LTC3831EGN#PBF Linear Technology, LTC3831EGN#PBF Datasheet - Page 9

• Manufacturer Part Number: LTC3831EGN#PBF
• Description: IC SW REG CONTROLLR SYNC 16-SSOP
• Manufacturer: Linear Technology

Specifications of LTC3831EGN#PBF

• Applications: Controller, DDR
• Voltage - Input: 3 ~ 8 V
• Number Of Outputs: 1
• Voltage - Output: 1.27 ~ 4 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 16-SSOP
• Primary Input Voltage: 8V
• No. Of Outputs: 1
• Output Current: 10A
• No. Of Pins: 16
• Operating Temperature Range: -40°C To +85°C
• Msl: MSL 1 - Unlimited
• Supply Voltage Range: 3V To 8V
• Rohs Compliant: Yes
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

APPLICATIONS INFORMATION
back signal is greater than 3% above V
two comparators from triggering due to noise, the MIN and
MAX comparators’ response times are deliberately delayed
by two to three microseconds. These two comparators
help prevent extreme output perturbations with fast output
load current transients, while allowing the main feedback
loop to be optimally compensated for stability.
Thermal Shutdown
The LTC3831 has a thermal protection circuit that dis-
ables both gate drivers if activated. If the chip junction
temperature reaches 150°C, both TG and BG are pulled
low. TG and BG remain low until the junction temperature
drops below 125°C, after which, the chip resumes normal
operation.
Soft-Start and Current Limit
The LTC3831 includes a soft-start circuit that is used for
start-up and current limit operation. The SS pin requires an
external capacitor, CSS, to GND with the value determined
by the required soft-start time. An internal 12μA current
source is included to charge C
COMP pin is clamped to a diode drop (B-E junction of QSS
in the Block Diagram) above the voltage at the SS pin.
This prevents the error amplifi er from forcing the loop to
maximum duty cycle. The LTC3831 operates at low duty
cycle as the SS pin rises above 0.6V (V
SS continues to rise, Q
takes over to regulate the output. The MIN comparator is
disabled during soft-start to prevent it from overriding the
soft-start function.
The LTC3831 includes yet another feedback loop to control
operation in current limit. Just before every falling edge
of TG, the current comparator, CC, samples and holds the
voltage drop measured across the external upper MOSFET,
Q1, at the I
voltage at the I
measured voltage across Q1 increases due to the drop
across the R
below I
the maximum level, CC starts to pull current out of C
cutting the duty cycle and controlling the output current
level. The CC comparator pulls current out of the SS pin
MAX
, indicating that Q1’s drain current has exceeded
FB
DS(ON)
pin. CC compares the voltage at I
MAX
of Q1. When the voltage at I
pin. As the peak current rises, the
SS
turns off and the error amplifi er
SS
. During power-up, the
REF
COMP
. To prevent these
≈ 1.2V). As
FB
FB
to the
drops
SS
,
in proportion to the voltage difference between I
I
gradually, creating a time delay before current limit takes
effect. Very short, mild overloads may not affect the output
voltage at all. More signifi cant overload conditions allow
the SS pin to reach a steady state, and the output remains
at a reduced voltage until the overload is removed. Serious
overloads generate a large overdrive at CC, allowing it to
pull SS down quickly and preventing damage to the output
components. By using the R
output current, the current limiting circuit eliminates an
expensive discrete sense resistor that would otherwise be
required. This helps minimize the number of components
in the high current path.
The current limit threshold can be set by connecting an
external resistor R
supply at the drain of Q1. The value of R
by:
where:
The R
To keep the current limit threshold constant, the internal
12μA sink current at I
temperature coeffi cient to provide fi rst order correction
for the temperature coeffi cient of R
In order for the current limit circuit to operate properly and
to obtain a reasonably accurate current limit threshold,
the I
MAX
R
I
I
I
f
L
R
I
LMAX
LOAD
RIPPLE
OSC
IMAX
O
IMAX
DS(ON)Q1
IMAX
. Under minor overload conditions, the SS pin falls
= Inductor value
DS(ON)
= LTC3831 oscillator frequency = 200kHz
= Internal 12μA sink current at I
= Maximum load current
= I
and I
= (I
= Inductor ripple current
=
LOAD
(
LMAX
of Q1 usually increases with temperature.
= On-resistance of Q1 at I
V
( )
FB
IN
f
OSC
pins must be Kelvin sensed at Q1’s drain
+ (I
– V
)(R
IMAX
RIPPLE
OUT
( )
DS(ON)Q1
L
O
from the I
MAX
)
(
( )
/2)
V
V
OUT
IN
is designed with a positive
DS(ON)
)/I
)
IMAX
MAX
DS(ON)Q1
of Q1 to measure the
pin to the main V
IMAX
LMAX
LTC3831
MAX
is determined
.
FB
3831fb
9
and
IN