Very high efficiency SimpleSync
TM
converter.
FEATURES
> 95% Efficiency
Fixed frequency (adjustable) PWM
Voltage mode to ensure excellent stability &
transient response
Low quiescent current in shutdown mode,15
A
Low battery flag
Output down to 2.0V
Overload protection
Demonstration boards available
Synchronous or non-synchronous operation
Cost effective solution
N or P channel MOSFETs
QSOP16 package
Fixed 3.3, 5V and adjustable outputs
Programmable soft start
APPLICATIONS
High efficiency 5 to 3.3V converters up to 4A
Sub-notebook computers
Embedded processor power supply
Distributed power supply
Portable instruments
Local on card conversion
GPS systems
DESCRIPTION
The ZXRD1000 series provides complete control and
protection functions for a high efficiency (> 95%) DC-DC
converter solution. The choice of external MOSFETs allow
the designer to size devices according to application. The
ZXRD1000 series uses advanced DC-DC converter
techniques to provide synchronous drive capability, using
innovative circuits that allow easy and cost effective
implementation of shoot through protection. The
ZXRD1000 series can be used with an all N channel
topology or a combination N & P channel topology.
Additional functionality includes shutdown control, a
user adjustable low battery flag and simple
adjustment of the fixed PWM switching frequency.
The controller is available with fixed outputs of 5V or
3.3V and an adjustable (2.0 to 12V) output.
4.5-10V
N1
ZXM64N02X
L1
15H
C6
1F
D1
ZHCS1000
C3
330pF
R3
3k
R1
100k
Fx
C1
1F
0.01R
C7
22F
D3
BAT54
C10
1F
R4
10k
C8
2.2F
68F
C4
1F
C5
1F
x2
680F
R6
10k
R5
6k
Cx2
0.01F
CX1
0.022F
RX
2k7
N2
ZXM64N02X
R2
680R
D2
BAT54
C11
1F
C2
1F
3.3V 4A
C9
1F
120F
V
CC
C
OUT
V
OUT
R
SENSE
13
Bootstrap
V
IN
G
ND
G
ND
PWR
LB
SET
Decoup
R
SENSE+
R
SENSE -
V
FB
C
T
LBF
SHDN
V
INT
Delay
Comp
V
DRIVE
2
1
7
8
16
15
3
4
6
5
10
14
11
9
C
IN
Low input flag
Shut Down
IC1
HIGH EFFICIENCY SIMPLESYNC
PWM DC-DC CONTROLLERS
1
ZXRD1000 SERIES
ISSUE 4 - OCTOBER 2000
ABSOLUTE MAXIMUM RATINGS
Input without bootstrap (P suffix)
20V
Input with bootstrap(N suffix)
10V
Bootstrap voltage
20V
Shutdown pin
V
IN
LB
SET
pin
V
IN
R
SENSE
+, R
SENSE -
V
IN
Power dissipation
610mW (Note 4)
Operating temperature
-40 to +85C
Storage temperature
-55 to +125C
2
ELECTRICAL CHARACTERISTICS
TEST CONDITIONS (Unless otherwise stated) T
amb
=25C
Symbol
Parameter
Conditions
Min
Typ
Max
Unit
V
IN(min)
Min. Operating Voltage
No Output Device
4.5
V
V
FB
(Note 1)
Feedback Voltage
V
IN
=5V,I
FB
=1mA
1.215
1.24
1.265
V
4.5<V
IN
<18V
1.213
1.24
1.267
V
50
A<I
FB
<1mA,V
IN
=5V 1.215
1.24
1.265
V
T
DRIVE
Gate Output Drive Capability
C
G
=2200pF(Note 2)
C
G
=1000pF
V
IN
=4.5V to maximim
supply (Note 3)
60
35
ns
ns
I
CC
Supply Current
V
IN
=5V
16
20
mA
Shutdown Current
V
SHDN
= 0V;V
IN
=5V
15
50
A
f
osc
(Note 5)
Operating frequency range
Frequency with timing capacitor C3=1300pF
C
3
=330pF
50
50
200
300
kHz
f
osc(tol)
Oscillator Tol.
25
%
DC
MAX
Max Duty Cycle
N Channel
P Channel
15
0
94
100
%
%
V
RSENSE
R
SENSE
voltage differential
-40 to +85C
50
mV
V
CMRSENSE
Common mode range of V
RSENSE
-40 to +85C
2
V
IN
V
LBF
SET
Low Battery Flag set voltage
1.5
V
IN
V
LBF
OUT
Low Battery Flag output
Active Low
0.2
0.4
V
LBF
HYST
Low Battery Flag Hysteresis
10
20
50
mV
LBF
SINK
Low Battery Flag Sink Current
-40 to +85C
2
mA
V
SHDN
Shutdown Threshold Voltage
Low(off)
High(on)
1.5
0.25
V
V
I
SHDN
Shutdown Pin Source Current
10
A
ISSUE 4 - OCTOBER 2000
Note 1. V
FB
has a different function between fixed and adjustable controller options.
