I(TURN_OFF) =- 1 A
V(THRESHOLD)
r
DS(on)
-10mV
10mW
I(TURN_OFF) =
(3)
GATE DRIVE, CHARGE PUMP AND C(BYP)
VDD, BYP, and POWERING OPTIONS
V
DD
A
C
G
N
D
G
A
T
E
Input
Voltage
3.3V-18V
Common
Bus
CommonBusPowering
*OptionalFiltering
10*
V
DD
A
C
G
N
D
G
A
T
E
Input
Voltage
0.8V-18V
Common
Bus
SeparateBusPowering
*OptionalFiltering
5V
22
00
pF
B
Y
P
2
20
0p
F
B
Y
P
0.01
F
m
0.01
F
m
10*
SLVS728B – JANUARY 2007 – REVISED SEPTEMBER 2008.......................................................................................................................................... www.ti.com
To obtain a -10 mV fast turnoff ( V(A) is less than V(C) by 10 mV ), R(RSET) = (–470.02/ ( –0.01–0.00314) ) ≈
35,700
. If a 10 m rDS(on) MOSFET was used, the reverse turnoff current would be calculated as follows.
The sign indicates that the current is reverse, or flows from the MOSFET drain to source ( C to A ).
The turn-off speed of a MOSFET is influenced by the effective gate-source and gate-drain capacitance ISS).
Since these capacitances vary a great deal between different vendor parts and technologies, they should be
considered when selecting a MOSFET where the fastest turn-off is desired.
Gate drive of 270
A typical is generated by an internal charge pump and current limiter. A separate supply, V
DD,
is provided to avoid having the large charge pump currents interfere with voltage sensing by the A and C pins.
The GATE drive voltage is referenced to V(A) as GATE will only be driven high when V(A) > V). The recommended
capacitor on BYP (bypass) must be used in order to form a quiet supply for the internal high-speed comparator.
V(GATE) must not exceed V(BYP).
The separate VDD pin provides flexibility for operational power and controlled rail voltage. While the internal
UVLO has been set to 2.5 V, the TPS2412/13 requires at least 3 V to generate the specified GATE drive voltage.
Sufficient BYP voltage to run internal circuits occurs at VDD voltages between 2.5 V and 3 V. There are three
choices for power, A, C, or a separate supply, two of which are demonstrated in
Figure 14. One choice for
voltage rails over 3.3 V is to power from C, since it is typically the source of reliable power. Voltage rails below
3.3 V nominal, e.g. 2.5 V and below, should use a separate supply such as 5 V. A separate VDD supply can be
used to control voltages above it, for example 5 V powering VDD to control a 12-V bus.
VDD is the main source of power for the internal control circuits. The charge pump that powers BYP draws most
of its power from VDD. The input should be low impedance, making a bypass capacitor a preferred solution. A
10-
series resistor may be used to limit inrush current into the bypass capacitor, and to provide noise filtering
for the supply.
BYP is the interconnection point between a charge pump, V(AC) monitor amplifiers and comparators, and the gate
driver. C(BYP) must be used to filter the charge pump. A 2200 pF is recommended, but the value is not critical.
Figure 14. VDD Powering Examples
14
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