Datasheet

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-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
LDO Design Guidelines
TPS51200
SLUS812 – FEBRUARY 2008
OUTPUT VOLTAGE
vs
OUTPUT CURRENT
Figure 6. DC Regulaltion Figure 7. Transient
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 × 10 µ F. 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.
14 Copyright © 2008, Texas Instruments Incorporated
Product Folder Link(s): TPS51200