E-L6911C STMicroelectronics, E-L6911C Datasheet - Page 11

• Manufacturer Part Number: E-L6911C
• Description: IC CTRLR 5BIT PROGR STPDN 20SOIC
• Manufacturer: STMicroelectronics
• Type: Step-Down (Buck)r

Specifications of E-L6911C

• Internal Switch(s): No
• Synchronous Rectifier: Yes
• Number Of Outputs: 1
• Voltage - Output: 1.3 ~ 3.5 V
• Current - Output: 1.3A
• Frequency - Switching: 200kHz
• Voltage - Input: 5 ~ 12 V
• Operating Temperature: -40°C ~ 150°C
• Mounting Type: Surface Mount
• Package / Case: 20-SOIC (7.5mm Width)
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Power - Output: -
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

Figure 6. Output transient response without (a) and with (b) the droop function
As shown in figure 6, the ESR drop is present in any case, but using the droop function the total deviation of the
output voltage is minimized. In practice the droop function introduces a static error (Vdroop in figure 6) propor-
tional to the output current. Since a sense resistor is not present, the output DC current is measured by using
the intrinsic resistance of the inductance (a few m ). So the low-pass filtered inductor voltage (that is the induc-
tor current) is added to the feedback signal, implementing the droop function in a simple way. Referring to the
schematic in figure 7, the static characteristic of the closed loop system is:
Where V
resistance. The second term of the equation allows a positive offset at zero load ( V
the droop effect ( V
Figure 7. Compensation network
Considering the previous relationships R2, R3, R8 and R9 may be determined in order to obtain the desired
droop effect as follow:
V
Choose a value for R2 in the range of hundreds of K
components.
NOM
PROG
is the output voltage of the digital to analog converter (i.e. the set point) and R
V
C O M P
C 1 8
ESR DROP
DROOP
V
OUT
Z
F
(a)
). Note that the droop effect is equal the ESR drop if:
V
=
P R O G
V
PRO G
+
V
P W M
R 2
PRO G
C 2 0
R
---------------------------------- -
L
R 3
R 8 // R9
R8
R 4
R3
-------------------------------------
V
V
MAX
MIN
+
R 8 // R9
R2
V
I N
=
V
to obtain realistic values for the other
P H A S E
ESR
Z
I
–
R
---------------------------------- - I
R 8
L
ESR DROP
L 2
R8 // R9
R8
C 2 5
R 9
(b)
R
L
+
); the third term introduces
OUT
V
O U T
L
is the inductance
E S R
C 6 - 1 5
L6911C
V
DROOP
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