SRK2000 STMicroelectronics, SRK2000 Datasheet - Page 10

• Manufacturer Part Number: SRK2000
• Description: SYNCHRONOUS RECTIFIER SMART DRIVER FOR LLC RESONANT CONVERTER
• Manufacturer: STMicroelectronics

Application information
Note:
10/17
Equation 2
If V
of V
some care needs to be taken only as far as the selection of the -12/-25 mV threshold is
concerned: in fact, the large spread of I
the device turns on, a value that can be found by solving the first of (1) for V
Equation 3
A couple of examples clarify the suggested calculation methodology.
Example 1 V
In this case, V
From the second of (2), the nominal ratio of R1 to R2 is (10 – 1.8) / 1.8 = 4.555. Substituting
the appropriate extreme values in (3) it must be (4.75 - 7·10
solving for R1 yields R1 > 425 kΩ; let us consider an additional 4% margin to take both the
tolerance and the granularity of the R1 and R2 values into account, so that: R1 > 425·1.04 =
442 kΩ . Choose R1 = 442 kΩ (E48 standard value) and, from the second of (2), R2 =
442/4.555 = 97 kΩ; use 97.6 kΩ (E48 standard value).
Example 2 V
In this case, V
From the second of (2), the nominal ratio of R1 to R2 is (10 – 1.8) / 1.8 = 4.555. Substituting
the appropriate extreme values in (3) it must be (4.25 - 13·10
solving for R1 yields R1 < 156 kΩ; with 4% additional margin R1 < 156/1.04 = 150 kΩ.
Choose R1 = 147 kΩ (E48 standard value) and, from the second of (2), R2 = 147/4.555 =
32.3 kΩ; use 32.4 kΩ (E48 standard value).
In both examples the gate drivers are disabled as Vcc falls below 9.75 V (nominal value), as
the voltage on the EN pin falls 45 mV below V
CC_G
EN_On
is not too low (<8÷9 V), its tolerance is not critical because it is related only to that
(±5.6%) and of the external resistors R1, R2 (±1% each is recommended). Then,
CC_G
CC_G
EN
EN
must definitely be lower than the minimum value of V
must definitely be higher than the maximum value of V
= 10 V, V
= 10 V, V
DVS1,2_Off
DVS1,2_Off
Doc ID 17811 Rev 2
⎧
⎪
⎪ ⎪
⎨
⎪
⎪
⎪
⎩
R
R
1
2
V
=
EN
=
= - 25 mV.
= - 12 mV.
V
R
EN
=
CCOn
1
V
V
considerably affects the voltage on the EN pin as
CC
CCOn
−
1
_
EN_On
V
G
V
+
I
EN
EN
EN
−
−
R
R
_
I
V
1
2
EN
On
V
V
EN
.
EN
CC
R
_
1
_
On
_
On
G
-6
-6
·R1) / (1 + 4.555) < 0.32;
·R1) / (1 + 4.555) > 0.4;
EN_Th
EN_Th
EN
(= 0.32 V).
(= 0.40 V).
:
SRK2000