LTC3523 datasheet(6/16 Pages) LINER

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LTC3523/LTC3523-2

3523fb

PIN FUNCTIONS

SW1 (Pin 5): Step-Up Converter Switch Pin. Connect the

inductor between SW1 and VIN1. Keep these PCB trace

lengths as short and wide as possible to reduce EMI and

voltage overshoot. If the inductor current falls to zero or

SHDN1 is low, an internal 150Ω anti-ringing resistor is

connected from SW1 to VIN1 to minimize EMI.

GND1 (Pin 6): Step-Up Converter Power Ground. Connect

this pin to the ground plane.

GND2 (Pin 7): Step-Down Converter Power Ground. Con-

nect this pin to the ground plane.

SW2 (Pin 8): Step-Down Converter Switch Pin. Connect

one end of the inductor to SW2. Keep these PCB trace

lengths as short and wide as possible to reduce EMI and

voltage overshoot.

VIN2 (Pin 9): Step-Down Converter Power Voltage Input.

This pin can be connected to a different supply than VIN1.

This pin must be connected to a valid supply voltage.

MODE (Pin 10): Step-Up and Step-Down Converter Mode

Selection Pin. Do not leave this pin ﬂoating.

• MODE = Low: PWM mode

• MODE = High: Automatic Burst Mode operation

PGOOD2 (Pin 11): Step-Down Converter Power Good

Comparator Output. This open-drain output is pulled low

when VFB2 < –9% of its regulation voltage.

FB2 (Pin 12): Step-Down Converter Feedback Input to the

Error ampliﬁer. Connect resistor divider tap to this pin. The

output voltage can be adjusted from 0.6V to 5.5V by:

VOUT(STEP-DOWN) =+

⎛

⎝⎜

⎞

⎠⎟

.•

See Block Diagram.

If large feedback resistors, above 500k are used, then it

will be necessary to use a lead capacitor connected to the

output voltage and FB2.

SHDN2 (Pin 13): Step-Down Converter Logic Controlled

Shutdown Input. Do not leave this pin ﬂoating.

• SHDN2 = High: Normal free-running operation,

1.2MHz/2.4MHz typical operating frequency.

• SHDN2 = Low: Shutdown, quiescent current < 1μA.

This pin cannot exceed the voltage on VIN2.

GND3 (Pin 14): Analog Ground. The feedback voltage

dividers for each converter must be returned to GND3

for best performance.

Note: When laying out your PCB provide a short direct

path between GND1 and the (–) side of the step-up output

capacitor(s) and GND2 and the step-down output capaci-

tor.These pins are not connected together internally.

VBAT (Pin 15): Analog Voltage Input. Connect this pin to

the higher of VIN1 or VIN2.

SHDN1 (Pin 16): Step-Up Converter Logic Controlled

Shutdown Input.

• SHDN1 = High: Normal free-running operation,

1.2MHz/2.4MHz typical operating frequency.

• SHDN1 = Low: Shutdown, quiescent current < 1μA.

This pin cannot exceed the voltage on VIN1.

Exposed Pad (Pin 17): Die attach pad must be soldered

to PCB ground for electrical contact and optimum thermal

performance.

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