ZE0120
20 VOLT 1 AMP IDEAL RECTIFIER LEG
DESCRIPTION
FEATURES
The ZE0120 implements a single leg of a bridge
rectifier with ideal diode characteristics. The device
uses low Rds(on) MOSFET switches to achieve
ultra-low forward conduction voltage drop and
thus high efficiency. The device is ideally suited for
applications in conductive wire-free power
applications. The device has fast reverse recovery
for compatibility with conductive wire-free power
sensing pulses commonly used for pad safety. The
device is designed to survive tough, real-life ESD
exposure.
Ultra low forward conduction drop
25mΩ Rds(on) typical
Low quiescent current drain
Wide operating voltage 8V – 20V
Fast reverse recovery
High ESD survivability
Combine to create multi-leg rectifiers
Industry standard series-connected diode array
SOT23 package pin-outs
Self-starting operation
Self-powering ideal diode circuitry
APPLICATIONS
Conductive wire-free powered phone cases
Wire-free powered cell phones
Wire-free powered heated coffee mug
Wire-free powered air fresheners
Wire-free powered BlueTooth headsets
High-efficiency linear power supplies
Non-polarized power connectors
Power management ideal diode
SOT-23 Package
Pin-Out
TYPICAL APPLICATION
15 Watt, 99.7% efficient Open Dots wire-free power receiver
Custom Ideal Bridge Rectifier Specification Rev A
1
ZE0120
ABSOLUTE MAXIMUM RATINGS
Symbol
Parameter
Conditions
Max
Ifmax
Ipkmax
Vopmax
Vfmax
TJmax
Maximum Average Forward Rectifier Current
Maximum Peak Forward Rectifier Current
Maximum Rectified Voltage (Vpin2 – Vpin1)
Maximum Forward Voltage Drop
Maximum Operating Junction Temp
Vpin2 – Vpin1 = 15V
Vpin2 – Vpin1 = 15V, 1ms
Iin = 0
At Ipkmax
Eesd
Maximum ESD discharge
Units
2.0
4.0
25
150
125
A
A
V
mV
C
15
kV
Pin 3, Pos or Neg, 100pF, 150Ω, 50
hits, No damage, Pins 1,2 grounded
ELECTRICAL CHARACTERISTICS
Symbol
Parameter
Conditions
Min
If
Vop
Vf
Iq
Toff
Ton
Rated Forward Rectifier Current
Operational Voltage
Rectifier Forward Voltage Drop
Quiescent Current
Rectifier turn-on time
Rectifier turn-off time
Ir
Rectifier Reverse Leakage current
Vth
Turn-on threshold voltage
Vpin2 – Vpin1 = 15V
At If
At If
Vpin2 – Vpin1 = 20V
Iin transition from zero to 90% Idmax
Iin transition from Idmax to zero
Vin = 20V, Rectifier under test Vr =
5V, over temperature range
Vpin2 – Vpin1 = 8V to 20V
Typ
Max
Units
50
200
0.4
0.8
1.0
20
60
250
1.0
1.0
A
V
mV
uA
us
us
1
10
uA
20
mV
8
10
ENVIRONMENTAL
To
Ts
Ho
Hs
Operating temperature
Storage temperature
Operating humidity
Storage humidity
0
-40
5
5
THEORY OF OPERATION
CANONICAL CIRCUIT
The ZE0120 implements two series-connected ideal
diode circuits as shown in the canonical block
diagram. The ideal diodes work using a circuit to
detect the voltage across each MOSFET. A positive
voltage across Q1 causes it to be turned on. A
negative voltage across Q2 causes it to be turned
on. The diodes D1, D2 and their current densities
are matched to the transistors Q3, Q4. When Vin is
between the voltages V+ and V-, Q3 and Q4 are on,
85
85
80
95
C
C
%RH
%RH
and the gate voltages of each FET Q1 and Q2 are
zero, thus the FETs are off. When Vin exceeds
either the positive rail V+, or the negative rail V-, by
a voltage of Ib * Ro, Q3 or Q4 turn off, thus
applying Ig * Rg across the corresponding FET
turning it on. The voltage Ib * Ro is ten millivolts to
prevent latch-up.
