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LTC1477/LTC1478 Single and Dual Protected High Side Switches
FEATURES
s s s s s s s s s s s
DESCRIPTION
The LTC (R)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 130C. 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.
Extremely Low RDS(ON) Switch: 0.07 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: 0.01A 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
APPLICATIONS
s s s s s s
Notebook Computer Power Management Power Supply/Load Protection Supply/Battery Switch-Over Circuits Circuit Breaker Function "Hot Swap" Board Protection Peripheral Power Protection
SI PLIFIED BLOCK DIAGRAM
VINS VIN1 VIN2
VIN3
5.20
OUTPUT VOLTAGE (V)
GATE CHARGE AND DISCHARGE CONTROL LOGIC
5.10
TA = 25C VIN1 = VIN2 = VIN3 = VINS = 5V
*
*
*
5.00 4.90 4.80 4.70 4.60
EN
CHARGE PUMP
CURRENT LIMIT AND THERMAL SHUTDOWN
VOUT
0
*NMOS SWITCHES WITH NO PARASITIC BODY DIODES
LTC1477/1478 * TA01
U
W
U
W
Switch Output Voltage
0.25
0.5 0.75 1.00 1.25 OUTPUT CURRENT (A)
1.50
LTC1477/1478 * TP02
1
LTC1477/LTC1478
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........................................... 110C Operating Temperature LTC1477C/LTC1478C .............................. 0C to 70C Storage Temperature Range ................. - 65C to 150C Lead Temperature (Soldering, 10 sec).................. 300C
PACKAGE/ORDER INFORMATION
ORDER PART NUMBER
TOP VIEW VOUT 1 VIN1 2 VINS 3 EN 4 8 7 6 5 VOUT VIN2 VIN3 GND
LTC1477CS8
S8 PART MARKING 1477
S8 PACKAGE 8-LEAD PLASTIC SO
TJMAX = 110C, JA = 120C/ W
Consult factory for Industrial and Military grade parts.
VINS = VIN1 = VIN2 = VIN3 = 5V (Note 2), TA = 25C, unless otherwise noted. Each channel of the LTC1478 is tested separately (Note 3).
SYMBOL PARAMETER VIN Supply Voltage Range Supply Current IVIN 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 = 100, COUT = 1F, to 90% of Final Value
q q q
ELECTRICAL CHARACTERISTICS
RON
ON Resistance
ILKG ISC VENH VENL IEN tD+R
Output Leakage Current OFF Short-Circuit Current Limit Enable Input High Voltage Enable Input Low Voltage Enable Input Current Delay and Rise Time
The q 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
2
U
U
W
WW U
W
TOP VIEW AVOUT 1 AVIN 2 AVINS 3 AEN 4 GND 5 BVIN3 6 BVIN2 7 BVOUT 8 16 AVOUT 15 AVIN2 14 AVIN3 13 GND 12 BEN 11 BVINS 10 BVIN1 9 BVOUT
ORDER PART NUMBER LTC1478CS
S PACKAGE 16-LEAD PLASTIC SO
TJMAX = 110C, JA = 100C/ W
MIN 2.7
TYP 0.01 120 80 0.07 0.08 0.12 0.13
q
q q q
1.60 0.68 2.0
2.00 0.85
MAX 5.5 10 180 120 0.12 0.12 0.20 0.20 20 2.40 1.02 0.8 1 2.00
0.50
1.00
UNITS V A A A A A A V V A 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 TYPICAL PERFORMANCE CHARACTERISTICS
Supply Current (ON)
300 250
SUPPLY CURRENT (A)
TA = 25C OUTPUT TURNED ON, NO LOAD
SWITCH RESISTANCE ()
200 150 100 50 0
0.20 0.15 0.10 0.05 0 ALL VIN PINS CONNECTED 1 2 3 4 5 INPUT VOLTAGE (V) 6 7 VIN2 = VIN3 = NC
SWITCH RESISTANCE ()
0
1
2 3 4 SUPPLY VOLTAGE (V)
LTC1477/1478 * TPC01
Switch Resistance (3.3V)
0.30 0.25 3.0
SHORT-CIRCUIT CURRENT (A)
SWITCH RESISTANCE ()
OUTPUT CURRENT (A)
0.20 0.15 0.10 0.05 0 0
VINS = VIN1 = 3.3V VIN2 = VIN3 = NC
ALL VIN PINS = 3.3V
