Datasheet
LTC3458
8
3458fa
Detailed Description
The LTC3458 provides high efficiency, low noise power
for boost applications with output voltages up to 7.5V. The
true output disconnect feature eliminates inrush current,
and allows V
OUT
to go to zero during shutdown. The
current mode architecture with adaptive slope compensa-
tion provides ease of loop compensation with excellent
transient load response. The low R
DS(ON)
, low gate charge
synchronous switches eliminate the need for an external
Schottky rectifier, and provide efficient high frequency
pulse width modulation (PWM) control. High efficiency is
achieved at light loads when Burst Mode operation is
entered, where the IC’s quiescent current is a low 15μA
typical on V
IN
. The LTC3458 is designed to provide custom
performance in a variety of applications with program-
mable feedback, current limit, oscillator frequency, soft-
start, and Burst Mode threshold.
BLOCK DIAGRA
W
PGND
PGND
V
BEST
V
BEST
V
SELECT
3
6
9
OSC/SYNC
MAX
DUTY
SYNC
GND I
LIM
PGND SS COMP SHDN
R
T
V
CC
V
CC
V
CC
SW
V
OUT
FB
BURST
PWM
AND
BURST MODE
DRIVE LOGIC
P-DRIVE
P-DRIVE
P-DRIVE
N-DRIVE
N-DRIVE
N-DRIVE
I
ZERO
DETECT
BURST MODE
CONTROL
FIXED
FREQUENCY
BURST MODE
MUX
SOFT-START THERMAL SD
4%
UNDERVOLTAGE
REFERENCE/
BIAS
PEAK CURRENT
COMPARATOR
I
COMP
, I
LIMIT
,
I
BURST_PEAK
,
SLOPE COMP
SLEEP
SLEEP
CONTROL
MODE
MODE
MODE
I
COMP/LIMIT_PEAK
I
BURST_PEAK
SLOPE
SLOPE
SLEEP TO
ALL BLOCKS
I_SENSE
BURST ACTIVE
(DISABLED IN
BURST MODE)
+
–
+
–
TSD
5 13 10 8 4
11 1 2
12
7
ANTIRING
SW1
UNDER
UNDER
SD
TO ALL BLOCKS
SDB
I
PEAK
CLOCK
BIAS
CURRENTS
UVLO
I
ZERO
3458 BD
ERROR AMPLIFIER/
BURST COMPARATOR
APPLICATIO S I FOR ATIO
WUUU
LTC3458 Programmable Functions
Current Limit/Peak Burst Current. The programmable
current limit circuit sets the maximum peak current in the
internal N-channel MOSFET switch. This clamp level is
programmed using a resistor to ground on I
LIM
. In Burst
Mode operation, the current limit is automatically set to
~1/4 of the programmed current limit for optimal effi-
ciency. A 124k R
ILIM
resistor is recommended in most
applications unless a lower limit is needed to prevent the
external inductor from saturating.
I
R
LIM
=
200
I is in amps and R is in kΩ.
II
BURSTPEAK LIM
≈
1
4
•