MIC2505/2506
Micrel
Duplicate IN and OUT leads are not internally connected.
Connect both IN pins to the supply. Connect both OUT leads
to the load.
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.
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).
Overcurrent Limit
The overcurrent limit is preset internally. The preset level
prevents damage to the output MOSFET but allows a mini-
mum 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.
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).
Fault Flag
FLG is an N-channel, open-drain MOSFET output. The fault-
flag is active (low) for one or more of the following conditions:
open load (except MIC2505-1 and -2 versions), undervolt-
age, current limit, or thermal shutdown. The flag output
MOSFET is capable of sinking a 10mA load to typically
100mV above ground.
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
turnoff when enabled.
Control Input
CTL (control input) activates the oscillator, thermal shut-
down, UVLO, 1.2V reference, and gate control circuits. If
there are no fault conditions, the output MOSFET turns on
when enabled.
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.
Oscillator/Charge Pump
The oscillator produces an 80kHz square wave output which
drives the charge pump. The oscillator is enabled when CTL
is active.
The charge pump is a voltage quintupler (5×). The charge
pump capacitors are self contained.
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
UVLO (undervoltage lockout).
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 “MIC2505 Turn-On
Delay” graph.) Since 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.
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 conven-
tional 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.)
MIC2505 Series Only
MIC2505/2506
8
April 1998
MICREL [ MICREL SEMICONDUCTOR ]
