Datasheet

7
LTC1153
TEST CIRCUIT
S
TI I G DIAGRA
WW
U
LTC1153 OPERATIO
U
The LTC1153 is an electronic circuit breaker with built-in
MOSFET gate charge pump, over-current detection and
auto-reset circuitry. The LTC1153 consists of the follow-
ing functional blocks:
TTL and CMOS Compatible Inputs
The LTC1153 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.
Auto-Reset Timer
An external timing capacitor, C
T
, is ramped up by a small
current whenever a fault is detected, i.e., the switch
latched off. When the timing capacitor ramps up to ap-
proximately 2.5V, the switch is turned back on and the
timing capacitor discharged. If the circuit breaker output
is still in an overload state, the breaker will latch off and this
cycle will continue until the fault condition is removed.
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
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 LTC1153 is configured to sense the current flowing
into the drain of an N-channel MOSFET switch. 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 relatively large N-channel
transistor.
OVER-CURRENT
(AUTO-CURRENT)NORMALOFF
NOR-
MAL
SHUT-
DOWN OFF
*90ms
*200µs
S1 CLOSED S1 OPEN
*TIMES FOR COMPONENTS SHOWN IN TEST CIRCUIT
LTC1153 • TD01
INPUT
OUTPUT
STATUS
TIMING
CAP
SHUT-
DOWN
IN
C
T

STATUS
GND
V
S

DS
G
SD
LTC1153
SHUTDOWN
8
7
6
5
1
2
3
4
R
SEN

0.05Ω
IRLZ24
OUTPUT
S1
1Ω10Ω
C
P

0.01µF
R
D
100k
0.1µF
Z5U
51k
STATUS
INPUT
5V
LTC1153 • TC01