Datasheet

LM10010
www.ti.com SNVS717C –JULY 2011–REVISED MARCH 2013
The change in the output voltage can be analyzed based on the resolution of the current DAC from the LM10010
compared to the desired resolution of the output swing of the regulator. R
FB1
is designed to provide the desired
LSB for V
OUT
with the equation:
(2)
Based on the desired default V
OUT
(with IDAC_OUT = 0 µA), R
FB2
can be solved from Eq. 1 above.
Example Solution
Assuming a 400 mV output range, 64 VID codes, and an IDAC LSB of 0.940 µA, it is desired to have a V
OUT
with
an LSB of 6.4 mV and a default value of 1.1V using an LM21215A-1 regulator:
(3)
(4)
(5)
(6)
Using 1% resistor values, R
FB1
can be set to 6.81 kΩ and R
FB2
can be set to 8.06 kΩ. This will yield a regulator
output range of 0.704V to 1.107V. At startup, the code of the LM10010 will be 46d (101110b) and will output a
15.97 µA. This will give an output voltage of approximately 1.0V (0.998V) when power is applied and both the
LM10010 and the LM21215A-1 come out of UVLO. Of course, values calculated here will be dependent on the
accuracy of the regulator, the LM10010 IDAC, and the resistor values used in the circuit.
Table 1 shows the codes and some of the resultant values of the IDAC current and the corresponding regulator
output voltage for the previous example.
Table 1. VID Codes with IDAC Current and Regulator Voltage for the Example
VID Code IDAC Current (µA) Regulator Voltage (V)
000000b 59.20 0.7038
000001b 58.26 0.7102
000010b 57.32 0.7166
000011b 56.38 0.7230
...
111100b 2.82 1.0878
111101b 1.88 1.0941
111110b 0.94 1.1005
111111b 0.00 1.1069
PC Board Guidelines
The following guidelines should be followed when designing the PC board for the LM10010:
• Place the LM10010 close to the regulator feedback pin to minimize the FB trace length.
• Place a small capacitor, C
VDD
, (1 nF) directly adjacent to the VDD and GND pins of the LM10010 to help
minimize transients which may occur on the input supply line.
• The high current path from the board’s input to the load and the return path should be parallel and close to
each other to minimize loop inductance.
• The ground connections for the various components around the LM10010 should be connected directly to
each other, and to the LM10010’s GND pins, and then connected to the system ground at one point. Do not
connect the various component grounds to each other through the high current ground line.
• For additional information about the operation of the regulator, please consult the respective datasheet and
application notes on the respective evaluation boards.
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