MIC5020 Micrel, Inc.

MIC5020
Current-Sensing Low-Side MOSFET Driver

General Description Features

The MIC5020 low-side MOSFET driver is designed to operate • 11V to 50V operation
at frequencies greater than 100kHz (5kHz PWM for 2% to • 175ns rise/fall time driving 2000pF
100% duty cycle) and is an ideal choice for high-speed ap- • TTL compatible input with internal pull-down resistor
plications such as motor control, SMPS (switch mode power • Overcurrent limit
supplies), and applications using IGBTs. The MIC5020 can • Fault output indication
also operate as a circuit breaker with or without automatic • Gate to source protection
retry. The MIC5020’s maximum supply voltage lends itself • Compatible with current sensing MOSFETs
to control applications using up to 50V. The MIC5020 can
control MOSFETs that switch voltages greater than 50V.
Applications
• Lamp control
A rising or falling edge on the input results in a current source
• Heater control
or sink pulse on the gate output. This output current pulse
• Motor control
can turn on or off a 2000pF MOSFET in approximately 175ns.
• Solenoid switching
The MIC5020 then supplies a limited current (< 2mA), if
• Switch-mode power supplies
necessary, to maintain the output state.
• Circuit breaker
An overcurrent comparator with a trip voltage of 50mV makes
the MIC5020 ideal for use with a current sensing MOSFET.
An external low value resistor may be used instead of a
sensing MOSFET for more precise overcurrent control. An
optional external capacitor connected to the CT pin may be
Ordering Information
used to control the current shutdown duty cycle from 20%
to < 1%. A duty cycle from 20% to about 75% is possible Part Number Temperature
with an optional pull-up resistor from CT to VDD. An open Standard Pb-Free Range Package
collector output provides a fault indication when the sense MIC5020BM MIC5020YM –40ºC to +85ºC 8-pin SOIC
inputs are tripped.
The MIC5020 is available in 8-pin SOIC package.
Other members of the MIC502x series include the MIC5021
high-side driver and the MIC5022 half-bridge driver with a
cross-conduction interlock.

Typical Application
V+

+11V to +50V MIC5020

10µF 1 8 N-Channel
V DD Gate Power MOSFET
2 7
150kHz max. Input Sense-
3 6
Fault Sense+ R S E N S E = 50mV
4 5 I TR IP
optional* CT Gnd
R SENSE

* increases time before retry

Low-Side Driver with Overcurrent Trip and Retry

Micrel, Inc. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel + 1 (408) 944-0800 • fax + 1 (408) 474-1000 • http://www.micrel.com

July 2005 1 MIC5020

MIC5020 Micrel, Inc.

Pin Configuration

1 V DD Gate 8

2 Input Sense- 7

3 Fault Sense+ 6

4 CT Gnd 5

SOIC Package
(M)
Block Diagram
6V Internal Regulator

I1
Fault
CT
CINT Normal
2I1 Fault

Q1

Sense+ VDD
Sense-
50mV ON

OFF
6V
↑ ONE-
Input 10I2 I2 Gate
↓ SHOT

Transistor Count: 82

Pin Description
Pin Number Pin Name Pin Function
1 VDD Supply: +11V to +50V. Decouple with ≥ 10µF capacitor.
2 Input TTL Compatible Input: Logic high turns the external MOSFET on. An internal
pull-down returns an open pin to logic low.

3 Fault Overcurrent Fault Indicator: When the sense voltage exceeds threshold,
open collector output is open circuit for 5µs (tG(ON)), then pulled low for
tG(OFF). tG(OFF) is adjustable from CT.
4 CT Retry Timing Capacitor: Controls the off time (tG(OFF)) of the overcurrent
retry cycle. (Duty cycle adjustment.)
• Open = 20% duty cycle.
• Capacitor to Ground = approx. 20% to <1% duty cycle.
• Pull-Up resistor = approx. 20% to approx. 75% duty cycle.
• Ground = maintained shutdown upon overcurrent condition.
5 Gnd Circuit Ground
6 Sense + Current Sense Comparator (+) Input: Connect to high side of sense resistor
or current sensing MOSFET sense lead. A built-in offset in conjunction with
RSENSE sets the load overcurrent trip point.
7 Sense – Current Sense Comparator (–) Input: Connect to the low side of the sense
resistor (usually power ground).
8 Gate Gate Drive: Drives the gate of an external power MOSFET. Also limits VGS
to 15V max. to prevent Gate to Source damage. Will sink and source
current.

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MIC5020 Micrel, Inc.

