DEMO MANUAL DC1899A
LTC4228-1/LTC4228-2
Dual Ideal Diode and
Hot Swap Controller
DESCRIPTION
Demonstration circuit 1899A controls two independent
power rail circuits each with Hot Swap™ and ideal diode
functionality provided by the LTC4228-1/LTC4228-2 dual
ideal diode and Hot Swap controller.
DC1899A facilitates evaluation of LTC4228 performance
in different operation modes such as supply ramp-up,
power supply switchover, steady state, and overcurrent
faults. Power supply switchover mode can be realized as
either an ideal diode or as a prioritizer.
Each DC1899A circuit is assembled to operate with a
12V supply and 9A maximum current load. The main
components of the board are the LTC4228 controller, two
MOSFETs operating as ideal diodes, two MOSFETs operat-
ing as Hot Swap devices, two current sense resistors, two
jumpers for independently enabling each rail, six LEDs to
indicate status, power good and fault conditions separately
for each channel, and input voltage snubbers. There are
pads for optional RC circuits for each Hot Swap MOSFET
gate in order to adjust output voltage slew rate. In addition
to this there are jumpers allowing monitoring of supply
undervoltage conditions at either IN or SENSE+ pins.
The standard configuration (as DC1899A populated by
default) places the ideal diode MOSFET ahead of the Hot
Swap MOSFET. The board also has pads for an alternative
configuration with the Hot Swap MOSFET located ahead
of the ideal diode MOSFET.
Design files for this circuit board are available at
http://www.linear.com/demo
L,
LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks and
Hot Swap is a trademark of Linear Technology Corporation. All other trademarks are the
property of their respective owners.
PERFORMANCE SUMMARY
SYMBOL
V
IN
V
INTVCC(UVL)
PARAMETER
Input Supply Range
Internal V
CC
Undervoltage Lockout
Specifications are at T
A
= 25°C
CONDITIONS
INTV
CC
Rising
MIN
2.9
2.1
30
10
ΔV
FWD
= 0.1V
IN < 7V
IN = 7V to 18V
CPO = IN = 2.9V
CPO = IN = 18V
ΔV
FWD
= 0.2V, ΔV
DGATE
= 0V, CPO = 17V
ΔV
FWD
= –0.2V, ΔV
DGATE
= 5V
47.5
55
Gate Drive On, HGATE = 0V
Gate Drive Off, OUT = 12V, HGATE = OUT + 5V
Fast Turn-Off, OUT = 12V, HGATE = OUT + 5V
–7
150
100
5
10
–60
–50
2.2
60
25
7
12
–95
–85
–1.5
1.5
50
65
–10
300
200
52.5
75
–13
500
300
TYP
MAX
18
2.3
90
40
14
14
–120
–110
UNITS
V
V
mV
mV
V
V
μA
μA
A
A
mV
mV
μA
μA
mA
dc1899af
V
INTVCC(HYST)
Internal V
CC
Undervoltage Lockout Hysteresis
Ideal Diode Control
ΔV
FWD(REG)
ΔV
DGATE
Forward Regulation Voltage (V
IN
– V
OUT
)
External N-Channel Gate Drive
(V
DGATE
– V
IN
)
CPO Pull-Up Current
DGATE Fast Pull-Up Current
DGATEn Fast Pull-Down Current
Circuit Breaker Trip Sense Voltage
(V
SENSEEn+
– V
SENSEEn–
)
Active Current Limit Sense Voltage
(V
SENSEEn+
– V
SENSEEn–
)
External N-Channel Gate Pull-Up Current
External N-Channel Gate Pull-Down Current
External N-Channel Gate Fast Pull-Down Current
I
CPO(UP)
I
DGATE(FPU)
I
DGATE(FPD)
ΔV
SENSE(CB)
ΔV
SENSE(ACL)
I
HGATE(UP)
I
HGATE(DN)
I
HGATE(FPD)
Hot Swap Control
1
DEMO MANUAL DC1899A
PERFORMANCE SUMMARY
SYMBOL
V
ON(TH)
V
ON(RESET)
V
EN(TH)
V
TMR(TH)
I
TMR(UP)
I
TMR(DN)
I
TMR(RATIO)
PARAMETER
ONn On Pin Threshold Voltage
ONn Pin Fault Reset Threshold Voltage
EN
Pin Threshold Voltage
TMRn Pin Threshold Voltage
TMRn Pin Pull-Up Current
TMRn Pin Pull-Down Current
TMRn Current Ratio I
TMR(DN)
/I
TMR(UP)
Input/Output Pin
ON Rising
ON Falling
EN
Rising
TMR Rising
TMR Falling
TMR = 1V, In Fault Mode
TMR = 2V, No Faults
1.21
0.55
1.185
1.198
0.15
–75
1.4
1.4
1.235
0.6
1.235
1.235
0.2
–100
2
2
1.26
0.63
1.284
1.272
0.25
–125
2.6
2.7
V
V
V
V
V
μA
μA
%
Specifications are at T
A
= 25°C
CONDITIONS
MIN
TYP
MAX
UNITS
OPERATING PRINCINPLES
The LTC4228 functions as an ideal diode with inrush
current limiting and overcurrent protection by controlling
two external back-to-back N-channel MOSFETs in a power
path. The LTC4228 has two ideal diode and two Hot Swap
controllers. Each ideal diode MOSFET is intended to oper-
ate with a defined Hot Swap MOSFET, because they are
tied by common on/off control, and ideal diode controller
sense voltage includes both MOSFETs and sense resistor
voltage drop. Therefore, LTC4228 provides independent
control for the two input supplies.