25 50 75 100 JUNCTION TEMPERATURE (C)
LTC1477/1478 * TPC04
Output Current (3.3V)
6 TA = 25C 5
INRUSH CURRENT (A)
3 2 1 0
INRUSH CURRENT (A)
OUTPUT CURRENT (A)
4 3 ALL VIN PINS = 3.3V 2 1 0 VIN2 = VIN3 = NC
OUTPUT VOLTAGE (V)
OUTPUT VOLTAGE (V)
0
1
2 3 4 OUTPUT VOLTAGE (V)
LTC1477/1478 * TPC07
UW
5 6 5 6
Switch Resistance
0.30 TA = 25C 0.25 0.25 0.20 0.15 0.10 0.05 0 0.30
Switch Resistance (5V)
VINS = VIN1 = 5V VIN2 = VIN3 = NC
ALL VIN PINS = 5V
0
25 50 75 100 JUNCTION TEMPERATURE (C)
125
LTC1477/1478 * TPC02
LTC1477/1478 * TPC03
Short-Circuit Current
6 TJ = 25C 2.5 2.0 1.5 1.0 0.5 0 VIN2 = VIN3 = NC ALL VIN PINS CONNECTED 5 4 3
Output Current (5V)
TA = 25C
ALL VIN PINS = 5V 2 1 0 VIN2 = VIN3 = NC
125
0
1
2 3 4 SUPPLY VOLTAGE (V)
5
6
0
1
2 3 4 OUTPUT VOLTAGE (V)
5
6
LTC1477/1478 * TPC05
LTC1477/1478 * TPC06
Inrush Current (5V)
CURRENT LIMITED
Inrush Current (3.3V)
3 2 1 0 COUT = 10F ROUT = 10 6 4 2 0 -0.4 0 0.4 0.8 1.2 1.6 TIME (ms) 2.0 2.4 2.8 COUT = 470F ROUT = 10 CURRENT LIMITED TJ = 25C ALL VIN PINS = 3.3V
COUT = 10F ROUT = 10 6 4 2 0 -0.4 0 0.4
COUT = 470F ROUT = 10
TJ = 25C ALL VIN PINS = 5V 0.8 1.2 1.6 TIME (ms) 2.0 2.4 2.8
LTC1477/1478 * TPC08
LTC1477/1478 * TPC09
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LTC1477/LTC1478
PIN FUNCTIONS
LTC1477
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. 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 130C.
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U
U
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LTC1478
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. 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 130C.
LTC1477/LTC1478
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 1A. 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 20s). 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 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 130C which limits the power dissipation to safe levels. LTC1478 Operation
BLOCK DIAGRAM
EN
TTL-TO-CMOS CONVERTER
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) 0.07 ILIMIT 2A Note: 5V Operation
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W
W
U
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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)
VINS VIN1 VIN2 VIN3
GATE CHARGE AND DISCHARGE CONTROL LOGIC
OSCILLATOR AND BIAS
CHARGE PUMP
CURRENT LIMIT AND THERMAL SHUTDOWN VOUT
LTC1477/1478 * BD01
VIN3 DISCONNECTED
0.09 1.5A
VIN2 AND VIN3 DISCONNECTED
0.12 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
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 0.07 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 0.14. 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 1.0F 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 0.1F 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 1F capacitor for noise reduction and smoothing. Supply and Input Sequencing The LTC1477 is designed to operate with continuous power (quiescent current drops to < 1A when disabled). If the power must be turned off, for example to enter a system "sleep" mode, the enable input must be turned off 100s 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.
