MIC2198
Micrel, Inc.
MIC2198
500kHz 4mm
×
4mm Synchronous Buck Controller
General Description
The MIC2198 is a high-power 500kHz synchronous buck
DC-to-DC controller housed in a small 4mm
×
4mm MLF™
12-pin package. The MIC2198 operates from a wide 4.5V
to 32V input and can be programmed for output voltages
from 0.8V to 6V. The wide input voltage capability makes
the MIC2198 an ideal solution for point-of-load DC-to-DC
conversion in 5V, 12V and higher systems.
The 500kHz switching frequency allows the use of a small
inductor and small output capacitors. The current mode PWM
control along with the external COMP pin allows for ease of
stability compensation and fast transient response across a
wide range of applications.
An all N-Channel synchronous architecture and powerful
output drivers allow up to 20A of output current capability.
For higher efficiency at higher input voltages, refer to the
300kHz MIC2199.
The MIC2198 is available in a 12-pin 4mm
×
4mm MLF™
package with a junction temperature range from –40°C to
125°C.
Features
•
•
•
•
•
•
•
•
•
•
•
4.5V to 32V input range
4mm
×
4mm MLF™ package
500kHz PWM operation
>90% efficiency
Output voltage adjustable down to 0.8V
20A output current capability
Drives all N-Channel MOSFETs
Logic controlled micropower shutdown
Cycle-by-cycle current limiting
Adjustable undervoltage lockout
Frequency foldback overcurrent protection
Applications
• Point-of-load DC-to-DC conversion from 5V, 12V
and higher supplies
• Telecom equipment
• Wireless modems
• Servers
• Base stations
Typical Application
V
IN
5.5V to 24V
U1 MIC2198BML
22µF
SD103BWS
VIN
VDD
BST
4.7µF
0.1µF
IRF7821
1µH
IRF7821
1nF
10kΩ
6.04kΩ
0.01Ω
EN/UVLO
HSD
VSW
LSD
CSH
V
OUT
3.3V/7A
220µF
COMP
VOUT
FB
GND
2kΩ
2.2nF
100
95
90
85
80
75
70
65
60
55
50
Efficiency
vs. Load Current
V
IN
= 5.5V
V
OUT
= 3.3V
0
2
4
I
LOAD (A)
6
8
5.5V–24V to 3.3V/7A Converter
MLF and MicroLeadFrame are trademarks of Amkor Technology, Inc.
Micrel, Inc. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel + 1 (408) 944-0800 • fax + 1 (408) 474-1000 • http://www.micrel.com
October 2005
1
MIC2198
MIC2198
Micrel, Inc.
Ordering Information
Part Number
Standard
MIC2198BML
Pb-Free
MIC2198YML
Voltage
Adj
Temperature Range
–40ºC to +125ºC
Package
12-Pin 4x4 MLF™
Pin Configuration
COMP
EN/UVLO
FB
CSH
VOUT
VIN
1
2
3
4
5
6
12
11
10
9
8
7
HSD
VSW
BST
GND
LSD
VDD
12-Pin 4×4 MLF (ML)
Pin Description
Pin Number
1
2
Pin Name
COMP
EN/UVLO
Pin Function
Compensation (Output): Internal error amplifier output. Connect to capacitor
or series RC network to compensate the regulator control loop.
Enable/Undervoltage Lockout (Input): Low-level signal powers down the
controller. Input below the 2.5V threshold disables switching and functions as
an accurate undervoltage lockout (UVLO). Input below the threshold forces
complete micropower (<0.1µA) shutdown.
Feedback (Input): Regulates FB pin to 0.8V. See “Applications Information”
for resistor divider calculations.
Current-Sense High (Input): Current limit comparator non-inverting input. A
built-in offset of 75mV between CSH and V
OUT
pins in conjunction with the
current-sense resistor set the current limit threshold level. This is also the
non-inverting input to the current sense amplifier.
Current-Sense Low (Input): Output voltage feedback input and inverting
input for the current limit comparator and the current sense amplifier.
Unregulated Input (Input): +4.5V to +32V supply input.
5V Internal Linear-Regulator (Output): V
DD
is the external MOSFET gate
drive supply voltage and internal supply bus for the IC. Bypass to GND with
4.7µF.
