®
RT2660
6A, 6V, Synchronous Step-Down Converter with REFIN
General Description
The RT2660 in thermally enhanced VQFN-20L 3.5x4
package is a full featured 6V, 6A synchronous step-down
DC/DC converter designed specifically for Double Data
Rate (DDR) memory termination, which provides a
continuous 6A sink and source current and fixed 1/2 DDQ
at output. The current mode COT architecture with
external compensation allows the transient response to
be optimized over a wide range of loads and achieves
nearly constant switching frequency over line, load, and
output voltage ranges. The multiple sets of over-current
limit and switching frequency offer an optimized power
chain for application design.
Efficiency is maximized through the integrated 20mΩ/
10mΩ MOSFETs, and cycle-by-cycle current limit provides
protection against shorted outputs. Output external
tracking function, output soft discharge, power good
indicating, output droop support are all featured in the
RT2660. In addition, the device is specified from 0°C to
85°C to perform an excellent regulation with an accurate
1% reference voltage over temperature.
Features
Continuous 6A Sink or Source Output Current ability
and Droop Design for DDR Memory Termination
Applications
Low R
DS(ON)
Power N-MOSFET Switches 20mΩ/
Ω
10mΩ
Ω
Input Voltage Range : 1V to 6V
Output Adjustable from 0.6V to 2V
Current-Mode Constant On-Time Control Design
Enables Fast Transient Response
Supports All MLCC Output Capacitor and SP/
POSCAP with Robust Loop Stabilization
Selectable 600kHz or 1MHz Switching Frequency
Supports Pre-Biased Start-Up
Selectable Over-Current Protection
Various Operation Mode Selection for Different
Application Requirements
External Tracking Start-Up Application
Enable Input Control and Power Good Indicator
Under-Voltage and Over-Voltage Protection
Applications
DDR-2/3/4 VTT Regulation (1/2V
DDQ
) for Enterprise
Servers, Ethernet Switches and Routers, Global Storage,
GSM Base Station, and Industrial equipments
Enterprise POL (using precision internal VREF)
Simplified Application Circuit
V
IN
VIN
C
IN
EN
MODE
C
COMP
COMP
VREF
C
REF
R2
R1
REFIN
PGOOD
PGND
GND
BOOT
RT2660
SW
C
BOOT
L
C
OUT
VOUT
V5IN
C
V5IN
R
PGOOD
PGOOD
V
V5IN
V
OUT
Enable
Mode
R
COMP
Copyright
©
2015 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
DS2660-00
September 2015
www.richtek.com
1
RT2660
Ordering Information
RT2660
Package Type
QV : VQFN-20L 3.5x4 (V-Type)
Lead Plating System
G : Green (Halogen Free and Pb Free)
L : Latched OVP and UVP
H : OVP Non-latch, UVP Hiccup
Note :
Richtek products are :
½
Pin Configurations
(TOP VIEW)
V5IN
PGOOD
MODE
EN
BOOT
20 19 18 17 16
PGND
PGND
PGND
VIN
VIN
1
2
3
4
5
6
7
8
9
21
10
15
14
PGND
13
12
11
SW
SW
SW
SW
SW
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.
½
VQFN-20L 3.5x4
Marking Information
RT2660HGQV
05= : Product Code
RT2660LGQV
04= : Product Code
YMDNN : Date Code
05=YM
DNN
04=YM
DNN
YMDNN : Date Code
Functional Pin Description
Pin No.
1, 2, 3,
21 (Exposed Pad)
4, 5
6
7
8
9
10
11 to 15
16
Pin Name
PGND
VIN
GND
VREF
COMP
REFIN
VOUT
SW
BOOT
Pin Function
Power Ground. Provide the ground return path for the low-side power MOSFET
and positive input of an internal amplifier for current sensing circuit. The
exposed pad must be soldered to a large PCB and connected to PGND for
minimum power dissipation.
Power Input. Supplies the power switches of the device.
Signal Ground. Provides the return path for control circuitry and internal
reference.
Reference Output. A specified 2V reference output is supplied by internal linear
regulator. Decouple with a 0.22F capacitor between this pin and GND.
Compensation Node. The current comparator threshold increases with this
control voltage. Connect external compensation elements between this pin and
VREF pin to stabilize the control loop.
Reference Input. The output voltage is targeted by reference input, which is
applied from 0.6V to 2V.
