ZXRD1000 SERIES
HIGH EFFICIENCY SIMPLESYNC PWM DC-DC CONTROLLERS
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
FEATURES
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> 95% Efficiency
Fixed frequency (adjustable) PWM
Voltage mode to ensure excellent stability &
transient response
Low quiescent current in shutdown mode,15µA
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
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.
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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
Very high efficiency SimpleSync
TM
converter.
V
CC
4.5-10V
D2
BAT54
R1
100k
Shut Down
9
IC1
13
V
IN
V
DRIVE
Bootstrap
2
1
ZXM64N02X
C10
1µF
C11
1µF
C6
1µF
N1
L1
15µH
R
SENSE
V
OUT
3.3V 4A
SHDN
LB
SET
C5
1µF
Low input flag
0.01R
R6
10k
Cx2
0.01µF
C
OUT
11 LBF
14
10
6
5
Delay
Decoup
V
INT
C
T
G
ND
R
SENSE+
7
R
SENSE -
8
V
FB
16
Comp
15
PWR
G
ND
3
C9
1µF
RX
R2 CX1
2k7
680R 0.022µF
R4
10k
D3
BAT54
Fx
D1
C8
2.2µF
ZHCS1000
R5
6k
x2
680µF
120µF
C
IN
68µF
C1
1µF
C2
330pF
1µF
C4
4
1µF C3
C7
22µF
N2
ZXM64N02X
R3
3k
ISSUE 4 - OCTOBER 2000
1
ZXRD1000 SERIES
ABSOLUTE MAXIMUM RATINGS
Input without bootstrap (P suffix)
Input with bootstrap(N suffix)
Bootstrap voltage
20V
Shutdown pin
V
IN
LB
SET
pin
V
IN
20V
10V
R
SENSE
+, R
SENSE -
Power dissipation
Operating temperature
Storage temperature
V
IN
610mW (Note 4)
-40 to +85°C
-55 to +125°C
ELECTRICAL CHARACTERISTICS
TEST CONDITIONS (Unless otherwise stated) T
amb
=25°C
Symbol
V
IN(min)
V
FB
(Note 1)
Parameter
Min. Operating Voltage
Feedback Voltage
Conditions
No Output Device
V
IN
=5V,I
FB
=1mA
4.5<V
IN
<18V
Gate Output Drive Capability
C
G
=2200pF(Note 2)
C
G
=1000pF
V
IN
=4.5V to maximim
supply (Note 3)
V
IN
=5V
V
SHDN
= 0V;V
IN
=5V
50
50
200
±25
N Channel
P Channel
-40 to +85°C
-40 to +85°C
Active Low
10
-40 to +85°C
Low(off)
High(on)
1.5
10
2
1.5
0.2
20
15
0
50
V
IN
V
IN
0.4
50
2
0.25
94
100
%
%
%
mV
V
V
V
mV
mA
V
V
µA
Min
4.5
1.215
1.213
1.24
1.24
1.24
60
35
1.265
1.267
1.265
Typ
Max
Unit
V
V
V
V
ns
ns
50µA<I
FB
<1mA,V
IN
=5V 1.215
T
DRIVE
I
CC
f
osc
(Note 5)
f
osc(tol)
DC
MAX
Supply Current
Shutdown Current
16
15
20
50
300
mA
µA
kHz
Operating frequency range
Frequency with timing capacitor C3=1300pF
C
3
=330pF
Oscillator Tol.
Max Duty Cycle
R
SENSE
voltage differential
Low Battery Flag set voltage
Low Battery Flag output
Low Battery Flag Hysteresis
Low Battery Flag Sink Current
Shutdown Threshold Voltage
Shutdown Pin Source Current
V
RSENSE
LBF
SET
LBF
OUT
LBF
HYST
LBF
SINK
V
SHDN
I
SHDN
V
CMRSENSE
Common mode range of V
RSENSE
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.
2
ISSUE 4 - OCTOBER 2000
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 format, 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.
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 to r o f a n o n - sy n ch r o n o u s so 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 ce fo r the few na n o seco nd s that
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 ti o n a l b e n e fi ts wh il st lo we r in 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.
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
ISSUE 4 - OCTOBER 2000
5
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