MIC38C42A Datasheet, PDF (8/9 Pages) Micrel Semiconductor – BiCMOS Current-Mode PWM Controllers

MIC38C42A/43A/44A/45A
Magnetic components are carefully chosen for minimal loss
at 500kHz. CT1 and T1 are wound on Magnetics, Inc. P-type
material toroids. L1 is wound on a Siemens N49 EFD core.
Micrel, Inc.
Test
Conditions
Line Regulation V_IN = 26V to 80V, I_O = 2A
Load Regulation V_IN = 48V, I_O = 0.2A to 2A
Efficiency
V_IN = 48V, I_O = 2A
Output Ripple V_IN = 48V, I_O = 2A (20MHz BW)
Results
0.5%
0.6%
90%
100mV
Symbol
Custom Coil¹
ETS²
CT1
4923
ETS 92420
T1
4924
ETS 92419
L1
4925
ETS 92421
1. Custom Coils, Alcester, SD tel: [phone]
2. Energy Transformation Systems, Inc. tel: [phone].
Synchronous Buck Converter
Refer to figure 2. This MIC38C43 synchronous buck con-
verter uses an MIC5022 half-bridge driver to alternately drive
the PWM switch MOSFET (driven by GATEH, or high-side
output) and a MOSFET which functions as a synchronous
rectifier (driven by the GATEL, or low-side output).
The low-side MOSFET turns on when the high-side MOSFET
is off, allowing current to return from ground. Current flows
through the low-side MOSFET in the source to drain direc-
tion.
+12V
The on-state voltage drop of the low-side MOSFET is lower
than the forward voltage drop of an equivalent Schottky
rectifier. This lower voltage drop results in higher efficiency.
A sense resistor (5mΩ) is connected to the driver’s high-side
current sense inputs to provide overcurrent protection. Refer
to the MIC5020, MIC5021, and MIC5022 data sheets for
more information.
10k
0.15µF
0.1µF
NC
6.8k
300k ^{4.7nF MIC38C43A}
NC
COMP VREF
4.3k
47k
FB
VDD
470µF
25V
NC
ISNS VOUT
0.1µF*
2200
RT/CT GND
MKS2
pF 3.3k 10k
*Locate near the MIC38C43 supply pins.
MIC5022
VDD GATEH
FLT
VB
EN GATEL
IN
SH+
CT
SH–
SL+
GND
SL–
0.1µF
SMP60N06-14
5mΩ
35µH
V_OUT
5V, 8A
1000µF
Low ESR
Figure 2. 100kHz, Synchronous Buck Converter
M9999-042205
8
April 2005