Datasheet
Slave Regulator
FB
V
OUT
LM10010
RFB1
RFB2
+
-
VOUT
VFB
+
-
+
-
IRFB2
IDAC_OUT
IRFB1
VRFB1
+
-
IDAC_OUT
VID
LM10010
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Theory of Operation
8 Theory of Operation
The LM10010 can be thought of as a D/A converter, converting the VID communication to analog outputs.
In this device, the output is a current DAC (IDAC_OUT), which is connected to the feedback node of a
slave regulator. Therefore, all VID data words are decoded into a 6-bit current DAC output. The
impedance of the feedback node at DC appears as the top feedback resistor. This is because the control
loop of the slave regulator effectively maintains a constant current/voltage across the bottom feedback
resistor, and creates low impedance at the V
OUT
node. Therefore, as more current is sourced into the
feedback node, the more the output voltage is reduced. See Figure 2.
Figure 2. Output voltage is controlled via current injection into the feedback node
Looking at the schematic shown above, the following equation defines V
OUT
for a given regulator (valid for
V
OUT
> V
FB
).
(1)
For the LM21215A-1, V
FB
is 600mV. For the LM10010, the I
DAC_OUT
maximum current is 59.2 µA, with 64
settings at a resolution of 940 nA, adjustable with the 6-bit VID word. Note that as the VID codes count up,
the output current counts down starting from the highest current. This allows for the V
OUT
voltage to
increment up with the VID code. For a more in-depth analysis of the circuit, see the LM10010 data sheet.
Table 1 shows the codes and some of the resultant values of IDAC current and corresponding regulator
output voltage for the default resistor values on the evaluation board.
Table 1. VID Codes with IDAC Current and Regulator Voltage for the Evaluation Board.
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
5
SNVA498B–July 2011–Revised May 2013 AN-2176 LM10010 Evaluation Board
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