MIC5021 Micrel Semiconductor, MIC5021 Datasheet - Page 5

• Manufacturer Part Number: MIC5021
• Description: High-Speed High-Side MOSFET Driver
• Manufacturer: Micrel Semiconductor

Functional Description
Refer to the MIC5021 block diagram.
Input
A signal greater than 1.4V (nominal) applied to the MIC5021
INPUT
turning the MOSFET on.
An internal pull-down resistor insures that an open
remains low, keeping the external MOSFET turned off.
Gate Output
Rapid rise and fall times on the
because each input state change triggers a one-shot which
activates a high-value current sink (10I
draws a high current though a current mirror circuit causing
the output transistors to quickly charge or discharge the
external MOSFET’s gate.
A second current sink continuously draws the lower value of
current used to maintain the gate voltage for the selected
state.
An internal charge pump utilizes an external “boost” capacitor
connected between V
MOSFET. (Refer to typical application.) The boost capacitor
stores charge when the MOSFET is off. As the MOSFET
turns on, its source to ground voltage increases and is added
to the voltage across the capacitor, raising the V
voltage. The boost capacitor charge is directed through the
GATE
maximum above V
the gate voltage.
Applications Information
The MIC5021 MOSFET driver is intended for high-side
switching applications where overcurrent limiting and high
speed are required. The MIC5021 can control MOSFETs that
switch voltages up to 36V.
High-Side Switch Circuit Advantages
High-side switching allows more of the load related compo-
nents and wiring to remain near ground potential when
compared to low-side switching. This reduces the chances
of short-to-ground accidents or failures.
Speed Advantage
The MIC5021 is about two orders of magnitude faster than
the low cost MIC5014 making it suitable for high-frequency
high-efficiency circuit operation in PWM (pulse width modu-
lation) designs used for motor control, SMPS (switch mode
power supply) and heating element control.
Switched loads (on/off) benefit from the MIC5021’s fast
switching times by allowing use of MOSFETs with smaller
safe operating areas. (Larger MOSFETs are often required
when using slower drivers.)
October 1998
MIC5021
pin to quickly charge the MOSFET’s gate to 16V
causes gate enhancement on an external MOSFET
DD
. The internal charge pump maintains
BOOST
and the source of the external
GATE
2
) for a short time. This
output are possible
BOOST
INPUT
pin
5-173
An internal zener diode protects the external MOSFET by
limiting the gate to source voltage.
Sense Inputs
The MIC5021’s 50mV (nominal) trip voltage is created by
internal current sources that force approximately 5 A out of
SENSE
When
steals base current from an internal drive transistor shutting
off the external MOSFET.
Overcurrent Limiting
Current source I
external capacitor connected to C
a MOSFET Q1.
A fault condition (> 50mV from
the overcurrent comparator to enable current sink 2I
overcomes current source I
When C
off the gate output, and C
When the gate output turns the MOSFET off, the overcurrent
signal is removed from the sense inputs which deactivates
current sink 2I
connected to C
retry while the capacitor(s) recharge. Retry delay is in-
creased by connecting a capacitor to C
The retry cycle will continue until the fault is removed or the
input is changed to TTL low.
If C
fault condition.
Supply Voltage
The MIC5021’s supply input (V
supply voltage must be equal to or greater than the voltage
applied to the drain of the external N-channel MOSFET.
A 16V minimum supply is recommended to produce continu-
ous on-state, gate drive voltage for standard MOSFETs (10V
nominal gate enhancement).
When the driver is powered from a 12V to 16V supply, a logic-
level MOSFET is recommended (5V nominal gate enhance-
ment).
PWM operation may produce satisfactory gate enhancement
at lower supply voltages. This occurs when fast switching
repetition makes the boost capacitor a more significant
voltage supply than the internal charge pump.
T
is connected to ground, the circuit will not retry upon a
SENSE
+ and approximately 15 A (at trip) out of
INT
is discharged, the
1
– is 50mV or more below
. This allows C
T
1
to recharge. A Schmitt trigger delays the
charges C
INT
1
INT
to discharge C
and C
INPUT
INT
SENSE
DD
upon power up. An optional
T
and the optional capacitor
is kept discharged through
T
) is rated up to 36V. The
are ready to be charged.
is disabled, which turns
+ to
T
SENSE
(optional).
INT
SENSE
in a short time.
+,
–) causes
SENSE
SENSE
1
Micrel
which
–.
–
5