LTC1154
TRUTH TABLE
The Truth Table demonstrates how the LTC1154 receives
inputs and returns status information to the µP. The
ENABLE and input signal from the µP 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
dangerousconditions.Thestatuspinremainshighaslong
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.
INPUTS
OUTPUTS
SD GATE STATUS
SWITCH
CONDITION
IN
X
EN
H
X
X
X
L
L
L
L
H
L
H
H
H
L
SWITCH OFF
SWITCH OFF
SWITCH ON
L
H
H
L
L
SWITCH LATCHED OFF
(OVER CURRENT)
H
L
L
L
SWITCH LATCHED OFF
(SHUTDOWN)
L = LOGIC LOW
H = LOGIC HIGH
X = IRRELEVANT
= EDGE TRIGGERED
U
LTC1154 OPERATIO
The LTC1154 is a single micropower MOSFET driver with
built-inprotection,statusfeedbackandgatechargepump.
The LTC1154 consists of the following functional blocks:
pump logic is not coupled into the 100mV reference or the
analog comparator.
Gate Charge Pump
TTL and CMOS Compatible Inputs
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
thereforenoexternalcomponentsarerequiredtogenerate
the gate drive.
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.
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 0.002Ω to 0.10Ω) in
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.
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
Controlled Gate Rise and Fall Times
The output of the TTL-to-CMOS converter drives two
regulated supplies which power the low voltage CMOS
logicandanalogblocks.Theregulatoroutputsareisolated
from each other so that the noise generated by the charge
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
7
Linear [ Linear ]