Custom Ideal Bridge Rectifier Specification Rev A
2
ZE0120
PRACTICAL IMPLEMENTATION
A practical implementation is shown in the circuit
schematic below. The buffers are constructed of
simple bipolar emitter followers comprised of
Q5,Q6, and Q7,Q8. A junction resistor Rn allows
the voltage to follow when the buffer current is
low. The current sources are comprised of pairs of
NPN transistors arranged to maintain the drop
across Ri at about 550mV. Thus they provide
approximately 100uA of current over the 8V to 20V
supply voltage range.
The diodes are implemented as transistors Q11 and
Q12 to provide matched forward junction voltage
over temperature with transistors Q3 and Q4
respsectively. In this example, Rn is 470K so as to
provide a good base drive, yet still bring the offset
to zero for light loads. Rg is 8K so that 100uA of
current provides an 8V gate drive. Ri is 5.2K to
program 100uA in the current sources, and Rb is
1.5 megohm to provide the needed base drive with
only a small effect on the programmed current. Ro
is 200 ohms so that the 100uA programmed
current generates just 20mV of zero-crossing offset
to prevent latch-up.
Custom Ideal Bridge Rectifier Specification Rev A
3
ZE0120
SELF-POWERING AND SELF-STARTING
Power is not overtly applied to the chip across pins
1 and 2. Rather, the device derives its own power
in the process of its intended operation. In the
intended applications, the device rectifies the
voltage applied to Vin (pin 3) so as to charge an
external rectification capacitor across pins 1 and 2.
This rectified voltage provides the supply current to
operate the device’s ideal diode circuitry.
Before a rectified potential grows across pins 1 and
2, the circuit inherently self-starts via the body
diodes of the MOSFET devices. Below a rectified
voltage of 8V it can be expected that the body
diode current will be small, and thus there is no
concern of significant die heating or damage during
this bootstrap phase.
CROSSOVER VOLTAGE OFFSET
It is important that the ideal diodes turn off when
the voltage across them is zero. If not, the circuitry
will not recognize the turn-off condition, and
consequently the MOSFET will be in a latch-up
condition. This is ensured through the addition of a
slight offset threshold developed across Ro. The
idea is that over temperature and production
variations it is always guaranteed that the MOSFET
turns off when zero volts is across it.
For lower currents, the circuit will act to regulate
the forward drop across the conducting MOSFET to
the offset. In this chip, the offset is 10mV. Once the
voltage exceeds 10mV across either MOSFET in the
forward direction, that MOSFET will turn on to
reduce the forward drop to a value of 10mV. At
some point, the forward current induces a drop
across Rds(on) that is greater than 10mV, resulting
in full gate drive.
It is best if the offset is as small as practical, so that
the forward drop of the MOSFET is made as small
as possible. Obviously, when the current increases,
the Rds(on) will define the forward drop, but below
a certain current, the forward drop is defined by
the crossover offset.
REVERSE LEAKAGE
Schottky diodes exhibit reverse leakage much
greater than standard diodes. In a rectifier
application, this reverse leakage passes across the
power rails, but also flows into the Vin junction.
Further, this current increases with temperature.
The reverse leakage current flowing into the Vin
junction can interfere with wire-free power pad
protection circuitry causing a false foreign object
fault. Diodes with lower forward conduction losses
tend to have higher reverse leakage.
The reverse leakage problem is eliminated with the
ideal diode design of this chip. Whereas, decent
schottky diodes may exhibit 50uA of leakage,
thereby causing a fault, the ideal diodes of this chip
exhibit 1uA or less of leakage current.
SWITCHING SPEED
The circuit provides on and off times of submicrosecond speed. This is necessary to
accommodate the safety test pulses used on the
pad. A typical test pulse removes pad drive for 5us.
In that time the pad surface is tested for foreign
objects. The chip reacts within 1us so as not to
interfere with the safety test pulse.
CONCLUSION
The rectifier leg chip provides an ideal diode
solution with 99.7% efficiency. This solution
becomes the go-to solution for conductive wirefree power receivers. It solves the problems
inherent with conventional Schottky diodes. It also
prevents headaches for designers who discover the
subtle pitfalls of Schottky diodes only after the
product is in production.
Custom Ideal Bridge Rectifier Specification Rev A
4