en5335 Enpirion, en5335 Datasheet - Page 8

• Manufacturer Part Number: en5335
• Description: 3a Voltage Mode Synchronous Buck Pwm Dc-dc Converter With Integrated Inductor 3-pin Programmable Output
• Manufacturer: Enpirion

Rev 1.0 November 2006
impedance, denoted as Z, is comprised of
effective series resistance, ESR, and effective
series inductance, ESL:
Z = ESR + ESL.
Placing output capacitors in parallel reduces the
impedance and will hence result in lower ripple
voltage.
Typical ripple versus capacitance is given below:
Table 3. Recommended output capacitors.
Enable Operation
The ENABLE pin provides a means to shut down
the device, or enable normal operation. A logic
low will disable the converter and cause it to shut
down. A logic high will enable the converter into
normal operation.
asserted high, the device will undergo a normal
soft start.
Soft-Start Operation
Soft start is a method to reduce in-rush current
when the device is enabled. The output voltage
is ramped up slowly upon start-up.
rise time is controlled by choice of a soft-start
capacitor, which is placed between the SS pin
(pin 37) and the AGND pin (pin 29).
©Enpirion 2006 all rights reserved, E&OE
Z
Output Capacitor
Total
1
Configuration
Description
5 x 10 uF
1 x 47uF
10uF, 6.3V,
22uF, 6.3V,
47uF, 6.3V,
X7R, 1206
X5R, 1206
X5R, 1206
=
Z
1
1
+
Z
1
2
+
Taiyo Yuden
Taiyo Yuden
Taiyo Yuden
...
Murata
Murata
Murata
+
MFG
Typical Output Ripple (mVp-p)
When the ENABLE pin is
Z
(as measured on EN5335QI
1
n
Evaluation Board)
GRM31CR71A476ME19L
GRM319R60J106KE19D
GRM31CR60J226KE19L
LMK316BJ106KD-T
LMK316BJ226KL-T
LMK316BJ476KL-T
20
10
P/N
The output
Rise Time: T
During start-up of the converter, the reference
voltage to the error amplifier is gradually
increased to its final level by an internal current
source of typically 10uA. Typical soft-start rise
time is 1mS to 3mS. Typical SS capacitor values
are in the range of 15nF to 30 nF.
POK Operation
The POK signal is an open drain signal from the
converter indicating the output voltage is within
the specified range. The POK signal will be a
logic high when the output voltage is within 90% -
120% of the programmed output voltage. If the
output voltage goes outside of this range, the
POK signal will be a logic low until the output
voltage has returned to within this range. In the
event of an over-voltage condition the POK
signal will go low and will remain in this condition
until the output voltage has dropped to 95% of
the programmed output voltage before returning
to the high state (see also: Over Voltage
Protection)
Over-Current Protection
The current limit function is achieved by sensing
the current flowing through the sense P-
MOSFET. When the sensed current exceeds the
current limit, both NFET and PFET switches are
turned off. If the over-current condition is
removed, the over-current protection circuit will
enable the PWM operation. If the over-current
condition persists, the soft start capacitor will
eventually discharge and cause the converter to
go through a full soft-start cycle. This circuit is
designed to provide high noise immunity.
It is possible to adjust the over-current set point
by connecting a resistor between ROCP (pin 27)
and GND (increase the trip point) or PVIN
(decrease the trip point). The nominal over
current trip point is set to 4.5A. The voltage at the
ROCP pin is designed to be 0.8V.
8
R
= C
ss
* 80K Ω
www.enpirion.com
EN5335QI