LTC4214-1CMS Linear Technology, LTC4214-1CMS Datasheet - Page 18

• Manufacturer Part Number: LTC4214-1CMS
• Description: IC CTRLR HOTSWAP NEGVOLT 10MSOP
• Manufacturer: Linear Technology
• Type: Hot-Swap Controllerr

Specifications of LTC4214-1CMS

• Applications: General Purpose
• Internal Switch(s): No
• Voltage - Supply: 6 V ~ 16 V
• Operating Temperature: 0°C ~ 70°C
• Mounting Type: Surface Mount
• Package / Case: 10-TFSOP, 10-MSOP (0.118", 3.00mm Width)
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

APPLICATIO S I FOR ATIO
LTC4214-1/LTC4214-2
for C
load capacitor to charge. That time is given by:
The maximum current flowing in the DRAIN pin is given
by:
Approximating a linear charging rate as I
I
be approximated with 0.5 • I
tion, TIMER capacitor C
Returning to Equation (3), the TIMER period is calculated
and used in conjunction with V
I
tive MOSFET.
As a numerical design example, consider a 10W load,
which requires 1.1A input current at – 10.8V. If
V
tion (8) gives R
To account for errors in R
TIMER threshold (3V), R
DRAIN voltage clamp (V
be multiplied by 1.5, giving the nearest standard value of
C
If a short-circuit occurs, a current of up to 80mV/
40m = 2A will flow in the MOSFET for 0.9ms as dictated
by C
selected based on this criterion. The IRF7413 can handle
20V and 2A for 9ms and is safe to use in this application.
Computing the maximum soft-start capacitor value during
soft-start to a load short is complicated by the nonlinear
MOSFET’s SOA characteristics and the R
An overly conservative but simple approach begins with
18
DRN(MAX)
SHORTCIRCUIT(MAX)
SUPPLY(MAX)
T
I
C
t
= 56nF.
DRN MAX
CL CHARGE
T
T
T
is calculated based on the maximum time it takes the
(
= 56nF in Equation (3). The MOSFET must be
(
t
CL CHARGE
to zero, the I
(
)
)
= 13.2V and C
S
V
= 40m ; Equation (13) gives C
SUPPLY MAX
C V
to check the SOA curves of a prospec-
U
)
•
I
•
DRN
DRNCL
40
T
(
D
is given by:
3
U
C V
, DRAIN current multiplier and
component in Equation (3) can
R
S
V
DRN(MAX)
A
L
, C
L
D
), the calculated value should
•
I
)
INRUSH MIN
= 100 F, R
T
4
, TIMER current (40 A),
SUPPLY MAX
V
•
DRNCL
I
DRN MAX
W
(
. Rearranging equa-
SUPPLY(MAX)
(
(
SS
)
D
DRN
C
= 475k, Equa-
)
)
SS
drops from
response.
U
T
= 34nF.
(11)
(12)
(13)
and
the maximum circuit breaker current, given by:
From the SOA curves of a prospective MOSFET, determine
the time allowed, t
In the above example, 56mV/40m gives 1.4A. t
for the IRF7413 is 8ms for 1.4A at 30V. From Equation
(15), C
C
t
the time-out period expiring. This gauge is determined
empirically with board level evaluation.
SUMMARY OF DESIGN FLOW
To summarize the design flow, consider the application
shown in Figure 2. It was designed for 12W for a –10V to
–14V supply.
Calculate the maximum load current: 12W/10V = 1.2A;
allowing for 75% converter efficiency, I
Calculate R
Calculate I
I
Select a MOSFET that can handle 3.2A at 14V: IRF7413.
Calculate C
C
t
Consult MOSFET SOA curves: the IRF7413 can handle
3.2A at 20V for 3.5ms, so it is safe to use in this
application.
Calculate C
C
FREQUENCY COMPENSATION
The LTC4214 typical frequency compensation network for
the analog current limit loop is a series R
connected to V
CL(CHARGE)
SHORTCIRCUIT(MAX)
MAX
SS
T
SS
I
C
= 47nF, which gives the circuit breaker time-out period
CB MAX
= 22nF.
SS
= 33nF was appropriate. The ratio (R
= 0.7ms.
(
SS
1 61
t
= 68nF. Actual board evaluation showed that
)
SOA MAX
. •
S
is a good gauge as a large ratio may result in
T
SS
: from Equation (8) R
SHORTCIRCUIT(MAX)
: from Equation (13) C
56
: using Equations (14) and (15) select
(
R
EE
R
mV
S
SS
. Figure 6 depicts the relationship be-
SOA(MAX)
)
= 3.2A.
. C
SS
: from Equation (10)
is given by:
S
= 25m .
T
IN(MAX)
= 24nF. Select
C
(10 ) and C
SS
• C
= 1.6A.
SOA(MAX)
SS
421412f
(14)
(15)
) to
C