LTC3816_15 Datasheet, PDF (37/44 Pages) Linear Technology – Single-Phase Wide VIN Range DC/DC Controller for Intel IMVP-6/IMVP-6.5 CPUs

LTC3816
APPLICATIONS INFORMATION
Therefore R_SER is calculated to be 13.99k and standard
value R_SER = 14k is used. Next, the resistor R_AVPDCRN value
is obtained from the AVP slope requirement:
( ) _A
AVP=
=
3mV/A
=
R_SER
+ R_PAR ||R_NTC
R_AVPDCRN
 _•RDCR
⇒ R _AVPDCRN
=
14k
+ (10k||10k)
3mV/A
• 1.3mΩ
=
8.233k
Select the standard value 8.25k. The capacitor value C_VDCRN
is given by the following equation:
( ) ^{CVDCRN = R}_SER ⁺
L
R_PAR ||R_NTC
 •R_DCR
=
14k
+
0.33µH
(10k || 10k )
•
1.3mΩ
=
13.36nF
Use the standard value C_VDCRN = 15nF.
To program the I_MON voltage, first select the resistor
R_PREIMON such that I_PREIMON bias current is around 10µA
to 20µA:
R_PREIMON
=
I_LOAD(MAX) • R_DCR
I_PREIMON
•
R_NTCNET
R_AVPDCRN
=
27A • 1.3mΩ
15µA
•
14k
+ (10k||10k
8.25k
)
= 5.389k
Select a standard value R_PREIMON = 5.1k. Once the resistor
R_PREIMON value is chosen, the R_IMON resistor value can
be obtained from the following equation:
( ) ^RIMON
=
3
V_IMON •R_PREIMON
• I_LOAD(MAX) •R_DCR
• ^RAVPDCRN
R_NTCNET
=
3
•
1.0V • 5.1k
(27A •1.3mΩ)
•
14k
8.25k
+ (10k||10k
)
= 21.03k
Select R_IMON = 21k. The value of C_IMON is selected to
satisfy the desired I_MON time constant:
C_IMON
=
t_IMON
R_IMON
=
300µs
21k
=
14.28nF
Select C_IMON = 15nF.
The power MOSFETs chosen for this application are the
Renesas RJK0305DPB (top) and 2 × RJK0330DPB (bot-
tom). The upper MOSFET, which is optimized for low
switching losses, has a typical R_DS(ON) of 10mΩ at V_GS
= 4.5V, a total gate charge of 8nC, and a minimum BV_DSS
of 30V. The bottom MOSFET which is optimized for low
on-resistance, has a typical R_DS(ON) of 2.8mΩ at V_GS =
4.5V, a total gate charge of 27nC, and a minimum BV_DSS
of 30V.
From the RJK0305DPB upper MOSFET data sheet, the
Miller capacitance is calculated to be:
C_MILLER
≈
∆Q_G
∆V_DS
=
2nC
12V
= 167pF
Assuming a top MOSFET junction temperature of 75°C,
δ = 0.25 and the power dissipation in this MOSFET is:
( ) ^{( ) P}_MAIN
=
V_OUT
V_IN
I_LOAD(MAX)
2
1+ δ
R_DS(ON) + t
( ) ( )( ) ^V_IN
2 ^ILOAD(MAX)
2
R_DR
C_MILLER •
( ) ^


V_INTVCC
1
– V_GS(MIL)
+
1
V_GS(MIL)



f_OSC
P_MAIN
=
0.75V
12V
(27A)²
(1+
0.25)10mΩ
+
(12V)²
27A
2
(2.6Ω)(167pF
)
•


1
5.2V –
3V
+
1
3V
 _{( 400kHz}
)
P_MAIN = 0.57W + 0.266W ≈ 0.836W
3816f
37