Preliminary
RT8805C
Two Phase General Purpose PWM Controller
General Description
The RT8805C is the most compact dual-phase
synchronous buck controller in the industry specifically
designed for high power density applications. This part is
capable of delivering up to 60A output current due to its
embedded bootstrapped drivers that support 12V + 12V
driving capability.
The phase currents are sensed by innovative time sharing
R
DS(ON)
current sensing technique for current balance and
over current balance. Using one common GM amplifier to
sense two phase currents eliminates offset and
nonlinearity of the GM amplifier and yields good current
balance. Other features include adjustable operation
frequency from 50kHz to 1MHz, adjustable soft-start,
PGOOD, external compensation, enable/shutdown for
various application and performance consideration.
The RT8805C comes to a tiny footprint package of
VQFN-16L 3x3 and VQFN-24L 4x4 packages.
Features
12V Power Supply Voltage
2 Phase Power Conversion
Embedded 12V Boot Strapped Driver
Precise Core Voltage Regulation
Low Side MOSFET R
DS(ON)
Current Sensing for
Power Stage Current Balance
External Compensation
Adjustable Soft-Start
Adjustable Frequency and Typical at 300kHz Per
Phase
Power Good Indication
Adjustable Over Current Protection
External Reference Voltage Tracking (RT8805CxQVA)
Small 16-Lead and 24-Lead VQFN Packages
RoHS Compliant and 100% Lead (Pb)-Free
Applications
Middle-High End GPU Core Power
High End Desktop PC Memory Core Power
Low Output Voltage, High Power Density DC-DC
Converters
Voltage Regulator Modules
Ordering Information
RT8805C
Package Type
QV : VQFN-16L 3x3 (V-Type)
QVA : VQFN-24L 4x4 (V-Type)
Operating Temperature Range
P : Pb Free with Commercial Standard
G : Green (Halogen Free with Commer-
cial Standard)
Marking Information
For marking information, contact our sales representative
directly or through a Richtek distributor located in your
area, otherwise visit our website for detail.
Note :
Richtek Pb-free and Green products are :
RoHS compliant and compatible with the current require-
ments of IPC/JEDEC J-STD-020.
Suitable for use in SnPb or Pb-free soldering processes.
100% matte tin (Sn) plating.
DS8805C-03 August 2007
www.richtek.com
1
Preliminary
Functional Pin Description
Pin No.
VQFN-16L 3x3
16
12
1
11
2
10
3
4
--
5
Exposed Pad (17)
6
7
8
VQFN-24L 4x4
1
19
2
18
3
17
4
5
6, 8, 9, 10, 24
7
Pin Name
PHASE1
PHASE2
UGATE1
UGATE2
BOOT1
BOOT2
AGND
IMAX
NC
RT
Pin Function
RT8805C
These pins are return nodes of the high-side driver. Connect
These pins to high-side MOSFET sources together with the
low-side MOSFET drains and the inductors.
Upper Gate Drive. These pins drive the gates of the high
side MOSFETs.
Bootstrap Power Pin. These pins power the high-side
MOSFET drivers. Connect These pins to the junctions of the
bootstrap capacitors.
Chip Analog Ground.
Maximum Current Setting. This pin sets the current limiting
level. Connect this pin with resistor to ground to set the
current limit.
No Internal Connection.
Timing Resistor. Connect a resistor from RT to AGND to set
the clock frequency.
The exposed pad must be soldered to a large PCB and
connected to GND for maximum power dissipation.
Soft-Start Pin. This pin provides soft-start function for
controller. The COMP voltage of the converter follows the
ramping voltage on the SS pin.
Compensation Pin. This pin is output node of the error
amplifier.
Feedback Pin. This pin is negative input pin of the error
amplifier.
Power Good. PGOOD is an open drain output used to
indicate the status of the voltages on SS pin and FB pin.
PGOOD will go high impedance when SS > 3.7V and FB >
0.6V.
Lower Gate Drive. These pins drive the gate of the lowside
MOSFETs.
The VCC pin is the external 12V power. Internal 5V power
(V
DD
) is regulated from this pin. This pin also powers the low
side MOSFET drivers.
External reference voltage pin. This pin sets the voltage of
FB pin when close loop.
11,
GND
Exposed Pad (25)
12
13
14
SS
COMP
FB
9
15
13
14
--
16
23
20
21, 22
15
PGOOD
LGATE1
LGATE2
VCC
PI
DS8805C-03 August 2007
www.richtek.com
5
Power technology
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