LINER LTC1477

LTC1477/LTC1478
Single and Dual Protected
High Side Switches
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DESCRIPTION
FEATURES
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■
■
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Extremely Low RDS(ON) Switch: 0.07Ω
No Parasitic Body Diode
Built-In Short-Circuit Protection: 2A
Built-In Thermal Overload Protection
Operates from 2.7V to 5.5V
Inrush Current Limited
Ultralow Standby Current: 0.01µA
Built-In Charge Pump
Controlled Rise and Fall Times: tR = 1ms
Single Switch in 8-Pin SO Package
Dual Switch in Narrow 16-Pin SO Package
The LTC ®1477/LTC1478 protected high side switches
provide extremely low RDS(ON) switching with built-in
protection against short-circuit and thermal overload conditions. A built-in charge pump generates gate drive
higher than the supply voltage to fully enhance the internal
NMOS switch. This switch has no parasitic body diode and
therefore no current flows through the switch when it is
turned off and the output is forced above the input supply
voltage. (DMOS switches have parasitic body diodes that
become forward biased under these conditions.)
Two levels of protection are provided by the
LTC1477/LTC1478. The first level of protection is shortcircuit current limit which is set at 2A. The short-circuit
current can be reduced to as low as 0.85A by disconnecting portions of the power device (see Applications Information). The second level of protection is provided by
thermal overload protection which limits the die temperature to approximately 130°C.
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APPLICATIONS
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Notebook Computer Power Management
Power Supply/Load Protection
Supply/Battery Switch-Over Circuits
Circuit Breaker Function
"Hot Swap" Board Protection
Peripheral Power Protection
The LTC1477 single is available in 8-lead SO packaging.
The LTC1478 dual is available in 16-lead SO packaging.
, LTC and LT are registered trademarks of Linear Technology Corporation.
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SI PLIFIED BLOCK DIAGRAM
VINS
VIN1
VIN2
VIN3
Switch Output Voltage
5.20
GATE CHARGE
AND
DISCHARGE
CONTROL LOGIC
EN
CHARGE
PUMP
TA = 25°C
VIN1 = VIN2 = VIN3 = VINS = 5V
5.10
*
CURRENT LIMIT
AND THERMAL
SHUTDOWN
*
OUTPUT VOLTAGE (V)
*
VOUT
5.00
4.90
4.80
4.70
4.60
*NMOS SWITCHES WITH NO PARASITIC BODY DIODES
LTC1477/1478 • TA01
0
0.25
0.5
0.75 1.00
1.25
OUTPUT CURRENT (A)
1.50
LTC1477/1478 • TP02
1
LTC1477/LTC1478
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ABSOLUTE MAXIMUM RATINGS
Supply Voltage .......................................................... 7V
Enable Input Voltage ...................... (7V) to (GND – 0.3V)
Output Voltage (OFF) (Note 1) ....... (7V) to (GND – 0.3V)
Output Short-Circuit Duration .......................... Indefinite
Junction Temperature........................................... 110°C
Operating Temperature
LTC1477C/LTC1478C .............................. 0°C to 70°C
Storage Temperature Range ................. – 65°C to 150°C
Lead Temperature (Soldering, 10 sec).................. 300°C
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PACKAGE/ORDER INFORMATION
ORDER PART
NUMBER
TOP VIEW
VOUT
LTC1477CS8
AVOUT 1
16 AVOUT
AVIN 2
15 AVIN2
AVINS 3
14 AVIN3
VOUT 1
8
VIN1 2
7
VIN2
AEN 4
13 GND
VINS 3
6
VIN3
GND 5
12 BEN
GND
BVIN3 6
11 BVINS
BVIN2 7
10 BVIN1
BVOUT 8
9
EN 4
5
S8 PART MARKING
S8 PACKAGE
8-LEAD PLASTIC SO
1477
TJMAX = 110°C, θJA = 120°C/ W
ORDER PART
NUMBER
TOP VIEW
LTC1478CS
BVOUT
S PACKAGE
16-LEAD PLASTIC SO
TJMAX = 110°C, θJA = 100°C/ W
Consult factory for Industrial and Military grade parts.
