Page 1
MIC2193 Micrel
V
IN
3.3V
0.012Ω
Si9803
(×2)
3.8µH
2k
120µF
6.3V
(×2)
2.2nF
MIC2193BM
VIN
VDDCSOUTP
GND
COMP OUTN
FB
V
OUT
1.8V, 5A
Si9804
(×2)
22.6k
10k
220µF
6.3V
(×2)
1µF
MIC2193
400kHz SO-8 Synchronous Buck Control IC
General Description
Micrel’s MIC2193 is a high efficiency, PWM synchronous
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 MIC2193 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 MIC2193 can implement allceramic capacitor solutions.
The MIC2193 drives a high-side P-channel MOSFET, eliminating the need for high-side boot-strap circuitry. This feature
allows the MIC2193 to achieve maximum duty cycles of
100%, which can be useful in low headroom applications. A
low output driver impedance of 4Ω allows the MIC2193 to
drive large external MOSFETs to generate a wide range of
output currents.
The MIC2193 is available in an 8 pin SOIC package with a
junction temperature range of –40°C to +125°C.
Features
• 2.9V to 14V input voltage range
• 400kHz oscillator frequency
• PWM current mode control
• 100% maximum duty cycle
• Front edge blanking
• 4Ω output drivers
• Cycle-by-cycle current limiting
• Frequency foldback short circuit protection
• 8 lead SOIC package
Applications
• Point of load power supplies
• Distributed power systems
• Wireless Modems
• ADSL line cards
• Servers
• Step down conversion in 3.3V, 5V, and 12V systems
• 1-and 2-cell Li Ion battery operated equipment
T ypical Application
Adjustable Output Synchronous Buck Converter
Micrel, Inc. • 1849 Fortune Drive • San Jose, CA 95131 • USA • tel + 1 (408) 944-0800 • fax + 1 (408) 474-1000 • http://www.micrel.com
April 2004 1 M9999-042704
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MIC2193 Micrel
Ordering Information
Part Number Voltage Frequency Temperature Range Package Lead Finish
MIC2193BM Adjustable 400KHz –40°C to +125°C 8-lead SOP Standard
MIC2193YM Adjustable 400KHz –40°C to +125°C 8-lead SOP Pb-Free
Pin Configuration
COMP
FB
CS
Pin Description
Pin Number Pin Name Pin Function
1 VIN Controller supply voltage. Also the (+) input to the current sense amp.
2 COMP Compensation (Output): Internal error amplifier output. Connect to a
3 FB Feedback Input: The circuit regulates this pin to 1.245V.
4 CS The (–) input to the current limit comparator. A built in offset of 110mV
5 VDD 3V internal linear-regulator output. VDD is also the supply voltage bus for the
6 GND Ground.
7 OUTN High current drive for the synchronous N-channel MOSFET. Voltage swing
8 OUTP High current drive for the high side P-channel MOSFET. Voltage swing is
1VIN
2
3
4
8 OUTP
OUTN
7
GND
6
VDD
5
8 Lead SOIC (M)
capacitor or series RC network to compensate the regulator’s control loop.
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.
chip. Bypass to GND with 1µF.
is from ground to VIN. On-resistance is typically 6Ω at 5VIN.
from ground to VIN. On-resistance is typically 6Ω at 5VIN.
