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TD230ID-TD230IDT-TD230IN
ELECTRONIC CIRCUIT BREAKER
TWO N-CHANNEL MOSFETs CONTROLAND DUAL INDEPENDENT CURRENTSUPERVISION FOR OVER CURRENT
PROTECTION� DUAL SUPPLY OPERATION� FROM +3/-5V OPERATING VOLTAGE� STEP-UP CONVERTER : VCC +13.5V
OUTPUT VOLTAGE� ADJUSTABLE PROTECTION MODE
(CTRIP 1/2)� SHUTDOWN OUTPUT STATUS� FEW EXTERNAL COMPONENTS
DESCRIPTIONThe TD230 is designed to control two N-channel
MOSFETs used as power switches in circuit
breaking applications.
Its current supervision and immediate action on
the switches ensure high security for the boards
and the supplies thus protected agains short-cir-
cuit or over current.
In case of short-circuit or over current detection,
the TD230 immediately switches off the corre-
sponding MOSFET, thus disconnecting the board
from the supply. After several automatic restart at-
tempts, a definitive shutdown of the circuit is done
if the shortcuircuit or over current persists over an
externally adjustable time, until the TD230 is reset
by temporary INHIBIT signal or temporary switch-
ing off of the power supply (hot disconnection/re-
connection).
If the board is disconnected from the positive sup-
ply by the TD230 it will automatically be disjoncted
from the negative supply too.
TD230 integrates an induction step-up converter
that provides 13.5V above the positive rail to drive
the high side MOSFET.
ORDER CODE
N = Dual in Line Package (DIP)D = Small Outline Package (SO
PIN CONNECTIONS (top view) ELECTRONIC CIRCUIT BREAKER
TD230
TD230
BLOCK DIAGRAM
ABSOLUTE MAXIMUM RATINGS
OPERATING CONDITIONS
INSTRUCTION FOR USE
TD230ELECTRICAL CHARACTERISTICSVCC = ±5V, Tamb = 25°C, Lboost = 220μH, Cboost = 100nF (unless otherwise specified)
TD230
Figure 1 : DUAL ELECTRONIC CIRCUIT BREAKER APPLICATION
Figure 2 : SINGLE ELECTRONIC CIRCUIT BREAKER APPLICATION
TD230TIMING DIAGRAMS
INTRODUCTIONOver current and short circuit protection is a con-
stant concern for today’s engineers. More and
more applications in different segments (Telecom,
Automotive, Industrial, Computer...) require al-
ways improved reliability after delivery : mainte-
nance costs are an ever more worrying source of
expenses and customers’ dissatisfaction.
Alternatives for short circuit or over current protec-
tions are the fuses and the PTC (Positive Temper-
ature Coefficient) resistors. The first are a cheap
but destructive solution ; the second are tied to a
time constant due to self heating which is often in-
compatible with the host equipment’s require-
ments.
In both cases, a coil can be added for an efficient
limitation of current surges, to the detriment of
weight and volume.
None of these solutions is fully satisfactory for a
reliable, immediate and non destructible short cir-
cuit and over current protection.
1. ELECTRONIC CIRCUIT BREAKERThe electronic circuit breaker TD230 is the conve-
nient solution for any industrial who wants at the
same time : immediate, efficient and resettable protec-
tion for his equipment versatility regarding different applications easy and quick design-in low component count low cost
The electronic circuit breaker TD230 is to be used
with a minimal amount of external and low cost
components to drive one or two N-channel MOS-
FETs (in respectively single or dual supply appli-
cations) used as power switches between the DC
power supplies and the equipments to be
protected.
The TD230 immediately reacts (3μs max. without
load) whenever an over current is detected by
switching off the corresponding MOSFET. Several
automatic restart attempts are made unless the
fault persists over an externally adjustable amount
of time after which the power MOSFET is defini-
tively switched off, waiting for a reset.
If the fault is detected on the positive supply, the
definitive shutdown will also disconnect the nega-
tive power supply and set a warning low level on
the Shutdown pin. If the fault is detected on the
negative supply, the definitive shutdown will dis-
connect only the negative power supply, and let
the positive part of the circuit undisturbed.
The whole system can be reset in three ways : by switching off the power supplies by unplugging and re-plugging the card
(live insertion) by setting the INHIBIT pin active during a
short time (allowing remote reset)
2. HOW TO USE THE TD230 The typical configuration of the TD230 - Electronic
Circuit Breaker - in a dual supply topology is
shown in figure 1.
In this configuration, both NMOS 1/2 are used as
power switches which connect the equipments to
the power supplies, thus ensuring low voltage
drop through the ON-resistances (Rdson) of
NMOS 1/2.
2.1. Current LimitationWhen an over current condition (IOC) is detected
through the low ohmic shunt resistors RS 1/2 as giv-
en under equation (i) : VRS 1/2 = IOC x RS > 63mV typ. (i)
the gate of the corresponding MOSFET 1/2 is dis-
charged immediately, thus disconnecting the
board/equipment from the power supply.
Note that the over current condition is given by the
constant product IOC x RS = 63mV, which means
that the IOC limit is directly given by the choice of
the shunt resistors RS1/2 values.
