LTC3824EMSE-PBF LINER [Linear Technology], LTC3824EMSE-PBF Datasheet - Page 7

• Manufacturer Part Number: LTC3824EMSE-PBF
• Description: High Voltage Step-Down Controller With 40?A Quiescent Current
• Manufacturer: LINER [Linear Technology]

APPLICATIONS INFORMATION
Burst Mode Operation
The LTC3824 can be confi gured for Burst Mode operation to
enhance light load effi ciency (only 40μA quiescent current)
and extend battery run time by leaving the SYNC/MODE
pin open or pulling it higher than 2V. In this mode, when
output load drops the loop control voltage V
and when V
the LTC3824 goes into sleep mode with the switch turned
off. During sleep mode the output voltage drops and V
rises up. When V
will turn on the switch and the burst cycle repeats. If the
SYNC/MODE pin is grounded the Burst Mode operation will
be disabled and the LTC3824 skips cycles at light load.
Oscillation Frequency Setting and Synchronization
The switching frequency of the LTC3824 can be set up
to 600kHz by a resistor, R
ground.
For 200kHz, R
vs R
section. With a 100ns one-shot timer on-chip, the LTC3824
provides fl exibility on the sync pulse width. The sync pulse
threshold voltage level is about 1.2V.
Short-Circuit Protection
In normal operation when the output voltage is in regulation,
V
and V
reduced to 50kHz to allow the inductor current to discharge
and prevent current runaway. Note that synchronization
is enabled only when V
Soft-Start
During soft-start, the voltage on the SS pin (V
reference voltage that controls the output voltage and the
output ramps up following V
is from 0V to 0.8V. The typical time for the output to reach
the programmed level is:
FB
t
is regulated to 0.8V. If the output is shorted to ground
SS
FREQ
FB
=
drops below 0.5V the switching frequency will be
graph in the Typical Performance Characteristics
C
SS
C
7μ
reaches approximately 0.9V at low duty cycle
• . 0 8
FREQ
A
C
V
goes up to around 70mV the LTC3824
= 392k. See the Switching Frequency
FB
is above 0.5V.
SS
FREQ
. The effective range of V
, from the R
C
also drops
SET
SS
) is the
pin to
SS
C
where C
GND.
Overvoltage Protection
To achieve good output regulation in Burst Mode operation,
an overvoltage comparator, OVP , with a threshold adap-
tive to the V
In Burst Mode operation with low V
threshold is approximately 2% above V
is also shifted lower by 2% to contain the output ripple
and to keep output regulation constant. As output load
increases, OVP threshold increases with V
to 8% above V
Undervoltage Lockout and Shutdown
The undervoltage lockout threshold on V
switch is allowed to turn on only when V
than 4V. When the V
the LTC3824 goes into micropower shutdown mode and
only draws 7μA.
Output Voltage Programming
With a 0.8V feedback reference voltage, V
voltage, V
shown in the Block Diagram.
Current Sense Resistor R
The maximum current the LTC3824 can deliver is deter-
mined by:
where 100mV is the internal 100mV threshold across V
and V
current. R
with very short traces. Good kelvin sensing is required for
accurate current limit.
V
I
OUT(MAX)
OUT
SENSE
SS
= 0.8V (1+R
S
OUT
, and I
is the capacitor connected from the SS pin to
should be placed very close to the power switch
C
= 100mV/R
, is programmed by a resistor divider as
voltage is used to monitor the FB voltage.
REF
RIPPLE
.
F1
C
/R
is the inductor peak-to-peak ripple
pin is pulled down below 25mV
S
F2
– I
S
)
and Current Limit
RIPPLE
/2
C
LTC3824
voltage, the OVP
REF
C
REF
CC
voltage to up
and the V
CC
, the output
is 4V. The
is higher
3824fc
7
REF
CC