参数资料
型号: LTC3812IFE-5#TR
厂商: LINEAR TECHNOLOGY CORP
元件分类: 稳压器
英文描述: 1 A SWITCHING CONTROLLER, PDSO16
封装: 4.40 MM, PLASTIC, TSSOP-16
文件页数: 4/32页
文件大小: 425K
代理商: LTC3812IFE-5#TR
LTC3812-5
12
38125fb
level to initiate another cycle. In this mode, frequency is
proportional to load current at light loads.
Pulse skip mode operation is disabled by comparator F
when the FCB pin is brought below 0.8V, forcing continuous
synchronous operation. Forced continuous mode is less
efcient due to resistive losses, but has the advantage of
better transient response at low currents, approximately
constant frequency operation, and the ability to maintain
regulation when sinking current.
Fault Monitoring/Protection
Constant on-time current mode architecture provides ac-
curate cycle-by-cycle current limit protection—a feature
that is very important for protecting the high voltage power
supply from output short-circuits. The cycle-by-cycle cur-
rent monitor guarantees that the inductor current will never
exceed the value programmed on the VRNG pin.
Foldback current limiting provides further protection if the
output is shorted to ground. As VFB drops, the buffered
current threshold voltage ITHB is pulled down and clamped
to 1V. This reduces the inductor valley current level to
one-sixth of its maximum value as VFB approaches 0V.
Foldback current limiting is disabled at start-up.
Overvoltage and undervoltage comparators OV and UV
pull the PGOOD output low if the output feedback voltage
exits a ±10% window around the regulation point after the
internal 120μs power bad mask timer expires. Furthermore,
in an overvoltage condition, M1 is turned off and M2 is
turned on immediately and held on until the overvoltage
condition clears.
The LTC3812-5 provides an undervoltage lockout com-
parator for the INTVCC supply. The INTVCC UV threshold
is 4.2V to guarantee that the MOSFETs have sufcient
gate drive voltage before turning on. If INTVCC is under
the UV threshold, the LTC3812-5 is shut down and the
drivers are turned off.
Strong Gate Drivers
The LTC3812-5 contains very low impedance drivers ca-
pable of supplying amps of current to slew large MOSFET
gates quickly. This minimizes transition losses and allows
paralleling MOSFETs for higher current applications. A
60V oating high side driver drives the topside MOSFET
and a low side driver drives the bottom side MOSFET
(see Figure 3). The bottom side driver is supplied directly
from the INTVCC pin. The top MOSFET drivers are biased
from oating bootstrap capacitor CB, which normally is
recharged during each off cycle through an external diode
from INTVCC when the top MOSFET turns off. In pulse
skip mode operation, where it is possible that the bottom
MOSFET will be off for an extended period of time, an
internal timeout guarantees that the bottom MOSFET is
turned on at least once every 25μs for one on-time period
to refresh the bootstrap capacitor.
Figure 3. Floating TG Driver Supply and Negative BG Return
OPERATION
IC/Driver Supply Power
The LTC3812-5’s internal control circuitry and top and
bottom MOSFET drivers operate from a supply voltage
(INTVCC pin) in the range of 4.2V to 14V. The LTC3812-5
has two integrated linear regulator controllers to easily
generate this IC/driver supply from either the high voltage
input or from the output voltage. For best efciency the
supply is derived from the input voltage during start-up
and then derived from the lower voltage output as soon
as the output is higher than 4.7V. Alternatively, the supply
can be derived from the input continuously if the output is
<4.7V or an external supply in the appropriate range can
be used. The LTC3812-5 will automatically detect which
mode is being used and operate properly.
BOOST
TG
SW
BG
PGND
INTVCC
LTC3812-5
M1
M2
+
VIN
CIN
VOUT
COUT
DB
CB
L
38125 F03
相关PDF资料
PDF描述
LTC3812EFE-5#TR 1 A SWITCHING CONTROLLER, PDSO16
LTC3812IFE-5 1 A SWITCHING CONTROLLER, PDSO16
LTC3831IGN SWITCHING CONTROLLER, 500 kHz SWITCHING FREQ-MAX, PDSO16
LTC3833IUDC#PBF SWITCHING CONTROLLER, 2000 kHz SWITCHING FREQ-MAX, PQCC20
LTC3833EFE#TRPBF SWITCHING CONTROLLER, 2000 kHz SWITCHING FREQ-MAX, PDSO20
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