LT1641
-
1, LT1641
-
2, LT4256
-
1, AND LT4256
-
2
DESCRIPTION
Demonstration circuit 1354 is a Positive High Voltage
Hot Sw ap Controller featuring either the LT1641-1,
LT1641-2, LT4256-1, or LT4256-2.
The board facilitates measurement of transient condi-
tions, steady state operation w ith different loads, and
fault conditions. The Controller responds to fault condi-
tions such as input undervoltage(UV), output pow er
good (PW RGD) fault, and overcurrent and response can
be verified by the output voltage (VOUT) LED state and
PW RGD pin signal.
The LT1641-1 and LT4256-1 latch off, if M OSFET shuts
off under overcurrent condition, w hile LT1641-2 and
LT4256-2 automatically restart after time-out delay.
The DC1354 contains one Hot Sw ap Controller, pow er
M OSFET, current sense resistor, enable circuit, input
voltage clamp, gate protection circuit, resistive output
voltage divider for feedback signal, and three LEDs to
indicate the presence of input and output voltages and
pow er good condition.
Design files for this circuit board are available. Call the
LTC factory.
L, LTC, LTM , LT, Burst M ode, OPTI-LOOP, Over-The-Top and PolyPhase are registered
trademarks of Linear Technology Corporation. Adaptive Pow er, C-Load, DirectSense, Easy
Drive, FilterCAD, Hot Sw ap, LinearView , ยตM odule, M icropow er Sw itcherCAD, M ultimode
Dimming, No Latency ๎˜๎˜‚, No Latency Delta-Sigma, No R
SENSE
, Operational Filter, PanelProtect,
Pow erPath, Pow erSO T, SmartStart, SoftSpan, Stage Shedding, Sw itcherCAD, ThinSOT,
UltraFast and VLDO are trademarks of Linear Technology Corporation. Other product names
may be trademarks of the companies that manufacture the products.
PERF ORM A NCE SU M M A RY
Specifications are at TA = 25ยฐC
SYM BOL PAR AM ETER CON DITIONS M IN TYP M AX UNITS
V
CC
Operating Voltage
LT1641
LT4256
9.0
10.8
80
80
V
V
V
LKO
V
CC
Undervoltage Lockout
LT1641
LT4256
7.5
8.3
9.8
8.8
V
V
V
UNLH
Undervoltage Threshold
LT1641, ON pin voltage Low to High transition
LT4256, UV pin voltage Low to High transition
1.280
3.96
1.313
4
1.345
4.04
V
V
V
FB
Feedback Voltage Threshold
LT1641, FB Low -to-High Transition,
FB High-to-Low Transition
LT4256, FB Low -to-High Transition,
FB High-to-Low Transition
1.280
1.221
3.95
4.2
1.313
1.233
3.99
4.45
1.345
1.245
4.03
4.65
V
V
V
V
V
SENSETRIP
SENSE Pin Trip-Voltage(V
CC
-V
SENSE
)
LT1641,
V
FB
=0V
V
FB
=1V,
LT4256,
V
FB
=0V,
V
FB
โ‰ฅ
2V
8
39
5.5
45
12
47
14
55
17
55
22
65
mV
mV
mV
mV
โˆ†
V
GATE
External N-Channel Gate Drive
LT1641,
V
GATE
-
V
CC
,
10.8V
โ‰ค
V
CC
โ‰ค
20V
20 V
โ‰ค
V
CC
โ‰ค
80V,
LT4256,
V
GATE
-
V
CC
, 10.8
โ‰ค
V
CC
โ‰ค
20V
20 V
โ‰ค
V
CC
โ‰ค
80V,
4.5
10
4.5
10
8.8
11.6
18
18
12.5
12.8
V
V
V
V
I
GATEU P
GATE Pin Pull-U p Current
LT1641
LT4256
5
16
10
32
20
63
ยต
A
ยต
A
I
GATEDN
GATE Pin Pull-Dow n Current
LT1641
LT4256
35
40
70
62
100
80
mA
mA
DEMO CIRCUIT
1354
Q UICK S TA RT G UIDE
L T1 6 4 1 -1 , L T1 6 4 1 -2, L T4 25 6 -1 , a n d LT4 25 6 -
2
P o sitiv e H ig h V o lta g e H o t S w a p Co n tro lle r
LT1641
-
1, LT1641
-
2, LT4256
-
1, AND LT4256
-
2
OPERA TING PRINCIPL ES
The LT1641-1, LT1641-2, LT4256-1, and LT4256-2 are
Positive High Voltage Hot Sw ap Controllers that have
absolute maximum supply voltage (V
CC
) 100V and oper-
ating range (9-80) V for LT1641 and (10.8-80) V for
LT4256. In the DC1354A any controller operates on the
+48V rail. Each board can easily be readjusted for any
rated voltage by replacing the enable circuit (R5, R11),
input voltage clamp (D1), gate protection circuit (R8,
R14, D3, D6), and resistive output voltage divider (R10,
R12). The DC1354A as supplied by the factory is assem-
bled w ith the SUM 90N10-8m2p M OSFET in a D2PAK
package and 7m
โ„ฆ
current sense resistor (R1).
