mic33153yhj Micrel Semiconductor, mic33153yhj Datasheet - Page 10

• Manufacturer Part Number: mic33153yhj
• Description: 4mhz Pwm 1.2a Internal Inductor Buck Regulator With Hyperlight Load And Power Good
• Manufacturer: Micrel Semiconductor

Functional Description
VIN
The input supply (VIN) provides power to the internal
MOSFETs for the switch mode regulator along with the
internal control circuitry. The VIN operating range is 2.7V
to 5.5V so an input capacitor, with a minimum voltage
rating of 6.3V, is recommended. Due to the high
switching speed, a minimum 2.2µF bypass capacitor
placed close to VIN and the power ground (PGND) pin is
required. Refer to the layout recommendations for
details.
EN
A logic high signal on the enable pin activates the output
voltage of the device. A logic low signal on the enable
pin deactivates the output and reduces supply current to
0.01µA. MIC33153 features external soft start circuitry
via the soft start (SS) pin that reduces in rush current
and prevents the output voltage from overshooting at
start up. Do not leave the EN pin floating.
SW
The switch (SW) connects directly to one end of the
inductor and provides the current path during switching
cycles. The other end of the inductor is connected to the
load, SNS pin and output capacitor. Due to the high
speed switching on this pin, the switch node should be
routed away from sensitive nodes whenever possible.
SNS
The sense (SNS) pin is connected to the output of the
device to provide feedback to the control circuitry. The
SNS connection should be placed close to the output
capacitor. Refer to the layout recommendations for more
details.
AGND
The 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.
PGND
The power ground pin is the ground path for the high
current in PWM mode. The current loop for the power
ground should be as small as possible and separate
from the analog ground (AGND) loop as applicable.
Refer to the layout recommendations for more details.
Micrel Inc.
September 2010
10
Power Good PG
The Power Good (PG) pin is an open drain output which
indicates logic high when the output voltage is typically
above 92% of its steady state voltage. When the output
voltage is below 86%, the PG pin indicates logic low. A
pull up resistor of more than 10kΩ should be connected
from PG to V
SS
The soft start (SS) pin is used to control the output
voltage ramp up time. The approximate equation for the
ramp time in milliseconds is:
where:
T is the time in milliseconds and C
start capacitance (in Farads).
For example, for a C
See the Typical Characteristics curve for a graphical
guide. The minimum recommended value for C
100pF.
FB
The feedback (FB) pin is provided for the adjustable
voltage option (no internal connection for fixed options).
This is the control input for programming the output
voltage. A resistor divider network is connected to this
pin from the output and is compared to the internal
0.62V reference within the regulation loop.
The output voltage can be programmed between 0.65V
and 3.6V using the following equation:
where:
R1 is the top resistor, R2 is the bottom resistor.
Example feedback resistor values:
V
1.2V
1.5V
1.8V
2.5V
3.3V
T(ms) = 270x10
V
OUT
OUT
OUT
=
.
V
REF
SS
×
⎛
⎜
⎝
= 470pF, T
3
1
x ln (10) x C
+
274k
316k
301k
324k
309k
R2
R1
R1
⎞
⎟
⎠
rise
SS
SS
is the external soft
~ 0.3ms or 300µs.
M9999-092910-A
71.5k
MIC33153
294k
221k
158k
107k
R2
SS
is