MIC2194 DATA SHEET (11/05/2015) DOWNLOAD

MIC2194
Micrel
MIC2194
400kHz SO-8 Buck Control IC
General Description
Features
Micrel’s MIC2194 is a high efficiency PWM buck control IC
housed in the SO-8 package. Its 2.9V to 14V input voltage
range allows it to efficiently step down voltages in 3.3V, 5V,
and 12V systems as well as 1- or 2-cell Li Ion battery powered
applications. The flexible architecture of the MIC2194 allows
for it to be configured as a buck or a buck-boost converter.
The MIC2194 solution saves valuable board space. The
device is housed in the space-saving SO-8 package, whose
low pin-count minimizes external components. Its 400kHz
PWM operation allows a small inductor and small output
capacitors to be used. The MIC2194 can implement allceramic capacitor solutions.
The MIC2194 drives a high-side P-channel MOSFET. A low
output driver impedance of 2Ω allows the MIC2194 to drive
large external MOSFETs to generate a wide range of output
currents. The MIC2194 can achieve maximum duty cycles of
100%, which can be useful in low headroom applications.
The MIC2194 is available in an 8 pin SOIC package with a
junction temperature range of –40°C to +125°C.
•
•
•
•
•
•
•
•
•
•
•
2.9V to 14V input voltage range
400kHz oscillator frequency
PWM current mode control
2Ω output drivers
100% maximum duty cycle
0.5µA micro-power shutdown
Programmable UVLO
Front edge blanking
Cycle-by-cycle current limiting
Frequency foldback short circuit protection
8-lead SOIC package
Applications
•
•
•
•
•
•
•
•
•
Point of load power supplies
Negative voltage buck-boost power supplies
Distributed power systems
Base stations
Wireless modems
ADSL line cards
Servers
Step down conversion in 3.3V, 5V, 12V systems
1-and 2-cell Li Ion battery operated equipment
Typical Application
VIN
12V
0.012Ω
47µF
20V
(×2)
MIC2194BM
Si4431A
(×2)
VIN
CS
EN/ OUTP
UVLO
VDD
FB
1µF
2k
5.2µH
VOUT
5V, 5A
B530 10k
COMP GND
2.2nF
3.32k
220µF
10V
(×2)
Adjustable Output Buck Converter
VIN
+3.3V
0.040Ω
10µF
16V
Si9803
22µH
MIC2194BM
VIN
CS
EN/ OUTP
UVLO
VDD
FB
10µF
16V
1µF
22nF
B530
3.01k
4.99k COMP
GND
220µF
10V
(×2)
1k
10nF
VOUT
–5V, 0.6A
Positive-to-Negative Buck-Boost Converter
Micrel, Inc. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel + 1 (408) 944-0800 • fax + 1 (408) 474-1000 • http://www.micrel.com
April 2005
1
MIC2194
MIC2194
Micrel
Ordering Information
Part Number
Standard
MIC2194BM
Lead-Free
Output Voltage
Frequency
Junction Temp. Range
Package
MIC2194YM
Adjustable
400kHz
–40°C to +125°C
8-lead SOP
Pin Configuration
COMP 1
8 VIN
FB 2
7 OUTP
EN/UVLO 3
6 GND
CS 4
5 VDD
8 Lead SOIC (M)
Pin Description
Pin Number
Pin Name
1
COMP
2
FB
3
EN/UVLO
Enable/Undervoltage Lockout (Input): A low level on this pin will power down
the device, reducing the quiescent current to under 0.5µA. This pin has two
separate thresholds, below 1.5V the output switching is disabled, and below
0.9V the device is forced into a complete micropower shutdown. The 1.5V
threshold functions as an accurate undervoltage lockout (UVLO) with
hysteresis.
4
CS
The (–) input to the current limit comparator. A built-in offset of 110mV
between VIN and CSL in conjunction with the current sense resistor sets the
current limit threshold level. This is also the (–) input to the current amplifier.
5
VDD
3V internal linear-regulator output. VDD is also the supply voltage bus for the
chip. Bypass to GND with 1µF.
6
GND
Ground.
