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MIC5021
Micrel
MIC5021
High-Speed High-Side MOSFET Driver
General Description
The MIC5021 high-side MOSFET driver is designed to operate at frequencies up to 100kHz (5kHz PWM for 2% to 100% duty cycle) and is an ideal choice for high speed applications such as motor control, SMPS (switch mode power supplies), and applications using IGBTs. The MIC5021 can also operate as a circuit breaker with or without automatic retry. A rising or falling edge on the input results in a current source pulse or sink pulse on the gate output. This output current pulse can turn on a 2000pF MOSFET in approximately 550ns. The MIC5021 then supplies a limited current (< 2mA), if necessary, to maintain the output state. An overcurrent comparator with a trip voltage of 50mV makes the MIC5021 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 placed from the CT pin to ground may be used to control the current shutdown duty cycle (dead time) from 20% to < 1%. A duty cycle from 20% to about 75% is possible with an optional pull-up resistor from CT to VDD. The MIC5021 is available in 8-pin SOIC and plastic DIP packages. Other members of the MIC502x family include the MIC5020 low-side driver and the MIC5022 half-bridge driver with a cross-conduction interlock.
Features
12V to 36V operation 550ns rise/fall time driving 2000pF TTL compatible input with internal pull-down resistor Overcurrent limit Gate to source protection Internal charge pump 100kHz operation guaranteed over full temperature and operating voltage range * Compatible with current sensing MOSFETs * Current source drive reduces EMI * * * * * * *
Applications
* * * * * * Lamp control Heater control Motor control Solenoid switching Switch-mode power supplies Circuit breaker
Ordering Information
Part Number MIC5021BM MIC5021BN Temperature Range -40C to +85C -40C to +85C Package 8-pin SOIC 8-pin Plastic DIP
5
Typical Application
+12V to +36V
MIC5021 10F TTL Input optional* 1 2 3 4 VDD Input CT Gnd VBOOST Gate Sense Sense 8 7 6 5 2.7 nF RSENSE RSENSE = 50mV ITRIP * increases time before retry N-Channel Power MOSFET
High-Side Driver with Overcurrent Trip and Retry
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MIC5021
Micrel
Pin Configuration
1 VDD 2 Input 3 CT 4 Gnd VBOOST 8 Gate 7 Sense- 6 Sense+ 5 1 2 3 4 VDD Input CT VBOOST 8 Gate 7 Sense- 6
Gnd Sense+ 5
DIP Package (N)
SOIC Package (M)
Block Diagram
6V Internal Regulator I1 CINT 2I1
Fault
CT
Normal
VDD CHARGE PUMP VBOOST
Q1
Sense + Sense -
ON
15V 50mV
OFF
Input
ONE SHOT
6V Gate
10I2
I2
Transistor: 106
Pin Description
Pin Number 1 2 3 Pin Name VDD Input CT Pin Function Supply: +12V to +36V. Decouple with 10F capacitor. TTL Compatible Input: Logic high turns the external MOSFET on. An internal pull-down returns an open pin to logic low. Retry Timing Capacitor: Controls the off time (tG(OFF)) of the overcurrent retry cycle. (Duty cycle adjustment.) * Open = approx. 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. Circuit Ground 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. Current Sense Comparator (-) Input: Connect to the low side of the sense resistor (usually the high side of the load). 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. Charge Pump Boost Capacitor: A bootstrap capacitor from VBOOST to the FET source pin supplies charge to quickly enhance the Gate output during turn-on.