M9999-042704 2 April 2004
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MIC2193 Micrel
Absolute Maximum Ratings (Note 1)
Supply Voltage (V
Digital Supply Voltage (VDD) ...........................................7V
Comp Pin Voltage (V
Feedback Pin Voltage (VFB) .......................... –0.3V to +3V
) .....................................................15V
IN
)............................ –0.3V to +3V
COMP
Operating Ratings (Note 2)
Supply Voltage (V
Junction Temperature ....................... –40°C ≤ TJ ≤ +125°C
Package Thermal Resistance
θJA 8-lead SOP .................................................140°C/W
) .................................... +2.9V to +14V
IN
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
Electrical Characteristics
VIN = 5V, V
Parameter Condition Min Typ Max Units
Regulation
Feedback Voltage Reference (1%) 1.233 1.245 1.257 V
Feedback Bias Current 50 nA
Output Voltage Line Regulation 5V ≤ VIN ≤12V 0.09 % / V
Output Voltage Load Regulation 0mV < (VIN – VCS) < 75mV 0.9 %
Output Voltage Total Regulation 5V ≤VIN ≤12V, 0mV < (VIN – VCS) < 75mV (±3%) 1.208 1.282 V
Input & VDD Supply
VIN Input Current (IQ) (excluding external MOSFET gate current) 1 2 mA
Digital Supply Voltage (VDD)I
Digital Supply Load Regulation IL = 0 to 1mA 0.1 V
Undervoltage Lockout VDD upper threshold (turn on threshold) 2.65 V
UVLO Hysteresis 100 mV
Current Limit
Current Limit Threshold Voltage V
Error Amplifier
Error Amplifier Gain 20 V/V
Current Amplifier
Current Amplifier Gain 3.0 V/V
Oscillator Section
Oscillator Frequency (fO) 360 400 440 kHz
Maximum Duty Cycle VFB = 1.0V 100 %
Minimum On Time VFB = 1.5V 165 ns
Frequency Foldback Threshold Measured on FB 0.3 V
Frequency Foldback Frequency 90 kHz
= 3.3V, TJ = 25°C, unless otherwise specified. Bold values indicate –40°C<TJ<+125°C.
OUT
(2%) 1.22 1.245 1.27 V
= 0 2.82 3.0 3.18 V
L
– VCS voltage to trip current limit 90 110 130 mV
IN
April 2004 3 M9999-042704
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MIC2193 Micrel
Parameter Condition Min Typ Max Units
Gate Drivers
Rise/Fall Time CL = 3300pF 50 ns
Output Driver Impedance Source, VIN = 12V 4 10 Ω
Sink, VIN = 12V 4 10 Ω
= 5V 6 12 Ω
IN
Driver Non-overlap Time V
Source, V
Sink, VIN = 5V 6 12 Ω
= 12V 50 ns
IN
= 5V 80 ns
V
IN
VIN = 3.3V 160 ns
Note 1. Absolute maximum ratings indicate limits beyond which damage to the component may occur. Electrical specifications do not apply when
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.
operating the device outside of its operating ratings. The maximum allowable power dissipation is a function of the maximum junction
temperature, T
, the junction-to-ambient thermal resistance, θJA, and the ambient temperature, TA.
J(Max)
M9999-042704 4 April 2004
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MIC2193 Micrel
2.80
2.85
2.90
2.95
3.00
3.05
3.10
3.15
051015
V
DD
(V)
INPUT VOLTAGE (V)
VDDvs. Input Voltage
1.200
1.210
1.220
1.230
1.240
1.250
1.260
1.270
1.280
1.290
1.300
-40 -20 0 20 40 60 80 100 120
REFERENCE VOLTAGE (V)
TEMPERATURE (°C)
Reference Voltage
vs. Temperature
VIN = 5V
90
95
100
105
110
115
120
125
130
02468101214
CURRENT LIMIT THRESHOLD (mV)
INPUT VOLTAGE (V)
Overcurrent Threshold
vs. Input Voltage
0
2
4
6
8
10
12
14
051015
IMPEDANCE (Ω)
INPUT VOLTAGE (V)
OUTN Drive Impedance vs.