ELECTRICAL CHARACTERISTICS
VINS = VIN1 = VIN2 = VIN3 = 5V (Note 2), TA = 25°C, unless otherwise noted. Each channel of the LTC1478 is tested separately (Note 3).
SYMBOL PARAMETER
VIN
Supply Voltage Range
Supply Current
IVIN
RON
ON Resistance
ILKG
ISC
Output Leakage Current OFF
Short-Circuit Current Limit
VENH
VENL
IEN
tD+R
Enable Input High Voltage
Enable Input Low Voltage
Enable Input Current
Delay and Rise Time
CONDITIONS
Switch OFF, Enable = 0V
Switch ON, Enable = 5V, VIN = 5V
Switch ON, Enable = 3.3V, VIN = 3.3V
VINS = VIN1 = VIN2 = VIN3 = 5V, IOUT = 1A
VINS = VIN1 = VIN2 = VIN3 = 3.3V, IOUT = 1A
VINS = VIN1 = 5V, VIN2 = VIN3 = NC, IOUT = 0.5A
VINS = VIN1 = 3.3V, VIN2 = VIN3 = NC, IOUT = 0.5A
Switch OFF, Enable = 0V
VINS = VIN1 = VIN2 = VIN3 = 5V, VOUT = 0V, (Note 4)
VINS = VIN1 = 5V, VIN2 = VIN3 = NC, VOUT = 0V, (Note 4)
3.0V ≤ VINS ≤ 5.5V
3.0V ≤ VINS ≤ 5.5V
0V ≤ VEN ≤ 5.5V
ROUT = 100Ω, COUT = 1µF, to 90% of Final Value
The ● denotes specifications which apply over the full operating
temperature range.
Note 1: The VOUT pins must be connected together.
Note 2: The VINS and VIN1 pins must be connected together. The VIN2 and
VIN3 pins are typically connected to VINS and VIN1 pins but can be
selectively disconnected to reduce the short-circuit current limit and
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MIN
2.7
TYP
2.00
0.85
MAX
5.5
10
180
120
0.12
0.12
0.20
0.20
±20
2.40
1.02
1.00
0.8
±1
2.00
0.01
120
80
0.07
0.08
0.12
0.13
●
●
●
●
●
1.60
0.68
2.0
●
●
0.50
UNITS
V
µA
µA
µA
Ω
Ω
Ω
Ω
µA
A
A
V
V
µA
ms
increase the ON resistance of the switch. The LTC1478 GND pins must be
connected together. (See Pin Functions and Block Diagram for more detail.)
Note 3: Other channel turned OFF, i.e. AEN and BEN = 0V.
Note 4: The output is protected with fold-back current limit which reduces
the short-circuit (0V) currents below peak permissible current levels at
higher output voltages. (See Typical Performance Characteristics for
further detail on output current versus output voltage).
