LTC4210 LINER [Linear Technology], LTC4210 Datasheet - Page 11

• Manufacturer Part Number: LTC4210
• Description: Dual Supply Hot Swap Controller for Advanced Mezzanine Card
• Manufacturer: LINER [Linear Technology]

Several conditions must be met before the external and
internal switches are allowed to turn on. First V
the input supplies (12V
undervoltage lockout thresholds. Next TIMER must be
<0.2V and ⎯ E ⎯ N must be pulled low.
Once these conditions are met, a debounce timing cycle is
initiated when AUXON or 12ON pin is toggled from low to
high. These two control pins turn on/off the 3.3V auxiliary
and 12V supplies. At the end of the debounce cycle, the
ON pins and fault status are checked. If both ON pins are
high and fault is cleared, the 3.3V auxiliary supply starts
up fi rst followed by the 12V supply. Note that the turn-on
delay for the AUXON and 12ON pins is 15μs and 30μs.
Figure 2 shows the two supplies turning on in sequence
after ⎯ E ⎯ N goes low.
By default, the internal pass transistor turns on fi rst if
both ON pins are high and start-up conditions met. The
output is current limited at 240mA by its internal ACL
amplifi er as the load current charging the output capaci-
tor increases. This causes the TIMER to ramp up with a
10μA pull-up. Normally the AUXOUT voltage exceeds its
power-good threshold before TIMER time-out and then
⎯ A ⎯ U ⎯ X ⎯ P ⎯ G ⎯ O ⎯ O ⎯ D pulls low.
APPLICATIONS INFORMATION
AUXPGOOD
12PGOOD
AUXOUT
Figure 2. Normal Power-Up Sequence
12V
5V/DIV
2V/DIV
5V/DIV
5V/DIV
5V/DIV
5V/DIV
TIMER
OUT
EN
IN
, AUXIN) must exceed their
20ms/DIV
422312 F02
CC
and
Once AUXOUT signals power is good and the TIMER pin
returns to <0.2V, the external MOSFET is then allowed to
turn on by charging up the GATE with a 10μA current source
(Figure 2). The voltage at the GATE pin rises with a slope
equal to 10μA/C
into the load capacitor C
The 12V output follows the GATE voltage when the MOSFET
turns on. If the voltage across the current sense resistor
R
internal current limit circuitry. Once the output, 12V
exceeds its power-good threshold, ⎯ 1 ⎯ 2 ⎯ P ⎯ G ⎯ O ⎯ O ⎯ D also pulls
low.
If only the 12ON pin is high at the end of debounce cycle,
the external MOSFET turns on fi rst. After that, if AUXON
pulls high, the internal switch turns on only after the 12V
output signals power is good and TIMER <0.2V.
Table 1. 12V and Auxiliary Supply Turn-Off Conditions
CONDITION
AUXON Goes
Low
12ON Goes Low
⎯ E ⎯ N Goes High
UVLO on V
UVLO on AUXIN
UVLO on 12V
AUX Overcurrent
Fault
12V Overcurrent
Fault
Thermal
Shutdown
S
I
INRUSH
becomes too high, the inrush current is limited by the
CC
IN
=
LTC4223-1/LTC4223-2
C
C
L
G
1
G
Turns Off
No Effect
Turns Off
Turns Off
Turns Off
No Effect
Turns Off
No Effect
Turns Off
•
10
AUX
and the supply inrush current fl owing
µA
RESULT
L1
(see Figure 14) is limited to:
Turns Off
Turns Off
Turns Off
Turns Off
Turns Off
Turns Off
Turns Off
No Effect
No Effect
12V
AUXON High
12ON High
⎯ E ⎯ N Low
V
AUXIN > UVLO
12V
AUXON and 12ON Low,
⎯ E ⎯ N High-to-Low, UVLO
on V
12ON Low, ⎯ E ⎯ N High-to-
Low, UVLO on V
AUXON and 12ON Low,
⎯ E ⎯ N High-to-Low, UVLO
on V
120°C
CC
IN
> UVLO
CC
CC
CLEARED BY
> UVLO
, Temperature <
11
CC
422312f
OUT