Input Voltage
Source (Ω)
Sink (Ω)
Typical Characteristics
Quiescent Current
vs. Supply Voltage
6
5
4
3
2
1
QUIESCENT CURRENT (mA)
0
0 5 10 15
SUPPLY VOLTAGE (V)
VDDvs. Load
0 0.2 0.4 0.6 0.8 1 1.2
VDD LOAD CURRENT (mA)
(V)
V
3.10
3.08
3.06
3.04
3.02
3.00
DD
2.98
2.96
2.94
2.92
2.90
VIN = 12V
VIN =5V
VIN = 3.3V
Quiescent Current
vs. Temperature
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
QUIESCENT CURRENT (mA)
0
-40 -20 0 20 40 60 80 100 120
TEMPERATURE (°C)
VDDvs. Temperature
3.50
3.40
3.30
3.20
3.10
3.00
2.90
VDD (V)
2.80
2.70
2.60
2.50
-40 -20 0 20 40 60 80 100 120
TEMPERATURE (°C)
VIN = 5V
VIN = 5V
2.5
2.0
1.5
1.0
0.5
0
-0.5
-1.0
-1.5
FREQUENCY VARIATION (%)
-2.0
0 5 10 15
Current Limit Threshold
120
115
110
105
100
April 2004 5 M9999-042704
95
90
85
80
CURRENT LIMIT THREHOLD (mV)
-40 -20 0 20 40 60 80 100 120
Switching Frequency
vs. Input Voltage
INPUT VOLTAGE (V)
vs. Temperature
VIN = 5V
TEMPERATURE (°C)
Switching Frequency
vs. Temperature
5
0
-5
-10
-15
FREQUENCY VARIATION (%)
-20
-40 -20 0 20 40 60 80 100 120
TEMPERATURE (°C)
OUTN Drive Impedance
vs. Input Voltage
14.0
12.0
10.0
8.0
6.0
4.0
IMPEDANCE (Ω)
2.0
0.0
02468101214
INPUT VOLTAGE (V)
VIN = 5V
Source (Ω)
Sink (Ω)
Page 6
MIC2193 Micrel
Functional Diagram
V
IN
VDD 5
C
DECOUP
VDD
VIN
BIAS
C
IN
1
OVERCURRENT
VREF
1.245V
ON
COMPARATOR
CURRENT
SENSE
AMP
VIN
GAIN
R
SENSE
3
CSL4
COMP
fs/4
OSC
COMPARATOR
2
CONTROL
RESET
SLOPE
COMPENSATION
PWM
100k
fs/4
∑
gm = 0.0002
gain = 20
FREQUENCY
FOLDBACK
ERROR
AMP
0.3V
OUTP8
OUTN7
V
REF
FB
3
GND6
Q1
Q2
D1
L1
V
OUT
C
OUT
Figure 1. MIC2193 Block Diagram
Functional Characteristics
Controller Overview and Functional Description
The MIC2193 is a BiCMOS, switched mode, synchronous
step down (buck) converter controller. It uses both N- and Pchannel MOSFETs, which allows the controller to operate at
100% duty cycle and eliminates the need for a high-side drive
boot-strap 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 MIC2193 configured as a
synchronous buck converter. At the beginning of the switch-
ing cycle, the 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, R
, is amplified inside the MIC2193 and com-
SENSE
bined 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,
until the synchronous, N-channel MOSFET turns on. The
voltage drop across the MOSFET is less than the forward
voltage drop of the diode, which improves the converter
efficiency. At the end of the switching period, the synchronous MOSFET is turned off and the switching cycle repeats.
M9999-042704 6 April 2004
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MIC2193 Micrel
The MIC2193 controller is broken down into five functions.
• Control loop
- PWM operation
- Current mode control
• Current limit
• Reference and V
DD
• MOSFET gate drive
• Oscillator
Control Loop
PWM Control Loop
The MIC2193 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.
V
IN
Switching
Converter
Switch
Driver
I
INDUCTOR
V
ERROR
t
ON
t
PER
V
ERROR
D = tON/t
PER
I
INDUCTOR
V
REF
V
OUT
Voltage
Divider
Figure 2. Current Mode Control Example
As shown in Figure 1, the inductor current is sensed by
measuring the voltage across the resistor, R
SENSE
. 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.
Current Limit
The output current is detected by the voltage drop across the
external current sense resistor (R
in Figure 1.). The
SENSE
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:
MIN CURRENT SENSE THRESHOLD
R
SENSE
___
=
I
_
OUT MAX
The maximum output current is:
MAX CURRENT SENSE THRESHOLD
I
OUT MAX
_
___
=
R
SENSE
The current sense pins VIN (pin 1) and CSL (pin 4) are noise
sensitive due to the low signal level and high input impedance
and switching noise on the VIN pin. The PCB traces should
be short and routed close to each other. A 10nF 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 approximately 1/4 of the switching
frequency. This limits the maximum output power delivered to
the load under a short circuit condition.
