DEMO CIRCUIT 1134
LTC4222
QUICK START GUIDE
LTC4222
Dual Hot Swap Controller
with I
2
C Compatible Monitoring
DESCRIPTION
Demonstration Circuit DC1134A allows evaluation
of the performance of the LTC®4222_UF Dual Hot
Swap Controller with I2C Compatible Monitoring in
+12V/5A and +3.3V/5A applications.
The DC1134A can demonstrate turn-on and turn-
off transients as well as the steady state mode of
the LTC4222. The Controller responds to fault
conditions such as input overvoltage (OV), input
undervoltage (UV), output power good (PWRGD)
fault and overcurrent fault, and response may be
verified by the Fault Alert LED.
The board contains one LTC®4222_UF Controller,
two rail channels, input clamps, input and output
voltage dividers for setting the UV, OV and
PWRGD comparator thresholds, LEDs to indicate
the presence of input and output voltages, I2C and
ALERT signals, three jumpers ADR0, ADR1, and
ADR3 for I2C address programming, jumper
TIMER SELECT for timer off period selection,
jumper “ON” for ON pin signal selection, jumper
“ON CONFIG” for selecting independent or cou-
pled rail operation, two jumpers “ADIN1” and
“ADIN2” for selecting ADC1 and ADC2 input sig-
nals, two jumpers “EN1 and EN2” for selection
EN1 and EN2 pin signals, I2C port and turret ter-
minals for critical signals to facilitate evaluation in a
working system. Each rail channel includes a se-
ries connected power MOSFET and sense resis-
tor.
The I2C port designed to interface with the
DC590A allows providing full control of the
DC1134 with LTC's QuickEval software.
Design files for this circuit board are available.
Call the LTC factory.
registered trademarks of Linear Technology Corporation. Adaptive Power, C-Load,
DirectSense, Easy Drive, FilterCAD, Hot Swap, LinearView, µModule, Micropower
SwitcherCAD, Multimode Dimming, No Latency , No Latency Delta-Sigma, No
R
SENSE
, Operational Filter, PanelProtect, PowerPath, PowerSOT, SmartStart,
SoftSpan, Stage Shedding, SwitcherCAD, ThinSOT, UltraFast and VLDO are
trademarks of Linear Technology Corporation. Other product names may be trade-
marks of the companies that manufacture the products.
L
, LTC, LTM, LT, Burst Mode, OPTI-LOOP, Over-The-Top and PolyPhase are
PERFORMANCE SUMMARY
SYMBOL
PARAMETER
V
DDN
Input Supply Range
V
DDN(UVL)
Input Supply Undervoltage Lockout
∆V
SENSE(TH)
Circuit Breaker Threshold (VV
DD-
V
SENSED
)
∆V
SENSE
Current Limit Voltage (VV
DD-
V
SENSED
)
Specifications are at TA = 25°
C
CONDITIONS
V
DD
Rising
MIN
2.9
2.34
47.5
TYP
2.43
50
MAX
29
2.53
52.5
UNITS
V
V
mV
V
FB-
=1.3V
V
FB-
=0V
Start-Up Timer Expired
46
14
130
V
DD1
V
DD2
I
LIMIT
dU
OUT
/
DT
V
INPUT(TH)
First Rail Operating Voltage
Second Rail Operating Voltage
Circuit Breaker Current Limit in both Rails Steady State Condition, after Power-Up
Both Rails Output Voltage Slew Rate
Rail Current Lower Current Limit Threshold
CONFIG, ENn, FBn, ONn, OVn and UVn V
IN
Rising
Pin Input Threshold
4.6
850
1.215
50
16.6
150
12
3.3
5
1200
1.235
54
19
165
5.4
1900
1.255
mV
mV
mV
V
V
A
V/s
V
1
LTC4222
PERFORMANCE SUMMARY
SYMBOL
I
GATE(UP)
Specifications are at TA = 25°
C
MIN
8
PARAMETER
CONDITIONS
External N-Channel Gate Pull-Up Current Gate On, V
GATE
= 0V
TYP
12
MAX
18
UNITS
µA
OPERATING PRINCIPLES
The LTC4222 is a low voltage dual hot swap con-
troller that has 2.9V to 29V operating range and
35V absolute maximum voltage for the VDD pins.
