Datasheet LTC3458L (Analog Devices) - 7

LTC3458L
U U U PI FU CTIO S SW (Pin 1):
Switch Pin for Inductor Connection. During compensate the loop. See the section “Compensating the discontinuous conduction mode an antiring resistor con- Feedback Loop” for guidelines. nects SW to VIN to reduce noise.
GND (Pin 9):
Signal Ground Pin.
VIN (Pin 2):
Input Supply Pin. Connect this to the input
SS (Pin 10):
Connect a capacitor between this pin and supply and decouple with 1μF minimum. ground to set soft-start period. 5μA of current is sourced
SYNC (Pin 3):
Oscillator Synchronization Pin. A clock from SS during soft-start. pulse width of 100ns to 2μs is required to synchronize the t(msec) = C internal oscillator. This pin is disabled when grounded. SS (μF )• 200
BURST (Pin 11):
Burst Mode Threshold Adjust Pin. A
SHDN (Pin 4):
Shutdown Pin. Grounding this pin shuts resistor/capacitor combination from this pin to ground down the IC. Connect to >1.25V to enable. programs the average load current at which automatic
ILIM (Pin 5):
Adjustable Peak Current Limit. Connect a Burst Mode operation is entered, according to the formula: resistor from ILIM to GND to program the peak inductor current according to the following formula: RBURST = 10 IBURST ILIMIT = 180 R where RBURST is in kΩ and IBURST is in amps. ILIM where ILIMIT is in amps and RILIM is in kΩ. C V C OUT OUT = •
R
BURST
T (Pin 6):
Connect a resistor to ground to program the , 10 000 oscillator frequency, according to the formula: where CBURST(MIN) and COUT are in μF. 1 f To force fixed frequency PWM mode, connect BURST to OSC = 0 2 . + 0 0 . 04 •RT VOUT through a 51k resistor. where fOSC is in MHz and RT is in kΩ.
VOUT (Pin 12):
Output of the Synchronous Rectifier and Oscillator frequency can be programmed between 400kHz Internal Gate Drive Source for the Power Switches. and 1.5MHz. ⎛ R ⎞ 1 V 1.225 1
FB (Pin 7):
Connect Resistor Divider Tap Here. The output OUT = + ⎝⎜ R2⎠⎟ voltage can be adjusted from 2V to 6V. Feedback reference
Exposed Pad (PGND) (Pin 13):
Must be soldered to PCB voltage is typically 1.225V. ground, for electrical contact and optimum thermal
COMP (Pin 8):
gm Error Amp Output. A frequency com- performance. pensation network is connected from this pin to ground to 3458lfa 7