
Part Name  LM10011  Texas Instruments 
Description  6/4Bit VID Programmable Current DAC for Point of Load Regulators with Adjustable StartUp Current 
LM10011 Datasheet PDF : 24 Pages

LM10011
SNVS822A – DECEMBER 2012 – REVISED NOVEMBER 2014
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Typical Application (continued)
8.2.1 Design Requirements
Table 4 lists the design parameters.
Table 4. Design Parameters
DESIGN PARAMETER
Output voltage range
Startup voltage
Mode
EXAMPLE VALUE
0.7 V to 1.1 V
1.1 V
0
8.2.2 Detailed Design Procedure
8.2.2.1 Setting the VOUT Range and LSB
Looking at the Typical Application Circuit in Figure 12, the following equation defines VOUT of a given regulator
(valid for VOUT > VFB):
VOUT
=
VFB
x
1+
RFB1
RFB2
 IDAC_OUT x RFB1
(1)
Here, the output voltage is a function of the resistor divider from RFB1 and RFB2. Using the LM10011, there is a
current supplied by the IDAC_OUT pin that helps drive current through the feedback resistor RFB2, thus lowering
the necessary current supplied through RFB1, and hence lowering VOUT. To calculate the nominal (maximum)
VOUT, use an IDAC_OUT value of 0 µA.
The change in the output voltage can be analyzed based on the resolution of the current DAC from the LM10011
compared to the desired resolution of the output swing of the regulator. RFB1 is designed to provide the desired
VOUT_LSB with the equation:
VOUT_LSB = LSB x RFB1
(2)
Where LSB = LSB_6 (940 nA) from the electrical characteristics table (see Electrical Characteristics). Based on
the desired nominal VOUT (with IDAC_OUT = 0 µA) and the calculated RFB1 from Equation 2, RFB2 can be solved
using Equation 1.
8.2.2.2 4Bit Mode Design Example
Designing with the LM10011 in 4bit mode is similar to designing in 6bit mode. The only differences are the LSB
value (LSB = LSB_4 = 3.76 µA) in Equation 2 and fullscale current range (IDAC_OUT = 56.4 µA).
8.2.2.3 Setting the StartUp Voltage with RSET
RSET is chosen depending on the required startup voltage for the particular application. The user must use
Equation 3 and solve for the required IDAC_OUT by inputting the known values of RFB1 and RFB2, VFB, and the
desired startup output voltage, VOUT. Once IDAC_OUT is solved for, choose an RSET based on Table 2 to select
a startup code to yield a current closely matching the calculated result. Use the equation below to solve for the
required IDAC_OUT value at startup.
1
IDAC_OUT = RFB1
VFB x
1+
RFB1
RFB2
 VOUT
(3)
8.2.2.4 Example Solution
While in 6bit mode, assuming a 400mV output range, 64 VID codes, and an IDAC LSB of 0.940 µA, it is desired
to have a VOUT with an LSB of 6.4 mV and a default value of 1.1 V with a 1.05V startup voltage using an
LM21215A1 regulator (VFB = 0.6 V):
6.4mV = 0.940µA x RFB1
(4)
RFB1 = 6.8k
(5)
Using 1% standard resistor values, RFB1 can be set to 6.81 kΩ. Now calculate RFB2 based on RFB1 and the
maximum VOUT of 1.1 V using Equation 1.
14
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