Absolute Maximum Ratings Operating Ratings

Supply Voltage (VDD)................................................... +55V Supply Voltage (VDD)......................................+11V to +50V
Input Voltage .................................................–0.5V to +15V Temperature Range
Sense Differential Voltage .......................................... ±6.5V SOIC ....................................................... –40°C to +85°C
Sense + or Sense – to Gnd ...........................–0.5V to +50V
Fault Voltage ............................................................... +50V
Current into Fault ........................................................ 50mA
Timer Voltage (CT) ...................................................... +5.5V

Electrical Characteristics
TA = 25°C, Gnd = 0V, VDD = 12V, Sense +,– = 0V, Fault = Open, CT = Open, Gate CL = 1500pF unless otherwise specificed
Symbol Parameter Condition Min Typ Max Units
D.C. Supply Current VDD = 12V, Input = 0V 0.8 2 mA
VDD = 50V, Input = 0V 2 10 mA
VDD = 12V, Input = 5V 0.8 2 mA
VDD = 50V, Input = 5V 4 25 mA
Input Threshold 0.8 1.4 2.0 V
Input Hysteresis 0.1 V
Input Pull-Down Current Input = 5V 10 20 40 µA
Fault Output Fault Current = 1.6mA 0.15 0.4 V
Saturation Voltage Note 1
Fault Output Leakage Fault = 50V –1 0.01 +1 µA
Current Limit Threshold Note 2 30 50 70 mV
Gate On Voltage VDD = 12V 10 11 V
VDD = 50V 14 15 18 V
tG(ON) Gate On Time, Fixed Sense Differential > 70mV 2 5 10 µs
tG(OFF) Gate Off Time, Adjustable Sense Differential > 70mV, CT = 0pF 10 20 50 µs
tDLH Gate Turn-On Delay Note 3 400 800 ns
tR Gate Rise Time Note 4 700 1500 ns
tDLH Gate Turn-Off Delay Note 5 900 1500 ns
tF Gate Fall Time Note 6 500 1500 ns
fmax Maximum Operating Frequency Note 7 100 150 kHz
Note 1 Voltage remains low for time affected by CT.
Note 2 When using sense MOSFETs, it is recommended that RSENSE < 50Ω. Higher values may affect the sense MOSFET’s current transfer ratio.
Note 3 Input switched from 0.8V (TTL low) to 2.0V (TTL high), time for Gate transition from 0V to 2V.
Note 4 Input switched from 0.8V (TTL low) to 2.0V (TTL high), time for Gate transition from 2V to 10V.
Note 5 Input switched from 2.0V (TTL high) to 0.8V (TTL low), time for Gate transition from 11V (Gate ON voltage) to 10V.
Note 6 Input switched from 2.0V (TTL high) to 0.8V (TTL low), time for Gate transition from 10V from 2V.
Note 7 Frequency where gate on voltage reduces to 10V with 50% input duty cycle.

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MIC5020 Micrel, Inc.

Typical Characteristics

Supply Current vs. Turn-On Time vs. Turn-Off Time vs.

Supply Voltage Supply Voltage Supply Voltage
3.5 900 1200
VIN = 5V VG AT E = 4V
3.0 CL = 1500pF 1100
800
VIN = 0 to 5V Sq. Wave
2.5
ISUPPLY (mA)

1000 VG AT E = 4V

tOFF (ns)
700

tON (nS)
2.0 CL = 1500pF
900 VIN = 0 to 5V
600
1.5 Sq. Wave
VIN = 0V 800
1.0 500
INCLUDES PROPAGATION DALAY
INCLUDES PROPAGATION DELAY
700
0.5 400 5 10 15 20 25 30
5 10 15 20 25 30 35 40 45 50 5 10 15 20 25 30 35 40 45 50 VSUPPLY (V)
VSUPPLY (V) VSUPPLY (V)

Input Current vs. Turn-On Time vs. Overcurrent Shutdown

Input Voltage Gate Capacitance Retry Duty Cycle
100 1200 25.0
VSUPPLY = 12V VG AT E = 4V tON = 5µs

Shutdown Duty Cycle (%)

80 1000 20.0 VSUPPLY = 12V

60 800 15.0
tON (ns)
IIN (µA)

40 600 10.0

20 400 5.0
INCLUDES PROPAGATION DELAY

0 200 0.0
0 5 10 15 20 25 1x102 1x103 1x104 1x105 0.1 1 10 100 1000 10000
VIN (V) CGATE (pF) CT (pF)

Sense Threshold vs.

