MIC2111B Datasheet, PDF (15/35 Pages) Micrel Semiconductor – High-Performance, Multi-Mode, Step-Down Controller

Micrel, Inc.
Table 1. PWM Truth Table
LS
HS
High-Side
FET
0
0
OFF
0
1
ON
X Tri-State
OFF
1
0
OFF
1
1
ON
Low-Side
FET
ON to OFF
OFF
OFF
ON
OFF
Switch
Node
Diode
Emulation
High
Tri-State
(Pre-Bias/
Fault
Shutdown)
Low
High
The MIC2111B will output a PWM signal on the HS pin
with levels of 0 (turn on the low-side driver) and 1 (turn on
the high-side driver). HS will be turned high-impedance
(tri-state) when a fault condition exists which should be
interpreted by the power stage to turn-off both the high-
side driver and low-side driver. MIC2111B supports 3.3V
logic-compatible PWM thresholds on HS. These levels
can found in the “Oscillator and PWM” section within the
Electrical Characteristics.
Programmable Current-Limit and Hiccup Mode
MIC2111B has a dedicated current-sense amplifier and
can support high load currents up to 40A in single-phase
configuration. The MIC2111B also features differential
current sense input pins (ISEN+ and ISEN−).
With the MIC2111B, it is possible to sense current across
inductor DCRs for low-cost applications. As the DCR of
the inductor will be less than 1mΩ for a high-current
application, the MIC2111B features a current-sense
amplifier with a gain of 30V/V. This amplified signal is
used for control and cycle-by-cycle current limit. These
high-current applications need thermal compensation
from the current-sense signal because of DCR variation
with temperature. External thermal compensation could
be provided using a NTC resistor in series with the RC
across the inductor. See Application Information for more
details about thermal compensation and filter
calculations.
MIC2111B
Current limit can be programmed through an external
resistor connected at the LS pin. The MIC2111B provides
two selectable current-limit thresholds. During start-up, a
current source of 8µA is injected into the external resistor
connected between the LS pin and GND. The voltage
developed across the resistor is measured as part of the
power-up sequence and the current threshold determined
as illustrated in Table 2.
Once the voltage has been measured, the current source
is turned off. If LS is connected to the MODE pin of
DrMOS, current-limit setting resistance must be adjusted
for the input resistance of the MODE pin.
Many high-current applications require hiccup mode
protection for current limit because they can see peak
load currents for a very short duration. The MIC2111B
uses a proprietary hiccup current-limit algorithm to avoid
inductor saturation. An internal counter increments by
two in each cycle over current is detected, and
decrements by one each cycle when the current is not
over the limit. When the counter reaches 16, the part will
shut down and wait for 8ms before restarting again
(Figure 2 and Figure 3).
E24 Range Resistance
88kΩ
63kΩ
MIC2111B Current-Limit
Threshold
23.3mV
18.3mV
October 13, 2015
15
Revision 2.1