In the DC1134A the first channel operates on the
+12V rail and the second channel on the +3.3V
rail. Each channel can easily be readjusted for any
voltage between 2.9V and 29V by replacing the
top resistors in the UV, OV and FB dividers (R1,
R2, R7 for the first channel and R101, R102, R107
for the second one). The DC1134 as supplied by
the factory is assembled with the Si4864DP MOS-
FETs in an SO-8 package and with 10mΩ current
sense resistors, setting a minimum of 4.6A current
limit and 4.75A circuit breaker threshold. The cur-
rent limit and circuit breaker thresholds can be ad-
justed by changing the channel’s sense resistor
(RS1 and RS2). To enable demonstration of higher
current applications up to 25A, provisions have
been made to replace the provided sense resistor
with a 1W, 2512 size and replace Q1 and Q101
with MOSFETs in a PowerPAK SO-8, such as the
Si7476ADP. The large turrets may be removed to
permit installation of up to a 12 gauge wire for di-
rect, low resistance connections to the board.
None of the turrets are swaged.
QUICK START PROCEDURE
Demonstration circuit 1134 is easy to set up to
evaluate the performance of the LTC4222. Refer to
Figure 1 for proper measurement equipment setup
and follow the procedure below:
The DC1134 is factory set up to operate with 12V
and 3.3V rails and up to 5A. If the LTC4222 is to
be evaluated at different operating conditions, fol-
low steps 1 through 3 below, otherwise skip to step
4.
1.
If evaluating at a voltage other than 12V and
3.3V, R1, R2, R101 and R102 must be ad-
justed for proper UV and OV comparator re-
sponse. The values of the bottom resistor in
the divider R3 (14.7k) and R103 (4.12k) may
be assigned arbitrarily.
Select a voltage divider top resistor R1 and
R101 as
R1
≤
14.7(V
MAX/12
/1.255)[1-1.215/V
MIN12
]k,
R101
≤
4.12(V
MAX3.3
/1.255)[1-1.215/V
MIN3.3
]k.
Select a voltage divider middle resistor R2 and
R102 as
R2
≤
14.7(1.215V
MAX12
/1.255V
MIN12
-1)k
R102
≤
4.12(1.215V
MAX3.3
/1.255V
MIN3.3
-1) k.
where V
MIN
and V
MAX
are the minimum and
maximum output voltages expected for normal
operation.
Select resistors in the feedback dividers R7 or
R107 as
R = 3.01[V
MIN
/1.255-1]k
where V
MIN
is the minimum output voltage ac-
cepted as a good output.
2.
If the DC1134 will operate at other than 5A
max, change the value of the sense resistor
R
SENSE
= 0.99•47.5mV/I
LOAD(MAX)
for a 1% tol-
erance current sense resistor.
2
LTC4222
3.
If the DC1134 will operate above 10A, replace
Q1 with a suitable PowerPAK SO-8 package
MOSFET such as the Si7880ADP suitable for
up to 20A. The SO-8 pads on the front of the
board include the extra heat-sinking area this
package requires. Alternately, for low power
applications, Q1 may be replaced with a
MOSFET in a SSOT-6 package using pads on
the back of the board.
4.
The “TIMER SELECT” jumper chooses the
startup time limit. It may enable either the ad-
justable timer with external timer capacitor CT
or the built in internal timer with a fixed startup
time 100ms. CT is stuffed with a 0.68µF ca-
pacitor at the factory, which provides a 8ms
startup time. To customize the startup time, se-
lect CT = T
START
/12.3(ms/µF).
5.
The soft start capacitor, CSS, sets the current
ramp rate at which the inrush current will in-
crease when turning on. CSS is stuffed with a
68nF capacitor at the factory, which provides a
5mV/ms inrush sense resistor voltage ramp or
0.5A/ms for both rails.
6.
