
(0.25 – 0.38)
0.005 – 0.009
(0.13 – 0.22)
0
° – 8°
0.022 – 0.037
(0.55 – 0.95)
0.205 – 0.212**
(5.20 – 5.38)
DIMENSIONS DO NOT INCLUDE MOLD FLASH. MOLD FLASH
SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE
DIMENSIONS DO NOT INCLUDE INTERLEAD FLASH. INTERLEAD
FLASH SHALL NOT EXCEED 0.010" (0.254mm) PER SIDE
*
**
N28 1197
0.505 – 0.560*
(12.827 – 14.224)
1.455*
(36.957)
MAX
12
3
4
5
6
7
8
9
10
27
19
20212224
23
252628
11 12 13 14
15
16
1718
0.070
(1.778)
TYP
0.015
(0.381)
MIN
0.125
(3.175)
MIN
0.150 ± 0.005
(3.810 ± 0.127)
0.018 ± 0.003
(0.457 ± 0.076)
0.035 – 0.080
(0.889 – 2.032)
0.100 ± 0.010
(2.540 ± 0.254)
0.045 – 0.065
(1.143 – 1.651)
0.009 – 0.015
(0.229 – 0.381)
0.625
+0.035
–0.015
+0.889
–0.381
15.87
()
0.600 – 0.625
(15.240 – 15.875)
*THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS.
MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.010 INCH
0.254mm
NW Package
28-Lead PDIP (Wide 0.600)
(LTC DWG # 05-08-1520)
