MIC23250-G4YMT EV Micrel, MIC23250-G4YMT EV Datasheet - Page 3

• Manufacturer Part Number: MIC23250-G4YMT EV
• Description: Power Management IC Development Tools High Efficiency Dual 400mA Synchronous Buck Switcher - Evaluation Board
• Manufacturer: Micrel
• Type: DC/DC Converters, Regulators & Controllersr

Specifications of MIC23250-G4YMT EV

• Product: Evaluation Boards
• Tool Is For Evaluation Of: MIC23250
• Input Voltage: 2.7 V to 5.5 V
• Output Voltage: 1.2 V, 1.8 V
• Description/function: Evaluation Board
• Maximum Operating Temperature: + 125 C
• Minimum Operating Temperature: - 40 C
• Output Current: 100 mA
• For Use With: MIC23250

HyperLight Load Mode™
MIC23250 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
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 MIC23250 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
MIC23250 during light load currents by only switching
when it is needed. As the load current increases, the
MIC23250 goes into continuous conduction mode (CCM)
and switches at a frequency centered at 4MHz. The
equation to calculate the load when the MIC23250 goes
into continuous conduction mode may be approximated
by the following formula:
Micrel, Inc.
July 2009
I
LOAD
=
⎛
⎜ ⎜
⎝
V
IN
−
2
V
L
OUT
×
f
×
D
⎞
⎟ ⎟
⎠
3
As shown in the previous equation, the load at which
MIC23250 transitions from HyperLight Load™ mode to
PWM mode is a function of the input voltage (V
voltage (V
frequency (f). This is illustrated in the graph below. Since
the inductance range of MIC23250 is from 0.47µH to
4.7µH, the device may then be tailored to enter
HyperLight Load™ mode or PWM mode at a specific
load current by selecting the appropriate inductance. For
example in the graph below, when the inductance is
4.7µH the MIC23250 will transition into PWM mode at a
load of approximately 4mA. Under the same condition,
when the inductance is 1µH, the MIC23250 will transition
into PWM mode at approximately 70mA.
OUT
), duty cycle (D), inductance (L) and
4MHz
0.01
0.1
10
1
1
L = 4.7µH
Switching Frequency
vs. Output Current
OUTPUT CURRENT (mA)
10
MIC23250 Evaluation Board
L = 2.2µH
V
V
C
L = 1µH
IN
OUT
100
OUT
= 3.6V
= 1.8V
= 4.7µF
M9999-070909-C
1000
IN
), output