7
OUTP
High current drive for the synchronous N-channel MOSFET. Voltage swing
is from ground to VIN. On-resistance is typically 3Ω @ 5VIN.
8
VIN
MIC2194
Pin Function
Compensation (Output): Internal error amplifier output. Connect to a
capacitor or series RC network to compensate the regulator’s control loop.
Feedback (Input): The circuit regulates this pin to 1.245V.
Input voltage to the circuit. Also the high side input to the current sense
amplifier supplies power to the gate drive circuit.
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April 2005
MIC2194
Micrel
Absolute Maximum Ratings (Note 1)
Operating Ratings (Note 2)
Supply Voltage (VIN) ..................................................... 15V
Digital Supply Voltage (VDD) ........................................... 7V
Enable Pin Voltage (VEN) ............................. –0.3V to +15V
Comp Pin Voltage (VCOMP) ............................ –0.3V to +3V
Feedback Pin Voltage (VFB) .......................... –0.3V to +3V
Current Sense Voltage (VIN –VCS) ................. –0.3V to +1V
Power Dissipation (PD) ..................... 285mW @ TA = 85°C
Ambient Storage Temp ............................ –65°C to +150°C
ESD Rating, Note 3 ...................................................... 2kV
Supply Voltage (VIN) .................................... +2.9V to +14V
Junction Temperature ....................... –40°C ≤ TJ ≤ +125°C
Package Thermal Resistance
θJA 8-lead SOP ................................................. 140°C/W
Electrical Characteristics
VIN = 5V, VOUT = 3.3V, TJ = 25°C, unless otherwise specified. Bold values indicate –40°C<TJ<+125°C.
Parameter
Condition
Min
Typ
Max
Units
1.233
1.22
1.245
1.245
1.257
1.27
V
V
Regulation
Feedback Voltage Reference
(1%)
(2%)
Feedback Bias Current
50
nA
Output Voltage Line Regulation
5V ≤ VIN ≤ 9V
0.15
%/V
Output Voltage Load Regulation
0mV < (VIN – VCS) < 75mV
0.9
%
Output Voltage Total Regulation
5V ≤VIN ≤ 9V, 0mV < (VIN – VCS) < 75mV (±3%)
1.208
1.282
V
1
2
mA
0.5
5
µA
3.0
3.18
V
Input & VDD Supply
VIN Input Current (IQ)
(excluding external MOSFET gate current)
Shutdown Current (ISD)
VEN = 0V
Digital Supply Voltage (VDD)
IL = 0
Digital Supply Load Regulation
IL = 0 to 1mA
0.1
V
Undervoltage Lockout
VDD upper threshold (turn on threshold)
2.65
V
100
mV
2.82
UVLO Hysteresis
Enable/UVLO
Enable Input Threshold
0.6
0.9
1.2
V
UVLO Threshold
1.4
1.5
1.6
V
0.2
5
µA
110
130
mV
Enable Input Current
VEN/UVLO = 5V
Current Limit
Current Limit Threshold Voltage
VIN – VCS voltage to trip current limit
90
Error Amplifier
Error Amplifier Gain
20
V/V
3.0
V/V
Current Amplifier
Current Amplifier Gain
Oscillator Section
Oscillator Frequency (fO)
360
400
100
440
kHz
Maximum Duty Cycle
VFB = 1.0V
Minimum On Time
VFB = 1.5V
165
ns
Frequency Foldback Threshold
Measured on FB
0.3
V
90
kHz
Frequency Foldback Frequency
April 2005
3
%
MIC2194
MIC2194
Parameter
Micrel
Condition
Min
Typ
Max
Units
Gate Drivers
Rise/Fall Time
CL = 3300pF
25
Output Driver Impedance
Source, VIN = 12V
Sink, VIN = 12V
Source, VIN = 5V
Sink, VIN = 5V
2
2
3
3
ns
Ω
Ω
Ω
Ω
6
6
7
7
Note 1.
Absolute maximum ratings indicate limits beyond which damage to the component may occur. Electrical specifications do not apply when
operating the device outside of its operating ratings. The maximum allowable power dissipation is a function of the maximum junction
temperature, TJ(Max), the junction-to-ambient thermal resistance, θJA, and the ambient temperature, TA.
