MIC28500
75V/4A Hyper Speed Control™
Synchronous DC-DC Buck Regulator
SuperSwitcher II™
General Description
The Micrel MIC28500 is an adjustable frequency,
synchronous buck regulator featuring a unique adaptive on-
time control architecture. The MIC28500 operates over an
input supply range of 30V to 75V and provides a regulated
output of up to 4A of output current. The output voltage is
adjustable down to 0.8V with a guaranteed accuracy of ±1%.
Micrel’s Hyper Speed Control™ architecture allows for ultra-
fast transient response while reducing the output capacitance
and also makes (High V
IN
)/(Low V
OUT
) operation possible.
This adaptive t
ON
ripple control architecture combines the
advantages of fixed-frequency operation and fast transient
response in a single device.
The MIC28500 offers a full suite of protection features to
ensure protection of the IC during fault conditions. These
include undervoltage lockout to ensure proper operation
under power-sag conditions, internal soft-start to reduce
inrush current, foldback current limit, “hiccup” mode short-
circuit protection and thermal shutdown.
All support documentation can be found on Micrel’s web
site at:
www.micrel.com.
Features
•
Hyper Speed Control™ architecture enables
-High
Delta V operation (V
IN
= 75V and V
OUT
= 0.8V)
-Small
output capacitance
30V to 75V voltage input
Adjustable output down to 0.8V
±1% FB accuracy
Any Capacitor™ Stable
-
Zero-ESR to high-ESR output capacitors
4A output current capability, up to 90% efficiency
100kHz to 500kHz switching frequency
Internal compensation
Foldback current-limit and “hiccup” mode short-circuit
protection
Thermal shutdown
Supports safe startup into a pre-biased load
–40°C to +125°C junction temperature range
28-pin 5mm
×
6mm MLF
®
package
•
•
•
•
•
•
•
•
•
•
•
•
Applications
•
Distributed power systems
•
Communications/networking infrastructure
•
Set-top box, gateways and routers
•
Printers, scanners, graphic cards and video cards
___________________________________________________________________________________________________________
Typical Application
Efficiency (V
IN
= 48V)
vs. Output Current
100
90
80
EFFICIENCY (%)
70
60
50
40
30
20
10
0
1
2
3
4
5
6
OUTPUT CURRENT (A)
f
SW
= 250kHz
5.0V
3.3V
2.5V
1.8V
1.5V
1.2V
1.0V
0.8V
Hyper Speed Control, SuperSwitcher II and Any Capacitor are trademarks of Micrel, Inc.
MLF and
MicroLeadFrame
are registered 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
June 2011
M9999-060311-B
Micrel, Inc.
MIC28500
Ordering Information
Part Number
MIC28500YJL
Voltage
Adjustable
Switching Frequency
Adjustable
Junction Temperature Range
−40°C
to
+125°C
Package
28-pin 5mm
×
6mm MLF
®
Lead Finish
Pb-Free
Pin Configuration
28-Pin 5mm
×
6mm MLF
®
(YJL)
Pin Description
Pin
Number
13, 14, 15,
16, 17, 18,
19
Pin Name
Pin Function
High-Side internal N-channel MOSFET Drain Connection (Input): The PVIN operating voltage range
is from 30V to 75V. Input capacitors between the PVIN pins and the power ground (PGND) are
required and keep the connection short. Enabling the device below 30V VIN and under maximum
loading could heat up the device beyond safe operating conditions.
Enable (Input): A logic level control of the output. The EN pin is CMOS-compatible. Logic high or
floating = enable, logic low = shutdown. In the off state, the V
DD
supply current of the device is
reduced (typically 0.7mA). Do not pull the EN pin above the V
DD
supply. Enabling the device below
30V VIN and under maximum loading could heat up the device beyond safe operating conditions.
Feedback (Input): Input to the transconductance amplifier of the control loop. The FB pin is regulated
to 0.8V. A resistor divider connecting the feedback to the output is used to adjust the desired output
voltage.
Signal ground. SGND must be connected directly to the ground planes. Do not route the SGND pin to
the PGND Pad on the top layer, see PCB layout guidelines for details.
VDD Bias (Input): Power to the internal reference and control sections of the MIC28500. The VDD
operating voltage range is from 4.5V to 5.5V. A 2.2µF ceramic capacitor from the VDD pin to the
PGND pin must be placed next to the IC. VDD must be powered up at the same time or after PVIN to
make the soft-start function correctly.
Power Ground. PGND is the ground path for the MIC28500 buck converter power stage. The PGND
pin connects to the sources of low-side N-Channel internal MOSFETs, the negative terminals of input
capacitors, and the negative terminals of output capacitors. The loop for the power ground should be
as small as possible and separate from the signal ground (SGND) loop.
Current Sense (Input): High current output driver return. The CS pin connects directly to the switch
node. Due to the high-speed switching on this pin, the CS pin should be routed away from sensitive
nodes. CS pin also senses the current by monitoring the voltage across the low-side internal
MOSFET during OFF-time.
PVIN
24
EN
25
26
FB
SGND
27
VDD
2, 5, 6, 7,
8, 21
PGND
22
CS
June 2011
2
M9999-060311-B
Micrel, Inc.
MIC28500
Pin Description (Continued)
Pin
Number
20
4, 9, 10,
11, 12
23
28
1, 3
Pin Name
BST
SW
FS
PVDD
NC
Pin Function
Boost (Output): Bootstrapped voltage to the high-side N-channel internal MOSFET driver. A Schottky
diode is connected between the VDD pin and the BST pin. A boost capacitor of 0.1μF is connected
between the BST pin and the SW pin.
