MIC2182 Micrel Semiconductor, MIC2182 Datasheet - Page 12

• Manufacturer Part Number: MIC2182
• Description: High-Efficiency Synchronous Buck Controller Final Information
• Manufacturer: Micrel Semiconductor

MIC2182
A hysteretic comparator is used in place of the PWM error
amplifier and a current-limit comparator senses the inductor
current. A one-shot starts the switching cycle by momentarily
turning on the low side MOSFET to insure the high side drive
boost capacitor, Cbst, is fully charged. The high side MOS-
FET is turned on and current ramps up in the inductor, L1.
The high side drive is turned off when either the peak voltage
on the input of the current-sense comparator exceeds the
threshold, typically 35mV, or the output voltage rises above
the hysteretic threshold of the output voltage comparator.
Once the high side MOSFET is turned off, the load current
discharges the output capacitor, causing V
cycle repeats when V
1%.
The maximum peak inductor current depends on the skip-
mode current-limit threshold and the value of the current-
sense resistor, R
MIC2182
I
inductor(peak)
CS
.
R
35mV
OUT
sense
falls below the lower threshold, –
V
one-shot
Reset
Pulse
V
V
V
V
V
V
V
I
HSD
HSD
OUT
OUT
LSD
LSD
SW
I
SW
I
L1
L1
V
V
IN
I
NOMINAL
LIM(skip)
+ V
I
LOAD
V
V
V
V
V
V
OUT
+1%
V
V
–1%
0A
0V
0V
0V
0V
0A
0V
0V
0A
0V
DD
DD
0V
DD
DD
DD
0V
DD
IN
IN
OUT
Figure 5a. PWM-Mode Timing
Figure 5b. Skip-Mode Timing
to fall. The
12
Figure 6 shows the improvement in efficiency that skip mode
makes when at lower output currents.
100
80
60
40
20
0.01
Figure 6. Efficiency
0
Skip
OUTPUT CURRENT (A)
0.1
1
10
PWM
100
June 2000
Micrel