Note 2.
The device is not guaranteed to function outside its operating rating.
Note 3.
Devices are ESD sensitive, handling precautions required. Human body model, 1.5kΩ in series with 100pF.
MIC2194
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April 2005
MIC2194
Micrel
Typical Characteristics
Quiescent Current
vs. Input Voltage
Quiescent Current
vs. Temperature
3.5
3
2.5
2
1.5
1
0.5
Standby
5
10
INPUT VOLTAGE (V)
3.00
1.2
1.0
2.95
0.8
0.6
0.4
0.2
3.01
2.99
3.30
3.20
2.93
2.91
VIN = 12V
2.89
2.87
VDD (V)
3.50
3.40
0.2 0.4 0.6 0.8
1
1.2
VDD LOAD CURRENT (mA)
2.50
-40 -20 0 20 40 60 80 100 120
TEMPERATURE (°C)
1.2440
1.2435
1.2430
0
0
-0.5
-1
-1.5
-2
0
Overcurrent Threshold vs.
Input Voltage
125
115
CURRENT LIMIT (mV)
120
120
115
110
105
100
95
90
0
2
4
6
8 10 12
INPUT VOLTAGE (V)
14
4 6 8 10 12 14
INPUT VOLTAGE (V)
420
410
400
390
380
370
360
350
-50 -30 -10 10 30 50 70 90 110
TEMPERATURE (°C)
OUTP Drive Impedance
vs. Input Voltage
4.5
VIN = 5V
110
105
100
95
90
85
2
VIN = 5V
440
430
Current Limit Threshold
vs. Temperature
130
4 6 8 10 12 14
INPUT VOLTAGE (V)
450
SOFT START CURRENT (µA)
1.21 VIN = 5V
1.2
-40 -20 0 20 40 60 80 100 120
TEMPERATURE (°C)
2
Frequency Variation vs.
Temperature
4
IMPEDANCE (Ω)
1.23
1.22
THRESHOLD (mV)
1.2445
Frequency Variation
vs. Input Voltage
FREQUENCY VARIATION (%)
REFERENCE VOLTAGE (V)
1.25
1.24
April 2005
VIN = 5V
1.2450
0.5
1.27
1.26
15
Error Amp Reference Voltage
vs. Input Voltage
2.90
2.80
1.3
1.29
1.28
5
10
INPUT VOLTAGE (V)
1.2455
3.10
3.00
Error Amp Reference Voltage
vs. Temperature
2.90
2.80
0
VDD vs. Temperature
2.70
2.60
2.85
0
VDD vs. Input Voltage
2.85
0
-40 -20 0 20 40 60 80 100 120
TEMPERATURE (°C)
15
VIN = 5V
VIN = 5V
1.6
1.4
VDD vs. Load
3.05
3.03 VIN = 3.3V
2.97
2.95
3.05
VDD (V)
Switching
2.0
1.8
REFERENCE VOLTAGE (V)
4
0
0
VDD (V)
QUIESCENT CURRENT (mA)
QUIESCENT CURRENT (mA)
4.5
3.5
3
2.5
Source(Ω)
2
1.5
Sink (Ω)
1
0.5
80
-40 -20 0 20 40 60 80 100 120
TEMPERATURE (°C)
5
0
0
2
4 6 8 10 12 14
INPUT VOLTAGE (V)
MIC2194
MIC2194
Micrel
Functional Diagram
VIN
CIN
CDECOUP
VIN
8
OVERCURRENT
COMPARATOR
VREF
1.245V
0.1V
Threshold
EN/UVLO
VDD
9
CSH
4
CSL
7
OUTP
3
RSENSE
BIAS
5
GAIN
3
VDD
CURRENT
SENSE
AMP
ON
VIN
fs/4
CONTROL
Q1
L1
VOUT
D1
OSC
COUT
RESET
SLOPE
COMPENSATION
∑
PWM
COMPARATOR
gm = 0.0002 VREF
gain = 20
COMP
1
ERROR
AMP
2
FB
6
GND
100k
0.3V
fs/4
FREQUENCY
FOLDBACK
Figure 1. MIC2194 Block Diagram
Functional Characteristics
Controller Overview and Functional Description
The MIC2194 is a BiCMOS, switched-mode, step down
(buck) converter controller. It uses a P-channel MOSFET,
which allows the controller to operate at 100% duty cycle and
eliminates the need for a high side drive bootstrap circuit.