The LTC4222 does not require an RC network
on the GATE pin for compensation. However,
an RC network may be used to limit the rate at
which the GATE rises to provide an inrush cur-
rent below the internal current limit. Pads for
R6, R106, CG1 and CG2 on the back of the
board are available for this purpose. R6 and
CG1, as well as R106 and CG2 may be stuffed
with 100K resistor, and CG = C
LOAD
*
20uA/I
INRUSH
for this purpose.
7.
The ADIN1 and ADIN2 turrets may be used to
provide signals to take 10 bit measurements of
any voltage. Jumpers “ADIN1 SELECT” and
“‘ADIN2 SELECT” choose between measuring
the input rail voltage or measuring the voltage
on the ADIN1, ADIN2 turrets respectively. The
rail input voltages are measured through resis-
tor dividers. The +12V divider is assembled to
a 15.4V full scale range to match the range of
the Q1 SOURCE voltage measurement. The
+3.3V divider is assembled to a 4.3V full scale
range to match the range of the Q101
SOURCE voltage measurement. To change
the full scale of the input measurement, select
R11 or R111 as
R = V
RANGE
*12.4k/1.23-12.4k.
The signals at the ADIN1 and ADIN2 turrets
are also measured through a voltage dividers,
but the bottom resistor is not stuffed at the fac-
tory, defaulting to a 1.28V full scale voltage. To
select a larger full scale voltage, choose R17
and R117 as
R = 12.8/(V
RANGE
-1.28)k.
8.
If the system uses short connector pins to
sense board insertion, place “EN1” and “EN2”
jumpers to position SHORT PIN1 and SHORT
PIN2, respectively. Using the SHORT PIN1
and SHORT PIN2 turrets, connect the afore-
mentioned short pins. Those are direct connec-
tions to the LTC4222's EN1 and EN2 pins; if
deleterious voltages are anticipated, add a se-
ries resistor and clamping. EN1 and EN2 are
good for -0.3 to +12V on their own. EN1 and
EN2 are also logic compatible with a 1.235V
threshold and 130mV hysteresis.
9.
The I
2
C address, assigned to the board, is se-
lected on the board by using jumpers “ADR0”,
“ADR1” and “ADR2” to pull the address pins
high, low, or allow them to float. An address ta-
ble is shown in the data sheet. The evaluation
software automatically scans and identifies the
I2C address, regardless of the setting.
10.
After any necessary component changes have
been made, connect suitable loads between
+12V/5A OUTPUT and GND and +3.3V/5A
OUTPUT and GND. This may be a passive re-
sistive load or an active electronic load box. If
long leads are present between the DC1134
and load, install 10µF or more at C1 and C101.
This should eliminate the chance of MOSFET
oscillation and large negative excursions at
+12V/5A OUTPUT.
11.
Connect power supplies capable of supplying
10A to the +12V INPUT and GND turrets and
3
LTC4222
the +3.3V INPUT and GND turrets. The mini-
mum current capability of the supply must ac-
commodate the tolerance of the circuit breaker
threshold of ±10%. With the 10mΩ,
1%,
factory
installed sense resistor, the overload circuit
breaker will trip at (5.0±0.3)A.
12.
Connect the ribbon cable from a DC590 to the
I2C PORT on the DC1134. LTC’s QuickEval
software will automatically recognize the
DC1134 and load software to read and write to
the LTC4222’s registers. During an I2C trans-
action, D5 and D7 will flicker faintly. If the I2C
port (JP7) is disconnected, the turret terminals
SDA and SCL can be connected directly to an
I2C bus. Power for D4, D5, and D7 is supplied
by JP7, pin 2, so in this mode the LEDs will not
light unless 5V is connected to this pin.
13.
The following experiments can be run. Turn on
into a nominal load. Turn on into an overload.
Turn on into a short circuit. Turn on into a
nominal load and increase the load until the
LTC4222 trips off. A digital storage scope pro-
vides a convenient means of observing the
turn-on and overload events. Observe the input
or output current using a current probe. A
probe ground turret on the board provides a
low current connection to the LTC4222’s
ground.
4
LTC4222
Figure 1. Proper Measurement Equipment Setup
5
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