TPS51200
www.ti.com
SLUS812–FEBRUARY 2008
OUTPUT VOLTAGE
vs
OUTPUT CURRENT
790
V
= 3.3 V
IN
0°C
780
770
760
750
740
730
25°C
-40°C
DDR3
-40°C
0°C
720
710
700
85°C
25°C
85°C
-3
-2
-1
0
1
– Output Current – A
2
3
I
OUT
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 (VLDOINMIIN – VOMAX) is needed in order to
support a Gm driven sourcing current of 2 A based on a design of VIN = 3.3 V and COUT = 3 × 10µF. Because the
TPS51200 is essentially a Gm driven LDO, its impedance characteristics are both a function of the 1/Gm and
RDS(on) of the sourcing MOSFET (see Figure 8). The current inflection point of the design is between 2 A and 3 A.
When ISRC is less than the inflection point, the LDO is considered to be operating in the Gm region; when ISRC is
greater than the inflection point but less than the overcurrent limit point, the LDO is operating in the RDS(on)
region. The maximum sourcing RDS(on) is 0.144 Ω with VIN = 3.0 V and TJ = 125°C.
14
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