Datasheet LTC3458 (Analog Devices) - 7

LTC3458
U U U PI FU CTIO S SW (Pin 1):
Switch Pin for Inductor Connection. During
GND (Pin 9):
Signal Ground Pin. discontinuous conduction mode an antiring resistor con-
SS (Pin 10):
Connect a capacitor between this pin and nects SW to VIN to reduce noise. ground to set soft-start period. 5μA of current is sourced
VIN (Pin 2):
Input Supply Pin. Connect this to the input from SS during soft-start. supply and decouple with 1μF minimum. t(msec) = CSS (μF )• 200
SYNC (Pin 3):
Oscillator Synchronization Pin. A clock
BURST (Pin 11):
Burst Mode Threshold Adjust Pin. A pulse width of 100ns to 2μs is required to synchronize the resistor/capacitor combination from this pin to ground internal oscillator. This pin is disabled when grounded. programs the average load current at which automatic
SHDN (Pin 4):
Shutdown Pin. Grounding this pin shuts Burst Mode operation is entered, according to the formula: down the IC. Connect to >1.25V to enable.
I
= 10
LIM (Pin 5):
Adjustable Peak Current Limit. Connect a RBURST I resistor from I BURST LIM to GND to program the peak inductor current according to the following formula: where RBURST is in kΩ and IBURST is in amps. I C V LIMIT = 200 OUT OUT R CBURST = • ILIM , 10 000 where ILIMIT is in amps and RILIM is in kΩ. where CBURST(MIN) and COUT are in μF.
RT (Pin 6):
Connect a resistor to ground to program the oscillator frequency, according to the formula: To force fixed frequency PWM mode, connect BURST to VOUT through a 50k resistor. 1 f
V
OSC =
OUT (Pin 12):
Output of the Synchronous Rectifier and 0 2 . + 0 0 . 04 •RT Internal Gate Drive Source for the Power Switches. where fOSC is in MHz and RT is in kΩ. ⎛ R2⎞ VOUT = 1 2 . 3 1+ ⎝⎜ R ⎠⎟ 1
FB (Pin 7):
Connect Resistor Divider Tap Here. The output
Exposed Pad (PGND) (Pin 13):
Must be soldered to PCB voltage can be adjusted from 2V to 7.5V. Feedback refer- ground, for electrical contact and optimum thermal ence voltage is typically 1.23V. performance.
COMP (Pin 8):
gm 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. 3458fa 7