LTC3523-2_15 Datasheet, PDF (6/16 Pages) Linear Technology – Synchronous 600mA Step-Up and 400mA Step-Down DC/DC Converters

LTC3523/LTC3523-2
PIN FUNCTIONS
SW1 (Pin 5): Step-Up Converter Switch Pin. Connect the
inductor between SW1 and V_IN1. 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 V_IN1 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.
V_IN2 (Pin 9): Step-Down Converter Power Voltage Input.
This pin can be connected to a different supply than V_IN1.
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 V_FB2 < –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:
V_{OUT(STEP-DOWN)}
=
0.6V
•
⎛⎝⎜₁₊
R3⎞
R4⎠⎟
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 V_IN2.
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.
V_BAT (Pin 15): Analog Voltage Input. Connect this pin to
the higher of V_IN1 or V_IN2.
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 V_IN1.
Exposed Pad (Pin 17): Die attach pad must be soldered
to PCB ground for electrical contact and optimum thermal
performance.
See Block Diagram.
3523fb
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