Note 2. 2200pF is the maximum recommended gate capacitance.
Note 3. Maximum supply for P phase controllers is 18V,maximum supply for N phase controllers is 10V.
Note 4. See V
IN
derating graph in Typical Characteristics.
Note 5. The maximum frequency in this application is 300kHz. For higher frequency operation contact Zetex
Applications Department.
ZXRD1000 SERIES
DETAILED DESCRIPTION
The ZXRD1000 series can be configured to use either
N or P channel MOSFETs to suit most applications.
The most popular f ormat , an a ll N channel
synchronous solution gives the optimum efficiency. A
feature of the ZXRD1000 series solution is the unique
method of generating the synchronous drive, called
SimpleSync
. Most solutions use an additional
output from the controller, inverted and delayed from
the main switch drive. The ZXRD1000 series solution
uses a simple overwinding on the main choke (wound
on the same core at no real cost penalty) plus a small
ferrite bead . This means that the synchronous FET is
only enhanced when the main FET is turned off. This
reduces the `blanking period' required for shoot-
through protection, increasing efficiency and allowing
smaller catch diodes to be used, making the controller
simpler and less costly by avoiding complex timing
circuitry. Included on chip are numerous functions that
allow flexibility to suit most applications. The nominal
switching frequency (200kHz) can be adjusted by a
simple timing capacitor, C3. A low battery detect circuit
is also provided. Off the shelf components are available
from major manufacturers such as Sumida to provide
either a single winding inductor for non-synchronous
applications or a coil with an over-winding for
synchronous applications. The combination of these
switching characteristics, innovative circuit design and
excellent user flexibility, make the ZXRD1000 series
DC-DC solutions some of the smallest and most cost
effective and electrically efficient currently available.
Using Zetex's HDMOS low R
DS(on)
devices, ZXM64N02X
for the main and synchronous switch, efficiency can
peak at upto 95% and remains high over a wide range
of operating currents. Programmable soft start can also be
adjusted via the capacitor, C7, in the compensation loop.
What is SimpleSync
TM
?
Conventional Methods
In the conventional approach to the synchronous
DC-DC solution, much care has to be taken with the
timing constraints between the main and synchronous
switching devices. Not only is this dependent upon
individual MOSFET gate thresholds (which vary from
device to device within data sheet limits and over
temperature), but it is also somewhat dependent upon
magnetics, layout and other parasitics. This normally
means that significant `dead time' has to be factored
in to the design between the main and synchronous
devices being turned off and on respectively.
Incorrect application of dead time constraints can
potentially lead to catastrophic short circuit conditions
between V
IN
and G
ND
. For some battery operated
systems this can not only damage MOSFETs, but also
the battery itself. To realise correct `dead time'
implementation takes complex circuitry and hence
implies additional cost.
The ZETEX Method
Zetex has taken a different approach to solving these
problems. By looking at the basic architecture of a
synchronous converter, a novel approach using the
main circuit inductor was developed. By taking the
inverse waveform found at the input to the main
i n d u c t o r o f a n o n - s y n c h r o n o u s s o l u t i on , a
synchronous drive waveform can be generated that is
always relative to the main drive waveform and
inverted with a small delay. This waveform can be
used to drive the synchronous switch which means no
complex circuitry in the IC need be used to allow for
shoot-through protection.
Implementation
Implementation was very easy and low cost. It simply
meant peeling off a strand of the main inductor
winding and isolating it to form a coupled secondary
winding. These are available as standard items
referred to in the applications circuits parts list.The use
of a small, surface mount, inexpensive 'square loop'
ferrite bead provides an excellent method of
eliminating shoot-through due to variation in gate
thresholds. The bead essentially acts as a high
i mp e da n c e f o r t he f e w na n o s e c o nd s t ha t
shoot-through would normally occur. It saturates very
quickly as the MOSFETs attain steady state operation,
reducing the bead impedance to virtually zero.
Benefits
The net result is an innovative solution that gives
a d d i t i o n a l b e n e f i t s w h i l s t l o w e r i n g o v e ra l l
implementation costs. It is also a technique that can
be simply omitted to make a non-synchronous
controller, saving further cost, at the expense of a few
efficiency points.
5
ZXRD1000 SERIES
ISSUE 4 - OCTOBER 2000
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