MAX8720ETX+ Maxim Integrated Products, MAX8720ETX+ Datasheet - Page 13

• Manufacturer Part Number: MAX8720ETX+
• Description: IC CNTRL VID STP DWN 36-TQFN
• Manufacturer: Maxim Integrated Products

Specifications of MAX8720ETX+

• Applications: Controller, CPU GPU
• Voltage - Input: 2 ~ 28 V
• Number Of Outputs: 1
• Voltage - Output: 0.28 ~ 1.85 V
• Operating Temperature: 0°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 36-TQFN Exposed Pad
• Output Voltage: 0.275 V to 1.85 V
• Input Voltage: 2 V to 28 V
• Mounting Style: SMD/SMT
• Maximum Operating Temperature: + 85 C
• Minimum Operating Temperature: - 40 C
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Table 1. Component Selection for
Standard Applications
The quick-PWM control architecture is a pseudo-fixed-
frequency, constant-on-time, current-mode type with
voltage feed-forward (Figure 2). This architecture relies
on the output filter capacitor’s ESR to act as the cur-
rent-sense resistor, so the output ripple voltage pro-
vides the PWM ramp signal. The control algorithm is
simple: the high-side switch on-time is determined sole-
ly by a one-shot whose period is inversely proportional
to input voltage and directly proportional to output volt-
age. Another one-shot sets a minimum off-time (400ns
typ). The on-time one-shot is triggered if the error com-
parator is low, the low-side switch current is below the
current-limit threshold, and the minimum off-time one-
shot has timed out.
The heart of the PWM core is the one-shot that sets the
high-side switch on-time. This fast, low-jitter, adjustable
one-shot includes circuitry that varies the on-time in
response to battery and output voltage. The high-side
switch on-time is inversely proportional to the battery
voltage as measured by the V+ input, and proportional
to the output voltage. This algorithm results in a nearly
constant switching frequency despite the lack of a
fixed-frequency clock generator. The benefits of a con-
Input Voltage
Output Voltage
C
C
N
N
D
L1 Inductor
IN
OUT
H
L
L
Low-Side MOSFET
Schottky Rectifier
High-Side MOSFET
Input Capacitor
COMPONENT
Output Capacitor
Free-Running, Constant-On-Time PWM
Controller with Input Feed-Forward
______________________________________________________________________________________
On-Time One-Shot (TON)
V
V
(2) 10µF, 25V
TDK C3225X7R1E106M
AVX 12103D106M
Taiyo Yuden TMK325BJ106MM
(3) 470µF, 2.5V, 9mΩ low-ESR
polymer capacitor
Sanyo 2R5TPE470M9
Siliconix SI7390DP
Siliconix SI7356DP
3A, 30V, 0.45V
Nihon EC31QS03L
0.8µH, 20A, 4.9mΩ
Sumida CDEP104-0R8MC-50
IN
OUT
= 7V to 24V
= 1.25V
15A/300kHz
Dynamically Adjustable 6-Bit VID
f
stant switching frequency are twofold: first, the frequen-
cy can be selected to avoid noise-sensitive regions
such as the 455kHz IF band; second, the inductor rip-
ple-current operating point remains relatively constant,
resulting in easy design methodology and predictable
output voltage ripple.
where K is set by the TON pin-strap connection and
0.075V is an approximation to accommodate the expect-
ed drop across the low-side MOSFET switch (Table 3).
The on-time one-shot has good accuracy at the operat-
ing points specified in the Electrical Characteristics
table (±10% at 200kHz and 300kHz, and ±12% at
550kHz and 1000kHz). On-times at operating points far
removed from the conditions specified in the Electrical
Characteristics table can vary over a wider range. For
example, the 1000kHz setting typically runs approxi-
mately 10% slower with inputs much greater than +5V
due to the very short on-times required.
Table 2. Component Suppliers
Table 3. K-Factor
AVX
Central Semiconductor
Coiltronics
Fairchild Semiconductor
Kemet
Nihon
Panasonic
Sanyo
Siliconix (Vishay)
Sumida
Taiyo Yuden
TDK
TOKO
TON SETTING
Step-Down Controller
Open
GND
SUPPLIER
V
REF
CC
On-Time = K (V
TON FREQUENCY
(kHz)
1000
200
300
550
OUT
www.avx.com
www.centralsemi.com
www.coiltronics.com
www.fairchildsemi.com
www.kemet.com
www.niec.co.jp
www.panasonic.com/industrial
www.secc.co.jp
www.vishay.com
www.sumida.com
www.t-yuden.com
www.component.tdk.com
www.tokoam.com
+ 0.075V) / V
WEBSITE
K-FACTOR (µs)
1.8 ±12.5
1.0 ±12.5
3.3 ±10
IN
5 ±10
13