The LTC4228 gate drive amplifiers monitor the voltage
between the INn and OUTn pins and drive the DGATEn
pins. The amplifier quickly pulls up the DGATE pin, turning
on the MOSFET (Q1 or Q3), for ideal diode control when
it senses a large forward voltage drop. Pulling the ON pin
high and
EN
pins low initiates a 100ms debounce timing
cycle. After this timing cycle, a 10μA current source from
the charge pump ramps up the HGATEn pin. When the Hot
Swap MOSFET (Q2 or Q4) turns on, the inrush current
is limited to a set level set by an external sense resistor
placed between IN and SENSE pins.
An active current limit amplifier servos the gate of the Hot
Swap MOSFET to 65mV across the current sense resistor.
Inrush current can be further reduced, if desired, by add-
ing a capacitor from HGATE to GND. When the MOSFET’s
gate overdrive (HGATE to OUT voltage) exceeds 4.2V, the
PWRGD pin pulls low. When both MOSFETs (Q1 and Q2 or
Q3 and Q4) are turned on, the gate drive amplifier controls
DGATE to servo the forward voltage drop (V
IN
– V
OUT
)
across the sense resistor and the back-to-back MOSFETs
to 25mV. If the load current causes more than 25mV of
voltage drop, the gate voltage rises to enhance the MOSFET
used for ideal diode control. For large output currents the
MOSFET’s gate is driven fully on and the voltage drop is
equal to the sum of the I
LOAD
• R
DS(ON)
of the two MOS-
FETs in series.
In the case of an input supply short-circuit when the
MOSFETs are conducting, a large reverse current starts
flowing from the load towards the input. The gate drive
amplifier detects this failure condition as soon as it ap-
pears and turns off the ideal diode MOSFET by pulling
down the DGATE pin.
dc1899af
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DEMO MANUAL DC1899A
QUICK START PROCEDURE
Demonstration circuit 1899A can be easily set up to evaluate
the performance of the LTC4228-1/LTC4228-2. Refer to
the Figure 1 for proper measurement equipment setup and
follow the procedure below. The DC1899A test includes
independent tests of the LTC4228 Hot Swap functionality,
ideal diode functionality and two power rails prioritizer
functionality with the channel 1 highest priority.
HOT SWAP FUNCTIONALITY TEST
This test is identical for each 12V rail and is performed
in the three steps by the measuring of the transient’s
parameters in the different operation modes.
Install the jumpers in the following positions:
JP4, RON1_SEL and JP5, RON2_SEL in position OFF;
JP1, EN1_SEL and JP2, EN2_SEL in position LOW.
R
L1
PSU
SW1
C
L1
SW2
R
L2
PSU
SW3
C
L2
SW4
Figure 1. Measurement Equipment Setup for Hot Swap Functionality Test
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DEMO MANUAL DC1899A
QUICK START PROCEDURE
No-Load Rampup
Connect a 12V power supply to the board input turrets
IN1 (IN2) and GND. Do not load the output. Place current
probe on the 12V supply and voltage probes on the OUT1
(OUT2) turret. Provide ON1 (ON2) signal at the ON1 (ON2)
pin by moving the RON1_SEL (RON2_SEL) jumper from
OFF position to the 12V position. Observe the transient. The
output voltage rise time should be in the range of 12ms
to 29ms. PWRGD1 (PWRGD2) green LED should be lit.
Turn off the rail using the RON1_SEL (RON2_SEL) jumper.
Current Limit
Initially adjust an electronic resistive load to 10Ω to 12Ω
and connect it to the OUT1 (OUT2) turret and GND. Turn
on the rail and slowly increase load current up to the
circuit breaker threshold level. The current limit range
should be between 9A and 12.3A. Turn off the rail using
the RON1_SEL (RON2_SEL) jumper.
V
OUT
INPUT CURRENT
dn1899a F02
Figure 2. Turn-On Output Transient Test
CURRENT LIMIT AT 10A
CURRENT 2A/DIV
OUTPUT VOLTAGE
DROPPING DUE
TO SHUTDOWN
dn1899a F03
Figure 3. Current Limiting Test
dc1899af
4
DEMO MANUAL DC1899A
QUICK START PROCEDURE
Power-Up into Output Short
Short the output to ground with a wire. Place the current
probe on this wire. Turn on the rail and record the current
shape. The maximum current should be in the 11.6A to
16.9A range. The LTC4228-1 latches off after overcurrent
condition, but the LTC4228-2 automatically retries after
200ms to 450ms.
IDEAL DIODE FUNCTIONALITY TEST
Use an individual 12V power supply for each rail; connect
the two outputs together at a common load. Adjust each
input voltage to 12V with maximum possible accuracy.
In this test, both rails are active and small variations in
the input voltage will force one channel off and the other
channel on. Place a voltmeter between IN1 and IN2 turrets
to measure the difference between two input voltages.
Activate both rails and keep a load around 1A to 3A. Ad-
just the input voltage level of one supply such that IN1 is
40mV more positive than IN2. Verify that only channel 1
is drawing current. Repeat this test with IN1 at –40mV
with respect to IN2. In this case channel only channel 2
is drawing current.
PRIORITIZER FUNCTIONALITY TEST
The DC1899A is assembled with components to implement
a power prioritizer with channel 1 having the higher priority.
Place JP7 PPR_SEL (power priority select) jumper in
position ON2 and JP5 RON2_SEL (ON2 select) in posi-
tion OFF.
Apply independent supply voltages (12V) to both inputs.
Channel 1 will be connected to load. Reduce channel 1
input voltage until it reaches an undervoltage condition
and D6 (PWRGD2) lights. At the same time channel 2
power supply will deliver power to the load.
CURRENT PROFILE DURING
SHORT-CIRCUIT TURN-ON
dn1899a F04
Figure 4. Short-Circuit Test (2A/Div)
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