Current mode control is used to achieve superior transient
line and load regulation. An internal corrective ramp provides
slope compensation for stable operation above a 50% duty
cycle. The controller is optimized for high efficiency, high
performance DC-DC converter applications.
Figure 1 is a block diagram of the MIC2194 configured as a
buck converter. At the beginning of the switching cycle, the
MIC2194
OUTP pin pulls low and turns on the high-side P-channel
MOSFET, Q1. Current flows from the input to the output
through the current sense resistor, MOSFET and inductor.
The current amplitude increases, controlled by the inductor.
The voltage developed across the current sense resistor,
RSENSE, is amplified inside the MIC2194 and combined with
an internal ramp for stability. This signal is compared to the
output of the error amplifier. When the current signal equals
the error voltage signal, the P-channel MOSFET is turned off.
The inductor current flows through the diode, D1. At the
beginning of the next switching cycle, the P-channel MOSFET
is turned on which turns off the diode, D1.
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April 2005
MIC2194
Micrel
The MIC2194 controller is broken down into several functions.
• Control loop
• PWM operation
• Current mode control
• Current limit
• Reference, enable and UVLO
• MOSFET gate drive
• Oscillator
Control Loop
Current Limit
The output current is detected by the voltage drop across the
external current sense resistor (RSENSE in Figure 1.). The
current sense resistor must be sized using the minimum
current limit threshold. The external components must be
designed to withstand the maximum current limit. The current
sense resistor value is calculated by the equation below:
RSENSE =
The maximum output current is:
PWM Control Loop
The MIC2194 uses current mode control to regulate the
output voltage. This dual control loop method (illustrated in
Figure 2) senses the output voltage (outer loop) and the
inductor current (inner loop). It uses inductor current and
output voltage to determine the duty cycle of the buck
converter. Sampling the inductor current effectively removes
the inductor from the control loop, which simplifies compensation.
IOUT _ MAX =
VOUT
Voltage
Divider
IINDUCTOR
Switch
Driver
VERROR
VREF
IINDUCTOR
VERROR
tON
tPER
D = tON/tPER
Figure 2. Current Mode Control Example
As shown in Figure 1, the inductor current is sensed by
measuring the voltage across the resistor, RSENSE. A ramp is
added to the amplified current sense signal to provide slope
compensation, which is required to prevent unstable operation at duty cycles greater than 50%.
A transconductance amplifier is used for the error amplifier,
which compares an attenuated sample of the output voltage
with a reference voltage. The output of the error amplifier is
the compensation pin (COMP), which is compared to the
current sense waveform in the PWM block. When the current
signal becomes greater than the error signal, the comparator
turns off the high side drive. The COMP pin provides access
to the output of the error amplifier and allows the use of
external components to stabilize the voltage loop.
April 2005
MAX _ CURRENT _ SENSE _ THRESHOLD
RSENSE
The current sense pins VIN (pin 8) and CSL (pin 4) are noise
sensitive due to the low signal level, high input impedance
and input ripple voltage. The PCB traces should be short and
routed close to each other. A 0.1µF capacitor across the pins
will attenuate high frequency switching noise.
When the peak inductor current exceeds the current limit
threshold, the overcurrent comparator turns off the high-side
MOSFET for the remainder of the switching cycle, effectively
decreasing the duty cycle. The output voltage drops as
additional load current is pulled from the converter. When the
voltage at the feedback pin (FB) reaches approximately 0.3V,
the circuit enters frequency foldback mode and the oscillator
frequency will drop to 1/4 of the switching frequency. This
limits the maximum output power delivered to the load under
a short circuit condition.
Reference, Enable and UVLO Circuits
The output drivers are enabled when the following conditions
are satisfied:
• The VDD voltage (pin 5) is greater than its
undervoltage threshold.