Temperature
80
TTL (H)
70
Input 0V
15V (max.)
VOLTAGE (mV)

60 Gate
0V
50 Sense +,– 50mV
Differential 0V
40
Off

30 Fault On

20 Timing Diagram 1. Normal Operation

-60 -30 0 30 60 90 120 150
TEMPERATURE (°C)

5µs 20µs
5µs
TTL (H)
Input TTL (H)
0V Input 0V
15V (max.)
Gate Gate
15V (max.)
0V
0V
Sense +,– 50mV Sense +,– 50mV
Differential 0V Differential 0V
Off Off
Fault On Fault On

Timing Diagram 2. Fault Condition, CT = Open Timing Diagram 3. Fault Condition, CT = Grounded

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MIC5020 Micrel, Inc.

Functional Description
Refer to the MIC5020 block diagram. MOSFET Q1.
Input A fault condition (> 50mV from SENSE + to SENSE –) causes
A signal greater than 1.4V (nominal) applied to the MIC5020 the overcurrent comparator to enable current sink 2I1 which
INPUT causes gate enhancement on an external MOSFET overcomes current source I1 to discharge CINT in a short time.
turning the external MOSFET on. When CINT is discharged, the INPUT is disabled, which turns
An internal pull-down resistor insures that an open INPUT off the GATE output; the FAULT output is enabled; and CINT
remains low, keeping the external MOSFET turned off. and CT are ready to be charged.
Gate Output When the GATE output turns the MOSFET off, the overcurrent
signal is removed from the sense inputs which deactivates
Rapid rise and fall times on the GATE output are possible current sink 2I1. This allows CINT and the optional capacitor
because each input state change triggers a one-shot which connected to CT to recharge. A Schmitt trigger delays the
activates a high-value current sink (10I2) for a short time. retry while the capacitor(s) recharge. Retry delay is increased
This draws a high current through a current mirror circuit by connecting a capacitor to CT (optional).
causing the output transistors to quickly charge or discharge
the external MOSFET’s gate. The retry cycle will continue until the the fault is removed or
the input is changed to TTL low.
A second current sink continuously draws the lower value
of current used to maintain the gate voltage for the selected If CT is connected to ground, the circuit will not retry upon a
state. fault condition.
An internal 15V Zener diode protects the external MOSFET Fault Output
by limiting the gate output voltage when VDD is connected The FAULT output is an open collector transistor. FAULT is
to higher voltages. active at approximately the same time the output is disabled
Overcurrent Limiting by a fault condition (5µs after an overcurrent condition is
sensed). The FAULT output is open circuit (off) during each
Current source I1 charges CINT upon power up. An optional successive retry (5µs).
external capacitor connected to CT is discharged through

Applications Information
The MIC5020 MOSFET driver is intended for low-side switch- and SENSE – comparator inputs.
ing applications where higher supply voltage, overcurrent The adjustable retry feature can be used to handle loads
sensing, and moderate speed are required. with high initial currents, such as lamps, motors, or heating
Supply Voltage elements and can be adjusted from the CT connection.
A feature of the MIC5020 is that its supply voltage rating of CT to ground causes maintained gate drive shutdown follow-
up to 50V is higher than many other low-side drivers. ing overcurrent detection.
The minimum supply voltage required to fully enhance an CT open, or through a capacitor to ground, causes automatic
N-channel MOSFET is 11V. retry . The default duty cycle (CT open) is approximately
A lower supply voltage may be used with logic level MOS- 20%. Refer to the electrical characteristics when selecting
FETs. Approximately 6V is needed to provide 5V of gate a capacitor for a reduced duty cycle.
enhancement. CT through a pull-up resistor to VDD increases the duty cycle.
Low-Side Switch Circuit Advantages Increasing the duty cycle increases the power dissipation in
A moderate-speed low-side driver is generally much faster the load and MOSFET. Circuits may become unstable at a
than a comparable high-side driver. The MIC5020 can pro- duty cycles of about 75% or higher, depending on the condi-
vide the gate drive switching times and low propagation delay tions. Caution: The MIC5020 may be damaged if the voltage
times that are necessary for high-frequency high-efficiency on CT exceeds the absolute maximum rating.
circuit operation in PWM (pulse width modulation) designs An overcurrent condition is externally signaled by an open
used for motor control, SMPS (switch mode power supply) collector (FAULT) output.
and heating element control. Switched loads (on/off) can The MIC5020 may be used without current sensing by con-
benefit from the MIC5020’s fast switching times by allowing necting SENSE + and SENSE – to ground.
use of MOSFETs with smaller safe operating areas. (Larger Current Sense Resistors
MOSFETs are often required when using slower drivers.)
Lead length can be significant when using low value (< 1Ω)
Overcurrent Limiting resistors for current sensing. Errors caused by lead length
A 50mV comparator is provided for current sensing. The low can be avoided by using four-terminal current sensing re-
level trip point minimizes I2R losses when power resistors sistors. Four-terminal resistors are available from several
are used for current sensing. Flexibility in choosing drain or manufacturers.
source side sensing is provided by access to both SENSE +

