Datasheet

-3 -1-2 0 1 2 3
I
OUT
– Output Current – A
730
700
720
760
740
750
790
770
780
V
OUT
– Output Voltage – mV
85°C
V
IN
= 3.3 V
0°C
-40°C
25°C
710
0°C
25°C
85°C
DDR3
-40°C
I
SRC
- Source Current - A
Overcurrent
Limit
Inflection
Point
(between
2 A and 3 A)
UDG-08026
1/Gm
1/R
DS(on)
V
VO
– Output Voltage – V
TPS51200-Q1
www.ti.com SLUS984A –NOVEMBER 2009–REVISED APRIL 2012
OUTPUT VOLTAGE
vs
OUTPUT CURRENT
Figure 6. DC Regulaltion Figure 7. Transient
LDO Design Guidelines
The minimum input to output voltage difference (headroom) decides the lowest usable supply voltage Gm-driven
to drive a certain load. For TPS51200, a minimum of 300 mV (VLDOIN
MIIN
– VO
MAX
) is needed in order to
support a Gm driven sourcing current of 2 A based on a design of V
IN
= 3.3 V and C
OUT
= 3 × 10μF. Because the
TPS51200 is essentially a Gm driven LDO, its impedance characteristics are both a function of the 1/Gm and
R
DS(on)
of the sourcing MOSFET (see Figure 8). The current inflection point of the design is between 2 A and 3 A.
When I
SRC
is less than the inflection point, the LDO is considered to be operating in the Gm region; when I
SRC
is
greater than the inflection point but less than the overcurrent limit point, the LDO is operating in the R
DS(on)
region. The maximum sourcing R
DS(on)
is 0.144 Ω with V
IN
= 3.0 V and T
J
= 125°C.
Figure 8. TPS51200 Impedance Characteristics
Copyright © 2009–2012, Texas Instruments Incorporated 15
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