MAX17020ETJ+T Maxim Integrated Products, MAX17020ETJ+T Datasheet - Page 20

• Manufacturer Part Number: MAX17020ETJ+T
• Description: IC CTLR PWM DUAL STEP DN 32-TQFN
• Manufacturer: Maxim Integrated Products
• Series: Quick-PWM™r

Specifications of MAX17020ETJ+T

• Applications: Power Supplies
• Current - Supply: 1mA
• Voltage - Supply: 6 V ~ 24 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 32-TQFN Exposed Pad
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

The Quick-PWM control architecture is a pseudo-fixed-
frequency, constant on-time, current-mode regulator
with voltage feed-forward. This architecture relies on
the output filter capacitor’s ESR to act as a current-
sense resistor, so the feedback ripple voltage provides
the PWM ramp signal. The control algorithm is simple:
the high-side switch on-time is determined solely by a
one-shot whose pulse width 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
valley 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 sensed by the IN input, and proportional to
the output voltage:
Dual Quick-PWM Step-Down Controller
with Low-Power LDO, RTC Regulator
Table 3. Approximate K-Factor Errors
20
REGULATOR
SWITCHING
SMPS 1
SMPS 2
______________________________________________________________________________________
Free-Running Constant-On-Time PWM
Controller with Input Feed-Forward
TON = REF or GND
On-Time = K (V
TON = REF or V
TON SETTING
TON = GND
TON = V
200kHz
400kHz
300kHz
500kHz
(kHz)
CC
CC
OUT
On-Time One-Shot
/V
TYPICAL K-FACTOR
IN
)
(µs)
5.0
2.5
3.3
2.0
K-FACTOR ERROR
where K (switching period) is set by the tri-level TON
input (see the Pin Description section). High-frequency
(400kHz/500kHz) operation optimizes the application
for the smallest component size, trading off efficiency
due to higher switching losses. This might be accept-
able in ultra-portable devices where the load currents
are lower and the controller is powered from a lower
voltage supply. Low-frequency (200kHz/300kHz) oper-
ation offers the best overall efficiency at the expense of
component size and board space.
For continuous conduction operation, the actual switching
frequency can be estimated by:
where V
in the inductor discharge path, including synchronous
rectifier, inductor, and PCB resistances; V
sum of the voltage drops in the charging path, includ-
ing the high-side switch, inductor, and PCB resis-
tances; and t
MAX17020.
±12.5
±12.5
±10
±10
(%)
DROP1
f
SW
ON
=
is the sum of the parasitic voltage drops
Use for absolute best efficiency.
Useful in 3-cell systems for lighter loads
than the CPU core or where size is key.
Considered mainstream by current
standards.
Good operating point for compound buck
designs or desktop circuits.
t
ON IN
is the on-time calculated by the
(
V
V
OUT
+
V
DROP
+
COMMENTS
V
DROP
1
−
V
1
DROP
2
DROP2
)
is the