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MIC5020 Micrel, Inc.
Lamp Driver Application Current Sensing MOSFET Application
Incandescent lamps have a high inrush current (low resis- A current sensing MOSFET allows current sensing without
tance) when turned on. The MIC5020 can perform a “soft adding additional resistance to the power switching circuit.
start” by pulsing the MOSFET (overcurrent condition) until A current sensing MOSFET has two source connections: a
the filament is warm enough for its current to decrease (re- “power source” for power switching and a “current source”
sistance increases). The sense resistor is selected so the for current sensing. The current from the current source is
voltage across the sense resistor drops below the sense approximately proportional to the current through the power
threshold (50mV) as the filament becomes warm. The source, but much smaller. A current sensing ratio (ISOURCE/
MOSFET is no longer pulsed to limit current and the lamp ISENSE) is provided by the MOSFET manufacturer.
turns completely on. V+
V+ (+13.2V, > 4.4A)
(+11V to +12V)
(3Ω, > 60W)
Incandescent
Lamp (#1157) +11V to +50V N-Channel
MIC5020 (+13.2V) MIC5020
1 8 Current Sensing
10µF 1 8 N-Channel 10µF V DD Gate Power MOSFET
V DD Gate Power MOSFET
(IRF540) 2 7 (IRCZ24)
TTL Input 2 7 TTL Input Input
Input Sense- (0V/5V) Sense-
(0V/5V) 3 6
3 6 Fault Sense+
Fault Sense+ R SENSE
4 5 4 5 (10Ω)
RS E N S E CT Gnd
CT Gnd
(0.041Ω)
“( )” values apply to “( )” values apply to
demo circuit. See text. demo circuit. See text.

Figure 1. Lamp Driver with Figure 3. Using a Current Sensing MOSFET

Current Sensing The MOSFET current source is used to develop a voltage
A lamp may not fully turn on if the filament does not heat up across a sense resistor. This voltage is monitored by the
adequately. Changing the duty cycle, sense resistor, or both to MIC5020 (SENSE + and SENSE – pins) to identify an over-
match the filament characteristics can correct the problem. current condition.
Soft start can be demonstrated using a #1157 dual-filament The value of the sense resistor can be estimated with:
automotive lamp. The value of RS shown in figure 1 allows RSENSE = (r VTRIP RDS(ON)) / (ILOAD RDS(ON) – VTRIP)
for soft start of the higher-resistance filament (measures where:
approx. 2.1Ω cold or 21Ω hot).
RSENSE = external “sense” resistor
Solenoid Driver Application
VTRIP = 50mV (0.050V) for the MIC5020
The MIC5020 can be directly powered by the control voltage
r = manufacturer’s current sense ratio: (ISOURCE/ISENSE)
supply in typical 11Vdc through 50Vdc control applications.
Current sensing has been omitted as an example. RDS(ON) = manufacturer’s power source on resistance
V+ ILOAD = load current (power source current)
The drain to source voltage under different fault conditions
affects the behavior of the MOSFET current source; that is, the
Solenoid Diode
+11V to +50V current source will respond differently to a slight over-current
condition (VDS(ON) very small) than to a short circuit (where
MIC5020
10µF 1 8 N-Channel
VDS(ON) is approximately equal to the supply voltage).
V DD Gate Power MOSFET
2 7 Adjustment of the sense resistor value by experiment starting
TTL Input Input Sense-
3 6
from the above formula will provide the quickest selection
Fault Sense+ of RSENSE.
4 5
CT Gnd Refer to manufacture’s data sheets and application notes
for detailed information on current sensing MOSFET char-
acteristics.
Figure 2. Solenoid Driver, Figure 3 includes values which can be used to demonstrate
Without Current Sensing circuit operation. The IRCZ24 MOSFET has a typical sense
ratio of 780 and a RDS(ON) of 0.10Ω. A large 3Ω wirewound
A diode across the load protects the MOSFET from the volt- load resistor will cause inductive spikes which should be
age spike generated by the inductive load upon MOSFET suppressed using a diode (using the same configuration as
turn off. The peak forward current rating of the diode should figure 2).
be greater than the load current.

