FAN1851AMX Fairchild Semiconductor, FAN1851AMX Datasheet - Page 2

• Manufacturer Part Number: FAN1851AMX
• Description: IC CTRLR AC GRND FAULT 8SOIC
• Manufacturer: Fairchild Semiconductor

Specifications of FAN1851AMX

• Product: Voltage References
• Package / Case: SOIC-8
• Mounting Style: SMD/SMT
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

FAN1851A
Pin Assignments
Functional Description
The voltage at the supply pin is clamped to +26V by the
internal shunt regulator D3. This shunt regulator also
generates an artificial ground voltage for the noninverting
input of A1 (shown as a +10V source). A1, Q1, and Q2
together act as a current mirror for fault current signals
(which are derived from an external transformer). When a
fault signal is present, the mirrored current charges the
external timing capacitor until its voltage exceeds the latch
trigger threshold (typically 17.5V). When this threshold is
exceeded, the latch engages and Q3 turns off, allowing I
drive the SCR connected to the "SCR Trigger" pin.
Extra Circuitry in the feedback path of A1 works with the
switched current source I
induced by noise in the transformer. If no fault current is
present, then I
Definition of Terms
Normal Fault:
An unintentional electrical path, R
nal of the hot line and the ground, as shown by the dashed
lines in Figure1.
2
Line
1
Neutral
discharges C
Hot
Figure 1. Normal Fault
1
to remove any charge on C
GFI
R
T
G
with a current equal to 3 I
B
, between the load termi-
R
Hot
Neutral
LOAD
SCR Trigger
Ground
– Input
+ Input
R
T
B
2
TH
to
,
1
2
3
4
where I
resistor. If fault signals are present at the input of A1 (which
is held at virtual ground, +10V), one of the two current
mirrors in the feedback path of A1 (Q4 and Q5) will become
active, depending on which half-cycle the fault occurs.
This action will raise the voltage at V
value equal to I
better allow fault currents to charge it.
Notice that I
line, while I
I
rent in one direction). Thus, during one half-cycle, I
charges C
it.
Grounded Neutral Fault:
An unintentional electrical path between the load terminal of
the neutral line and the ground, as shown by the dashed lines
in Figure 2.
F
8
7
6
5
exits the "- Input" pin (since Q1 will only carry fault cur-
Line
TH
+V
C
R
Amp Out
T
T
SET
S
, while during the other half-cycle I
is the value of current set by the external R
F
TH
Figure 2. Grounded Neutral Fault
only charges C
TH
discharges C
Neutral
, and reducing the discharge rate of C
Hot
T
T
GFI
R
during the half-cycle in which
during both half-cycles of the
G
PRODUCT SPECIFICATION
S
, switching I
Hot
Neutral
REV. 2.0.1 6/17/05
R
LOAD
TH
discharges
R
1
F
IN
to a
-I
SET
TH
T
to