The TD230 automatically makes restart attempts
by slowly recharging the gate of the MOSFET 1/2
with a 15μA typ. current source ensuring thus slow
ramp with the typical time constant before recon-
duction shown in equation (ii) : tON = CISS x VTH / 15μA (ii)
where CISS is the input capacitance of the power
MOSFET1/2 and VTH, the threshold voltage of the
MOSFET (typically 5V).
This reconduction time can be extended with an
external soft start capacitor CSS1/2 as shown in
APPLICATION NOTEELECTRONIC CIRCUIT BREAKER
by R. LIOU
TD230
figure 1 CISS will therefore simply be replaced byCISS + CSS 1/2.
Figure 1 : Dual Electronic Circuit BreakerApplication
If the fault (over current condition) still remains af-
ter the reconduction state of the MOSFET1/2 has
been reached, the current through NMOS1/2 will
overpass the limitation given by equation (i), and
the NMOS 1/2 will immediately be switched off
again.
Figure 2 shows the current limitation which is op-erated on every restart attempt.
Figure 2 : TD230 as Current Limitor
Trace A represents the Gate-Source Voltage of
the Power Mosfet (0 to 13,4V).
Trace B represents the voltage across the SenseResistor (68mΩ) in direct relation with the current
through it (0 to ~1A).
Note that the first current peak which is due to an
over current is limited only by the reaction time of
the TD230.
This off time is tied to the value of the external soft
start capacitor CSS 1/2 by equation (iii) : tOFF = RDSON x CSS (iii)
While in current limitation mode, the NMOS1/2 dis-
sipates low power due to the fact that the ON/OFF
cycle time rate is very low.
Note that the higher the value of CSS1/2 are, the
more the NMOS1/2 will stay in linear mode during
current limitation.
Note that at Power ON, or in the case of live inser-
tion, the inrush current is automatically limited
thanks to the slow gate charge of the MOSFET
which switches ON softly due to the time constant
given in equation (ii).
2.2. Fault Time LimitationThe repetitive switching off of the MOSFET will
come to an end under two conditions : either the fault has disappeared, and the
current through the shunt resistors RS 1/2
has come back to its nominal value : the
system keeps running normally.
External line defaults (lightning, line breakage,
etc...) are usual causes for such temporary over
currents. either the repetitive switching off has lasted
over an externally adjustable time and the
TD230 has definitively switched off the cor-responding NMOS : the system waits to be
reset.
Equipment faults (component short circuit, over
heat, etc ...) are usual causes for lasting over cur-
rents.
This fault time supervision is done by the compar-
ison of the output voltage to 75% of the nominal
supply voltage. As soon as the output voltage is
detected under 0.75xVcc(+/-), the corresponding
external capacitors CTRIP1/2 is charged by a fixed
current source IP/N2 - IP/N3 (3μA). When the voltage
across CTRIP1/2 reaches 1.20V, the corresponding
NMOS is definitively switched off and the SHUT-
DOWN pin is active low.
To avoid cumulative charging of the protection ca-
pacitors CTRIP 1/2 in case of successive overcurrent
TD230conditions, the capacitors CTRIP 1/2 are constantly
discharged by another fixed current source IP/N3
which value is a fourth of IP/N2 (1μA).
Figure 3 : Fault Time Limitation
Trace 1 represents the CBOOST Voltage (0 to5+13,4 = 18,4V)
Trace 2 represents the CTRIP1 Voltage.The value of the capacitors CTRIP 1/2 should be cho-
sen in relation with the required protection time as
indicated in equation (iv) : CTRIP1/2 = (IP/N2 - IP/N3) x tPROTECT1/2 / VSPN/3(iv)
where tPROTECT 1/2 is the time defined by the user be-
fore a definitive resettable shutdown of MOS-
FET 1/2.
Equation (iv) can be translated to : CTRIP 1/2 = tPROTECT 1/2 x 3μA / 1.20V (iv)
Note that the positive power supply disjonction
leads to the negative power supply disjonction,
whereas the opposite is not true.
2.3. Step-Up ConverterTo ensure proper voltage on the gate of the posi-
tive supply NMOS1 (VGS = 13.4V typ), the TD230
integrates a step-up converter which is to be
boosted with two small low cost external compo-
nents : an inductor LBOOST and a capacitor CBOOST,
as shown in figure 4.
Figure 4 : Step Up Converter External Components
The principle of this inductive step-up converter is
to pump charges in the tank capacitor CBOOST fol-
lowing the equation (v) :
Figure 5 : Internal Step Up Schematic V(CBOOST) = VCC+ + 13.4V typ (v)
Charges are pumped by means of an oscillator
commanded switch, and stored in the CBOOST tank
capacitor through a diode as shown on figure 5.
When the voltage across CBOOST reaches
VCC+ +13.4V typ, the oscillator is stopped. This cre-
ates a ripple voltage with an amplitude of 0.2V.
Note that the min and max values of V(CBOOST)
comprised between VCC+ +10V and VCC+ +15V al-
ready take the ripple voltage into account.
