FAN5038 Datasheet, PDF (8/15 Pages) Fairchild Semiconductor – Dual Voltage Controller for DSP Power

FAN5038
PRODUCT SPECIFICATION
Table1. Bill of Materials for a FAN5038 DSP Application
Reference
Manufacturer Part # Qty.
Description
C1, C9, C11 Sanyo
10TPB100M
3 100µF, 10V Capacitor
C2, C10
Sanyo
6TPB150M
2 150µF, 6V Capacitor
C3, C5
Panasonic
ECU-V1C105ZFX
2 1µF, 16V Capacitor
C4
Panasonic
ECU-V1H101JCG
1 100pF Capacitor
C6, C8
Panasonic
ECU-V1C104ZFX
2 100nF, 16V Capacitor
C7
Panasonic
ECU-V1C103ZFX
1 10nF, 16V Capacitor
D1
Motorola
MBRS835
1 8A Schottky Diode
D2
Fairchild
MBRS320
1 3A Schottky Diode
L1
Any
1 4.7µH, 4A Inductor
Q1
Fairchild
NDS8425
1 N-Channel MOSFET
Q2
Fairchild
FDV301N
1 N-Channel MOSFET
Q3
Fairchild
MJD200
1 NPN
R1-2
Dale
WSL2010R015FRE4
2 15mΩ, 1/2W
R3
Any
R4
Any
R5, R8, R10 Any
R7
Any
R8
Any
R9
Any
1 2KΩ
1 100KΩ
3 10KΩ
1 4.7KΩ
1 6.49KΩ
1 12KΩ
U1
Fairchild
FAN5038M
1 DC/DC Controller
Requirements and Comments
IRMS = 1.9A
ESR ≤ 55mΩ
5%, COG
DCR ~ 2mΩ
RDS(ON) = 25mΩ @ VGS = 4.5V
40V, 5A
Application Information
The FAN5038 contains a precision trimmed low TC voltage
reference, a constant-on-time architecture controller, a high
current switcher output driver, a low offset op-amp, and
switches for selecting various output modes. The block dia-
gram in Figure 2 shows how the FAN5038 in combination
with the external components achieves a dual power supply
for DSP power.
Switch-Mode Control Loop
The main control loop for the switch-mode converter consists
of a current conditioning amplifier and one of the two voltage
conditioning amplifiers that take the raw voltage and current
information from the regulator output, compare them against
the precision reference and present the error signal to the
input of the constant-on-time oscillator. The two voltage
conditioning amplifiers act as an analog switch to select
between the internal resistor divider network (set for 3.5V)
or an external resistor divider network (adjustable for 1.5V
to 3.6V.) The switch-mode select pin determines which of
the two amplifiers is selected. The current feedback signals
come across the Iout sense resistor to the IFBH and IFBL
inputs of the FAN5038. The error signals from both the cur-
rent feedback loop and the voltage feedback loop are
summed together and used to control the off-time duration of
the oscillator. The current feedback error signal is also used
as part of the FAN5038 short-circuit protection.
8
REV. 1.0.2 7/6/00