LTC1477/LTC1478
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TYPICAL PERFORMANCE CHARACTERISTICS
Supply Current (ON)
0.30
TA = 25°C
OUTPUT TURNED ON, NO LOAD
0.30
TA = 25°C
0.25
200
150
100
50
0.25
0.20
VIN2 = VIN3 = NC
0.15
0.10
0.05
0
1
2
3
4
SUPPLY VOLTAGE (V)
5
0
6
SWITCH RESISTANCE (Ω)
SWITCH RESISTANCE (Ω)
SUPPLY CURRENT (µA)
250
0
Switch Resistance (5V)
Switch Resistance
300
6
3
4
5
INPUT VOLTAGE (V)
2
LTC1477/1478 • TPC01
VINS = VIN1 = 5V
VIN2 = VIN3 = NC
0.15
0.10
ALL VIN PINS = 5V
0.05
ALL VIN PINS
CONNECTED
1
0.20
0
7
0
LTC1477/1478 • TPC02
Switch Resistance (3.3V)
LTC1477/1478 • TPC03
Output Current (5V)
Short-Circuit Current
0.30
6
3.0
TA = 25°C
TJ = 25°C
0.15
ALL VIN PINS = 3.3V
0.05
0
0
25
50
75
100
JUNCTION TEMPERATURE (°C)
2.0
1.5
1
2
3
4
SUPPLY VOLTAGE (V)
INRUSH CURRENT (A)
TA = 25°C
4
6
CURRENT
LIMITED
2
1
0
3
ALL VIN PINS = 3.3V
2
VIN2 = VIN3 = NC
2
3
4
OUTPUT VOLTAGE (V)
5
6
LTC1477/1478 • TPC07
VIN2 = VIN3 = NC
0
1
2
3
4
OUTPUT VOLTAGE (V)
4
0
–0.4
TJ = 25°C
ALL VIN PINS = 5V
0
0.4
6
LTC1477/1478 • TPC06
3
2
CURRENT
LIMITED
0.8 1.2 1.6
TIME (ms)
2.0
2.4 2.8
LTC1477/1478 • TPC08
TJ = 25°C
ALL VIN PINS = 3.3V
1
0
COUT = 470µF
ROUT = 10Ω
6
2
5
Inrush Current (3.3V)
3
COUT = 10µF
ROUT = 10Ω
OUTPUT VOLTAGE (V)
OUTPUT CURRENT (A)
5
1
5
Inrush Current (5V)
6
0
ALL VIN PINS = 5V
2
LTC1477/1478 • TPC05
Output Current (3.3V)
0
3
0
0
LTC1477/1478 • TPC04
1
4
1
0.5
0
125
VIN2 = VIN3 = NC
1.0
INRUSH CURRENT (A)
0.10
ALL VIN PINS
CONNECTED
OUTPUT CURRENT (A)
VINS = VIN1 = 3.3V
VIN2 = VIN3 = NC
5
2.5
OUTPUT VOLTAGE (V)
0.20
SHORT-CIRCUIT CURRENT (A)
SWITCH RESISTANCE (Ω)
0.25
125
25
50
75
100
JUNCTION TEMPERATURE (°C)
COUT = 10µF
ROUT = 10Ω
COUT = 470µF
ROUT = 10Ω
6
4
2
0
–0.4
0
0.4
0.8 1.2 1.6
TIME (ms)
2.0
2.4 2.8
LTC1477/1478 • TPC09
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LTC1477/LTC1478
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PIN FUNCTIONS
LTC1477
LTC1478
EN (Pin 4): The enable input is a high impedance CMOS
gate with an ESD protection diode to ground and should
not be forced below ground. This input has about 100mV
of built-in hysteresis to ensure clean switching.
AEN, BEN (Pins 4,12): The enable inputs are high impedance CMOS gates with ESD protection diodes to ground
and should not be forced below ground. These inputs
have about 100mV of built-in hysteresis to ensure clean
switching.
VINS, VIN1 (Pins 3,2): The VINS supply pin must always be
connected to the VIN1 supply pin (see Block Diagram). The
VINS supply pin provides power for the input control logic,
the current limit and thermal shutdown circuitry; plus
provides a sense connection to the input power supply.
The gate of the NMOS switch is powered by a charge pump
from the VINS supply pin (see Block Diagram). The VIN1
supply pin provides connection to the drain of 1/2 of the
output power device.
VIN2, VIN3 (Pins 7,6): The VIN2 and VIN3 supply pins are
typically tied to the VINS and VIN1 supply pins for lowest ON
resistance; i.e., when all four VIN pins are connected
together the entire power device is connected (see Block
Diagram). Each auxiliary supply pin, VIN2 and VIN3, is
connected to the drain of 1/4 of the power device. The VIN2
and VIN3 pins can be selectively disconnected to reduce
the short-circuit current limit at the expense of higher
RDS(ON). (See Applications Information section for more
details.)
VOUT (Pins 1,8): The output pins of the LTC1477 must
always be tied together. The output is protected against
accidental short circuits to ground by a current limit circuit
which protects the system power supply and load against
damage. A second level of protection is provided by
thermal shutdown circuitry which limits the die temperature to 130°C.