4 5
Gnd Sense +
6 7
Sense - Gate
8
VBOOST
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Micrel
Absolute Maximum Ratings
Supply Voltage (VDD) .................................................. +40V Input Voltage ................................................ -0.5V to +15V Sense Differential Voltage .......................................... 6.5V Sense + or Sense - to Gnd .......................... -0.5V to +36V Timer Voltage (CT) ..................................................... +5.5V VBOOST Capacitor .................................................... 0.01F
Operating Ratings
Supply Voltage (VDD) .................................... +12V to +36V Temperature Range PDIP ....................................................... -40C to +85C SOIC ...................................................... -40C to +85C
Electrical Characteristics
TA = 25C, Gnd = 0V, VDD = 12V, CT = Open, Gate CL = 1500pF (IRF540 MOSFET) unless otherwise specified Symbol Parameter D.C. Supply Current Condition VDD = 12V, Input = 0V VDD = 36V, Input = 0V VDD = 12V, Input = 5V VDD = 36V, Input = 5V Input Threshold Input Hysteresis Input Pull-Down Current Current Limit Threshold Gate On Voltage Input = 5V Note 1 VDD = 12V Note 2 VDD = 36V Note 2 tG(ON) tG(OFF) tDLH tR tDLH tF fmax
Note 1 Note 2 Note 3 Note 4 Note 5 Note 6 Note 7
Min
Typ 1.8 2.5 1.7 2.5
Max 4 6 4 6 2.0
Units mA mA mA mA V V A mV V V s s ns ns ns ns kHz
0.8
1.4 0.1
10 30 16 46 2 10
20 50 18 50 6 20 500 400 800 400
40 70 21 52 10 50 1000 500 1500 500
5
Gate On Time, Fixed Gate Off Time, Adjustable Gate Turn-On Delay Gate Rise Time Gate Turn-Off Delay Gate Fall Time Maximum Operating Frequency
Sense Differential > 70mV Sense Differential > 70mV, CT = 0pF Note 3 Note 4 Note 5 Note 6 Note 7
100
150
When using sense MOSFETs, it is recommended that RSENSE < 50. Higher values may affect the sense MOSFET's current transfer ratio. DC measurement. Input switched from 0.8V (TTL low) to 2.0V (TTL high), time for Gate transition from 0V to 2V. Input switched from 0.8V (TTL low) to 2.0V (TTL high), time for Gate transition from 2V to 17V. Input switched from 2.0V (TTL high) to 0.8V (TTL low), time for Gate transition from 20V (Gate on voltage) to 17V. Input switched from 2.0V (TTL high) to 0.8V (TTL low), time for Gate transition from 17V to 2V. Frequency where gate on voltage reduces to 17V with 50% input duty cycle.
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Typical Characteristics
Supply Current vs. Supply Voltage
VIN = 0V
VGATE (V)
Gate Voltage Change vs. Supply Voltage
25 VGATE = VGATE - VSUPPLY 20 15 10 5 0
Gate Turn-On Delay vs. Supply Voltage
900 850 tON 4V (ns) 800 750
INCLUDES PROPAGATION DELAY
2.5 2.0 ISUPPLY (mA) 1.5 1.0 0.5 0.0
VGATE = VSUPPLY + 4V CL = 1500pF (IRCZ34) CBOOST = 0.01F
VIN = 5V
700 650
5
10
15
20 25 30 VSUPPLY (V)
35
40
5
10
15
20 25 30 VSUPPLY (V)
35
40
5
10
15
20 25 30 VSUPPLY (V)
35
40
Gate Turn-On Delay vs. Supply Voltage
1000 950 tON 10V (ns) 900 850 800
INCLUDES PROPAGATION DELAY
Gate Turn-On Delay vs. Gate Capacitance
2.5
Gate Turn-Off Delay vs. Supply Voltage
2000 VGATE = VSUPPLY + 4V RL = 400
VGATE = VSUPPLY + 10V CL = 1500pF (IRCZ34) CBOOST = 0.01F tON (s)
2.0 1.5 1.0 0.5
VGATE = VSUPPLY + 4V VSUPPLY = 12V
1750 tOFF 4V (ns) 1500 1250 1000
CGATE = 1500pF (IRCZ34)
INCLUDES PROPAGATION DELAY
INCLUDES PROPAGATION DELAY
750
5
10
15
20 25 30 VSUPPLY (V)
35
40
0.0 1x100 1x101 1x102 1x103 1x104 1x105 CGATE (pF)
750 5
10
15
20 25 30 VSUPPLY (V)
35
40
Overcurrent Retry Duty Cycle vs. Timing Capacitance
25 RETRY DUTY CYCLE (%) 20 15 10 5 0 0.1 NOTE: tON, tOFF TIME INDEPENDENT OF VSUPPLY 1 10 100 CT (pF) 1000 10000 tON = 5s VSUPPLY = 12V
IIN (A)
100 80
Input Current vs. Input Voltage
VSUPPLY = 12V VOLTAGE (mV)
Sense Threshold vs. Temperature
80 70 60 50 40 30
60 40 20 0
0
5
10 15 VIN (V)
20
25
20 -60 -30 0 30 60 90 120 150 TEMPERATURE (C)
Input Gate Sense +, - Differential
TTL (H) 0V 15V (max.) Source 50mV 0V
Timing Diagram 1. Normal Operation
6s 20s
6s
Input Gate Sense +, - Differential
TTL (H) 0V 15V (max.) Source 50mV 0V
Input Gate Sense +, - Differential
TTL (H) 0V 15V (max.) Source 50mV 0V
Timing Diagram 2. Fault Condition, CT = Open 5-172
Timing Diagram 3. Fault Condition, CT = Grounded October 1998
MIC5021
Micrel
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 5A out of SENSE + and approximately 15A (at trip) out of SENSE -. When SENSE - is 50mV or more below SENSE +, SENSE - steals base current from an internal drive transistor shutting off the external MOSFET. Overcurrent Limiting Current source I1 charges CINT upon power up. An optional external capacitor connected to CT is kept discharged through a MOSFET Q1. A fault condition (> 50mV from SENSE + to SENSE -) causes the overcurrent comparator to enable current sink 2I1 which overcomes current source I1 to discharge CINT in a short time. When CINT is discharged, the INPUT is disabled, which turns off the gate output, and CINT and CT are ready to be charged. When the gate output turns the MOSFET off, the overcurrent signal is removed from the sense inputs which deactivates current sink 2I1. This allows CINT and the optional capacitor connected to CT to recharge. A Schmitt trigger delays the retry while the capacitor(s) recharge. Retry delay is increased by connecting a capacitor to CT (optional). The retry cycle will continue until the fault is removed or the input is changed to TTL low. If CT is connected to ground, the circuit will not retry upon a fault condition.
