SRK2001
Adaptive synchronous rectification controller for LLC resonant
converter
Datasheet
-
production data
80+/85+ compliant ATX SMPS
90+/92+ compliant SERVER SMPS
Industrial SMPS
SSOP10
Description
The SRK2001 controller implements a control
scheme specific for secondary side synchronous
rectification in LLC resonant converters that use a
transformer with center tap secondary winding for
full wave rectification.
It provides two high current gate drive outputs,
each capable of driving one or more N-channel
power MOSFETs. Each gate driver is controlled
separately and an interlock logic circuit prevents
the two synchronous rectifier MOSFETs from
conducting simultaneously.
The control scheme in this IC provides for each
synchronous rectifier being switched on as the
corresponding half-winding starts conducting and
switched off as its current goes to zero.
The innovative turn-on logic with adaptive
masking time and the adaptive turn-off logic
allows maximizing the conduction time of the SR
MOSFETs eliminating the need of the parasitic
inductance compensation circuit.
The low consumption mode of the device allows
to meet the most stringent requirement for
converter power consumption in light-load/no load
conditions.
A noticeable feature is the very low external
component count required.
Table 1. Ordering codes
Package
SSOP10
Packing
Tube
Tape and reel
Standard gate MOSFETs
SRK2001
SRK2001TR
Features
Secondary side synchronous rectification
controller optimized for LLC resonant converter
Dual gate driver for N-channel MOSFETs
Adaptive turn-off logic
Turn-on logic with adaptive masking time
Auto-compensation of parasitic inductance
Low consumption mode: 50 µA quiescent
current
V
CC
operating voltage range 4.5 to 32 V
High voltage drain-to-source Kelvin sensing for
each SR MOSFET
Operating frequency up to 500 kHz
35 ns total delay at turn-off
Protection against current reversal
Safe management of load transient, light-load
and startup conditions
Intelligent automatic sleep mode at light-load
with user programmable enter/exit load levels,
with soft transitions and function disable
Programmable exit load levels from burst mode
Compatible with standard level MOSFETs
SSOP10 package
Applications
AC-DC adapters
All-in -one PC
High-end flat panel TV
February 2017
This is information on a product in full production.
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Contents
SRK2001
Contents
1
2
3
4
5
Block diagrams and pin connections . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Typical application schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Electrical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Operation description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
5.1
5.2
5.3
5.4
5.5
5.6
5.7
Drain voltage sensing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Turn-on . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Turn-off . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11
ZCD comparator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Gate drive . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Intelligent automatic sleep mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
EN and PROG pins: function and usage . . . . . . . . . . . . . . . . . . . . . . . . . 14
5.7.1
5.7.2
Automatic sleep mode function enabled . . . . . . . . . . . . . . . . . . . . . . . . 15
Automatic sleep mode function disabled . . . . . . . . . . . . . . . . . . . . . . . . 15
5.8
Layout guidelines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
6
Package information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
6.1
SSOP10 package information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
7
Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
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Block diagrams and pin connections
1
Block diagrams and pin connections
Figure 1. Internal block diagram
Figure 2. Typical system block diagram
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Block diagrams and pin connections
Figure 3. Pin connections (top view)
SRK2001
Table 2. Pin functions
No.
1
Name
VCC
Function
Supply voltage of the device. A bypass capacitor to GND, located as close to IC's pins as possible,
helps to get a clean supply voltage for the internal control circuitry and acts as an effective energy
buffer for the pulsed gate drive currents.
Return of the device bias current and return of the gate drive currents. Route this pin to the common
point where the source terminals of both synchronous rectifier MOSFETs are connected.
Gate driver output for section 1 (2). Each totem pole output stage is able to drive power MOSFETs
with high peak current levels. To avoid excessive gate voltages in case the device is supplied with
a high V
CC
, the high level voltage of these pins is clamped to about 11 V. The pin has to be
connected directly to the SR MOSFET gate terminal.
2
GND
3
(8)
GD1
(GD2)
4
(7)
5
(6)
Source voltage sensing for section 1 (2): it is the reference voltage of the corresponding drain
SVS1
sensing signal on the DVS1, 2 pin. These pins have to be connected directly to the respective source
(SVS2)
terminals of the corresponding synchronous rectifier MOSFET.
Drain voltage sensing for section 1 (2). These pins have to be connected to the respective drain
DVS1
terminals of the corresponding synchronous rectifier MOSFET using a series resistor at least of
(DVS2)
100
.
Programming pin for conduction duty cycle at sleep mode entering/exiting. A resistor connected from
this pin to GND, supplied by an internal precise current source, sets a voltage V
PROG
; depending on
this voltage level, during the startup phase, the user can chose, according to the application
PROG
requirements, the proper sleep mode or burst mode exiting the conduction duty cycle among the
ones contained into two internal lookup tables (the values are predefined inside
Table 6 on page 15,
Table 7 on page 15
and
Table 8 on page 16).
See
Table 5
or the proper choice of resistor value.
Enable pin function with internal pull-up and current source capability:
– Automatic sleep mode function enable/disable: the sleep mode is disabled if the pin voltage is
detected above an internal threshold (V
SM_off
) during the startup phase.
– Remote ON/OFF: during run the mode, when the pin voltage is sensed below the internal
threshold V
EN_OFF
, the controller stops operating and enters a low consumption state; it resumes
the operation if the pin voltage surpasses the threshold V
EN_ON
.
– During the startup phase, the pin voltage level allows to select the predefined conduction duty
cycle for sleep mode entering. A resistor connected from this pin to GND, supplied by an internal
precise current source allows the user for this choice (two predefined values). See the
Table 5
for
the proper choice of resistor value.
9
10
EN
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SRK2001
Maximum ratings
2
Maximum ratings
Table 3. Absolute maximum ratings
Symbol
V
CC
I
CCZ
V
PROG
V
EN
DVS1, 2
SVS1, 2
Pin
1
1
10
9
5, 6
4, 7
DC supply voltage
Internal Zener maximum current (V
CC
= V
CCZ
)
PROG pin voltage rating
EN pin voltage rating
Drain sense voltage referred to source SVS1, 2
Source sense voltage referred to GND
Parameter
Value
-0.3 to V
CCZ
25
-0.3 to 3.3
-0.3 to 3.3
-3 to 90
-3 to 3
Unit
V
mA
V
V
V
V
Stressing the device above the rating listed in
Table 3
may cause permanent damage to the
device. Exposure to absolute maximum rated conditions may affect device reliability.
Table 4. Thermal data
Symbol
R
th j-amb
R
th j-case
P
tot
T
j
T
stg
Parameter
Max. thermal resistance, junction to ambient
(1)
Max thermal resistance, junction to case top
(1)
Power dissipation at T
amb
= 50 °C
Junction temperature operating range
Storage temperature
Value
130
10
0.75
-40 to 150
-55 to 150
Unit
°C/W
°C/W
W
°C
°C
1. With the pin 2 soldered to a dissipating copper area of 25 mm
2
, 35 µm thickness (PCB material FR4
1.6 mm thickness).
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