April 2004
1
M9999-042704
MIC2193
Micrel
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 all-
ceramic capacitor solutions.
The MIC2193 drives a high-side P-channel MOSFET, elimi-
nating 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 4
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.
Typical Application
V
IN
3.3V
0.012
Si9803
(
2)
3.8
H
2k
120
F
6.3V
(
2)
2.2nF
MIC2193BM
VIN
VDD
CS
OUTP
GND
COMP OUTN
FB
V
OUT
1.8V, 5A
Si9804
(
2)
22.6k
10k
220
F
6.3V
(
2)
1
F
Adjustable Output Synchronous Buck Converter
Features
2.9V to 14V input voltage range
400kHz oscillator frequency
PWM current mode control
100% maximum duty cycle
Front edge blanking
4
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
Micrel, Inc. 1849 Fortune Drive San Jose, CA 95131 USA tel + 1 (408) 944-0800 fax + 1 (408) 474-1000 http://www.micrel.com
MIC2193
Micrel
M9999-042704
2
April 2004
Pin Configuration
1
VIN
COMP
FB
CS
8
OUTP
OUTN
GND
VDD
7
6
5
2
3
4
8 Lead SOIC (M)
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
capacitor or series RC network to compensate the regulator's control loop.
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
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 1
F.
6
GND
Ground.
7
OUTN
High current drive for the synchronous N-channel MOSFET. Voltage swing
is from ground to VIN. On-resistance is typically 6
at 5V
IN
.
8
OUTP
High current drive for the high side P-channel MOSFET. Voltage swing is
from ground to VIN. On-resistance is typically 6
at 5V
IN
.
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
April 2004
3
M9999-042704
MIC2193
Micrel
Electrical Characteristics
V
IN
= 5V, V
OUT
= 3.3V, T
J
= 25
C, unless otherwise specified. Bold values indicate 40
C<T
J
<+125
C.
Parameter
Condition
Min
Typ
Max
Units
Regulation
Feedback Voltage Reference
(1%)
1.233
1.245
1.257
V
(2%)
1.22
1.245
1.27
V
Feedback Bias Current
50
nA
Output Voltage Line Regulation
5V
V
IN
12V
0.09
% / V
Output Voltage Load Regulation
0mV < (V
IN
V
CS
) < 75mV
0.9
%
Output Voltage Total Regulation
5V
V
IN
12V, 0mV < (V
IN
V
CS
) < 75mV (
3%)
1.208
1.282
V
Input & V
DD
Supply
V
IN
Input Current (I
Q
)
(excluding external MOSFET gate current)
1
2
mA
Digital Supply Voltage (V
DD
)
I
L
= 0
2.82
3.0
3.18
V
Digital Supply Load Regulation
I
L
= 0 to 1mA
0.1
V
Undervoltage Lockout
V
DD
upper threshold (turn on threshold)
2.65
V
UVLO Hysteresis
100
mV
Current Limit
Current Limit Threshold Voltage
V
IN
V
CS
voltage to trip current limit
90
110
130
mV
Error Amplifier
Error Amplifier Gain
20
V/V
Current Amplifier
Current Amplifier Gain
3.0
V/V
Oscillator Section
Oscillator Frequency (f
O
)
360
400
440
kHz
Maximum Duty Cycle
V
FB
= 1.0V
100
%
Minimum On Time
V
FB
= 1.5V
165
ns
Frequency Foldback Threshold
Measured on FB
0.3
V
Frequency Foldback Frequency
90
kHz
Absolute Maximum Ratings
(Note 1)
Supply Voltage (V
IN
) ..................................................... 15V
Digital Supply Voltage (V
DD
) ........................................... 7V
Comp Pin Voltage (V
COMP
) ............................ 0.3V to +3V
Feedback Pin Voltage (V
FB
) .......................... 0.3V to +3V
Current Sense Voltage (V
IN
V
CS
) ................ 0.3V to +1V
Power Dissipation (P
D
) ..................... 285mW @ T
A
= 85
C
Ambient Storage Temp ............................ 65
C to +150
C
ESD Rating Note 3 ....................................................... 2kV
Operating Ratings
(Note 2)
Supply Voltage (V
IN
) .................................... +2.9V to +14V
Junction Temperature ....................... 40
C
T
J
+125
C
Package Thermal Resistance
JA
8-lead SOP ................................................. 140
C/W
MIC2193
Micrel
M9999-042704
4
April 2004
Parameter
Condition
Min
Typ
Max
Units
Gate Drivers
Rise/Fall Time
C
L
= 3300pF
50
ns
Output Driver Impedance
Source, V
IN
= 12V
4
10
Sink, V
IN
= 12V
4
10
Source, V
IN
= 5V
6
12
Sink, V
IN
= 5V
6
12
Driver Non-overlap Time
V
IN
= 12V
50
ns
V
IN
= 5V
80
ns
V
IN
= 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
operating the device outside of its operating ratings. The maximum allowable power dissipation is a function of the maximum junction
temperature, T
J(Max)
, the junction-to-ambient thermal resistance,
JA
, and the ambient temperature, T
A
.