Functional Description
Refer to the MIC5021 block diagram. Input A signal greater than 1.4V (nominal) applied to the MIC5021 INPUT causes gate enhancement on an external MOSFET turning the MOSFET on. An internal pull-down resistor insures that an open INPUT remains low, keeping the external MOSFET turned off. Gate Output Rapid rise and fall times on the GATE output are possible because each input state change triggers a one-shot which activates a high-value current sink (10I2) for a short time. This 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 VBOOST and the source of the external 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 VBOOST pin voltage. The boost capacitor charge is directed through the GATE pin to quickly charge the MOSFET's gate to 16V maximum above VDD. The internal charge pump maintains the gate voltage.
5
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 components 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 modulation) 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.)
Supply Voltage The MIC5021's supply input (VDD) is rated up to 36V. The 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 continuous on-state, gate drive voltage for standard MOSFETs (10V nominal gate enhancement). When the driver is powered from a 12V to 16V supply, a logiclevel MOSFET is recommended (5V nominal gate enhancement). 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.
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MIC5021
Logic-Level MOSFET Precautions Logic-level MOSFETs have lower maximum gate-to-source voltage ratings (typically 10V) than standard MOSFETs (typically 20V). When an external MOSFET is turned on, the doubling effect of the boost capacitor can cause the gate-tosource voltage to momentarily exceed 10V. Internal zener diodes clamp this voltage to 16V maximum which is too high for logic-level MOSFETs. To protect logic-level MOSFETs, connect a zener diode (5VVZener<10V) from gate to source. Overcurrent Limiting A 50mV comparator is provided for current sensing. The low level trip point minimizes I2R losses when a power resistor is used for current sensing. The adjustable retry feature can be used to handle loads with high initial currents, such as lamps or heating elements, and can be adjusted from the CT connection. CT to ground maintains gate drive shutdown following an overcurrent condition. CT open, or a capacitor to ground, causes automatic retry. The default duty cycle (CT open) is approximately 20%. Refer to the electrical characteristics when selecting a capacitor for reduced duty cycle. CT through a pull-up resistor to VDD increases the duty cycle. Increasing the duty cycle increases the power dissipation in the load and MOSFET under a "fault" condition. Circuits may become unstable at a duty cycle of about 75% or higher, depending on conditions. Caution: The MIC5021 may be damaged if the voltage applied to CT exceeds the absolute maximum voltage rating. Boost Capacitor Selection The boost capacitor value will vary depending on the supply voltage range.
+12V to +20V
Micrel
A 0.01F boost capacitor is recommended for best performance in the 12V to 20V range. Refer to figure 1. Larger capacitors may damage the MIC5021.
+12V to +36V
MIC5021 10F TTL Input 1 2 3 4 VDD Input CT Gnd VBOOST Gate Sense Sense 8 7 6 5 2.7 nF
Figure 2. 12V to 36V Configuration If the full 12V to 36V voltage range is required, the boost capacitor value must be reduced to 2.7nF. Refer to Figure 2. The recommended configuration for the 20V to 36V range is to place the capacitor is placed between VDD and VBOOST as shown in Figure 3.
