LTC3527-1_15 Datasheet, PDF (8/22 Pages) Linear Technology – Dual 800mA/400mA, 1.2MHz/2.2MHz Synchronous Step-Up DC/DC Converters

LTC3527/LTC3527-1
PIN FUNCTIONS
SHDN1 (Pin 1): Boost Converter 1 Logic-Controlled
Shutdown Input. There is an internal 4MΩ pull-down on
this pin.
• SHDN1 = High: Normal free running operation, 1.2MHz/
2.2MHz typical operating frequency.
• SHDN1 = Low: Shutdown, quiescent current < 2μA.
Note: Both converters must be shut down together to
achieve < 2μA quiescent current.
FB1 (Pin 2): Boost Converter 1 Feedback Input to the g_m
Error Amplifier. Connect resistor divider tap to this pin. The
output voltage can be adjusted from 1.6V to 5.25V by:
V_OUT1
=
1
.20V
•
⎡⎣⎢₁₊
R1⎤
R2 _⎦⎥
(See Block Diagram)
MODE (Pin 3): Logic-Controlled Mode Input for Both
Boost Converters.
• MODE = High: Fixed frequency operation
• MODE = Low: Automatic Burst Mode operation
MODE pin must be 1V or greater to ensure fixed frequency
over all operating conditions.
V_OUT1 (Pin 5): Boost Converter 1 Output Voltage Sense
Input and Drain of the Internal Synchronous Rectifier
MOSFET. Driver bias is derived from V_OUT1. PCB trace
length from V_OUT1 to the output filter capacitor(s) should
be as short and wide as possible.
SW1 (Pin 6): Boost Converter 1 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 100Ω anti-ringing switch is
connected from SW1 to V_IN1 to minimize EMI.
SW2 (Pin 7): Boost Converter 2 Switch Pin. Connect the
inductor between SW2 and V_IN2. 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
SHDN2 is low, an internal 100Ω anti-ringing switch is
connected from SW2 to V_IN2 to minimize EMI.
V_OUT2 (Pin 8): Boost Converter 2 Output Voltage Sense
Input and Drain of the Internal Synchronous Rectifier
8
MOSFET. Driver bias is derived from V_OUT2. PCB trace
length from V_OUT2 to the output filter capacitor(s) should
be as short and wide as possible.
FSEL (Pin 10): Logic-Controlled Frequency Select
Input.
• FSEL = High: 2.2MHz operation
• FSEL = Low: 1.2MHz operation
FB2 (Pin 11): Boost Converter 2 Feedback Input to the
g_m Error Amplifier. Connect resistor divider tap to this
pin. The output voltage can be adjusted from 1.6V to
5.25V by:
V_OUT2
=
1.20V
•
⎡⎣⎢₁₊
R3
R4
⎤
⎦⎥
(See Block Diagram)
SHDN2 (Pin 12): Boost Converter 2 Logic-Controlled
Shutdown Input. There is an internal 4MΩ pull-down on
this pin.
• SHDN2 = High: Normal free-running operation,
1.2MHz/2.2MHz typical operating frequency.
• SHDN2 = Low: Shutdown, quiescent current < 2μA.
Note: Both converters must be shut down together to
achieve < 2μA quiescent current.
PGOOD2 (Pin 13): Boost Converter 2 Power Good Com-
parator Output. This open-drain output is low when V_FB
is 9% below its regulation voltage.
GND (Pin 14): Signal Ground. This pin is used as a
ground reference for the internal circuitry of the LTC3527/
LTC3527-1.
V_IN, V_IN1, V_IN2 (Pins 15, 4, 9): Battery Input Voltage. See
Operation section for more information.
PGOOD1 (Pin 16) Boost Converter 1 Power Good Com-
parator Output. This open-drain output is low when V_FB
is 9% below its regulation voltage.
PGND (Exposed Pad Pin 17): Backplane. The exposed pad
is PGND and must be soldered to the PCB ground plane.
It serves as the power ground connection for V_OUT1 and
V_OUT2, and as a means of conducting heat away from the
package.
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