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MIC5020 Micrel, Inc.
Faster MOSFET Switching For test purposes, a 680Ω load resistor and 3Ω sense resistor
The MIC5020’s GATE current can be multiplied using a pair of will produce an overcurrent condition when the load’s supply
bipolar transistors to permit faster charging and discharging (V+) is approximately 12V or greater.
of the external MOSFET’s gate. Low-Temperature Operation
+40V max.
As the temperature of the MIC5020AJB (extended tempera-
ture range version—no longer available) approaches –55°C,
the driver’s off-state, gate-output offset from ground increases.
If the operating environment of the MIC5020AJB includes low
temperatures (–40°C to –55°C), add an external 2.2MΩ resis-
2N3904 tor as shown in Figures 6a or 6b. This assures that the driver’s
+11V to +50V MIC5020
10µF 1 8 N-Channel gate-to-source voltage is far below the external MOSFET’s
V DD Gate Power MOSFET
2 7 (IRF540) gate threshold voltage, forcing the MOSFET fully off.
150kHz max. Input Sense- V+
3 6 2N3906
Fault Sense+
4 5
CT Gnd

MIC5020
+11V to +50V 1 8
V DD Gate
Figure 4. Faster MOSFET Switching Circuit 10µF 2
Input
7
Sense-
3 6 2.2M
NPN and PNP transistors are used to respectively charge Fault Sense+
and discharge the MOSFET gate. The MIC5020 gate current 4
CT Gnd
5
RS E NS E
is multiplied by the transistor β.
The switched circuit voltage can be increased above 40V by
selecting transistors with higher ratings.
Figure 6a. Gate-to-Source Pull Down
Remote Overcurrent Limiting Reset
In circuit breaker applications where the MIC5020 maintains The gate-to-source configuration (refer to Figure 6a) is ap-
an off condition after an overcurrent condition is sensed, the propriate for resistive and inductive loads. This also causes
CT pin can be used to reset the MIC5020. the smallest decrease in gate output voltage.
V+
V+

MIC5020
+11V to +50V MIC5020 +11V to +50V 1 8
1 8 V DD Gate
10µF V DD Gate N-Channel 10µF
Power MOSFET 2 7
2 7 Input Sense-
TTL input Input Sense- 3 6
Fault Sense+
Retry (H)
3 6
Fault Sense+ 4 5
Maintained (L) CT Gnd
10k to 4 5 2.2M RS E N S E
100k CT Gnd
Q1 RS E N S E
2N3904
74HC04
(example) Figure 6b. Gate-to-Ground Pull Down
The gate-to-ground configuration (refer to Figure 6b) is ap-
Figure 5. Remote Control Circuit
propriate for resistive, inductive, or capacitive loads. This
Switching Q1 on pulls CT low which keeps the MIC5020 GATE configuration will decrease the gate output voltage slightly
output off when an overcurrent is sensed. Switching Q1 off more than the circuit shown in Figure 6a.
causes CT to appear open. The MIC5020 retries in about
20µs and continues to retry until the overcurrent condition
is removed.

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MIC5020 Micrel, Inc.

Package Information
0.026 (0.65)
MAX) PIN 1

0.157 (3.99) DIMENSIONS:

0.150 (3.81) INCHES (MM)

0.020 (0.51)
0.013 (0.33)
0.050 (1.27)
TYP 0.0098 (0.249) 45°
0.010 (0.25)
0.0040 (0.102) 0.007 (0.18)

0.197 (5.0) 0°–8° 0.050 (1.27)

0.064 (1.63) 0.189 (4.8) SEATING 0.016 (0.40)
0.045 (1.14) PLANE
0.244 (6.20)
0.228 (5.79)

8-Pin SOIC (M)

MICREL INC. 2180 FORTUNE DRIVE SAN JOSE, CA 95131 USA

TEL + 1 (408) 944-0800 FAX + 1 (408) 474-1000 WEB http://www.micrel.com

This information furnished by Micrel in this data sheet is believed to be accurate and reliable. However no responsibility is assumed by Micrel for its use.
Micrel reserves the right to change circuitry and specifications at any time without notification to the customer.
Micrel Products are not designed or authorized for use as components in life support appliances, devices or systems where malfunction of a product can
reasonably be expected to result in personal injury. Life support devices or systems are devices or systems that (a) are intended for surgical implant into
the body or (b) support or sustain life, and whose failure to perform can be reasonably expected to result in a significant injury to the user. A Purchaser's
use or sale of Micrel Products for use in life support appliances, devices or systems is a Purchaser's own risk and Purchaser agrees to fully indemnify
Micrel for any damages resulting from such use or sale.

© 1998 Micrel, Inc.

MIC5020 8 July 2005