Low-Side Drive (Output): High-current driver output for low-side N-Channel
MOSFET. Voltage swing is between ground and V
DD
.
Boost (Input): Provides drive voltage for the high-side MOSFET driver. The
drive voltage is higher than the input voltage by V
DD
minus a diode drop.
Switch (Return): High-side MOSFET driver return.
High-Side Drive (Output): High-current driver output for high-side MOSFET.
This node voltage swing is between ground and V
IN
+5V minus a diode drop.
3
4
FB
CSH
5
6
7
VOUT
VIN
VDD
8
9
10
11
12
LSD
GND
BST
VSW
HSD
Ground (Return).
MIC2198
2
October 2005
MIC2198
Micrel, Inc.
Absolute Maximum Ratings
(Note 1)
Analog Supply Voltage (V
IN
)........................................ +34V
Digital Supply Voltage (V
DD
).......................................... +7V
Driver Supply Voltage (B
ST
) ...................................V
IN
+ 7V
Sense Voltage (V
OUT
, C
SH
) ...............................7V to –0.3V
Enable Pin Voltage (V
EN/UVLO
) ....................................... V
IN
Power Dissipation (P
D
)
4×4 MLF™ ..................................665mW @ T
A
= 85°C
Ambient Storage Temperature (T
S
) .......... –65°C to +150°C
ESD,
Note 3
................................................................ 2kV
Operating Ratings
(Note 2)
Analog Supply Voltage (V
IN
)......................... +4.5V to +32V
Output Voltage Range (V
OUT
) ....................... +0.8V to +6V
Junction Temperature (T
J
) ........................ –40°C to +125°C
Package Thermal Resistance
4×4 MLF-12L (θ
JA
) ............................................... 60°C/W
Electrical Characteristics
(Note 4)
V
IN
= V
EN
= 12V; T
J
= 25°C, unless noted,
bold
values indicate –40°C ≤ T
J
≤ +125°C
Parameter
Condition
Feedback Voltage Reference
Feedback Voltage Reference
Feedback Voltage Reference
Feedback Bias Current
Output Voltage Range
Output Voltage Line Regulation
Output Voltage Load Regulation
Input and V
DD
Supply
Quiescent Current
Shutdown Quiescent Current
Digital Supply Voltage (V
DD
)
Undervoltage Lockout
25mV < (V
CSH
– V
OUT
) < 60mV
V
IN
= 4.5V to 32V, V
CSH
– V
OUT
= 60mV
(±1%)
(±2%)
4.5V < V
IN
< 32V, 0 < (V
CSH
– V
OUT
) < 60mV (±3%)
Min
0.792
0.784
0.776
10
0.8
0.03
0.5
3.5
0.1
4.7
3.95
0.6
2.2
5.0
4.25
4.1
1.1
2.5
0.1
55
75
0.2
450
70
measured at V
OUT
pin
0.25
500
76
150
0.40
125
60
5
3.5
80
8.5
6
200
0.55
550
1.6
2.8
5
95
5
5
5.3
4.4
6
Typ
0.8
Max
0.808
0.816
0.824
Units
V
V
V
nA
V
%/V
%
mA
µA
V
V
V
V
V
µA
mV
mS
kHz
%
ns
V
kHz
ns
Ω
Ω
ns
excluding external MOSFET gate drive current
I
L
= 0mA to 5mA
V
EN/UVLO
= 0V
V
IN
upper threshold (turn-on threshold)
V
IN
lower threshold (turn-off threshold)
Enable/UVLO
Enable Input Threshold
UVLO Threshold
Enable Input Current
Current Limit
Current Limit Threshold Voltage
Error Amplifier
Transconductance Error Amplifier GM
Oscillator Section
Oscillator Frequency
Maximum Duty Cycle
Minimum On-Time
Frequency Foldback Threshold
Foldback Frequency
Gate Drivers
Rise/Fall Time
Output Driver Impedance
Driver Non-Overlap Time
Note 1.
Note 2.
Note 3.
Note 4.
(rising)
(rising)
V
EN/UVLO
= 5V
(V
CSH
– V
OUT
)
C
L
= 3000pF
source
sink
Exceeding the absolute maximum rating may damage the device.