Reference and V
Circuits
DD
The output drivers are enabled when the VDD voltage (pin 5)
is greater than its undervoltage 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 MIC2193 is designed to drive a high-side, P-Channel
MOSFET and a low side, N-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 required a bootstrap circuit to boost the gate
voltage higher than the input, as would be required for an Nchannel MOSFET.
The VIN pin (pin 1) supplies the drive voltage to both gate
drive pins, OUTN and OUTP. The VIN pin must be well
decoupled to prevent noise from affecting the current sense
circuit, which uses VIN as one of the sense pins.
A non-overlap time is built into the MOSFET driver circuitry.
This dead time prevents the high-side and low-side MOSFET
drivers from being on at the same time. Either an external
diode or the low-side MOSFET internal parasitic diode conducts the inductor current during the dead time.
April 2004 7 M9999-042704
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MIC2193 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 MIC2193 will drive. MOSFETs with higher gate
charge will have slower turn-on and turn-off times. Slower
transition times will cause higher power dissipation in the
MOSFETs due to higher switching transition losses. The
MOSFETs must be able to completely turn on and off within
the driver non-overlap time If both MOSFETs are conducting
at the same time, shoot-through will occur, which greatly
increases power dissipation in the MOSFETs and reduces
converter efficiency.
The MOSFET gate charge is also limited by power dissipation
in the MIC2193. The power dissipated by the gate drive
circuitry is calculated below:
P
GATE_DRIVE
= Q
GATE
× VIN × f
S
where:
Q
is the total gate charge of both the N and P-
GATE
channel MOSFETs.
fS is the switching frequency
VIN is the gate drive voltage
The graph in Figure 3 shows the total gate charge that can be
driven by the MIC2193 over the input voltage range, for
different values of switching frequency.
Max. Gate Charge
100
90
80
70
60
50
40
30
20
10
MAXIMUM GATE CHARGE (nC)
0
02468101214
INPUT VOLTAGE (V)
Figure 3. MIC2193 Frequency vs Max. Gate Charge
Oscillator
The internal oscillator is free running and requires no external
components. The maximum duty cycle is 100%. This is
another advantage of using a P-channel MOSFET for the
high-side drive: it can continuously turned on.
A frequency foldback mode is enabled if the voltage on the
feedback pin (pin 3) 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 MIC2193 requires two resistors to set the output voltage
as shown in Figure 4.
V
MIC2193
Voltage
Amplifier
V
1.245V
Pin 3
REF
OUT
R1
R2
Figure 4
The output voltage is determined by the equation below.
R
VV
OUT
Where: V
=×+1
REF
for the MIC2193 is typically 1.245V.
REF
1
R
2
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.
VR
×
R
REF
21=
VV
–
OUT
REF
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
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.
Under heavy output loads the significant contributors to
power loss are (in approximate order of magnitude):
• Resistive on time losses in the MOSFETs
• Switching transition losses in the high side 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 MOSFETs. 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
M9999-042704 8 April 2004
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MIC2193 Micrel
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 de
crease 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.
April 2004 9 M9999-042704
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MIC2193 Micrel
Package Information
0.026 (0.65)
MAX)
PIN 1
0.157 (3.99)
0.150 (3.81)
0.050 (1.27)
0.064 (1.63)
0.045 (1.14)
TYP
0.197 (5.0)
0.189 (4.8)
DIMENSIONS:
INCHES (MM)
0.020 (0.51)
0.013 (0.33)
0.0098 (0.249)
0.0040 (0.102)
0°–8°
SEATING
PLANE
8-Pin SOIC (M)
45°
0.050 (1.27)
0.016 (0.40)
0.244 (6.20)
0.228 (5.79)
0.010 (0.25)
0.007 (0.18)
MICREL, INC. 1849 FORTUNE DRIVE SAN JOSE, CA 95131 USA
TEL + 1 (408) 944-0800 FAX + 1 (408) 474-1000 WEB http://www.micrel.com
The 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 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
M9999-042704 10 April 2004
Micrel reserves the right to change circuitry and specifications at any time without notification to the customer.
Micrel for any damages resulting from such use or sale.
© 2004 Micrel, Incorporated.
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