MIC2250 Datasheet, PDF (8/13 Pages) Micrel Semiconductor – High Efficiency Low EMI Boost Regulator

Micrel, Inc.
Functional Description
VIN
The input supply (VIN) provides power to the internal
MOSFETs and control circuitry for the switch mode
regulator. The operating input voltage range is from 2.5V
to 5.5V. An input capacitor with a minimum voltage
rating of 6.3V is recommended. Refer to the layout
recommendations for details.
EN
A logic level input of 1.5V or higher enables the
regulator. A logic input of 0.4V or less places the
regulator in shutdown mode which reduces the supply
current to less than 1µA. The MIC2250 features built-in
soft start circuitry that reduces in-rush current and
prevents the output voltage from overshooting during
startup. Do not leave the Enable pin floating.
SW
The MIC2250 has an internal MOSFET switch that
connects directly to one end of the inductor (SW pin) and
provides a current path to ground during switching
cycles. The source of the internal MOSFET connects
through a current sense resistor to ground.
MIC2250
PGND
The power ground pin is the high current path to ground.
The current loop for the power ground should be as
small as possible and separate from the analog ground
(AGND). Refer to the layout recommendations for more
details.
AGND
Analog ground (AGND) is the ground path for the biasing
and control circuitry. The current loop for the signal
ground should be separate from the power ground
(PGND) loop. Refer to the layout recommendations for
more details.
DITH
The DITH function is a frequency dithering technique
that reduces EMI noise by spreading the boost
regulators’ noise spectrum. This technique reduces the
EMI peaks by distributing the switching frequency across
a wider spectrum. Connect this pin high to enable the
pseudo-random on-time dithering. Connect this pin to
ground to disable this function.
FB
The feedback pin (FB) allows the regulated output
voltage to be set by applying an external resistor divider
network. The internal reference voltage is 1.24V. The
output voltage is calculated from the following equation:
V_OUT
= 1.24V⎜⎛1+
⎝
R1 _⎟⎞
R2 _⎠
November 2008
8
M9999-111708-A