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AVINS, AVIN1, BVINS, BVIN1 (Pins 3,2; 11,10): The AVINS
or BVINS supply pin must always be connected to the
AVIN1 or BVIN1 supply pin (see Block Diagram). The AVINS
and BVINS supply pins provide power for the input control
logic, the current limit and thermal shutdown circuitry;
plus, provides a sense connection to the input power
supply. The gate of the NMOS switch is powered by a
charge pump from the AVINS and BVINS supply pins (see
Block Diagram). The AVIN1 and BVIN1 supply pins provide
connection to the drain of 1/2 of the output power device.
AVIN2, AVIN3, BVIN2, BVIN3, (Pins 15,14; 7,6): The AVIN2,
AVIN3, BVIN2 and BVIN3 supply pins are typically tied to the
AVINS, AVIN1, BVINS and BVIN1 supply pins for lowest ON
resistance; i.e., when all four AVIN, BVIN pins are connected together the entire power device is connected (see
Block Diagram). Each auxiliary supply pin, AVIN2, AVIN3,
BVIN2 and BVIN3, is connected to the drain of approximately 1/4 of the corresponding power device. The AVIN2,
AVIN3, BVIN2 and BVIN3 pins can be selectively disconnected to reduce the short-circuit current limit at the
expense of higher RDS(ON). (See Applications Information
section for more details.)
AVOUT, BVOUT (Pins 1,16; 8,9): The outputs of the LTC1478
are protected against accidental short circuits to ground
by a current limit circuit which protects the system power
supplies and loads against damage. A second level of
protection is provided by thermal shutdown circuitry
which limits the die temperature to approximately 130°C.
LTC1477/LTC1478
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OPERATION (LTC1477 or single channel of LTC1478)
Input TTL-CMOS Converter
The LTC1477 enable input is designed to accommodate a
wide range of 3V and 5V logic families. The input threshold
voltage is approximately 1.4V with 100mV of hysteresis.
The input enables the bias generator, the gate charge
pump and the protection circuitry. Therefore, when the
enable input is turned off, the entire circuit is powered
down and the supply current drops below 1µA.
Ramped Switch Control
The LTC1477 gate charge pump includes circuitry which
ramps the NMOS switch on slowly (1ms typical rise time)
but turns it off much more quickly (typically 20µs).
Bias, Oscillator and Gate Charge Pump
When the switch is enabled, a bias current generator and
high frequency oscillator are turned on. The on-chip
capacitive charge pump generates approximately 12V of
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BLOCK DIAGRAM
gate drive for the internal low RDS(ON) NMOS switch from
the power supply. No external 12V supply is required to
switch the output.
Switch Protection
Two levels of protection are designed into the power
switch in the LTC1477. The switch is protected against
accidental short circuits with a current limit circuit which
limits the output current to typically 2A when the output is
shorted to ground. The LTC1477 also has thermal shutdown set at approximately 130°C which limits the power
dissipation to safe levels.
LTC1478 Operation
The LTC1478 dual protected switch can be thought of as
two independent LTC1477 single protected switches. The
input supply voltages may be from separate power sources.
The ground connection, however, is common to both
channels and must be connected to the same potential.
(LTC1477 or single channel of LTC1478)
VIN1
VINS
VIN2
VIN3
GATE CHARGE
AND
DISCHARGE
CONTROL LOGIC
EN
TTL-TO-CMOS
CONVERTER
OSCILLATOR
AND BIAS
CHARGE
PUMP
CURRENT LIMIT
AND THERMAL
SHUTDOWN
VOUT
LTC1477/1478 • BD01
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APPLICATIONS INFORMATION
Tailoring ILIMIT and RDS(ON) for Load Requirements
The LTC1477 is designed to current limit at approximately
2A during a short circuit with all the VIN pins connected to
the input power supply. It is possible however, to reduce
this current by selectively disconnecting two of the four
power supply pins (VIN2 and VIN3). Table 1 lists the effects
of disconnecting these pins on RDS(ON) and short-circuit
current limit
Table 1. Effects of Disconnecting VIN2 and VIN3
ALL VIN PINS
CONNECTED
RDS(ON)
0.07Ω
ILIMIT
2A
Note: 5V Operation
VIN3
DISCONNECTED
VIN2 AND VIN3
DISCONNECTED
0.09Ω
1.5A
0.12Ω
0.85A
Note that there is an inverse relationship between output
current limit and switch resistance. This allows the tailor-
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LTC1477/LTC1478
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APPLICATIONS INFORMATION
ing of the switch parameters to the expected load current
and system current limit requirements.