+12V to +36V
MIC5021 10F TTL Input 1 2 3 4 VDD Input CT Gnd VBOOST Gate Sense Sense 8 7 6 5
0.1 F
MIC5021 10F TTL Input 1 2 3 4 VDD Input CT Gnd VBOOST Gate Sense Sense 8 7 6 5 0.01 F
Figure 3. Preferred 20V to 36V Configuration Do not use both boost capacitor between VBOOST and the MOSFET source and VBOOST and VDD at the same time. Current Sense Resistors Lead length can be significant when using low value (< 1) resistors for current sensing. Errors caused by lead length can be avoided by using four-teminal current sensing resistors. Four-terminal resistors are available from several manufacturers.
Figure 1. 12V to 20V Configuration
Load
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Load
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MIC5021
Circuits Without Current Sensing
V+
Micrel
The diode should have a peak forward current rating greater than the load current. This is because the current through the diode is the same as the load current at the instant the MOSFET is turned off.
+20V to +36V N-Channel Power MOSFET 0.01 F Load 10F TTL Input 1 2 3 4 (+24V) MIC5021 VDD Input CT Gnd VBOOST Gate Sense Sense 8 7 6 5 RSENSE (< 0.08) 0.01 F N-Channel Power MOSFET (IRF540)
MIC5021 10F TTL Input 1 2 3 4 VDD Input CT Gnd VBOOST Gate Sense- Sense+ 8 7 6 5
Figure 4a. Connecting Sense to Source
V+
MIC5021 10F TTL Input 1 2 3 4 VDD Input CT Gnd VBOOST Gate Sense- Sense+ 8 7 6 5 0.01 F Load N-Channel Power MOSFET
Solenoid (24V, 47)
Schottky Diode (1N5822)
Figure 4b. Connecting Sense to Supply Current sensing may be omitted by connecting the SENSE + and SENSE - pins to the source of the MOSFET or to the supply. Connecting the SENSE pins to the supply is preferred for inductive loads. Do not connect the SENSE pins to ground. Inductive Load Precautions Circuits controlling inductive loads, such as solenoids (Figure 5) and motors, require precautions when controlled by the MIC5021. Wire wound resistors, which are sometimes used to simulate other loads, can also show significant inductive properties. An inductive load releases stored energy when its current flow is interrupted (when the MOSFET is switched off). The voltage across the inductor reverses and the inductor attempts to force current flow. Since the circuit appears open (the MOSFET appears as a very high resistance) a very large negative voltage occurs across the inductor. Limiting Inductive Spikes The voltage across the inductor can be limited by connecting a Schottky diode across the load. The diode is forward biased only when the load is switched off. The Schottky diode clamps negative transients to a few volts. This protects the MOSFET from drain-to-source breakdown and prevents the transient from damaging the charge pump by way of the boost capacitor. Also see Sense Pin Considerations below.
Figure 5. Solenoid Driver with Current Sensing Sense Pin Considerations The sense pins of the MIC5021 are sensitive to negative voltages. Forcing the sense pins much below -0.5V effectively reverses the supply voltage on portions of the driver resulting in unpredictable operation or damage.
MIC5021 1 2 3 4 VDD Input CT Gate 8 7 6 5
MOSFET Turnoff ~VDD 0V Negative Spike
5
Forward drop across diodes allows leads to go negative. Current flows from ground (0V) through the diodes to the load during negative transcients.
Inductive Load
Figure 6. Inductive Load Turnoff Figure 6 shows current flowing out of the sense leads of an MIC5021 during a negative transient (inductive kick). Internal Schottky diodes attempt to limit the negative transient by maintaining a low forward drop. Although the internal Schottky diodes can protect the driver in low-current resistive applications, they are inadequate for inductive loads or the lead inductance in high-current resistive loads. Because of their small size, the diodes' forward voltage drop quickly exceeds 0.5V as current increases.
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MIC5021 External Protection Resistors placed in series with each SENSE connection limit the current drawn from the internal Schottky diodes during a negative transient. This minimizes the forward drop across the diodes.
MIC5021 1 2 3 4 VDD Input CT Gnd VBOOST Gate Sense- Sense+ 8 7 6 5 R1 N-Channel Power MOSFET 10F TTL Input 1 2 3 4 RS 50mV nominal (at trip)
Micrel High-Side Sensing Sensing the current on the high side of the MOSFET isolates the SENSE pins from the inductive spike.
