Datasheet

www.ti.com Jumper Settings
6 Jumper Settings
Terminal Silkscreen Description
Sets the AVIN of the LM21305. Pins 2 and 3 connected gives AVIN = PVIN. Pins 1 and 2
JP1 connected gives AVIN = AVIN_EXT.
Default: pins 2 and 3 connected.
Enables the on-board LED, LD1. When J1 is ON, LD1 will be ON if PGOOD is high. When J1 is
J1 OFF, power used to drive LD1 is saved.
Default: ON.
Synchronizing clock input. When J2 is ON, C1 is connected to ground and switching frequency
is set by the on-board resistor R4. When J2 is OFF, the switch node waveform will be
J2
synchronized to the clock source connected to J2.
Default: ON.
Only should be connected when AVIN = 5V. When AVIN is below 5V, and especially below
3.3V, connecting J3 can result in better efficiency.
J3
Default: OFF.
Caution: if AVIN > 5.5V, connecting J3 could damage the device.
7 Other Design Examples
The LM21305 is designed to fit a wide variety of applications. A design calculator tool for the LM21305 is
available to accelerate the design process. Also, the LM21305 is enabled through Texas Instruments
WEBENCH
®
power designer. A few design examples are given here for convenience and only the
components that need to be modified are listed below. Design examples are for PVIN = 12V, f
s
= 500 kHz,
I
OUT-MAX
= 5A, and V
OUT
= 1.2V, 1.8V, 2.5V, 3.3V and 5V.
V
OUT
1.2V 1.8V 2.5V 3.3V 5V
C6 3300 pF 25V 3300 pF 25V 4700 pF 25V 4700 pF 25V 4700 pF 25V
L1 1.5 µH 10A 2.2 µH 10A 2.2 µH 10A 3.3 µH 10A 3.3 µH 10A
R5 10 kΩ 1% 20 kΩ 1% 31.6 kΩ 1% 45.3 kΩ 1% 73.2 kΩ 1%
R7 3.32 kΩ 1% 4.22 kΩ 1% 5.10 kΩ 1% 7.15 kΩ 1% 8.2 kΩ 1%
5
SNVA432C–March 2010–Revised May 2013 AN-2042 LM21305 Evaluation Board
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