MIC2505 Datasheet, PDF (12/24 Pages) Micrel Semiconductor – Single 2A / Dual 1A / High-Side Switches

MIC2505/6
5.0 FUNCTIONAL DESCRIPTION
The MIC2505-series and MIC2506 are high-side
N-Channel switches. The MIC2505, MIC2505-1, and
MIC2506 have active-high enable inputs. The
MIC2505-2 has an active-low input. Fault conditions
inhibit output transistor turn-on or turn-off when
enabled.
5.1 Control Input
CTL (control input) activates the oscillator, thermal
shutdown, UVLO, 1.2V reference, and gate control
circuits. If there are no fault conditions, the output
MOSFET turns on when enabled.
5.2 Reference
A 1.2V bandgap reference supplies a regulated voltage
to the thermal shutdown and undervoltage lockout
circuits. The reference is only active when CTL is
enabled.
5.3 Oscillator/Charge Pump
The oscillator produces an 80 kHz square wave output
that drives the charge pump. The oscillator is enabled
when CTL is active.
The charge pump is a voltage quintupler (5x). The
charge pump capacitors are self contained.
5.4 Gate Control
The gate control circuit charges the output MOSFET
gate from the charge pump output or discharges the
MOSFET gate to ground as determined by CTL,
thermal shutdown, or undervoltage lockout (UVLO).
An optional, external capacitor may be connected to
the MIC2505 GATE to lengthen the rise time. This
slows the turn on of the MOSFET output switch. (See
Figure 2-13) Because this pin connects directly to the
MOSFET gate, use ESD precautions when contacting
components connected to this pin. Leakage resistance
may increase turn on times.
5.5 Input and Output
IN (input) is the supply connection to the logic circuitry
and the drain of the output MOSFET. OUT (output) is
the source of the output MOSFET. In a typical circuit,
current flows through the switch from IN to OUT toward
the load.
The output MOSFET and driver circuitry are also
designed to allow the MOSFET source to be externally
forced to a higher voltage than the drain (V_OUT > V_IN)
when the output switch is off and V_IN > UVLO minimum.
In this situation, the MIC2505/6 avoids undesirable
drain to body diode reverse current flow by grounding
the body when the switch is off. The conventional
method for optimum turn-on threshold has the source
connected to the body. This would allow a large current
to flow when V_SOURCE > V_DRAIN + 0.6V.
5.5.1 MIC2505 SERIES ONLY
Duplicate IN and OUT leads are not internally
connected. Connect both IN pins to the supply.
Connect both OUT leads to the load.
5.6 Thermal Shutdown
Thermal shutdown shuts off the output MOSFET and
signals the fault flag if the die temperature exceeds
135°C. 10°C of hysteresis prevents the switch from
turning on until the die temperature drops to 125°C.
Overtemperature detection functions only when the
control input is enabled (output MOSFET is on). Both
MIC2506 outputs are shut off during overtemperature,
and both flags will go low.
5.7 Undervoltage Lockout
UVLO (undervoltage lockout) prevents the output
MOSFET from turning on until V_IN (input voltage)
exceeds 2.5V typical. After the switch turns on, if V_IN
drops below 2.3V typical, UVLO shuts off the output
MOSFET and turns the fault flag on (active-low) until
V_IN drops below 1.5V.
Undervoltage detection functions only when the control
input is enabled (output MOSFET is on).
5.8 Overcurrent Limit
The overcurrent limit is preset internally. The preset
level prevents damage to the output MOSFET, but
allows a minimum current of 2A through the output
MOSFET of the MIC2505-series and 1A for each
output MOSFET of the MIC2506. Output current is
monitored by sensing the voltage drop across the
output MOSFET drain metal resistance.
Overcurrent detection functions only when the control
input is enabled (output MOSFET is on) and V_IN is
above the UVLO threshold.
5.9 Open-Load Detection
Open-load detection is available only on the MIC2505
and MIC2506. The open-load detection feature is not
included in the MIC2505-1 or -2 versions.
Open-load detection indicates the absence of an output
load by activating the fault flag. Open-load detection is
optional and is enabled by connecting a high-value
pull-up resistor between IN and OUT. If there is no load,
the circuit detects a high OUT (output) voltage (typically
≥1V) and signals the fault flag. Under normal
conditions, the low resistance of a typical load pulls
OUT low. Open-load detection functions only when the
control input is low (output MOSFET is off).
DS20005579A-page 12
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