Datasheet

MAX17501 60V, 500mA, Ultra-Small, High-Efciency,
Synchronous Step-Down DC-DC Converter
www.maximintegrated.com
Maxim Integrated │ 16
Figure 3. External Compensation Network
External Loop Compensation for Adjustable
Output Versions
The MAX17501 uses peak current-mode control scheme
andneedsonlyasimpleRC network to have a stable,
high-bandwidth control loop for the adjustable output volt-
age versions. The basic regulator loop is modeled as a
power modulator, an output feedback divider, and an error
amplifier.Thepower modulatorhasDCgainG
MOD(dc)
,
withapoleandzeropair.Thefollowingequationdefines
the power modulator DC gain:
=

++

×

MOD(dc)
LOAD IN SW SEL
1
G
1 0.2 0.5 - D
R VfL
where R
LOAD
= V
OUT
/I
OUT(MAX)
, f
SW
is the switching
frequency, L
SEL
is the selected output inductance, D is
the duty ratio, D = V
OUT/
V
IN
.
The compensation network is shown in Figure 3.
R
Z
can be calculated as:
Z C SEL OUT
R 12000 f C V= ×× ×
whereR
Z
isinΩ.Choosef
C
to be 1/12th of the switching
frequency.
C
Z
can be calculated as follows:
SEL MOD(dc)
Z
Z
CG
C
R
×
=
C
P
can be calculated as follows:
=
π× ×
P
Z SW
1
C - 5pF
Rf
Power Dissipation
The exposed pad of the IC should be properly soldered to
thePCBtoensuregoodthermalcontact.Ensurethejunction
temperature of the device does not exceed +125°C under
the operating conditions specified for the power supply.
At high ambient temperatures, based on the operating
condition, the heat dissipated in the IC might exceed
themaximumjunctiontemperatureof+125°C.Heatsink
shouldbeusedtoreduce θ
JA
at such operating condi-
tions. For typical applications, refer to the temperature
derating curves included in the MAX17501 Evaluation Kit
data sheet.
To prevent the part from exceeding 125°C junction tem-
perature, users need to do some thermal analysis. At a
particular operating condition, the power losses that lead
to temperature rise of the device are estimated as follows:
(
)
2
LOSS OUT DCR
OUT
1
P (P ( - 1)) - I R
=××
η
OUT OUT OUT
P VI
= ×
where P
OUT
istheoutputpower,ηisistheefficiencyof
thedevice,andR
DCR
is the DC resistance of the output
inductor (refer to the Typical Operating Characteristics
in the evaluation kit data sheets for more information on
efficiency at typical operating conditions).
The maximum power that can be dissipated in the 10-pin
TDFN-EP package is 1188.7mW at +70°C temperature.
The power dissipation capability should be derated as
the temperature goes above +70°C at 14.9mW/°C. For a
typical multilayer board, the thermal performance metrics
for the package are given as:
JA
67.3 C Wθ= °
JC
18.2 C Wθ= °
The junction temperature of the device can be estimated
at any given maximum ambient temperature (T
A_MAX
)
from the following equation:
( )
J_MAX A_MAX JA LOSS
TT P= +θ ×
If the application has a thermal-management system that
ensures that the exposed pad of the device is maintained
at a given temperature (T
EP_MAX
) by using proper heat
sinks, then the junction temperature of the device can be
estimated at any given maximum ambient temperature as:
( )
J_MAX EP_MAX JC LOSS
TT P= +θ ×
R
Z
TO COMP PIN
C
Z
C
P