LTC4220 View Datasheet(PDF) - Linear Technology
Part Name
Description
Manufacturer
LTC4220 Datasheet PDF : 36 Pages
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LTC4252-1/LTC4252-2
LTC4252A-1/LTC4252A-2
APPLICATIONS INFORMATION
and R2 = 32.4k gives a typical operating range of 43.2V
to 82.5V. The undervoltage shutdown and overvoltage
recovery thresholds are then 39.2V and 74.4V. 1% divider
resistors are recommended to preserve threshold accuracy.
The R1-R2 divider values shown in the Typical Application
set a standing current of slightly more than 100μA and
define an impedance at UV/OV of 30kΩ. In most applica-
tions, 30kΩ impedance coupled with 300mV UV hysteresis
makes the LTC4252 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 are available in the 10-pin MS
package and can be used for a different operating range
such as 35.5V to 76V as shown in Figure 3. Other combi-
nations are possible with different resistor arrangements.
UV/OV COMPARATORS (LTC4252A)
A UV hysteretic comparator detects undervoltage condi-
tions at the UV pin, with the following thresholds:
UV low-to-high (VUV) = 3.08V
UV high-to-low (VUV – VUVHST) = 2.756V
An OV hysteretic comparator detects overvoltage condi-
tions at the OV pin, with the following thresholds:
OV low-to-high (VOV) = 5.09V
OV high-to-low (VOV – VOVHST) = 4.988V
The UV and OV trip point ratio is designed to match the
standard telecom operating range of 43V to 71V when
connected together as in Figure 2. A divider (R1, R2) is
used to scale the supply voltage. Using R1 = 390k and R2
= 30.1k gives a typical operating range of 43V to 71V. The
undervoltage shutdown and overvoltage recovery thresh-
olds are then 38.5V and 69.6V respectively. 1% divider
resistors are recommended to preserve threshold accuracy.
The R1-R2 divider values shown in Figure 2 set a standing
current of slightly more than 100μA and define an impedance
at UV/OV of 28kΩ. In most applications, 28kΩ impedance
coupled with 324mV UV hysteresis makes the LTC4252A
insensitive to noise. If more noise immunity is desired, add
a 1nF to 10nF filter capacitor from UV/OV to VEE.
The UV and OV pins can be used for a wider operat-
ing range such as 35.5V to 76V as shown in Figure 4.
Other combinations are possible with different resistor
arrangements.
UV/OV OPERATION
A low input to the UV comparator will reset the chip and pull
the GATE and TIMER pins low. A low-to-high UV transition
will initiate an initial timing sequence if the other interlock
–48RTN
–48RTN
(SHORT PIN)
R1
464k
1%
R2
10k
1%
R3
34k
1%
C2
10nF
RIN
10k
1/2W
1
DDIDNZ†13B**
VIN
LTC4252A-1
9 UV
PWRGD 2
8
OV
7
DRAIN
10
TIMER
6
GATE
CT
3
0.68μF
SS
4
VEE SENSE
CSS
5
68nF
R4
CL +
22k
100μF
Q2
CIN
1μF
R5
2.2k
LOAD
EN
*
RD 1M
Q1
IRF530S
RC
10Ω
CC
10nF
RS
0.02Ω
– 48V
* M0C207
Q2: MMBT5551LT1
**†DRIEOCDOEMSM, IENNCDED FOR HARSH ENVIRONMENTS
425212 F04
Figure 4. – 48V/2.5A Application with Wider Input Operating Range
425212fd
15
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