MIC23150-SYMT TR Micrel Inc, MIC23150-SYMT TR Datasheet - Page 12

• Manufacturer Part Number: MIC23150-SYMT TR
• Description: 2.0A 4MHz HyperLight LoadT Buck Regulator
• Manufacturer: Micrel Inc
• Series: HyperLight Load™r
• Type: Step-Down (Buck)r

Specifications of MIC23150-SYMT TR

• Internal Switch(s): Yes
• Synchronous Rectifier: Yes
• Number Of Outputs: 1
• Voltage - Output: 3.3V
• Current - Output: 2A
• Frequency - Switching: 4MHz
• Voltage - Input: 2.7 ~ 5.5 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 8-MLF®, QFN
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Power - Output: -
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: 576-3314-2

The figure above shows an efficiency curve. From no
load to 100mA, efficiency losses are dominated by
quiescent current losses, gate drive and transition
losses. By using the HyperLight Load™ mode, the
MIC23150 is able to maintain high efficiency at low
output currents.
Over 100mA, efficiency loss is dominated by MOSFET
R
will increase the Gate-to-Source threshold on the
internal MOSFETs, thereby reducing the internal R
This improves efficiency by reducing DC losses in the
device. All but the inductor losses are inherent to the
device. In which case, inductor selection becomes
increasingly critical in efficiency calculations. As the
inductors are reduced in size, the DC resistance (DCR)
can become quite significant. The DCR losses can be
calculated as follows:
From that, the loss in efficiency due to inductor
resistance can be calculated as follows:
Efficiency loss due to DCR is minimal at light loads and
gains significance as the load is increased. Inductor
selection becomes a trade-off between efficiency and
size in this case.
HyperLight Load™ Mode
MIC23150 uses a minimum on and off time proprietary
control loop (patented by Micrel). When the output
voltage falls below the regulation threshold, the error
comparator begins a switching cycle that turns the
PMOS on and keeps it on for the duration of the
minimum-on-time. This increases the output voltage. If
the output voltage is over the regulation threshold, then
Micrel Inc.
October 2009
DSON
Efficiency
and inductor losses. Higher input supply voltages
P
DCR
Figure 2. Efficiency Under Load
= I
Loss
100
OUT
90
80
70
60
50
40
0.1
V
2
=
IN
x DCR
= 2.7V
OUTPUT CURRENT (mA)
⎡
⎢
⎢
⎣
1
1
V
IN
−
V
= 4.2V
⎛
⎜
⎜
⎝
Efficiency
V
OUT
V
V
IN
10
IN
OUT
= 5.0V
= 3.0V
L = 1.0µH
C
= 1.8V
V
OUT
100 1000 10000
OUT
×
= 4.7µF
I
V
OUT
V
IN
IN
×
= 5.5V
= 3.6V
I
OUT
+
P
DCR
⎞
⎟
⎟
⎠
⎤
⎥
⎥
⎦
×
100
DSON
.
12
the error comparator turns the PMOS off for a minimum-
off-time until the output drops below the threshold. The
NMOS acts as an ideal rectifier that conducts when the
PMOS is off. Using a NMOS switch instead of a diode
allows for lower voltage drop across the switching device
when it is on. The asynchronous switching combination
between the PMOS and the NMOS allows the control
loop to work in discontinuous mode for light load
operations. In discontinuous mode, the MIC23150 works
in pulse frequency modulation (PFM) to regulate the
output. As the output current increases, the off-time
decreases, thus provides more energy to the output.
This switching scheme improves the efficiency of
MIC23150 during light load currents by only switching
when it is needed. As the load current increases, the
MIC23150 goes into continuous conduction mode (CCM)
and switches at a frequency centered at 4MHz. The
equation to calculate the load when the MIC23150 goes
into continuous conduction mode may be approximated
by the following formula:
As shown in the previous equation, the load at which
MIC23150 transitions from HyperLight Load™ mode to
PWM mode is a function of the input voltage (V
voltage (V
frequency (f). As shown in Figure 3, as the Output
Current
increases until the MIC23150 goes from HyperLight
Load
The MIC23150 will switch at a relatively constant
frequency around 4MHz once the output current is over
120mA.
TM
Figure 3. SW Frequency vs. Output Current
mode to PWM mode at approximately 120mA.
I
LOAD
increases,
OUT
), duty cycle (D), inductance (L) and
0.001
>
0.01
0.1
⎛
⎜ ⎜
⎝
10
1
(
1
V
V
IN
IN
OUTPUT CURRENT (mA)
= 3.0V
−
vs Output Current
2
the
10
V
SW Frequency
L
OUT
×
f
switching
V
100
)
IN
×
L = 4.7µH
V
C
V
= 4.2V
D
OUT
IN
OUT
⎞
⎟ ⎟
⎠
= 3.6V
1000
= 1.8V
= 4.7µF
10000
M9999-102309-B
frequency
MIC23150
IN
), output
also