LTC1154 Linear Technology, LTC1154 Datasheet - Page 7

• Manufacturer Part Number: LTC1154
• Description: High-Side Micropower MOSFET Driver
• Manufacturer: Linear Technology

LTC1154 OPERATIO
TRUTH TABLE
The LTC1154 is a single micropower MOSFET driver with
built-in protection, status feedback and gate charge pump.
The LTC1154 consists of the following functional blocks:
TTL and CMOS Compatible Inputs
The LTC1154 input and shutdown input have been de-
signed to accommodate a wide range of logic families.
Both input thresholds are set at about 1.3V with approxi-
mately 100mV of hysteresis.
A low standby current voltage regulator provides continu-
ous bias for the TTL-to-CMOS converter. The TTL-to-
CMOS converter output enables the rest of the circuitry. In
this way the power consumption is kept to a minimum in
the standby mode.
ENABLE Input
The ENABLE input is CMOS compatible and inhibits the
input signal whenever it is held logic high. This input
should be grounded when not in use.
Internal Voltage Regulation
The output of the TTL-to-CMOS converter drives two
regulated supplies which power the low voltage CMOS
logic and analog blocks. The regulator outputs are isolated
from each other so that the noise generated by the charge
L = LOGIC LOW
H = LOGIC HIGH
X = IRRELEVANT
IN
X
H
H
H
L
INPUTS
EN
H
X
L
L
L
SD
X
X
L
L
GATE
L
L
H
L
L
OUTPUTS
= EDGE TRIGGERED
STATUS
H
H
H
L
L
SWITCH LATCHED OFF
SWITCH LATCHED OFF
U
(OVER CURRENT)
(SHUTDOWN)
SWITCH OFF
SWITCH OFF
SWITCH ON
CONDITION
SWITCH
The Truth Table demonstrates how the LTC1154 receives
inputs and returns status information to the P. The
ENABLE and input signal from the P controls the switch
in its normal operating mode, where the rise and fall time
of the gate drive are controlled to limit EMI and RFI
emissions. The shutdown and over-current detection cir-
cuitry however, switch the gate off at a much higher rate
to limit the exposure of the MOSFET switch and the load to
dangerous conditions. The status pin remains high as long
as the switch is operating normally, and is driven low only
when a fault condition is detected. Note that the shutdown
pin is edge-sensitive and latches the output off even if the
shutdown pin returns to a low state.
pump logic is not coupled into the 100mV reference or the
analog comparator.
Gate Charge Pump
Gate drive for the MOSFET switch is produced by an
adaptive charge pump circuit which generates a gate
voltage substantially higher than the power supply volt-
age. The charge pump capacitors are included on chip and
therefore no external components are required to generate
the gate drive.
Drain Current Sense
The LTC1154 is configured to sense the current flowing
into the drain of the power MOSFET in a high-side applica-
tion. An internal 100mV reference is compared to the drop
across a sense resistor (typically 0.002
series with the drain lead. If the drop across this resistor
exceeds the internal 100mV threshold, the input latch is
reset and the gate is quickly discharged via a large
N-channel transistor.
Controlled Gate Rise and Fall Times
When the input is switched ON and OFF, the gate is
charged by the internal charge pump and discharged in a
controlled manner. The charge and discharge rates have
LTC1154
to 0.10 ) in
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