LT1237CG データシートの表示（PDF） - Linear Technology

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LT1237CG

5V RS232 Transceiver with Advanced Power Management and One Receiver Active in Shutdown

Linear Technology 

LT1237

APPLICATI S 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 ModeTM

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 VCC.

Burst Mode is a trademark of Linear Technology Corporation

U

PACKAGE DESCRIPTIO Dimensions in inches (millimeters) unless otherwise noted.

0.205 – 0.212**

(5.20 – 5.38)

G Package

28-Lead Plastic SSOP (0.209)

(LTC DWG # 05-08-1640)

0° – 8°

0.068 – 0.078

(1.73 – 1.99)

0.397 – 0.407*

(10.07 – 10.33)

28 27 26 25 24 23 22 21 20 19 18 17 16 15

0.005 – 0.009 0.022 – 0.037

(0.13 – 0.22) (0.55 – 0.95)

0.0256

(0.65)

BSC 0.010 – 0.015

(0.25 – 0.38)

*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

0.002 – 0.008

(0.05 – 0.21)

0.301 – 0.311

(7.65 – 7.90)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 G28 SSOP 0694

NW Package

28-Lead PDIP (Wide 0.600)

(LTC DWG # 05-08-1520)

0.600 – 0.625

(15.240 – 15.875)

0.150 ± 0.005

(3.810 ± 0.127)

0.045 – 0.065

(1.143 – 1.651)

0.070

(1.778)

TYP

0.009 – 0.015

(0.229 – 0.381)

0.015

(0.381)

MIN

0.505 – 0.560*

(12.827 – 14.224)

+0.035

0.625 –0.015

( ) 15.87

+0.889

–0.381

0.125

(3.175)

MIN

0.035 – 0.080

(0.889 – 2.032)

0.100 ± 0.010

(2.540 ± 0.254)

0.018 ± 0.003

(0.457 ± 0.076)

*THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS.

MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.010 INCH (0.254mm)

1.455*

(36.957)

MAX

28 27 26 25 24 23 22 21 20 19 18 17 16 15

1 2 3 4 5 6 7 8 9 10 11 12 13 14

N28 1197

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.

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