LTC4253ACUF-ADJ#TR Linear Technology, LTC4253ACUF-ADJ#TR Datasheet - Page 14

• Manufacturer Part Number: LTC4253ACUF-ADJ#TR
• Description: IC,Power Control/Management,CMOS,LLCC,20PIN,PLASTIC
• Manufacturer: Linear Technology

Specifications of LTC4253ACUF-ADJ#TR

• Family Name: LTC4253A-ADJ
• Package Type: QFN EP
• Operating Temperature (min): 0C
• Operating Temperature (max): 70C
• Operating Temperature Classification: Commercial
• Product Depth (mm): 4mm
• Product Length (mm): 4mm
• Mounting: Surface Mount
• Pin Count: 20
• Lead Free Status / Rohs Status: Not Compliant

APPLICATIO S I FOR ATIO
LTC4253A-ADJ
SHUNT REGULATOR
A fast responding regulator shunts the LTC4253A-ADJ V
pin. Power is derived from –48RTN by an external current
limiting resistor. The shunt regulator clamps V
(V
transients and contributes a short delay at start-up. R
should be chosen to accommodate both V
rent and the drive required for three optocouplers used by
the PWRGD signals. Higher current through R
higher dissipation for R
higher V
buffer as in Figure 16, V
cascodes as in Figure 17 or V
MOSFET cascodes replacing the NPNs in Figure 17. An
alternative is a separate NPN buffer driving the optocoupler
as shown in Figure 16. Multiple 1/4W resistors can replace
a single higher power R
INTERNAL UNDERVOLTAGE LOCKOUT (UVLO)
A hysteretic comparator, UVLO, monitors V
undervoltage. The thresholds are defined by V
hysteresis V
(–48V RTN)
14
SHORT PIN
Z
). A 1µF decoupling capacitor at V
UVIN
UVD
UVL
V
UV
IN
IN
UVLO
noise. Alternative circuits are V
LKH
1
UNDERVOLTAGE
V
Figure 2. Undervoltage/Overvoltage Recovery and Shutdown (All Waveforms are Referenced to V
. When V
LKO
SHUTDOWN
UVL
U
(2a) Undervoltage
IN
IN
IN
2
IN
U
and LTC4253A-ADJ as well as
resistor.
V
3.08V
38V
(UNDERVOLTAGE
RECOVERY VOLTAGE)
driving base resistors of NPN
NORMAL OPERATION
UVHI
rises above V
IN
W
driving the gates of
UV
IN
IN
LKO
3
UNDERVOLTAGE
IN
filters supply
SHUTDOWN
with an NPN
V
3.08V
36V
(UNDERVOLTAGE
SHUTDOWN
VOLTAGE)
supply cur-
IN
UVLO
LKO
the chip is
U
IN
results in
to 13V
and its
IN
4
(Refer to Block Diagram)
for
IN
IN
(–48V RTN)
SHORT PIN
enabled; below (V
pulled low. The UVLO function at V
confused with the UVL/UV and OVL/OV pins. These are
completely separate functions.
UNDERVOLTAGE AND OVERVOLTAGE COMPARATORS
The undervoltage comparator has inputs multiplexed from
UVL and UV. When comparator output UVD is high, UV is
multiplexed to the comparator input UVIN. When UVD is
low, UVL is multiplexed to UVIN. By tapping UVL and UV
off a resistive string across the supply such as in the Typi-
cal Application, the undervoltage function is implemented
as shown in Figure 2a. During UVLO, UVD is forced high
so UV is multiplexed to UVIN. At time point 1, V
past V
UVIN = UV is less than V
the part is in undervoltage shutdown. At time point 2, UV
ramps past V
part out of undervoltage and switching UVL to UVIN. UVL
is tied to UVIN until time point 3 when UVL ramps past
V
undervoltage shutdown and switching UV to UVIN.
OVIN
UVLO
OVD
OVL
V
OV
IN
UVLO
LKO
(3.08V) and UVD goes high, bringing the part into
1
and the undervoltage comparator is enabled.
V
LKO
0VL
OPERATION
UVHI
NORMAL
(3.08V) and UVD goes low, bringing the
LKO
(2b) Overvoltage
2
– V
OVERVOLTAGE SHUTDOWN
71V
(OVERVOLTAGE
SHUTDOWN VOLTAGE)
V
5.09V
UVHI
OVHI
LKH
(3.08V), so UVD is high and
) it is disabled and GATE is
OV
IN
EE
)
3
OPERATION
should not be
NORMAL
V
5.08V
69V
(OVERVOLTAGE
RECOVERY
VOLTAGE)
OVLO
IN
4
4253A F02
ramps
4253a-adjf