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PDF LTC1477 Data sheet ( Hoja de datos )
| Número de pieza | LTC1477 | |
| Descripción | Single and Dual Protected High Side Switches | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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LTC1477/LTC1478
Single and Dual Protected
High Side Switches
FEATURES
s Extremely Low RDS(ON) Switch: 0.07Ω
s No Parasitic Body Diode
s Built-In Short-Circuit Protection: 2A
s Built-In Thermal Overload Protection
s Operates from 2.7V to 5.5V
s Inrush Current Limited
s Ultralow Standby Current: 0.01µA
s Built-In Charge Pump
s Controlled Rise and Fall Times: tR = 1ms
s Single Switch in 8-Pin SO Package
s Dual Switch in Narrow 16-Pin SO Package
U
APPLICATIONS
s Notebook Computer Power Management
s Power Supply/Load Protection
s Supply/Battery Switch-Over Circuits
s Circuit Breaker Function
s "Hot Swap" Board Protection
s Peripheral Power Protection
DESCRIPTION
The LTC®1477/LTC1478 protected high side switches
provide extremely low RDS(ON) switching with built-in
protection against short-circuit and thermal overload con-
ditions. 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 short-
circuit current limit which is set at 2A. The short-circuit
current can be reduced to as low as 0.85A by disconnect-
ing portions of the power device (see Applications Infor-
mation). The second level of protection is provided by
thermal overload protection which limits the die tempera-
ture to approximately 130°C.
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.
SI PLIFIED BLOCK DIAGRAM
VINS
VIN1
VIN2
VIN3
GATE CHARGE
AND
DISCHARGE
CONTROL LOGIC
***
EN
CHARGE
PUMP
CURRENT LIMIT
AND THERMAL
SHUTDOWN
VOUT
*NMOS SWITCHES WITH NO PARASITIC BODY DIODES
LTC1477/1478 • TA01
Switch Output Voltage
5.20
TA = 25°C
5.10 VIN1 = VIN2 = VIN3 = VINS = 5V
5.00
4.90
4.80
4.70
4.60
0
0.25 0.5 0.75 1.00 1.25 1.50
OUTPUT CURRENT (A)
LTC1477/1478 • TP02
1
1 page  
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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
LTC1477/LTC1478
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 shut-
down 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.
BLOCK DIAGRAM (LTC1477 or single channel of LTC1478)
VINS
VIN1
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
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
VIN3
VIN2 AND VIN3
CONNECTED DISCONNECTED DISCONNECTED
RDS(ON)
0.07Ω
ILIMIT
2A
Note: 5V Operation
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-
5
5 Page | ||
| Páginas | Total 8 Páginas | |
| PDF Descargar | [ Datasheet LTC1477.PDF ] | |
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