Q U ICK STA RT PROCEDU RE
Demonstration circuit DC1354 is easy to set up to evalu-
ate the performance of the LT1641-1, LT1641-2,
LT4256-1, and LT4256-2. Refer Figure 1 for proper
measurement equipment setup and follow the procedure
below .
The board test is performed in several steps by measur-
ing some transient parameters and verifying successful
or failed pow er up actions under defined conditions. In
all test steps turn on sw itch SW _PS to connect demo
board to the +48V pow er supply, turn on sw itch SW _PS
to activate controller (connecting the ENABLE pin to the
VIN +48V) and turn +48V off for resetting controller after
fault.
1.
It should be noted that loading parameters such as
Low Capacitive Load, High Capacitive Load, Low
Resistive Load, and High Resistive are different for
LT4256 and for LT1641. These parameters are
show n below separately for each controller:
LTC1641
โ—
Low Capacitive load 1000uF,
โ—
High Capacitive load 8700uF,
โ—
Low Resistive load 10
โ„ฆ
, 50W ,
โ—
High Resistive load 5.5
โ„ฆ
.
LTC4256
โ—
Low Capacitive load 250uF,
โ—
High Capacitive load 3500uF,
โ—
Low Resistive load 11
โ„ฆ
, 50W ,
โ—
High Resistive load 5.0
โ„ฆ
.
2.
Place a scope probe to the VOUT turret, turn on
controller, and measure a pow er-up time w ith no
load. For LT4256 this time must be in the range
(13.7 - 54) ms, and for LT1641- (43 - 173) ms.
3.
Connect Low Capacitive Load to the output of hot
sw ap circuitry (VOUT +48V turret). Turn on control-
ler. This pow er up should be successful and tw o
LEDs (VOUT โ€“ green - and PW R GD - orange) must
light.
NOTE.
The follow ing tests verify loaded Controller performance. The
transients w ith Low Load should be successfully completed, w hile
transients w ith High Load should fail. The LT1641-1 and LT4256-1 in the
overcurrent fault condition are latched off, w hile the LT1641-2 and
LT4256-2 provide retry. To avoid pow er M OSFET damage in the LT1641-
2 and LT4256-2 High Load tests keep sw itch SW _ON in the on position
very short time.
4.
Connect High Capacitive Load to the output of hot
sw ap circuitry (VOUT +48V turret). Turn on control-
ler. This pow er up should be unsuccessful, and tw o
LEDs remaining off w ill confirm this.
For LT4256-1 and LT1641-1 the failed pow er-up is in-
dicated by the VOUT (green) and PW RGD (orange)
LED lights remaining off. Disconnect the ENABLE tur-
ret from the VIN +48V turret for short time and con-
nect them again. The controller should be latched off
in the shut off mode,
For LT4256-2 and LT1641-2 make short time connec-
tion of the ENABLE turret and VIN +48V. The VOUT
(green) and PW RGD (orange) LED w ill blink indicating
an autoretry in the failed pow er up.
LT1641
-
1, LT1641
-
2, LT4256
-
1, AND LT4256
-
2
5.
Load output w ith Low Resistive Load. Controller
should successfully keep this load.
6.
Turn controller on. Load output w ith High Resistive
Load. Controller should fail to keep this load.
7.
Verify that controller alive after overload test.
NOTE.
In the designing of the pow er-up transient w ith mentioned
Controllers special attention should be paid to correspondence betw een
pow er M O SFET safe operating area and transient parameters (current
limit level, duration of the transient, relationship betw een capacitive load
and resistive load and timer period).
Figure 1.
Proper M easurem ent Equipm ent Setup
LT1641
-
1, LT1641
-
2, LT4256
-
1, AND LT4256
-
2