LTC4214 View Datasheet(PDF) - Linear Technology
Part Name
Description
MFG CO.
'LTC4214' PDF : 32 Pages View PDF
LTC4214-1/LTC4214-2
APPLICATIO S I FOR ATIO
SUPPLY VOLTAGE
The LTC4214 requires a (VIN – VEE) voltage of 6V to 16V
to function. This can be derived from GND and –12V of a
–12V system or the 3.3V and –5.2V of a –5.2V system. The
positive supply is connected to VIN via an RC network
so that the LTC4214 can have a usable VIN during load
short or other transient events when (VIN – VEE) glitches
below 6V.
INTERNAL UNDERVOLTAGE LOCKOUT (UVLO)
A hysteretic comparator, UVLO, monitors VIN for
undervoltage. The thresholds are defined by VLKO and its
hysteresis, VLKH. When VIN rises above 5.1V (VLKO) the
chip is enabled; below 4.8V (VLKO – VLKH) it is disabled and
GATE is pulled low. The UVLO function at VIN should not
be confused with the UV/OV pins. These are completely
separate functions.
UV/OV COMPARATORS
An UV hysteretic comparator detects undervoltage condi-
tions at the UV pin, with the following thresholds:
UV low-to-high (VUVHI) = 2.25V
UV high-to-low (VUVHI – VUVHST) = 2V
An OV hysteretic comparator detects overvoltage condi-
tions at the OV pin, with the following thresholds:
OV low-to-high (VOVHI) = 3V
OV high-to-low (VOVHI – V0VHST) = 2.85V
In Figure 2, a divider (R1-R2) is used to scale the supply
voltage of 12V ±10%. Using R1 = 121k and R2 = 32.4k
gives a typical operating range of 10.7V to 13.5V. The
under and overvoltage shutdown thresholds are then 9.5V
to 14.2V. 1% divider resistors are recommended to pre-
serve threshold accuracy.
The R1-R2 divider values shown in Figure 2 set a standing
current of slightly more than 75µA and define an imped-
ance at UV/OV of 25kΩ. In most applications, 25kΩ
impedance coupled with 250mV UV hysteresis makes the
LTC4214 insensitive to noise. If more noise immunity is
desired, add a 1nF to 10nF filter capacitor from UV/OV
to VEE.
Separate UV and OV pins can be used for a wider
operating range such as 10V to 14V as shown in Figure␣ 3.
Other combinations are possible with different resistor
arrangements.
GND
RX
10Ω
CX
100nF
GND
(SHORT PIN)
R1
124k
1%
R2
3.65k
1%
R3
32.4k
1%
RIN
Z1
470Ω
R4
100k
1
VIN
LTC4214-1
9
UV
2
PWRGD
8
OV
7
DRAIN
10
TIMER
6
GATE
CT 3
47nF
SS
4
SENSE
VEE
C2
CSS
5
1nF
22nF
CIN
0.1µF
–12V
Z1: SMAJ15A
+
Q2
NDS0605
RD
475k
GND
CL
100µF
EN
RPULLDN
10k
VOUT
RC
10Ω
CC
10nF
Q1
IRF7413
RS
0.025Ω
4214 F03
Figure 3. – 12V/2A Application with Wider Input Operating Range
421412f
13
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