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, 1.5k
in series with 100pF.
April 2004
5
M9999-042704
MIC2193
Micrel
Typical Characteristics
0
1
2
3
4
5
6
0
5
10
15
QUIESCENT CURRENT (mA)
SUPPLY VOLTAGE (V)
Quiescent Current
vs. Supply Voltage
0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
-40 -20 0
20 40 60 80 100 120
QUIESCENT CURRENT (mA)
TEMPERATURE (
C)
Quiescent Current
vs. Temperature
V
IN
= 5V
2.80
2.85
2.90
2.95
3.00
3.05
3.10
3.15
0
5
10
15
V
DD
(V)
INPUT VOLTAGE (V)
V
DD
vs. Input Voltage
2.90
2.92
2.94
2.96
2.98
3.00
3.02
3.04
3.06
3.08
3.10
0
0.2
0.4
0.6
0.8
1
1.2
V
DD
(V)
V
DD
LOAD CURRENT (mA)
V
DD
vs. Load
V
IN
= 3.3V
V
IN
= 12V
V
IN
= 5V
2.50
2.60
2.70
2.80
2.90
3.00
3.10
3.20
3.30
3.40
3.50
-40 -20 0
20 40 60 80 100 120
VDD (V)
TEMPERATURE (
C)
V
DD
vs. Temperature
V
IN
= 5V
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
V
IN
= 5V
-2.0
-1.5
-1.0
-0.5
0
0.5
1.0
1.5
2.0
2.5
0
5
10
15
FREQUENCY VARIATION (%)
INPUT VOLTAGE (V)
Switching Frequency
vs. Input Voltage
-20
-15
-10
-5
0
5
-40 -20 0
20 40 60 80 100 120
FREQUENCY VARIATION (%)
TEMPERATURE (
C)
Switching Frequency
vs. Temperature
V
IN
= 5V
90
95
100
105
110
115
120
125
130
0
2
4
6
8
10 12 14
CURRENT LIMIT THRESHOLD (mV)
INPUT VOLTAGE (V)
Overcurrent Threshold
vs. Input Voltage
80
85
90
95
100
105
110
115
120
-40 -20 0
20 40 60 80 100 120
CURRENT LIMIT THREHOLD (mV)
TEMPERATURE (
C)
Current Limit Threshold
vs. Temperature
V
IN
= 5V
0.0
2.0
4.0
6.0
8.0
10.0
12.0
14.0
0
2
4
6
8
10 12 14
IMPEDANCE (
)
INPUT VOLTAGE (V)
OUTN Drive Impedance
vs. Input Voltage
Sink (
)
Source (
)
0
2
4
6
8
10
12
14
0
5
10
15
IMPEDANCE (
)
INPUT VOLTAGE (V)
OUTN Drive Impedance vs.
