Datasheet
V
OUT
= V
FB
x
1+
R
FB1
R
FB2
- IDAC_OUT x R
FB1
Slave Regulator
FB
V
OUT
LM10011
RFB1
RFB2
+
-
VOUT
VFB
+
-
+
-
IRFB2
IDAC_OUT
IRFB1
VRFB1
+
-
IDAC_OUT
VID
LM10011
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Theory of Operation
5 Theory of Operation
The LM10011 can be thought of as a D/A converter, converting the VID codes 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 and voltage through and across the bottom
feedback resistor. Therefore, as more current is sourced into the feedback node, less current is needed
from RFB1 and the output voltage is reduced. See Figure 2.
Figure 2. Current Injection into the Feedback Node
Looking at Figure 2, the following equation defines V
OUT
for a given regulator
(valid for V
OUT
> V
FB
, V
FB
= voltage at FB pin):
(1)
For the LM21215A-1, V
FB
is 600mV. For the LM10011, the IDAC_OUT maximum current is 59.2µA, with
64 settings at a resolution of 940nA, adjustable with the 6-bit VID word. Note that as the VID codes count
up, the output current (IDAC_OUT) counts down starting from the highest current. This allows for V
OUT
to
increment up with the VID code. For a more in-depth analysis of the circuit, see the LM10011 datasheet.
Table 1 shows the codes and some of the resultant values of IDAC_OUT 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 59.2 0.704
000001b 58.3 0.710
000010b 57.4 0.716
000011b 56.4 0.723
: : :
111100b 2.87 1.087
111101b 1.93 1.094
111110b 1.00 1.100
111111b 0.06 1.107
3
SNOU108A–December 2012–Revised April 2013 LM10011 Evaluation Module
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