LTC3458_15 Datasheet, PDF (7/16 Pages) Linear Technology – 1.4A, 1.5MHz Synchronous Step-Up DC/DC Converter with Output Disconnect

LTC3458
PI FU CTIO S
SW (Pin 1): Switch Pin for Inductor Connection. During
discontinuous conduction mode an antiring resistor con-
nects SW to V_IN to reduce noise.
V_IN (Pin 2): Input Supply Pin. Connect this to the input
supply and decouple with 1μF minimum.
SYNC (Pin 3): Oscillator Synchronization Pin. A clock
pulse width of 100ns to 2μs is required to synchronize the
internal oscillator. This pin is disabled when grounded.
SHDN (Pin 4): Shutdown Pin. Grounding this pin shuts
down the IC. Connect to >1.25V to enable.
I_LIM (Pin 5): Adjustable Peak Current Limit. Connect a
resistor from I_LIM to GND to program the peak inductor
current according to the following formula:
I_LIMIT
=
200
R_ILIM
where I_LIMIT is in amps and R_ILIM is in kΩ.
R_T (Pin 6): Connect a resistor to ground to program the
oscillator frequency, according to the formula:
f_OSC
=
0.2
+
1
0.004
• R_T
where f_OSC is in MHz and R_T is in kΩ.
FB (Pin 7): Connect Resistor Divider Tap Here. The output
voltage can be adjusted from 2V to 7.5V. Feedback refer-
ence voltage is typically 1.23V.
COMP (Pin 8): g_m Error Amp Output. A frequency com-
pensation network is connected from this pin to ground to
compensate the loop. See the section “Compensating the
Feedback Loop” for guidelines.
GND (Pin 9): Signal Ground Pin.
SS (Pin 10): Connect a capacitor between this pin and
ground to set soft-start period. 5μA of current is sourced
from SS during soft-start.
t(msec) = C_SS (μF )• 200
BURST (Pin 11): Burst Mode Threshold Adjust Pin. A
resistor/capacitor combination from this pin to ground
programs the average load current at which automatic
Burst Mode operation is entered, according to the formula:
R_BURST
=
10
I_BURST
where R_BURST is in kΩ and I_BURST is in amps.
C _BURST
=
C_OUT • V_OUT
10,000
where C_BURST(MIN) and C_OUT are in μF.
To force fixed frequency PWM mode, connect BURST to
V_OUT through a 50k resistor.
V_OUT (Pin 12): Output of the Synchronous Rectifier and
Internal Gate Drive Source for the Power Switches.
V_OUT
=
⎛
1.23_⎝⎜1+
R2^⎞
R1⎠⎟
Exposed Pad (PGND) (Pin 13): Must be soldered to PCB
ground, for electrical contact and optimum thermal
performance.
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