MAX15002 Datasheet, PDF (15/30 Pages) Maxim Integrated Products – Dual-Output Buck Controller with Tracking/Sequencing

Dual-Output Buck Controller with
Tracking/Sequencing
RATIOMETRIC TRACKING
V_IN
EN1
COINCIDENT TRACKING
V_IN
EN1
PGOOD SEQUENCING
V_IN
EN1
EN/TRACK2
SEL
V_OUT1
R_A
EN/TRACK2
REG
R_B
V_OUT2
R_A
FB2
R_B
REG
P_GOOD1
EN/TRACK2
SEL
SEL
REG
Figure 2. Ratiometric Tracking, Coincident Tracking, PGOOD Sequencing Configurations
Error Amplifier
The output of the internal error transconductance
amplifier (COMP_) is provided for frequency compen-
sation (see the Compensation Design Guidelines sec-
tion). The inverting input is FB_ and the output COMP_.
The error transamplifier has an 80dB open-loop gain
and a 10MHz GBW product.
Output Short-Circuit Protection
(Hiccup Mode)
The current-limit circuit employs a valley current-limiting
algorithm that either uses a shunt or the synchronous
MOSFET’s on-resistance as the current-sensing ele-
ment. Once the high-side MOSFET turns off, the volt-
age across the current-sensing element is monitored. If
this voltage does not exceed the current-limit threshold,
the high-side MOSFET turns on normally at the start of
the next cycle. If the voltage exceeds the current-limit
threshold just before the beginning of a new PWM
cycle, the controller skips that cycle. During severe
overload or short-circuit conditions, the switching fre-
quency of the device appears to decrease because the
on-time of the low-side MOSFET extends beyond a
clock cycle.
If the current-limit threshold is exceeded for more than
eight cumulative clock cycles (N_CL), the device shuts
down (both DH and DL are pulled low) for 4096 clock
cycles (hiccup timeout) and then restarts with a soft-
start sequence. If three consecutive cycles pass with-
out a current-limit event, the count of NCL is cleared
(see Figure 3). Hiccup mode protects against a contin-
uous output short circuit.
______________________________________________________________________________________ 15