A couple of examples are helpful:
1. If a nominal load of 1A was controlled by the switch
configured to current limit at 2A (all VIN pins connected
together), the RDS(ON) would be 0.07Ω and the voltage
drop across the switch would be 70mV. The power
dissipated by the switch would only be 70mW.
2. If a nominal load of 0.5A was controlled by the switch
configured to current limit at 0.85A (VIN2 and VIN3
disconnected), the RDS(ON) would increase to 0.14Ω.
But the voltage drop would remain at 70mV and the
switch power dissipation would drop to 35mW.
Supply Bypassing
For best results, bypass the supply input pins with a single
1.0µF capacitor as close as possible to the LTC1477.
Sometimes, much larger capacitors are already available
at the output of the power supply. In this case, it is still
good practice to use a 0.1µF capacitor as close as possible
to the LTC1477, especially if the power supply output
capacitor is more than 2 inches away on the printed circuit
board.
Output Capacitor
The output pin is designed to ramp on slowly, typically
1ms rise time. Therefore, very large output capacitors can
be driven without producing voltage spikes on the supply
pins (see graphs in Typical Performance Characteristics).
The output pin should have a 1µF capacitor for noise
reduction and smoothing.
Supply and Input Sequencing
The LTC1477 is designed to operate with continuous
power (quiescent current drops to < 1µA when disabled).
If the power must be turned off, for example to enter a
system “sleep” mode, the enable input must be turned off
100µs before the input supply is turned off to ensure that
the gate of the NMOS switch is completely discharged
before power is removed. However, the input control and
power can be applied simultaneously during power up.
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TYPICAL APPLICATIONS
2A Protected Switch
1.5A Protected Switch
2.7V TO 5.5V
2.7V TO 5.5V
ISC = 1.5A
ISC = 2A
0.1µF
+
0.1µF
VOUT
VOUT
VIN2
VIN1
VIN2
VINS
VIN3
VINS
VIN3
EN
GND
EN
GND
VOUT
VOUT
VIN1
1µF
ON/OFF
LTC1477/1478 • TA03
0.85A Protected Switch
ISC = 0.85A
LTC1477/1478 • TA04
2.7V TO 5.5V
VOUT
+
VOUT
VOUT
VIN1
VIN2
NC
VINS
VIN3
NC
EN
GND
1µF
0.1µF
VOUT
VOUT
VIN1
LTC1477
ON/OFF
NC
2A Protected Switch Driving a Large Capacitive Load
2.7V TO 5.5V
0.1µF
1µF
LTC1477
LTC1477
ON/OFF
+
+
CLOAD
100µF
VIN2
LTC1477
ON/OFF
VINS
VIN3
EN
GND
LTC1477/1478 • TA05
LTC1477/1478 • TA06
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LTC1477/LTC1478
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TYPICAL APPLICATIONS
Adding Short-Circuit Protection to an LT1301 Step-Up Switching Regulator (0.01µA Standby Current)
D1
MBRS130LT3
L1*
10µH
12V
+
5V
100µF
10V
0.1µF
VOUT
VOUT
VIN1
VIN2
2
6
7
VIN
SW
SEL
SENSE
+
LT1301
LTC1477