• The voltage on the enable pin (pin 3) is greater
than the enable UVLO threshold.
The enable pin (pin 3) has two threshold levels, allowing the
MIC2194 to shut down in a low current mode, or turn off output
switching in standby mode. An enable pin voltage lower than
the shutdown threshold turns off all the internal circuitry and
places the MIC2194 in a micropower shutdown mode.
If the enable pin voltage is between the shutdown and
standby thresholds, the internal bias, VDD and reference
voltages are turned on. The output drivers are inhibited from
switching. The OUTP pin is in a high state. Raising the enable
voltage above the standby threshold enables the output
driver. The standby threshold is specified in the electrical
characteristics. A resistor divider can be used with the enable
pin to prevent the power supply from turning on until a
specified input voltage is reached. The circuit in Figure 3
shows how to connect the resistors.
VIN
Switching
Converter
MIN _ CURRENT _ SENSE _ THRESHOLD
IOUT _ MAX
7
MIC2194
MIC2194
Micrel
MOSFET Selection
The P-channel MOSFET must have a VGS threshold voltage
equal to or lower than the input voltage when used in a buck
converter topology. There is a limit to the maximum gate
charge the MIC2194 will drive. MOSFETs with high gate
charge will have slower turn-on and turn-off times. Slower
transition times will cause higher power dissipation in the
MOSFET due to higher switching transition losses.
The MOSFET gate charge is also limited by power dissipation
in the MIC2194. The power dissipated by the gate drive
circuitry is calculated below:
PGATE_DRIVE = QGATE × VIN × fS
where: QGATE is the total gate charge of both the N- and Pchannel MOSFETs.
fS is the switching frequency
VIN is the gate drive voltage
The graph in Figure 4 shows the total gate charge that can be
driven by the MIC2194 over the input voltage range, for
different values of switching frequency.
MIC2194
VIN
1.5V
Typical
R1
R2
Bias
Circuitry
EN/UVLO
(3)
140mV
Hysteresis
(typical)
Figure 3. UVLO Circuitry
The line voltage turn on trip point is:
VINPUT _ ENABLE = VTHRESHOLD ×
R2
R1 + R2
where:
VTHRESHOLD is the voltage level of the internal
comparator reference, typically 1.5V.
The input voltage hysteresis is equal to:
VINPUT _ HYST = VHYST ×
R1 + R2
R2
Max Gate Charge
MAMIMUM GATE CHARGE (nC)
where:
VHYST is the internal comparator hysteresis level,
typically 140mV.
VINPUT_HYST is the hysteresis at the input voltage
The MIC2194 will be disabled when the input voltage drops
back down to:
VINPUT_OFF =
VINPUT_ENABLE – VINPUT_HYST =
R2
(VTHRESHOLD – VHYST) ×
R1 + R2
Either of 2 UVLO conditions will pull the soft start capacitor
low:
• When the VDD voltage drops below its
undervoltage lockout level.
• When the enable pin drops below the its enable
threshold
The internal bias circuit generates an internal 1.245V bandgap reference voltage for the voltage error amplifier and a 3V
VDD voltage for the internal control circuitry. The VDD pin
must be decoupled with a 1µF ceramic capacitor. The capacitor must be placed close to the VDD pin. The other end of the
capacitor must be connected directly to the ground plane.
MOSFET Gate Drive
The MIC2194 is designed to drive a high-side P-channel
MOSFET. The source pin of the P-channel MOSFET is
connected to the input of the power supply. It is turned on
when OUTP pulls the gate of the MOSFET low. The advantage of using a P-channel MOSFET is that it does not require
a bootstrap circuit to boost the gate voltage higher than the
input, as would be required for an N-channel MOSFET. The
VIN pin (pin 8) supplies the drive voltage to the gate drive pin,
OUTP.
MIC2194
250
200
150
100
50
0
0
5
10
INPUT VOLTAGE (V)
15
Figure 4. MIC2194 VIN vs Max. Gate Charge
Oscillator
The internal oscillator is free running and requires no external
components. The maximum duty cycle for both frequencies
is 100%. This is another advantage of using a P-channel
MOSFET for the high-side drive; it can be continuously turned
on.