+12V to +20V (+12V) MIC5021 VDD Input CT Gnd VBOOST Gate Sense Sense 8 7 6 5 0.01 F Wirewound Resistor (3) RSENSE (< 0.01) N-Channel Power MOSFET (IRFZ44)
5A VR1 R2
Load
VR1 = VR2 to avoid skewing the 50mV trip point.. (5mV suggested) R1 3 x R2
15A VR2
Figure 7. Resistor Voltage Drop During normal operation, sensing current from the sense pins is unequal (5A and 15A). The internal Schottky diodes are reverse biased and have no effect. To avoid skewing the trip voltage, the current limiting resistors must drop equal voltages at the trip point currents. See Figure 7. To minimize resistor tolerance error, use a voltage drop lower than the trip voltage of 50mV. 5mV is suggested. External Schottky diodes are also recommended. See D2 and D3 in Figure 8. The external diodes clamp negative transients better than the internal diodes because their larger size minimizes the forward voltage drop at higher currents.
+12V to +36V
Figure 9. High Side Sensing Lamp Driver Application Incandescent lamps have a high inrush current (low resistance) when turned on. The MIC5021 can perform a "soft start" by pulsing the MOSFET (overcurrent condition) until the filament is warm and its current decreases (resistance increases). The sense resistor value is selected so the voltage drop across the sense resistor decreases below the sense threshold (50mV) as the filament becomes warm. The FET is no longer pulsed and the lamp turns completely on.
V+ (+12V) 10F TTL Input 1 2 3 MIC5021 VDD Input CT Gnd VBOOST Gate Sense- Sense+ 8 7 6 5 0.01 F RSENSE (0.041) "( )" values apply to demo circuit. See text. Incandescent Lamp (#1157) N-Channel Power MOSFET (IRF540)
MIC5021 10F TTL Input 1 2 3 4 VDD Input CT Gnd VBOOST Gate Sense Sense 8 7 6 5 2.7 nF R1 1.0k RSENSE R2 D3 11DQ03 330 Inductive Load N-Channel Power MOSFET
4
D2 11DQ03
D1
Figure 8. Protection from Inductive Kick
Figure 10. Lamp Driver with Current Sensing A lamp may not fully turn on if the filament does not heat up adequately. Changing the duty cycle, sense resistor, or both to match the filament characteristics can correct the problem. Soft start can be demonstrated using a #1157 dual filament automotive lamp. The value of RS shown in Figure 10 allows for soft start of the higher-resistance filament (measures approx. 2.1 cold or 21 hot).
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Remote Overcurrent Limiting Reset In circuit breaker applications where the MIC5021 maintains an off condition after an overcurrent condition is sensed, the CT pin can be used to reset the MIC5021.
+12V to +20V
Micrel
+12V to +36V
MIC5021AJB 10F TTL Input 1 2 3 VDD Input CT Gnd VBOOST Gate Sense Sense 8 7 6 5 2.7 nF 2.2M RSENSE
MIC5021 10F TTL Input 10k to 100k 74HC04 (example)
Retry (H) Maintained (L)
4 8 7 6 5 0.01 F RSENSE N-Channel Power MOSFET
1 2 3
VDD Input CT
VBOOST Gate Sense Sense
2N3904 4 Q1 Gnd
Figure 12a. Gate-to-Source Pull Down The gate-to-source configuration (refer to Figure 12a) is appropriate for resistive and inductive loads. This also causes the smallest decrease in gate output voltage.
+12V to +36V
Figure 11. Remote Control Circuit Switching Q1 on pulls CT low which keeps the MIC5021 GATE output off when an overcurrent is sensed. Switching Q1 off causes CT to appear open. The MIC5021 retries in about 20s and continues to retry until the overcurrent condition is removed. For demonstration purposes, a 680 load resistor and 3 sense resistor will produce an overcurrent condition when the load's supply (V+) is approximately 12V or greater. Low-Temperature Operation As the temperature of the MIC5021AJB (extended temperature range version--no longer available) approaches -55C, the driver's off-state, gate-output offset from ground increases. If the operating environment of the MIC5021AJB includes low temperatures (-40C to -55C), add an external 2.2M resistor as shown in Figures 12a or 12b. This assures that the driver's gate-to-source voltage is far below the external MOSFET's gate threshold voltage, forcing the MOSFET fully off.
Load
MIC5021AJB 10F TTL Input 1 2 3 4 VDD Input CT Gnd VBOOST Gate Sense Sense 8 7 6 5 2.7 nF RSENSE
Load
add resistor for -40C to -55C operation
5
add resistor for -40C to -55C operation
2.2M
Figure 12b. Gate-to-Ground Pull Down The gate-to-ground configuration (refer to Figure 12b) is appropriate for resistive, inductive, or capacitive loads. This configuration will decrease the gate output voltage slightly more than the circuit shown in Figure 12a.
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Load

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