LTC3458_15 Datasheet, PDF (8/16 Pages) Linear Technology – 1.4A, 1.5MHz Synchronous Step-Up DC/DC Converter with Output Disconnect

LTC3458
BLOCK DIAGRA
SYNC 3
R_T 6
BURST
SW
V_CC
11
1
2
V_CC
OSC/SYNC
MAX
DUTY
SLOPE
I_ZERO
PWM
AND
BURST MODE
DRIVE LOGIC
P-DRIVE
N-DRIVE
UNDER
MODE
SLEEP
MODE
FIXED
FREQUENCY
BURST MODE
MUX
SLEEP
CONTROL
I_{COMP/LIMIT_PEAK}
I_{BURST_PEAK}
SLOPE
BURST MODE
CONTROL
I_ZERO
DETECT
ANTIRING
N-DRIVE
P-DRIVE ^VSELECT
–
+
V_BEST ^SW1
SLEEP TO
ALL BLOCKS
PEAK CURRENT
COMPARATOR
I_COMP, I_LIMIT,
I_{BURST_PEAK},
SLOPE COMP
I_SENSE
P-DRIVE
UNDER
4%
UNDERVOLTAGE
PGND
ERROR AMPLIFIER/
BURST COMPARATOR
BURST ACTIVE
–
(DISABLED IN
BURST MODE)
+
MODE
BIAS
CURRENTS
UVLO
TSD
V_CC
REFERENCE/
BIAS
12 VOUT
7 FB
V_BEST
SOFT-START
THERMAL SD
SD
N-DRIVE
PGND
9
5
13
10
8
4
GND
I_LIM
PGND
SS
COMP SHDN
SDB
TO ALL BLOCKS
3458 BD
APPLICATIO S I FOR ATIO
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.
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_LIM
=
200
R
I is in amps and R is in kΩ.
I_BURSTPEAK
≈
1
4
• I_LIM
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