E-L6919ETR STMicroelectronics, E-L6919ETR Datasheet - Page 27

• Manufacturer Part Number: E-L6919ETR
• Description: IC CTRLR 5BIT PROG 2PHASE 28SOIC
• Manufacturer: STMicroelectronics
• Type: Step-Down (Buck)r

Specifications of E-L6919ETR

• Internal Switch(s): No
• Synchronous Rectifier: Yes
• Number Of Outputs: 1
• Voltage - Output: 0.8 ~ 1.55 V
• Current - Output: 2A
• Frequency - Switching: 150kHz
• Voltage - Input: 5 ~ 12 V
• Operating Temperature: -40°C ~ 150°C
• Mounting Type: Surface Mount
• Package / Case: 28-SOIC (7.5mm Width)
• Power - Output: 2W
• Mounting Style: SMD/SMT
• Operating Supply Voltage: 6.5 V
• Maximum Operating Temperature: 85 C
• Minimum Operating Temperature: - 40 C
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: 497-4592-2

CPU Power Supply: 5 to 12V
Considering the high slope for the load transient, a high switching frequency has to be used. In addition to fast
reaction, this helps in reducing output and input capacitor. Inductance value is also reduced.
A switching frequency of 200kHz for each phase is then considered allowing large bandwidth for the compen-
sation network. Considering the high output current, power conversion will start from the 12V bus.
– Current Reading Network and Over Current:
– Inductor design:
– Output Capacitor:
– Compensation Network:
Further adjustments can be done on the work bench to fit the requirements and to compensate layout parasitic
components.
– Droop function Design:
Since the maximum output current is I
x 2)in the worst case (max mosfet temperature). Since the device limits the valley of the triangular ripple
across the inductors, the current ripple must be considered too. Considering the inductor core satura-
tion, a current ripple of 10A has to be considered so that the OCP threshold in worst case becomes
OCPx=17A (22.5A-5A). Considering to sense the output current across the low-side mosfet RdsON,
SUB85N03L-04P has 4.3m
variation; the resulting transconductance resistor Rg has to be:
Considering a voltage drop of 70mV at full load, the feedback resistor R
Transient response performance needs a compromise in the inductor choice value: the biggest the in-
ductor, the highest the efficient but the worse the transient response and vice versa.
Considering then an inductor value of 0.8 H, the current ripple becomes:
Five Rubycon MBZ (2200 F / 6.3V / 12m max ESR) has been used implementing a resulting ESR of
2.4m
A voltage loop bandwidth of 20kHz is considered to let the device fast react after load transient.
The R
R
F
=
R
----------------------------- - 5
F
F B
resulting in an ESR voltage drop of 45A · 2.4m = 108mV after a 45A load transient.
C
V
F
IN
network results:
V
O S
-- -
4
I
=
Rg
T
Vin Vout
---------------------------- -
------------------------------------------------------ -
2
=
C
IN
–
I
R
F
L
OCPx
; 1.2V
DROOP
max at 25°C that becomes 5.6m at 100ºC considering the temperature
=
L
------------------- -
OUT
Co
R
R
----------------- -
R
+
-----------
Fsw
35
F
d sO N
ESR
FB
MAX
d
; 45A
L
-- -
2
=
=
=
= 45A, the over current threshold has been set to 45A (22.5A
DC
=
70mV
--------------- -
=
70 A
---------------------------------------- -
12 1.2
-------------------- -
1K 2
-------------- - 5
6 2200
17
0.8
12
–
5.6m
-------------
35
2k
=
-- - 20K 2
4
1k
1.2
------- -
12
=
1
------ -
2
2.7k
------------ -
200k
(R7)
1
=
33nF
---------------------------------------------------------------
2
=


6.5A (L1, L2)
5.6m
------------- 1.2k
(R3 to R6)
2.7
(C2)
FB
0.8
has to be:
+
2.4m


=
2.0k
L6919E
(R8)
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