Switch Node (Output): Internal connection for the high-side MOSFET source and low-side MOSFET
drain.
Frequency Setting Pin.
Power Supply for gate driver of bottom MOSFET.
No Connect.
June 2011
3
M9999-060311-B
Micrel, Inc.
MIC28500
Absolute Maximum Ratings
(1, 2)
PV
IN
to PGND................................................
−0.3V
to +76V
FS to PGND ....................................................−0.3V to PV
IN
PV
DD
, V
DD
to PGND .........................................
−0.3V
to +6V
V
SW
, V
CS
to PGND ..............................
−0.3V
to (PV
IN
+0.3V)
V
BST
to V
SW
........................................................
−0.3V
to 6V
V
BST
to PGND ..................................................
−0.3V
to 82V
V
EN
to PGND ......................................
−0.3V
to (V
DD
+ 0.3V)
V
FB
to PGND.......................................
−0.3V
to (V
DD
+ 0.3V)
PGND to SGND ...........................................
−0.3V
to +0.3V
Junction Temperature .............................................. +150°C
Storage Temperature (T
S
).........................−65°C to +150°C
Lead Temperature (soldering, 10sec)........................ 260°C
Operating Ratings
(3)
Supply Voltage (PV
IN
) ........................................ 30V to 75V
Bias Voltage (PV
DD
, V
DD
).................................. 4.5V to 5.5V
Enable Input (V
EN
) ................................................. 0V to V
DD
Junction Temperature (T
J
) ........................
−40°C
to +125°C
Maximum Power Dissipation......................................Note 4
Package Thermal Resistance
(4)
5mm x 6mm MLF
®
(θ
JA
) ....................................36°C/W
Electrical Characteristics
(5)
PV
IN
= V
FS
= 48V, V
DD
= 5V; V
BST
– V
SW
= 5V; T
A
= 25°C, unless noted.
Bold
values indicate
−40°C
≤
T
J
≤
+125°C.
Parameter
Power Supply Input
Input Voltage Range ( PV
IN
)
FS Voltage Range
V
DD
Bias Voltage
Operating Bias Voltage (V
DD
)
Under-Voltage Lockout Trip Level
UVLO Hysteresis
Quiescent Supply Current (I
VDD
)
Shutdown Supply Current (I
VDD
)
Reference
Feedback Reference Voltage
Load Regulation
Line Regulation
FB Bias Current
Enable Control
EN Logic Level High
EN Logic Level Low
EN Bias Current
Notes:
1. Exceeding the absolute maximum rating may damage the device.
2. Devices are ESD sensitive. Handling precautions recommended. Human body model, 1.5kΩ in series with 100pF.
3. The device is not guaranteed to function outside operating range.
4. PD
(MAX)
= (T
J(MAX)
– T
A
)/
θ
JA
, where
θ
JA
depends upon the printed circuit layout. See “Applications Information.”
5. Specification for packaged product only.
Condition
Min.
Typ.
Max.
Units
30
2
4.5
V
DD
Rising
V
FB
= 1.5V
V
DD
= V
BST
= 5.5V, V
IN
= 48V
SW = unconnected, V
EN
= 0V
0°C
≤
T
J
≤
85°C (±1.0%)
−40°C
≤
T
J
≤
125°C (±1.5%)
I
OUT
= 0A to 4A
PV
IN
= 30 to 75V
V
FB
= 0.8V
4.5V < V
DD
< 5.5V
4.5V < V
DD
< 5.5V
V
EN
= 0V
-0.5
1.2
0.792
0.788
0.8
0.8
0.04
0.1
0.005
0.85
0.78
50
3.2
5
3.85
380
1.4
0.7
75
75
5.5
4.45
3
2
V
V
V
V
mV
mA
mA
0.808
0.812
V
%
%
0.5
µA
V
0.4
100
V
µA
June 2011
4
M9999-060311-B
Micrel, Inc.
MIC28500
Electrical Characteristics
(5)
(Continued)
PV
IN
= V
FS
= 48V, V
DD
= 5V; V
BST
– V
SW
= 5V; T
A
= 25°C, unless noted.
Bold
values indicate
−40°C
≤
T
J
≤
+125°C.
Parameter
Oscillator
Switching Frequency
(6)
Maximum Duty Cycle
Minimum Duty Cycle
Minimum Off-time
Soft-Start
Soft-Start time
Short Circuit Protection
Current-Limit Threshold
Short-Circuit Current
Internal FETs
Top-MOSFET R
DS (ON)
Bottom-MOSFET R
DS (ON)
SW Leakage Current
PV
IN
Leakage Current
Thermal Protection
Over-Temperature Shutdown
Over-Temperature Shutdown
Hysteresis
Notes:
6. Measured in test mode.
7. The maximum duty-cycle is limited by the fixed mandatory off-time t
OFF
of typically 360ns.
(7)
Condition
V
FS
=PV
IN
V
FB
= 0V, V
FS
=PV
IN
V
FB
> 0.8V
Min.
375
Typ.
500
82
0
360
6
Max.
625
Units
kHz
%
%
ns
ms
V
FB
= 0.8V, T
J
= 25°C
V
FB
= 0.8V, T
J
= 125°C
V
FB
= 0V
I
SW
= 1A
I
SW
= 1A
PV
IN
= 36V, V
SW
= 36V, V
EN
= 0V, V
BST
= 41V
PV
IN
= 36V, V
SW
= 0V, V
EN
= 0V, V
BST
= 41V
T
J
Rising
5.5
4.2
2
7
5.5
3.6
175
31
9
8.5
5.2
A
A
A
mΩ
mΩ
55
55
160
25
µA
µA
°C
°C
June 2011
5
M9999-060311-B
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