Electronic Components Datasheet Search
  English  ▼

Delete All
ON OFF
ALLDATASHEET.COM

X  

Preview PDF HTML

MIC24420 Datasheet(PDF) 19 Page - Micrel Semiconductor

Part No. MIC24420
Description  2.5A Dual Output PWM Synchronous Buck Regulator IC
Download  34 Pages
Scroll/Zoom Zoom In 100% Zoom Out
Maker  MICREL [Micrel Semiconductor]
Homepage  http://www.micrel.com
Logo 

MIC24420 Datasheet(HTML) 19 Page - Micrel Semiconductor

Zoom Inzoom in Zoom Outzoom out
 19 / 34 page
background image
Micrel, Inc.
MIC24420/MIC24421
damped switch node waveform.
Figure 11. Snubber Circuit
The snubber capacitor, CS, is charged and discharged
each switching cycle. The energy stored in CS is
dissipated by the snubber resistor, RS, two times per
switching period. This power is calculated in the
equation below.
June 2012
19
M9999-062012-C
2
IN
S
S
snubber
V
C
f
P
=
S
G
DD
f
Q
I
=
Where:
fS is the switching frequency for each phase
VIN is the DC input voltage
Low-side MOSFET Selection
An external N-channel logic level power MOSFET must
be used for the low-side switch. The MOSFET gate to
source drive voltage of the MIC24420/MIC24421 is
regulated by an internal 5V regulator. Logic level
MOSFETs, whose operation is specified at VGS = 4.5V
must be used. Use of MOSFETs with a lower specified
VGS (such as 3.3V or 2.5V) are not recommended since
the low threshold can cause them to turn on when the
high-side FET is turning on. When operating the
regulator below a 6V input, connect VDD to VIN to prevent
the VDD regulator from dropping out.
Total gate charge is the charge required to turn the
MOSFET on and off under specified operating conditions
(VDS and VGS). The gate charge is supplied by the
regulator’s gate drive circuit. Gate charge is a source of
power dissipation in the regulator due to the high
switching frequencies. At low output load this power
dissipation is noticeable as a reduction in efficiency. The
average current required to drive the MOSFETs is:
Where:
QG is the gate charge for both of the external MOSFETs.
This
information
should
be
obtained
from
the
manufacturer’s data sheet.
Since current from the gate drive is supplied by the input
voltage, power dissipated in the MIC24420/MIC24421
due to gate drive is:
IN
S
G
GATE_DRIVE
V
f
Q
P
=
Parameters that are important to MOSFET selection are:
Voltage rating
On resistance
Total gate charge
The MOSFET is subjected to a VDS equal to the input
voltage. A safety factor of 20% should be added to the
VDS(max) of the MOSFET to account for voltage spikes
due to circuit parasitics. Generally, 30V MOSFETs are
recommended for all applications since lower VDS rated
MOSFETs tend to have a VGS rating that is lower than
the recommended 4.5V.
RMS Current and MOSFET Power Dissipation
Calculation
Switching loss in the low-side MOSFET can be
neglected since it is turned on and off at a VDS of 0V.
The power dissipated in the MOSFET is mostly
conduction loss during the on-time (PCONDUCTION).
DS(ON)
2
SW_RMS
CONDUCTION
R
I
P
=
Where:
RDS(ON) is the on resistance of the MOSFET switch.
The RMS value of the MOSFET current is:
)
12
I
(I
D)
(1
I
2
PP
2
OUT_MAX
SW_RMS
+
=
Where:
D is the duty-cycle of the converter
IPP is the inductor ripple current
IN
OUT
V
η
V
D
=
Where:
η is the efficiency of the converter.
External Schottky Diode
A freewheeling diode in parallel with the low-side
MOSFET is needed to maintain continuous inductor
current flow while both MOSFETs are turned off (dead-
time). Dead-time is necessary to prevent current from
flowing unimpeded through both MOSFETs. An external
Schottky diode is used to bypass the low-side
MOSFET’s parasitic body diode. An external diode


Html Pages

1  2  3  4  5  6  7  8  9  10  11  12  13  14  15  16  17  18  19  20  21  22  23  24  25  26  27  28  29  30  31  32  33  34 


Datasheet Download




Link URL




Privacy Policy
ALLDATASHEET.COM
Does ALLDATASHEET help your business so far?  [ DONATE ]  

About Alldatasheet   |   Advertisement   |   Datasheet Upload   |   Contact us   |   Privacy Policy   |   Alldatasheet API   |   Link Exchange   |   Manufacturer List
All Rights Reserved© Alldatasheet.com


Mirror Sites
English : Alldatasheet.com  |   English : Alldatasheet.net  |   Chinese : Alldatasheetcn.com  |   German : Alldatasheetde.com  |   Japanese : Alldatasheet.jp
Russian : Alldatasheetru.com  |   Korean : Alldatasheet.co.kr  |   Spanish : Alldatasheet.es  |   French : Alldatasheet.fr  |   Italian : Alldatasheetit.com
Portuguese : Alldatasheetpt.com  |   Polish : Alldatasheet.pl  |   Vietnamese : Alldatasheet.vn