Output Voltage Monitor Node. A negative input of the gm error amplifier and it
is allowed to be a discharge path if any protection is triggered.
Switch Node. SW is the switching node that supplies power to the output and
connect the output LC filter from SW to the output load.
Bootstrap Supply for High-Side Gate Driver. Connect a 100nF or greater
capacitor from SW to BOOT to power the high-side switch.
is a registered trademark of Richtek Technology Corporation.
Copyright
©
2015 Richtek Technology Corporation. All rights reserved.
GND
VREF
COMP
REFIN
VOUT
www.richtek.com
2
DS2660-00
September 2015
RT2660
Pin No.
17
18
Pin Name
EN
MODE
Pin Function
Enable Control Input. Floating this pin or connecting this pin to logic high can
enable the device and connecting this pin to GND can disable the device.
Mode Selection Node. There are 8 modes in RT2660. Connect the specified
resistance to GND for selecting different modes of switching frequencies, OC
limit thresholds, and light-load operations.
Power Good Indicator Output. This pin is an open-drain logic output that is
pulled to ground when the output voltage is lower or higher than its specified
threshold under the conditions of OVP, OTP, dropout, EN shutdown, or during
slow start.
Fixed 5V Supply Voltage Input. Supplies the control circuitry and internal
reference of the device.
19
PGOOD
20
V5IN
Function Block Diagram
V
REFIN
+ 16%
V
REFIN
- 30%
+
UV
-
V
REFIN
- 16%
+
-
Delay
+
V
REFIN
+ 20%
VS
Amplifier
+
OV
-
-
15µA
UVP
OVP
Ramp
Comp
+
PWM
-
Current Sense
Amplifier
VBG
8R
+
OC
-
t
ON
One-
Shot
V5IN
DRVL
PGND
Discharge
GND
XCON
SW
Control Logic
On/Off Time
Minimum On/Off
SKIP/ODA/FPWM
OCL/OVP/UVP
Discharge
On-Time
Selection
MODE
BOOT
VIN
PGOOD
COMP
REFIN
EN
VREF
VOUT
-
+
+
SS
DAC
DRVH
+
-
R
SW
Current
Sense
ZC Threshold
Modulation
-
ZC
+
Copyright
©
2015 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
DS2660-00
September 2015
www.richtek.com
3
RT2660
Operation
The RT2660 is a synchronous low voltage step-down
converter that can support the V5IN range from 4.5V to
5.5V and the output current can be up to 6A. The RT2660
uses a constant on-time, current mode architecture. In
steady-state operation, the high-side N-MOSFET is turned
on when the current feedback reaches COMP level which
is the amplified difference between the reference voltage
and the feedback voltage.
The switching frequency of 600kHz or 1000kHz allows for
efficiency and size optimization when selecting the output
filter components. The switching frequency is set using
the mode pin.
The RT2660 reduces the external component count by
integrating the boot recharge MOSFET. The bias voltage
for the integrated high-side MOSFET is supplied by a
capacitor between the BOOT and SW pins. The boot
capacitor voltage is monitored by an BOOT detection circuit
and turns off the high-side MOSFET when the voltage falls
below a threshold voltage.
The SS pin is used to minimize inrush currents or provide
power supply sequencing during power up. A small value
capacitor should be coupled to the pin for slow start. The
SS pin is discharged before the output power up to ensure
a repeatable restart after an over-temperature fault, UVLO
fault or disable condition.
The error amplifier EA adjusts COMP voltage by comparing
the output voltage to the REFIN voltage. When the load
increases, it causes a drop in the feedback voltage relative
to the reference, then the COMP voltage rises to allow
higher inductor current to match the load current.
Bootstrap Voltage (Boot) and Low Dropout Operation
The RT2660 has an integrated boot regulator and requires
a small ceramic capacitor between the BOOT and SW
pins to provide the gate drive voltage for the high-side
MOSFET. The value of the ceramic capacitor should be
0.1μF. A ceramic capacitor with an X7R or X5R grade
dielectric with a voltage rating of 10V or higher is
recommended because of the stable characteristics over
temperature and voltage. When the BOOT voltage is lower
than the threshold voltage, low-side MOSFET turns on
Copyright
©
2015 Richtek Technology Corporation. All rights reserved.
and built-in bootstrap MOSFET will recharge the BOOT
capacitor. The high-side MOSFET is always turned off
when BOOT voltage is lower than threshold voltage.
