Datasheet

( )
HF
6
FB
1
C
2 1.5 10 R
=
p´ ´ ´
G
G
105
R
Q
=
10
8
7
6
VDD
GDRV
ISNS
GND
TPS40210/11
L
V
IN
R
G
V
OUT
UDG-07196
TPS40210, TPS40211
www.ti.com SLUS772E –MARCH 2008– REVISED OCTOBER 2011
While the error amplifier GBWP will usually be higher, it can be as low as 1.5 MHz. If 10 × K
Comp
× f
L
> 1.5 MHz,
the error amplifier gain-bandwidth product may limit the high-frequency response below that of the
high-frequency capacitor. To maintain a consistent high-frequency gain roll-off, C
HF
can be calculated by
Equation 29.
(29)
Where:
• C
HF
is the high-frequency roll-off capacitor value in F
• R
FB
is the mid band gain setting resistor value in Ω
GATE DRIVE CIRCUIT
Some applications benefit from the addition of a resistor connected between the GDRV pin and the gate of the
switching MOSFET. In applications that have particularly stringent load regulation (under 0.75%) requirements
and operate from input voltages above 5 V, or are sensitive to pulse jitter in the discontinuous conduction region,
this resistor is recommended. The recommended starting point for the value of this resistor can be calculated
from Equation 30.
(30)
Where:
• Q
G
is the MOSFET total gate charge at 8-V V
GS
in nC
• R
G
is the suggested starting point gate resistance in Ω
Figure 28. Gate Drive Resistor
TPS40211
The only difference between the TPS40210 and the TPS40211 is the reference voltage that the error amplifier
uses to regulate the output voltage. The TPS40211 uses a 260-mV reference and is intended for applications
where the output is actually a current instead of a regulated voltage. A typical example of an application of this
type is an LED driver. An example schematic is shown in Figure 29.
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