Input Voltage
Source (
)
Sink (
)
MIC2193
Micrel
M9999-042704
6
April 2004
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 P-
channel 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 correc-
tive 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-
Functional Diagram
FREQUENCY
FOLDBACK
ERROR
AMP
PWM
COMPARATOR
OVERCURRENT
COMPARATOR
L1
CURRENT
SENSE
AMP
0.3V
100k
V
REF
gm = 0.0002
gain = 20
fs/4
COMP
ON
GAIN
3
RESET
VREF
1.245V
2
VDD
SLOPE
COMPENSATION
OSC
fs/4
CONTROL
BIAS
VDD
5
CSL
4
VIN
OUTP
8
OUTN
7
Q2
Q1
D1
FB
3
VIN
C
DECOUP
1
C
IN
GND
6
C
OUT
V
OUT
R
SENSE
V
IN
Figure 1. MIC2193 Block Diagram
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
SENSE
, is amplified inside the MIC2193 and com-
bined with an internal ramp for stability. This signal is com-
pared 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 synchro-
nous MOSFET is turned off and the switching cycle repeats.
April 2004
7
M9999-042704
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 compen-
sation.
Switching
Converter
Voltage
Divider
V
REF
V
ERROR
V
ERROR
t
ON
t
PER
D = t
ON
/t
PER
I
INDUCTOR
I
INDUCTOR
Switch
Driver
V
OUT
V
IN
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 opera-
tion 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
SENSE
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:
R
MIN CURRENT
SENSE THRESHOLD
I
SENSE
OUT
MAX
=
_
_
_
_
The maximum output current is:
I
MAX
CURRENT
SENSE THRESHOLD
R
OUT MAX
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
DD
Circuits
The output drivers are enabled when the V
DD
voltage (pin 5)
is greater than its undervoltage threshold.
The internal bias circuit generates an internal 1.245V band-
gap reference voltage for the voltage error amplifier and a 3V
V
DD
voltage for the internal control circuitry. The VDD pin
must be decoupled with a 1
F ceramic capacitor. The capaci-
tor 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 N-
channel 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 con-
ducts the inductor current during the dead time.
MIC2193
Micrel
M9999-042704
8
April 2004
MOSFET Selection
The P-channel MOSFET must have a V
GS
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
V
IN
f
S
where:
Q
GATE
is the total gate charge of both the N and P-
channel MOSFETs.
f
S
is the switching frequency
V
IN
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.
0
10
20
30
40
50
60
70
80
90
100
0
2
4
6
8
10 12 14
MAXIMUM GATE CHARGE (nC)
INPUT VOLTAGE (V)
Max. Gate Charge
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
REF
1.245V
Voltage
Amplifier
Pin 3
MIC2193
V
OUT
R1
R2
Figure 4
The output voltage is determined by the equation below.
V
V
R
R
OUT
REF
=
+
1
1
2
Where: V
REF
for the MIC2193 is typically 1.245V.
Lower values of R1 are preferred to prevent noise from
appearing on the FB pin. A typically recommended value is
10k
. 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.
R
V
R
V
V
REF
OUT
REF
2
1
=
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 V
IN
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 capaci-
tance in the gate drive and high current paths. This
will allow the fastest transition times and waveforms
without oscillations. Low gate charge MOSFETs will
April 2004
9
M9999-042704
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.
MIC2193
Micrel
M9999-042704
10
April 2004
Package Information
45
0
8
0.244 (6.20)
0.228 (5.79)
0.197 (5.0)
0.189 (4.8)
SEATING
PLANE
0.026 (0.65)
MAX
)
0.010 (0.25)
0.007 (0.18)
0.064 (1.63)
0.045 (1.14)
0.0098 (0.249)
0.0040 (0.102)
0.020 (0.51)
0.013 (0.33)
0.157 (3.99)
0.150 (3.81)
0.050 (1.27)
TYP
PIN 1
DIMENSIONS:
INCHES (MM)
0.050 (1.27)
0.016 (0.40)
8-Pin SOIC (M)
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 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.
2004 Micrel, Incorporated.
PDF 
ZIP