PWM Frequency and Adaptive On-Time Control
The on-time can be roughly estimated by the equation :
T
ON
=
V
OUT
1
V
IN
f
SW
Error Amplifier
The RT2660 has a transconductance amplifier. The error
amplifier compares the V
OUT
voltage to the REFIN voltage
The REFIN voltage can comes from external power source
or taps off the voltage divider from the 2V VREF. The
transconductance of the error amplifier is 1000μA/V during
normal operation. The frequency compensation
components are placed between the COMP pin and
ground.
Auto-Zero Current Detector
The auto-zero current detector circuit senses the SW
waveform to adjust the zero current threshold voltage.
When the current of low-side MOSFET decreases to the
zero current threshold, the low-side MOSFET turns off to
prevent negative inductor current. In this way, the zero
current threshold can adjust for different conditions to get
better efficiency.
Protection Features
The RT2660 has many features to protect the device.
Under-Voltage Protection (UVLO)
The RT2660 continuously monitors the voltage on the V5IN
pin to ensure that the voltage level is high enough to bias
the device properly and to provide sufficient gate drive
potential to maintain high efficiency. The converter starts
with approximately 4.3V and has a nominal hysteresis of
440mV. If the 5V UVLO limit is reached, the converter
transitions the phase node into an off function. And the
converter remains in the off state until the device is reset
by cycling 5V until the 5V POR is reached (2.3V nominal).
The power input does not have an UVLO function.
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
4
DS2660-00
September 2015
RT2660
Power Good
The RT2660 has one open-drain power good (PGOOD)
pin. The PGOOD pin de-asserts as soon as the EN pin is
pulled low or an under-voltage condition on V5IN or any
other fault is detected.
Output Over-Voltage Protection (OVP)
In addition to the power good function described above,
the RT2660 has additional OVP and UVP thresholds and
protection circuits.
An OVP condition is detected when the output voltage is
approximately 120% x V
REFIN
. In this case, the converter
de-asserts the PGOOD signals and performs the over-
voltage protection function. During OVP, the low-side
MOSFET is always on before triggering a negative over-
current. When a negative OC is also tripped, the low-side
MOSFET is no longer continuously on, and pulsed signals
are generated to limit the negative inductor current.
For RT2660L OVP latch mode, when the VOUT pin voltage
drops below 400mV, the low-side MOSFET is turned off
and the converter latches off. The converter remains in
the off state until the device is reset by cycling 5V until
the 5V POR is reached or when the EN pin is toggled off
and on.
For RT2660H OVP non-latch, when the VOUT pin voltage
drops below 400mV, the low-side MOSFET is turned off
(non-latch), recovery until the VOUT pin voltage exceeds
400mV again.
Output Under-Voltage Protection (UVP)
Output under-voltage protection works in conjunction with
the current protection described in the over-current
protection and over-current limit sections. If the output
voltage drops below 68% of V
REFIN
, after approximately a
256μs delay, the device stops switching and enters UVP.
For RT2660L UVP latch mode, the device stop switching
and enter latch mode. The converter remain in the off state
until the device is reset by VIN or EN.
For RT2660H UVP hiccup mode, the device stops
switching and enters hiccup mode. After a hiccup waiting
time, a re-start is attempted. If the fault condition is not
cleared, hiccup mode operation may continue indefinitely.
Copyright
©
2015 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
Over-Current Protection (OCP)
Both positive and negative over-current protection are
provided in the RT2660 :
½
Over-Current Limit (OCL)
RT2660 has cycle-by-cycle over current limiting
protection. The inductor current is monitored during the
low-side MOSFET turning on. When the inductor current
is larger than the over current trip level, the high-side
MOSFET turns off until the current drops below the OCL
limit. Because RT2660 uses a valley current limiting
scheme, the average output current limit calculation is
valley OCL trip level plus half of the inductor ripple
current.
½
Negative OCL
The negative OCL circuit acts when the converter is
sinking current from the output capacitor(s). The
converter continues to act in a valley mode, the absolute
value of the negative OCL set point is typically
−9.3A
or
−7.3A
(depending on mode selection).
Over-Temperature Protection (OTP)
The RT2660 has an over-temperature protection. When
the device triggers the OTP, the device shuts down. Until
the temperature drops below the low temperature
threshold, the OTP relieves and the device re-soft starts.
DS2660-00
September 2015
www.richtek.com
5
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