TYPICAL APPLICATIONS
2A Protected Switch
2.7V TO 5.5V ISC = 2A 0.1F VOUT VIN1 LTC1477 VINS ON/OFF EN VIN3 GND
LTC1477/1478 * TA03
VOUT VIN2
+
1F
0.85A Protected Switch
2.7V TO 5.5V 0.1F VOUT VIN1 LTC1477 VINS ON/OFF EN VIN3 GND NC VOUT VIN2 NC ISC = 0.85A
+
1F
0.1F VOUT VIN1 LTC1477 VINS ON/OFF
LTC1477/1478 * TA05
6
U
W
U
U
U
1.5A Protected Switch
2.7V TO 5.5V ISC = 1.5A 0.1F VOUT VIN1 LTC1477 VINS ON/OFF EN VIN3 GND
LTC1477/1478 * TA04
VOUT VIN2 NC
+
1F
2A Protected Switch Driving a Large Capacitive Load
2.7V TO 5.5V VOUT VOUT VIN2 VIN3 GND
LTC1477/1478 * TA06
+
CLOAD 100F
EN
LTC1477/LTC1478
TYPICAL APPLICATIONS
Adding Short-Circuit Protection to an LT1301 Step-Up Switching Regulator (0.01A Standby Current)
L1* 10H 5V 0.1F VOUT VIN1 LTC1477 VINS ON/OFF EN VIN3 GND 3 SHDN PGND 8 *COILCRAFT DO1608-103 VOUT VIN2 LT1301 ILIM GND 1
DN117 * F03
5V to 3.3V Selector Switch with Slope Control and 0.01A Standby Current
5V 5V/2A OR 3.3V/2A 0.1F AVOUT AVIN1 AVINS 5V ON/OFF* AEN LTC1478 GND 3.3V 0.1F BVIN3 BVIN2 BVOUT BEN BVINS BVIN1 BVOUT AVOUT AVIN2 AVIN3 GND 1k
*ALLOW AT LEAST 100ms BETWEEN 5V AND 3.3V SWITCHING FOR DISCHARGE OF 100F OUTPUT CAPACITOR
Single Li-Ion Cell to 5V Converter/Switch with Load Disconnect Below 2.7V
22H SUMIDA CD54-220 562k 1% 3 220k NC SINGLE Li-Ion CELL* 6 1 432k 1% 7 VIN ILIM LBI SHDN 5 LBO 2 MBRS130LT3 (5V) 4 SW 8 VOUT VOUT VIN2 LTC1477 VINS EN VIN3 GND
LTC1477/1478 * TA09
(2.7V to 4.2V)
+
100F 16V
*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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D1 MBRS130LT3 12V
+
100F 10V 2
6 VIN SEL
7 SW SENSE 4
+
0.1F 5 NC
47F 16V TANT
+
100F 10V
3.3V ON/OFF*
LTC1477/1478 * TA08
+
VIN1 NC NC
5V 1F
SENSE LT1304CS8-5
+
100F 10V TANT
7
LTC1477/LTC1478
PACKAGE DESCRIPTION
0.010 - 0.020 x 45 (0.254 - 0.508) 0.008 - 0.010 (0.203 - 0.254)
0.053 - 0.069 (1.346 - 1.752) 0- 8 TYP
0.016 - 0.050 0.406 - 1.270
*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
0.010 - 0.020 x 45 (0.254 - 0.508) 0.008 - 0.010 (0.203 - 0.254) 0 - 8 TYP
0.016 - 0.050 0.406 - 1.270 *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
RELATED PARTS
PART NUMBER
LTC1153 LTC1154 LTC1155 LTC1470 LTC1471 LTC1472
DESCRIPTION
Electronic Circuit Breaker Single High Side Driver Dual High Side Driver 5V and 3.3V VCC Switch Dual 5V and 3.3V VCC Switch PCMCIA VCC and VPP Switches
SafeSlot is a trademark of Linear Technology Corporation.
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Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 q FAX: (408) 434-0507 q TELEX: 499-3977
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Dimension in inches (millimeters) unless otherwise noted.
S8 Package 8-Lead Plastic Small Outline (Narrow 0.150)
(LTC DWG # 05-08-1610)
8 0.004 - 0.010 (0.101 - 0.254) 0.228 - 0.244 (5.791 - 6.197) 0.150 - 0.157** (3.810 - 3.988) 0.189 - 0.197* (4.801 - 5.004) 7 6 5
0.014 - 0.019 (0.355 - 0.483)
0.050 (1.270) BSC
SO8 0695
1
2
3
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
0.228 - 0.244 (5.791 - 6.197)
0.150 - 0.157** (3.810 - 3.988)
1 0.053 - 0.069 (1.346 - 1.752)
2
3
4
5
6
7
8
0.004 - 0.010 (0.101 - 0.254)
0.014 - 0.019 (0.355 - 0.483)
0.050 (1.270) TYP
S16 0695
COMMENTS
MOSFET Driver with Adjustable Reset Time MOSFET Driver with Switch Status Output Dual MOSFET Driver with Protection SafeSlotTM Protected Switch in 8-Lead SO Dual Version of LTC1470 in 16-Lead SO Complete Single Channel SafeSlot Protection
LT/GP 0995 10K * PRINTED IN USA
(c) LINEAR TECHNOLOGY CORPORATION 1995

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