The device is not guaranteed to function outside its operating rating.
Devices are ESD protected; however, handling precautions are recommended. Human body model, 1.5k in series with 100pF.
Specification for packaged product only.
October 2005
3
MIC2198
MIC2198
Micrel, Inc.
Typical Characteristics
(V
IN
= 12V, unless otherwise noted)
Quiescent Current
vs. Temperature
PWM
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0
4
Quiescent Current
vs. Supply Voltage
PWM
0.805
V
FB
Line Regulation
0.800
UVLO
UVLO
0.795
0
-40 -20 02 04 06 08 0 100120140
TEMPERATURE (°C)
Shutdown
Shutdown
9
14 19 24 29 34
SUPPLY VOLTAGE (V)
0.790
0
5
10 15 20 25 30
SUPPLY VOLTAGE (V)
35
0.820
0.815
0.810
0.805
0.800
V
FB
vs. Temperature
6.0
5.0
4.0
3.0
2.0
1.0
0
0
V
DD
Line Regulation
5.02
5.01
5.00
4.99
4.98
4.97
4.96
4.95
4.94
0
V
DD
Load Regulation
0.795
-40 -20 02 04 06 08 0 100120140
TEMPERATURE (°C)
4
8 12 16 20 24 28
32
SUPPLY VOLTAGE (V)
5
10 15 20 25
LOAD CURRENT (mA)
30
V
5.20
5.15
5.10
5.05
5.00
4.95
4.90
4.85
vs. Temperature
DD
10
8
6
4
2
0
-2
-4
-6
-8
Oscillator Frequency
vs. Temperature
0.25
0.20
0.15
0.10
0.05
0.00
-0.05
-0.10
-0.15
0
Oscillator Frequency
vs. Supply Voltage
4.80
-40 -20 02 04 06 08 0 100120140
TEMPERATURE (°C)
-10
-40 -20 02 04 06 08 0 100120140
TEMPERATURE (°C)
5
10 15 20 25 30
SUPPLY VOLTAGE (V)
35
78
76
74
72
70
68
66
Overcurrent Threshold
vs. Temperature
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0
0
Current Limit
Foldback
V
IN
= 5V
V
OUT
= 3.3V
R
CS
= 20mV
64
-40 -20 02 04 06 08 0 100120140
TEMPERATURE (°C)
1
2
3
4
OUTPUT CURRENT (A)
5
MIC2198
4
October 2005
MIC2198
Micrel, Inc.
V
IN
C
IN
Block Diagram
EN/UVLO
2
V
DD
VDD
7
Reference
V
IN
VIN
6
D2
4.7µF
BST
10
Control
Logic
HSD
12
VSW
11
Q2
C
BST
L1
D1
R
CS
V
OUT
C
OUT
LSD
8
PGND
9
Q1
Current
Limit
PWM
RESET
CORRECTIVE
RAMP
Current
Sense
Amp
CSH
4
A
V
= 2
Error
Amp
VOUT
5
Oscillator
COMP
R1
FB
3
C
COMP
R
COMP
1
100k
MIC2198
G
m
= 0.2×10
-3
V
OUT
= 0.8V
1 + R1
R2
V
OUT(max)
= 6.0V
R2
Figure 1. Internal Block Diagram
Functional Description
The MIC2198 is a BiCMOS, switched-mode, synchronous
step-down (buck) converter controller. 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.
The MIC2198 block diagram is shown above.
The MIC2198 controller is divided into 5 functions.
• Control loop
• Current limit
• Reference, enable and UVLO
• MOSFET gate drive
• Oscillator
Control Loop
The MIC2198 operates in PWM (pulse-width-modulation)
mode. In PWM mode, the synchronous buck converter
forces continuous current to flow in the inductor which also
improves cross regulation of transformer coupled, multiple
output configurations.
PWM Control Loop
The MIC2198 uses current-mode control to regulate the output
voltage. This method 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 removes the inductor
from the control loop, which simplifies compensation.
A block diagram of the MIC2198 PWM current-mode control
loop is shown in Figure 2 and the PWM mode voltage and
current waveform is shown in Figure 3. The inductor current
is sensed by measuring the voltage across the resistor, R
CS
.
October 2005
5
MIC2198
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