ON/OFF
4
VINS
VIN3
EN
GND
3
47µF
16V
TANT
0.1µF
SHDN
ILIM
5
NC
GND
PGND
8
1
*COILCRAFT DO1608-103
DN117 • F03
5V to 3.3V Selector Switch with Slope Control and 0.01µA Standby Current
5V
5V/2A OR
3.3V/2A
0.1µF
5V ON/OFF*
AVOUT
AVOUT
AVIN1
AVIN2
AVINS
AVIN3
+
1k
100µF
10V
GND
AEN
LTC1478
BEN
GND
3.3V
BVIN3
BVINS
0.1µF
BVIN2
BVIN1
BVOUT
BVOUT
3.3V ON/OFF*
LTC1477/1478 • TA08
*ALLOW AT LEAST 100ms BETWEEN 5V AND 3.3V SWITCHING FOR DISCHARGE OF 100µF OUTPUT CAPACITOR
Single Li-Ion Cell to 5V Converter/Switch with Load Disconnect Below 2.7V
22µH
SUMIDA
CD54-220
(2.7V to 4.2V)
+
100µF
16V
562k
1%
220k
NC
SINGLE
Li-Ion
CELL*
6
1
432k
1%
7
MBRS130LT3
(5V)
3
4
VIN
SW
ILIM
SENSE
LT1304CS8-5
+
VOUT
8
+
LBI
LBO
SHDN
2
100µF
10V
TANT
1µF
VOUT
VIN1
5V
VIN2
NC
VIN3
NC
LTC1477
VINS
EN
5
GND
LTC1477/1478 • TA09
*PRIMARY Li-Ion BATTERY PROTECTION MUST BE PROVIDED BY AN INDEPENDENT CIRCUIT
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 representation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
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LTC1477/LTC1478
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PACKAGE DESCRIPTION
Dimension in inches (millimeters) unless otherwise noted.
S8 Package
8-Lead Plastic Small Outline (Narrow 0.150)
0.189 – 0.197*
(4.801 – 5.004)
(LTC DWG # 05-08-1610)
0.010 – 0.020
× 45°
(0.254 – 0.508)
0.008 – 0.010
(0.203 – 0.254)
6
5
0.004 – 0.010
(0.101 – 0.254)
0°– 8° TYP
0.016 – 0.050
0.406 – 1.270
7
8
0.053 – 0.069
(1.346 – 1.752)
*DIMENSION DOES NOT INCLUDE MOLD FLASH. MOLD FLASH
SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE
**DIMENSION DOES NOT INCLUDE INTERLEAD FLASH. INTERLEAD
FLASH SHALL NOT EXCEED 0.010" (0.254mm) PER SIDE
0.150 – 0.157**
(3.810 – 3.988)
0.228 – 0.244
(5.791 – 6.197)
0.050
(1.270)
BSC
0.014 – 0.019
(0.355 – 0.483)
SO8 0695
1
3
2
4
S Package
16-Lead Plastic Small Outline (Narrow 0.150)
(LTC DWG # 05-08-1610)
0.386 – 0.394*
(9.804 – 10.008)
16
15
14
13
12
11
10
9
0.150 – 0.157**
(3.810 – 3.988)
0.228 – 0.244
(5.791 – 6.197)
1
0.010 – 0.020
× 45°
(0.254 – 0.508)
0.008 – 0.010
(0.203 – 0.254)
2
3
5
4
0.053 – 0.069
(1.346 – 1.752)
0.014 – 0.019
(0.355 – 0.483)
7
8
0.004 – 0.010
(0.101 – 0.254)
0° – 8° TYP
0.016 – 0.050
0.406 – 1.270
6
0.050
(1.270)
TYP
S16 0695
*DIMENSION DOES NOT INCLUDE MOLD FLASH. MOLD FLASH
SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE
**DIMENSION DOES NOT INCLUDE INTERLEAD FLASH. INTERLEAD
FLASH SHALL NOT EXCEED 0.010" (0.254mm) PER SIDE
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SafeSlot is a trademark of Linear Technology Corporation.
8
Linear Technology Corporation
LT/GP 0995 10K • PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 ● FAX: (408) 434-0507 ● TELEX: 499-3977
 LINEAR TECHNOLOGY CORPORATION 1995