Rainbow Electronics MAX5097 - Manual (Page 14)

MAX5096/MAX5097
use typical values of V IN and f SW so that efficiency is opti-
mum for typical conditions. The switching frequency (f SW )
is fixed at 135kHz (MAX5096) and 330kHz (MAX5097).
f
SW can also be varied from 120kHz to 500kHz
(MAX5096) and from 300kHz to 500kHz (MAX5097) when
synchronized to an external clock (see the Oscillator/
Synchronization Input (SYNC) section). The peak-to-peak
inductor current, which reflects the peak-to-peak output
ripple, is worst at the maximum input voltage. See the
Output Capacitor Selection section to verify that the
worst-case output ripple is acceptable. The inductor satu-
rating current (I
SAT
) is also important to avoid runaway
current during continuous output short circuit. Select an
inductor with an I
SAT specification higher than the maxi-
mum peak current limit of 1.9A.
The Buck Mode operation determines the inductor and
output capacitor values. However, the values of the
inductor, its DCR, and the output capacitance/ESR
affect the closed-loop transfer function both in Buck
and LDO Modes. The internal compensation of the
MAX5096/MAX5097 in LDO Mode limits the values of
these external components. Make sure that the combi-
nation of output inductor, capacitor, and ESR falls with-
in the range specified in following Table 1.
Output Capacitor Selection
The allowable output voltage ripple and the maximum
deviation of the output voltage during load steps deter-
mine the output capacitance and its ESR. The output
40V, 600mA Buck Converters with Low-
Quiescent-Current Linear Regulator Mode
14 ______________________________________________________________________________________
PGND
OUT
LX
V IN
GND
BP
5V TO 40V
V IN
V OUT
ADJ
22 µH
C OUT
22 µF
COMP
SYNC
D1*
B260/
MURS105
C IN
100 µF
LDO/BUCK
RESET
EN
R C
C C
CT
SS
C
P
R PU
+
1.0 µF
MAX5096
MAX5097
R1
R2
C CT
C SS
RESET
*USE MURS105 IN APPLICATIONS
WHERE LDO MODE QUIESCENT
CURRENT IS CRITICAL.
Figure 4. Adjustable Output Voltage Configuration
INDUCTOR OUTPUT CAPACITOR (C OUT )
22µF, ESR = 5mΩ to 20mΩ (ceramic)
47µF, ESR = 40mΩ to 150mΩ
100µF, ESR = 30mΩ to 100mΩ
22µH
470µF / ESR = 60 Ω to 400mΩ
22µF, ESR = 5m Ω to 20mΩ (ceramic)
47µF / ESR = 40m Ω to 150mΩ
100µF / ESR = 30mΩ to 100mΩ
47µH
470µF / ESR = 60mΩ to 400mΩ
22µF, ESR = 5mΩ to 20mΩ (ceramic)
47µF / ESR = 40mΩ to 150mΩ
100µF / ESR = 30mΩ to 100mΩ
100µH
470µF / ESR = 60mΩ to 400mΩ
Table 1. Inductor/Output Capacitor
Selection