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PDF MP8670 Data sheet ( Hoja de datos )
| Número de pieza | MP8670 | |
| Descripción | 420KHz Step-Down Converter | |
| Fabricantes | MPS | |
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The Future of Analog IC Technology
MP8670
6A, 30V, 420KHz Step-Down Converter
with Synchronizable Gate Driver
DESCRIPTION
The MP8670 is a monolithic step-down switch
mode converter with a built-in internal power
MOSFET. It achieves 6A continuous output
current over a wide input supply range with
excellent load and line regulation.
Current mode operation provides fast transient
response and reliable over-current protection.
The MP8670 requires a minimum number of
readily available standard external components
and is available in an 8-pin SOIC package with
exposed pad.
FEATURES
• Wide 4.5V to 30V Operating Input Range
• 6A Continuous Output Current
• 50mΩ Internal Power MOSFET Switch
• Synchronizable Gate Driver Delivers up to
95% Efficiency
• Fixed 420KHz Frequency
• Synchronizable up to 1.5MHz
• Cycle-by-Cycle Over Current Protection
• Thermal Shutdown
• Output Adjustable from 0.8V
• Stable with Low ESR Output Ceramic
Capacitors
• Available in a Thermally Enhanced 8-Pin
SOIC Package
APPLICATIONS
• Digital Set Top Boxes
• Personal Video Recorders
• Broadband Communications
• Flat Panel Television and Monitors
“MPS” and “The Future of Analog IC Technology” are Registered Trademarks of
Monolithic Power Systems, Inc.
MP8670 Rev. 1.3
4/4/2011
www.MonolithicPower.com
MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited.
© 2011 MPS. All Rights Reserved.
1
1 page  
MP8670 – 6A, 30V, 420KHZ STEP-DOWN WITH SYNCHRONIZABLE GATE DRIVER
PIN FUNCTIONS
Pin #
1
2
3
4
5
6
7
8
Name Description
SW Switch Output.
BST
Bootstrap. This capacitor is needed to drive the power switch’s gate above the supply
voltage. It is connected between SW and BST pin to form a floating supply across the
power switch driver.
VCC BG Driver Bias Supply. Decouple with a 1µF ceramic capacitor.
BG Gate Driver Output. Connect this pin to the gate of the synchronous MOSFET.
GND
Ground. This pin is the voltage reference for the regulated output voltage. For this reason
care must be taken in its layout. This node should be placed outside of the M2 to C1 ground
path to prevent switching current spikes from inducing voltage noise into the part.
Feedback. An external resistor divider from the output to GND, tapped to the FB pin sets
FB
the output voltage. To prevent current limit run away during a short circuit fault condition,
the frequency foldback comparator lowers the oscillator frequency when the FB voltage is
below 250mV.
EN/SYNC On/Off Control and External Frequency Synchronization Input.
IN
Supply Voltage. The MP8670 operates from a +4.5V to +30V unregulated input. C1 is
needed to prevent large voltage spikes from appearing at the input.
MP8670 Rev. 1.3
4/4/2011
www.MonolithicPower.com
MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited.
© 2011 MPS. All Rights Reserved.
5
5 Page 
MP8670 – 6A, 30V, 420KHZ STEP-DOWN WITH SYNCHRONIZABLE GATE DRIVER
Enable/Synch Control
The MP8670 has a dedicated Enable/Synch
control pin (EN/SYNC). By pulling it high or low,
the IC can be enabled and disabled by EN. Tie
EN to VIN for automatic start up. To disable the
part, EN must be pulled low for at least 5µs.
The MP8670 can be synchronized to external
clock range from 300KHz up to 1.5MHz through
the EN/SYNC pin. The internal clock rising
edge is synchronized to the external clock rising
edge.
Under-Voltage Lockout (UVLO)
Under-voltage lockout (UVLO) is implemented
to protect the chip from operating at insufficient
supply voltage. The MP8670 UVLO comparator
monitors the output voltage of the internal
regulator, VCC. The UVLO rising threshold is
about 4.0V while its falling threshold is a
consistent 3.2V.
Internal Soft-Start
The soft-start is implemented to prevent the
converter output voltage from overshooting
during startup. When the chip starts, the
internal circuitry generates a soft-start voltage
(SS) ramping up from 0V to 1.2V. When it is
lower than the internal reference (REF), SS
overrides REF so the error amplifier uses SS as
the reference. When SS is higher than REF,
REF regains control.
Over-Current-Protection and Hiccup
The MP8670 has cycle-by-cycle over current
limit when the inductor current peak value
exceeds the set current limit threshold.
Meanwhile, output voltage starts to drop until
FB is below the Under-Voltage(UV) threshold,
typically 30% below the reference. Once a UV
is triggered, the MP8670 enters hiccup mode to
periodically restart the part. This protection
mode is especially useful when the output is
dead-short to ground. The average short circuit
current is greatly reduced to alleviate the
thermal issue and to protect the regulator. The
MP8670 exits the hiccup mode once the over
current condition is removed.
Thermal Shutdown
Thermal shutdown is implemented to prevent
the chip from operating at exceedingly high
temperatures. When the silicon die temperature
is higher than 150°C, it shuts down the whole
chip. When the temperature is lower than its
lower threshold, typically 140°C, the chip is
enabled again.
Floating Driver and Bootstrap Charging
The floating power MOSFET driver is powered
by an external bootstrap capacitor. This floating
driver has its own UVLO protection. This
UVLO’s rising threshold is 2.2V with a
hysteresis of 150mV. The bootstrap capacitor
voltage is regulated internally by VIN through D1,
M3, C4, L1 and C2 (Figure 2). If (VIN-VSW) is
more than 5V, U2 will regulate M3 to maintain a
5V BST voltage across C4.
D1
VIN
5V
+
--
+
U2
--
M3
BST
C4
SW L1
VOUT
C2
Figure 2—Internal Bootstrap Charging Circuit
Startup and Shutdown
If both VIN and EN are higher than their
appropriate thresholds, the chip starts. The
reference block starts first, generating stable
reference voltage and currents, and then the
internal regulator is enabled. The regulator
provides stable supply for the remaining
circuitries.
Three events can shut down the chip: EN low,
VIN low and thermal shutdown. In the shutdown
procedure, the signaling path is first blocked to
avoid any fault triggering. The COMP voltage
and the internal supply rail are then pulled
down. The floating driver is not subject to this
shutdown command.
MP8670 Rev. 1.3
4/4/2011
www.MonolithicPower.com
MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited.
© 2011 MPS. All Rights Reserved.
11
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| Páginas | Total 15 Páginas | |
| PDF Descargar | [ Datasheet MP8670.PDF ] | |
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