A frequency foldback mode is enabled if the voltage on the
feedback pin (pin 2) is less than 0.3V. In frequency foldback,
the oscillator frequency is reduced by approximately a factor
of 4. Frequency foldback is used to limit the energy delivered
to the output during a short circuit fault condition.
Voltage Setting Components
The MIC2194 requires two resistors to set the output voltage
as shown in Figure 5.
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April 2005
MIC2194
Micrel
Under heavy output loads the significant contributors to
power loss are (in approximate order of magnitude):
• Resistive on time losses in the MOSFET
• Switching transition losses in the MOSFET
• Inductor resistive losses
• Current sense resistor losses
• Input capacitor resistive losses (due to the capacitors
ESR)
To minimize power loss under heavy loads:
• Use low on-resistance MOSFETs. Use low threshold
logic level MOSFETs when the input voltage is below
5V. Multiplying the gate charge by the on-resistance
gives a figure of merit, providing a good balance
between low load and high load efficiency.
• Slow transition times and oscillations on the voltage
and current waveforms dissipate more power during
the turn on and turn off of the MOSFET. A clean
layout will minimize parasitic inductance and capacitance in the gate drive and high current paths. This
will allow the fastest transition times and waveforms
without oscillations. Low gate charge MOSFETs will
transition faster than those with higher gate charge
requirements.
• For the same size inductor, a lower value will have
fewer turns and therefore, lower winding resistance.
However, using too small of a value will require more
output capacitors to filter the output ripple, which will
force a smaller bandwidth, slower transient response
and possible instability under certain conditions.
• Lowering the current sense resistor value will decrease the power dissipated in the resistor. However,
it will also increase the overcurrent limit and will
require larger MOSFETs and inductor components.
• Use low ESR input capacitors to minimize the power
dissipated in the capacitors ESR.
VOUT
MIC2194
Voltage
Amplifier
R1
Pin 2
R2
VREF
1.245V
Figure 5
The output voltage is determined by:
R1
R2
Where: VREF for the MIC2194 is typically 1.245V.
Lower values of R1 are preferred to prevent noise from
appearing on the FB pin. A typically recommended value is
10kΩ. If R1 is too small in value it will decrease the efficiency
of the power supply, especially at low output loads.
Once R1 is selected, R2 can be calculated with the following
formula:
VOUT = VREF × 1 +
R2=
VREF × R1
VOUT – VREF
Efficiency Considerations
Efficiency is the ratio of output power to input power. The
difference is dissipated as heat in the buck converter. Under
light output load, the significant contributors are:
• The VIN supply current, which includes the current
required to switch the external MOSFET.
• Core losses in the output inductor.
To maximize efficiency at light loads:
• Use a low gate charge MOSFET or use the smallest
MOSFET, which is still adequate for maximum output
current.
• Use a ferrite material for the inductor core, which has
less core loss than an MPP or iron power core.
April 2005
9
MIC2194
MIC2194
Micrel
Package Information
0.026 (0.65)
MAX)
PIN 1
0.157 (3.99)
0.150 (3.81)
DIMENSIONS:
INCHES (MM)
0.020 (0.51)
0.013 (0.33)
0.050 (1.27)
TYP
0.064 (1.63)
0.045 (1.14)
45°
0.0098 (0.249)
0.0040 (0.102)
0.197 (5.0)
0.189 (4.8)
0°–8°
SEATING
PLANE
0.010 (0.25)
0.007 (0.18)
0.050 (1.27)
0.016 (0.40)
0.244 (6.20)
0.228 (5.79)
8-Pin SOP (M)
MICREL, INC. 1849 FORTUNE DRIVE SAN JOSE, CA 95131
TEL
+ 1 (408) 944-0800
FAX
+ 1 (408) 944-0970
WEB
USA
http://www.micrel.com
The information furnished by Micrel in this datasheet 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 at Purchaser’s own risk and Purchaser agrees to fully indemnify
Micrel for any damages resulting from such use or sale.
© 2005 Micrel, Incorporated.
MIC2194
10
April 2005